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Hello Riflemen: I am trying to reduce my shot to shot velocity spread of my handloads. I am using a Marlin 45/70, 1895, Win. brass, Fed. primer, h4198 powder, and a 350 Hornady FP bullet. My loads are pretty consistent around 2100fps but I know others here that obtain amazing low velocity SD's. Lets say I want to reduce the velocity spread by 5fps from an average of 20fps. What one or two tricks would you use to achieve this? How far down the bench rest trail do you Riflemen travel with the 45/70? Thanks, BestLever
 

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I'd start with getting really finicky about accuracy of powder measuring. I make sure mine are right on the mark with no deviations tolerated.

Second, get real finicky with OAL's. When seating bullets I go real slow. Little tricks like barely seating then turning a quarter turn and seat a little bit more...do this about 3 times until it's fully seated doing quarter turns. Then measure for length. I always adjust the seating depth shallow then when it's fully seated sneak it to the depth without coming up too short. Keep the lengths within .002 and you'll see consistency.

Have you tried IMR4198 or other powder? I was shooting stout loads like those you posted about in the BB forum...and they are fun. They were H4198 at 51gr and will rattle your cage. Then I backed it down and used a different powder. That made alot of diffence. Now using 44gr of IMR4198. They have less velocity but I can always sneak in one of those barn-burning H4198 loads :lol:

Just a few starters. Have fun!


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BestLever -

You might watch out for comparing convective ignition loads vs conductive ignition ones - generally even a poorly performing convective load will still have a smaller SD than the best conductive load. Since you're looking for hunting loads and using 4198 you're by definition using conductive ignition and hence aren't going to be seeing 2-3fps SDs (across 10 rounds).

With that as a given: like perf says - I'd make sure your loads are spot on the same. If you're going to be using 4198, given that neither throws loads well, you're going to have to weigh each charge. Make sure they're all the same to within 0.1gr. The other choice is to use a powder which throws well - 99.99% of the time (with a right powder), a thrown load will be more consistent than weighed [we throw at the +/- 0.02gr or better level to get our small SDs].

If one of the 4198s is not a given, then one might look for other powders which give you the velocity etc you need, but are engineered to burn more consistently - this choice only comes from experience and lots of chrono data. We generally like the VVN powders for this reason... but there are others that can do likewise... try a half dozen different powders, shoot 20 shots strings and see what the chrono tells you.

Beyond that: make sure you're using full case or *slightly* compressed loads - this reduces the degrees of freedom the flame front has to igniting the rest of the charge after the primer has done its job. Less than full case loads increase the DoF's and hence the velocity spread.

Pick your primers carefully - we use winchester primers for our convective loads, simply because they're cooler than the rest (we don't want the primer unseating the bullet on us)... but for consistency in full case loads, I'd look at the cci br primers, or rem's 7.5 (for sr primer cases). This is a case where you need to go out, buy 100 of each, build up the cartridges, and shoot them over a chrono with your powder of choice. All of us have preferences in terms of brands... in this case, let the numbers tell you which way to go.

Then lastly: bullet seating. Some powders will light consistently almost by just blinking an eye at them... and then there are the rest. If you're using full case loads, then keeping the charge confined initially as long as possible keeps the temperature up and the distance btwn grains down, ie, better more consistent ignition. In our book the best way to control this is via the bullet/neck tension. Crimps kind of work... but you're asking the last .050" of the case to do all the work. By sizing the neck tight you're making the entire neck resist the bullet's exit. Longer you can hang onto the bullet, the more grains will be fully ignited, the more consistent the resulting velocity.

A good load, well constructed and with carefully picked components should generate less than 10fps SDs, across 10 shots.

All said and done: there's as much of an art to fine reloading... as there is to fine shooting.

hope that helps, and do shoot straight,
greg
www.gmdr.com

ps. the other important point to remember: most powders burn hotter if they're hotter, ie, a round that has been sitting in a hot chamber (eg, while the shooter is trying for the perfect sight picture) will shoot hotter than one what was just chambered and shot. This you can easily see with your chrono. [We've posted before the mv difference btwn 32degF and 116degF loads: in 444 up to 180fps... just because the ambient is xx degrees, once the round has been sitting in a couple hundred degree chamber, it will get warmer, by definition.] If you're target shooting - set a limit on how long you're going to allow a round to sit in the chamber unshot, and after which you eject it, let it cool, and shoot the other rounds. For our target shooting our limit is 3-4 seconds. [this is the reason for the cold barrel religion - there's nothing special per se about cold barrels... other than one can take forever to get the right sight picture before dropping the hammer... with a hot barrel, the in the chamber time before pulling the trigger becomes a critical value.]

pps. make sure your rounds have all come to the ambient temperature before shooting them: when we're setting up at the range, the very first item on our to do list is - take all the ammo boxes, put them on the bench (in the shade) and with the tops open. By the time we've got the chronos setup, the computers going etc, they've had a good 20-30 minutes of come to ambient. To shoot them directly from either an a/c'd passenger compartment, or from a hot trunk... is asking for large SD's.
 

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I also try to make my brass as uniform as possible. Trim lengh, flash hole uniformity (Midway makes a tool for that)... I have even gone so far as to weigh specific cases to make my completed rounds as uniform as possible.

I reload for my 45-70, too, and it is nice to work with big cases instead of itty bitty cases like my .223, but with that much case volume your powder choice and charge weight must be monitored. I have read places where shooters will raise the rifle verticle after chambering a round to get the powder back against the primer before laying down and sighting in again. This may seem drastic but if you are trying to achieve +/- 5fps deviation you may have to go to that.

I have also read about reloading and your environment, i.e. humidity, temperature, etc. I guess you go on forever and try to eliminate every variable but that would be impractical and definitely 'unfun.'

I have given up on trying to make super-perfect rounds, been there, done that. Now I have fun crunching bullets that are fairly consistent and easy to make without having to scrutinize every detail.
 

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Greg, what powder would you suggest for the Hornady [email protected] avg velocity and good/better accuracy than the 4198's?

I'm currently using WW and R-P cases with CCI200primers





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Hello Riflemen: Thanks, that's good stuff. I'll chew on it for a bit and decide what I'm going to do. I'm not trying to benchrest the 45/70 so I'm not looking for super-perfect ammo. I'm just thinking about adding one or two steps to the quick handload to get better uniformity. All of your ideas are great. Uniformity being the goal, I think that changing to a BR primer and keeping the ammo temp. consistent might be enough to satisfy me. I don't want to spend a great deal of time making ammo for this rifle. Again, thanks for sharing your experience. I'll pass it on as needed:wink: BestLever
 

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Charlie98 said:
I also try to make my brass as uniform as possible. Trim lengh, flash hole uniformity (Midway makes a tool for that)... I have even gone so far as to weigh specific cases to make my completed rounds as uniform as possible.

-- if one is loading semiauto rounds (ie, rounds which headspace on the case mouth), then case length is crucial... but with the 4570, at least so far, have found little need for such, ie, we're still using the same 500 pieces of brass from 1996, most have been reloaded 20+ times, the mouths are all over the place... but with good convective loads they still shoot 1 moa (5 shots; and assuming no crimp); likewise for the flash hole, ie, they've never been cleaned up: from midway to the reloading blocks the first time, from the tumbler to the reloading blocks since.

I reload for my 45-70, too, and it is nice to work with big cases instead of itty bitty cases like my .223, but with that much case volume your powder choice and charge weight must be monitored. I have read places where shooters will raise the rifle verticle after chambering a round to get the powder back against the primer before laying down and sighting in again. This may seem drastic but if you are trying to achieve +/- 5fps deviation you may have to go to that.

-- have to agree with the ease of handling of the larger cases, likewise the lack of worry about powder bridging from the measure to the cases [we've posted earlier on our 223 bridging problems]. W/re forcing the powder to the rear of the case - if one is running low load density loads and using conductive ignition, then this is necessary (and with some people running 60% loads, this is what's keeping them alive, ie, the one time they forget, they're going to have a detonation on their hands... which is part of the reason why we're so much in favor of convective loads for target or plinking loads). If the 5fps you refer to is the SD over 10 rounds - they'd make good rounds, but not great ones... the best we've ever shot were some 500gr lead 4570 rounds which generated a 0.8fps SD across 10 shots; but we take very good rounds as producing 3-5fps SDs across 10. But again, when one is dealing with convective vs conductive, such SDs are not uncommon. [the 32ws rounds we shot for RDPM2 generated 5-6fps SDs and with a scope shot 1.5-2 bullet diameter 5 shot groups.]

I have also read about reloading and your environment, i.e. humidity, temperature, etc. I guess you go on forever and try to eliminate every variable but that would be impractical and definitely 'unfun.'

-- yes, the ambient conditions do affect the final load one produces... but only to the extent that the components are exposed to those conditions, ie, the powder is a sponge and will suck moisture out of the air... if given enough time. For our reloading, this means: throw the charges for a block of cartridges in 10 minutes or less; get the powder out of the measure as soon as done and back into the magazine; and get bullets into the freshly thrown rounds.

I have given up on trying to make super-perfect rounds, been there, done that. Now I have fun crunching bullets that are fairly consistent and easy to make without having to scrutinize every detail.

-- I don't know if we're trying to make such rounds... but we've found that being careful about how the rounds are made up has a serious affect on the quality of the shooting... and for us that's what it's all about ... 30+ years of reloading and we're still learning. ;-)
do shoot straight,
greg
www.gmdr.com
 

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Perferator said:
Greg, what powder would you suggest for the Hornady [email protected] avg velocity and good/better accuracy than the 4198's?

I'm currently using WW and R-P cases with CCI200primers

Perferator

Perf - how about vvn130, vvn133, rl10x and benchmark? We've had very good results with the vvn powders in general; likewise what work we've done with both rl10 and benchmark has been positive. The 130 tends to split the difference btwn the two 4198's, so it doesn't do much to improve the load densities, but it does measure reasonably well, and is much less temperature sensitive. The 133 is a little slower, ie, one can think about full case/slightly compressed loads which either helps the ignitions (read: smaller SDs). The rl10 (turns out to be made in sweden) again meters reasonably well, but for whatever reasons, seems to generate smaller SDs and groupsizes given the same handling as rl7 or rl12 - we've only gone through 1 lb so far, but unlike some powders, very much look forward to working with more. The benchmark, again, we're only 1 lb down the experience road with it, but like the rl10, are looking forward to working more with it. The benchmark also has the advantage of being very short cut extruded powder and meters like a hs6 or hs7, ie, very well. [if you're interested in the relative speeds of the 4, you might take a look under the "additional data" on our website, under the 500gr 450 marlin loads... and yes, the max loads are missing, ie, this is data from approaching a new cartridge with a new bullet and weren't sure where the max would be, so we started low and worked upward... and in the case of the vvn's didn't get there before we had our root canal etc problems... but the graph will show how the powder RQs relate.]

do shoot straight,
greg
www.gmdr.com
 

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BestLever said:
Hello Riflemen: Thanks, that's good stuff. I'll chew on it for a bit and decide what I'm going to do. I'm not trying to benchrest the 45/70 so I'm not looking for super-perfect ammo. I'm just thinking about adding one or two steps to the quick handload to get better uniformity. All of your ideas are great. Uniformity being the goal, I think that changing to a BR primer and keeping the ammo temp. consistent might be enough to satisfy me. I don't want to spend a great deal of time making ammo for this rifle. Again, thanks for sharing your experience. I'll pass it on as needed:wink: BestLever
Best -

If I were going to do two things to improve the loads: I would pick a powder which results in slightly compressed loads (ie, must be extruded - never compress ball powders), this by definition will bring the SDs down; pick a powder which ignites easily - this also helps keep the SDs under control; and I'd keep the subsequent rounds out of the chamber until they're ready to shoot (ie, keep all the rounds at the same temp), which also helps keep the SDs down. How's that for improvement at no cost? ;-)

ps. how was the summer on the north side of the border? (at least so far) we've had the coolest summer on record (6 days total over 100, 106 the highest) and 2 days of rain [last summer we had 5 days at 115 or above, 1996 had 21 days at 115 or above].

do shoot straight,
greg
www.gmdr.com
 

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Greg...

Back in the old days, when I actually had time to do such things, I was searching for other ways to make my handloads better. I am by no means a benchrest shooter, I just punch holes in paper and the occasional beer can. It's the actual reloading process that intrigues me; I have said before I almost like reloading more than shooting the stuff up.

I chose 2 rifle rounds to try to fine tune: The .223 and the 45-70. I was shooting the .223 in my AR-15 and found I could achieve performance equal to the factory ammo I was shooting but nothing extraordinary, even with the steps mentioned in my previous posts. I realize it now that part of it may have been my components. I was using Norinco cases (I get a split case about every 10 rounds) with standard 55 grain FMJ bullets (not the ideal set up for 1:7 bbls.) The time and cost consumed making that ammo... well, I was better off just buying factory ammo.

The 45-70, I realized, was not really intended for what I was asking. Too much case volume, I didn't have a great variety of powders to choose from for rounds fired in a lever action with it's own set of variables. I found I was going to the range with 100 rounds, 10 each with different powder charges and bullets, etc. and getting nowhere. They were all accurate, for the most part, and consistent, for the most part, and they would hit the inside circle of a paper plate at 100 yards, my barometer for minimum accuracy.

I also tried fine-tuning 45 Colt cases for my Ruger Bisley. I finally realized the accuracy of this particular pistol would never be what I wanted it to be and, sadly, traded it off.

Using the same round tuning for my .41's, however, I achieved great strides in accuracy!

So, in conclusion, I realized a number of things from my experiments in reloading: 1) I always measure every rifle charge on a balance scale. I still use a measure on my normal pistol rounds (and the velocity deviation reflects this) except on maximum loads; 2) I still trim out the primer flash hole. Trimming out 500 .41 cases is a exercise in tedium but I do it. And it's done and I can go on with my life; 3) I have given up roll crimps on pistol rounds, I use taper crimps on pistol ammo and Lee Factory Crimps on most of my rifle ammo. This makes case length much less a factor and adds in the longevity of my brass, my roll crimps were tearing up my case mouths; and 4) I have forced myself to broaden my horizons with different brands of powders and primers. I have switched from CCI primers to W-W because of better performance in identical loads. I am also having very good luck with Winchester powders in my pistol rounds and IMR in my rifle rounds. This is a departure from my 'Hercules (Alliant) powder for everything' mindset I had previously.

...so stick that in your case and smoke it... :wink:
 

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Charlie98... see >>>'s

Greg...

Back in the old days, when I actually had time to do such things, I was searching for other ways to make my handloads better. I am by no means a benchrest shooter, I just punch holes in paper and the occasional beer can. It's the actual reloading process that intrigues me; I have said before I almost like reloading more than shooting the stuff up.

>>> have to agree: seems most appreciate the "fine art of shooting"... only a limited few seem to appreciate the "fine art of reloading"... but we find both to be worthwhile endeavors.

I chose 2 rifle rounds to try to fine tune: The .223 and the 45-70. I was shooting the .223 in my AR-15 and found I could achieve performance equal to the factory ammo I was shooting but nothing extraordinary, even with the steps mentioned in my previous posts. I realize it now that part of it may have been my components. I was using Norinco cases (I get a split case about every 10 rounds) with standard 55 grain FMJ bullets (not the ideal set up for 1:7 bbls.) The time and cost consumed making that ammo... well, I was better off just buying factory ammo.

>>> probably done the same for 20ish cartridges: 218 bee thru 458 lott - each is a challenge, each has its own weirdnesses - but eventually for most the/a sweetspot is found... then we get bored and move onto another cartridge. This last winter it was the 256 win mag and the 300 wsm. We used what we learned about the 256 to shoot in RanchDog's Postal Match #2... though kind of frustrating using a load that'll shoot 5 at 50y at 2 bullet diameters, to go to iron sights and to be grateful for 1.1" groups (says something about the virtue of scopes). Now we're working on the 264 win mag and finishing up the 44-40.

The 45-70, I realized, was not really intended for what I was asking. Too much case volume, I didn't have a great variety of powders to choose from for rounds fired in a lever action with it's own set of variables. I found I was going to the range with 100 rounds, 10 each with different powder charges and bullets, etc. and getting nowhere. They were all accurate, for the most part, and consistent, for the most part, and they would hit the inside circle of a paper plate at 100 yards, my barometer for minimum accuracy.

>>> have to agree: if one is going to use conductive ignition, then the 4570 case is way too large for good shoot'ng... we went down that road for several years, tried about every slow rifle powder trying to find clean ignition and full cases - all we found were ok shooters, and lots of unburned powder left in the action. That's when we went back and read up on what the shooters of 100 years ago were doing... and came to understand convective ignition... and in that context the 4570 is just the right capacity for make a very fine bench rest shooter [last year's RD PM our 4570 target was just under 1 moa for 5 shots - 12gr vvn340 driving 405gr rnfp]. As far as trying powders, our std box is one powder type, five powder weights, 10 round per [can't get meaningful statistics with less than 10 shots per - 5 shots groups may offer hints of the underlying stats, 3 shots groups are meaningless]. Standard range trip is a minimum of 6 boxes, nominal 8 or 10, and when we have to turn out the statistics, as many as 14, ie, 700 rounds - absolutely necessary to have a computerized chronographing system to handle all the data and annotations.

I also tried fine-tuning 45 Colt cases for my Ruger Bisley. I finally realized the accuracy of this particular pistol would never be what I wanted it to be and, sadly, traded it off.

Using the same round tuning for my .41's, however, I achieved great strides in accuracy!

So, in conclusion, I realized a number of things from my experiments in reloading: 1) I always measure every rifle charge on a balance scale. I still use a measure on my normal pistol rounds (and the velocity deviation reflects this) except on maximum loads;

>>> we've found that we get much more consistent loads by throwing charges - find that most electronic scales are only +/- .1gr +/- .1gr in float, ie, .2gr errors aren't unusual. Found that most beams were somewhat better, but for light loads had stiction problems. Found the by using a good electronic balance and by throwing 10 loads we can get +/- .01gr on good days, .02gr accuracy on the rest. But clearly this is limited to powders which want to be thrown, ie, rl22, i4350 do not; titewat, waap, blc2, benchmark etc do.

2) I still trim out the primer flash hole. Trimming out 500 .41 cases is a exercise in tedium but I do it. And it's done and I can go on with my life;

>>> honestly have never seen any difference with or w/o cleaning the flash holes.

3) I have given up roll crimps on pistol rounds, I use taper crimps on pistol ammo and Lee Factory Crimps on most of my rifle ammo. This makes case length much less a factor and adds in the longevity of my brass, my roll crimps were tearing up my case mouths; and

>>> have basically given up on crimps entirely (other than to "unbell" the case mouth) - found that for most rifle cartridges they did little to enhance ignition (found much much more effect by undersizing the neck by a thou)... and for lead bullets want to stay as far away from crimps as possible - don't need the uncrimping process resizing my bullets.

4) I have forced myself to broaden my horizons with different brands of powders and primers. I have switched from CCI primers to W-W because of better performance in identical loads. I am also having very good luck with Winchester powders in my pistol rounds and IMR in my rifle rounds.

>>> have to agree with the winchester primers - gave most of the rest a try, but the chrono kept saying that the best SDs were associated with the WW's, ie, only a fool fights the chrono... though have found for special cases that the CCI BR primers are appropriate. But otherwise, the blue primer boxes arrive here in 5k or 10k bricks.

This is a departure from my 'Hercules (Alliant) powder for everything' mindset I had previously.

>>> strange how that happens - in the '70s it was AA powders... now with three powder magazines and probably 200lbs on hand - I suspect if I were count, we'd have easily 100++ powder types. Of note: of late have been having very good results with Vectan's $8/lb powders - BA10 and A0 are second to none for convective target loads. Also have been working with the Rex powders (also $8/lb) - though not as consistent as the Vectans, are significantly better than the average $20/lb powder.

...so stick that in your case and smoke it...

>>> can I just drop the hammer and see if the chuck does a backflip... 17/22-250's can be fun.
________________
Charlie Niner-Eight, out.

>>> do shoot straight,
greg
www.gmdr.com
 

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I haven't been reloading all that long, so could somebody tell me what a "convective" and a "conductive" load are? I've never heard of either term before. Thanks.
 

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retiredsf -

Conductive ignition is what most modern reloaders are used to; convective ignition is how most loads from 100 years ago ignited.

In conductive ignition: the primer goes off, ejects its hot gases and bit of molten metal into the base of the powder column. The heat from those gases are absorbed by a small number of grains of powder. From then until the whole charge flashes over the deflagration front is conductive, ie, the heat of one burning grain is transmitted to the next through physical contact. This process takes time, which is intended, and which is what gives the combustion vessel time to expand so that when the bulk of the charge ignites, there is room for all the generated gases and to not be over pressure. The progression during this time is on the order of 2-5m/sec (by no means an explosion). Once enough hot gases have been generated and all the grains have been brought up to and past their kindling point, then the whole charge flashes over and begins what would look like convective ignition. In the example I gave elsewhere, h4831 in a 264 win mag doesn't reach max pressure until the bullet is some 6+ inches down the barrel. This also means that the crown pressure is still quite high when the bullet exits the barrel (read: loud report) [if the bullet travels down another 18" of barrel, in doing such it has only increased the chamber volume by 2x, ie, the pressure is 1/3 of what it was a pmax, ie, 20kpsi crown pressures are not unusual.].

In convective ignition: the primers goes off, ejects its hot gases and molten metal into the powder chamber, but because the chamber is sufficiently "unfull", the powder's response is to be blown around in said chamber, where all of the surfaces of all the grains are being bathed in the primer's 4000-5000deg gases. If there was suffient heat generated by the primer to cause the surface of each grain to exceed its kindling point... then all the grains begin burning simultaneously, and continue to burn for a duration controlled by the physical geometry of the grains (all grains burn from the outside to the center at 2-5m/sec, ie, a 2mm thick flake will burn through in 200-500usecs, a .5mm flake will complete burning in 50-120usecs; conductive burning can last 1000-1500 usecs). In convective ignition, pmax is typically reached before the bullet is fully into the rifling and into the barrel. Also because pmax occurs essentially at t=0, it'll result in a much lower crown pressure (read: much less report/muzzle blast). Clean convective ignition can *only* occur if there is sufficient heat from the primer, for long enough (remember: once the primer goes off, the chamber walls are sucking up 70% of the heat, quickly), to bring the grains to their kindling points. If this is not the case, then one gets very ragged conductive ignition. [for wsr primers this means no more than ~ 12 grains of powder; for a wlr 15-16 grains.]

Other differences: because of the very different shape of the time-pressure curves, conductive will generate more (~2x+) more muzzle velocity while staying under the max pressure for a firearm [because it has a larger combustion chamber into which to generate its gases, hence can generate more gases and still stay under max allowable pressure (pressure = amount of gas / volume)]; but will also take 4-6x the amount of powder to do such, and will likewise waste more than half (or worse) of the pressure generated by the charge in the form of muzzle blast.

In convective ignition: because the powder burning occurs so early, it is rare for any powder to go unburned before the bullet exits the muzzle, ie, essentially all the energy that was theoretically available from the powder grains goes go propelling the bullet; and by the time the bullet leaves the muzzle the gases have been cooled by the expansion of the chamber, and by heat loss to the barrel, the result is a muchly attenuated muzzle blast/report. One other major difference in conductive is: one will *never* see sooted cartridges (where the pressure rose so slowly that the brass didn't seal the chamber quickly enough and some gases/unburned grains leaked down past the case sidewalls and out past the bolt). Likewise, because all the grains are ignited all at once, one will find zero unburned grains in their actions. The other advantage of convective is: the bullet engages the rifling while being driven by pmax or near pmax pressures, ie, the engagement is very clean and without hesitation, ie, very repeatable (desirable feature for target shooting).

We got into the conductive vs convective research a decade ago, then we were asked if we could develope CAS velocity loads for a 4570. Initially we approached this by reducing std 4570 loads... and saw very very ragged ignition; then we tried the other standard "trick" and tried using slower and slower (rifle) powders to get the velocities down... and saw again very ragged ignition and lots of unburned grains in the action. At that point we were left scratching our head, butts and whatever else we could find. Then an ahha occured... we were reading a copy of phil sharpes reloading book/history of reloading, and came to notice lots of 30-06 and 300hh etc (read large, maybe magnum sized, cartridges which one does not nominally think of as being powered by Unique and other what today we'd call pistol class powders). After doing a little research the 2nd ahha occured: they did this because... they didn't have any choice/anything slower (4350 didn't become available until 1945, 4831 until 1948 etc) - pre wwii, the slowest powder was dupont 17.5, or about the same RQ as today's i3031. Given that insight, instead of tying to make slow powders work (in the context of our 4570), we gave a half dozen pistol powders a try.... and were pleasantly surprised. Since then we've launch 100k +/- rounds downrange developing an understanding of the physics of convective vs conductive.

Note: detonation is simply an undesired/unplanned for form of convective ignition, ie, convective ignition turns a liability (unexpectly fast ignition) into a virtue, ie, a load designed to be convective can't detonate on one, in that it is already, by design. The failure mode for convective, is to revert to conductive ignition (which occurs with too much powder to be heated by the primer gases... or if (too much of) a ball powder is used, and initially all that happens is the balls get caught in a corner and use all the heat to simply melt into a mass, and then burn conductively).

Probably more than you'd care to read about the difference (but if you really want to read more - there is a paper on our 1999 discoveries of conductive vs convective on our website - url below, look under levergun data/studies - there is a 2004 paper in process covering the physics which have been learned since then).

Bottom line: if one isn't looking for the max possible velocity out of a gun, and/or is looking for much smaller SDs/ESs, and would like to use less powder, then convective is possibly a place to look. If one is using more than 12-16 grains of powder, and/or, is looking for maximum muzzle blast/flash, and/or is using long bearing surface bullets, then conductive is the place to operate.

Because of the reduced SDs generated by convective, for all our competitive shooting over the last 5-6 years we've used convective. [our 256 load used in RDPM2 generated 7-9fps SD's (7.5gr of AA9 driving a 75gr speer fnc); the 32ws load (6.0gr of waap driving a 170gr lead rnfp) generated 4-6fps SDs. The 256 load with 24x scope, from a bench, will drive 5 bullets through a 2+ bullet diameter hole (ie, .3" groupsizes); the 32ws load will do likewise, ie, .45" groups [5 shots, 50yards].]

Hope that helps, and do shoot straight,
greg
www.gmdr.com

ps. of note: becaused convective generally is used to generate target type velocities, it is generally used with lead bullets, where the chances of hanging a bullet in the barrel are almost nil; over the last year we've started looking at convective and jacketed bullets - and yes it is possible, but we'd like to talk less about such, in that the chances of hanging a bullet are 100x that of using lead. In lead shooting, we've had safe loads down to 550fps; in using jacketed, it's looking like 1400-1500fps is a minimum safe velocity. [our current delight is the 264 win mag, driving 85gr sra hp's in the 1400-2000fps range, with sub sub moa accuracy - the target we posted elsewhere was only the first, and since then the best has dropped to .5 moa or a little less (this is for 10 shots)]
 
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