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Here we have a statement that not only conveys the right idea with the wrong terminology, but the whole concept of "slugging your bore" invites you to focus on a condition that may be only a small part of what has to do with bullet fit. Specifically, cast bullet fit. There's a lot more to it than "slugging your bore."

First, let's define some terms:

Bore: Mistakenly used for "barrel." "Bore" has a precise meaning and is the land to land dimension in the barrel. It does NOT mean "the barrel" or "the grooves." When a person says he's "slugging the bore" he's really slugging the barrel, and the groove dimension, not the bore dimension, is what he thinks he's after. Learning just the groove dimension is shortchanging yourself in terms of cast bullet fit. Bore dimension matters a lot.

Groove: The cuts made in the rifled barrel that leave raised lands. It is the lands that guide the bullet. The groove defines the maximum side to side dimension of the rifled portion of the barrel and the is largest diameter the bullet is intended to fit....in the minds of most users, anyway. The guy that "slugs his bore" is usually trying to find his groove diameter. In barrels with odd numbers of lands or microgrooves finding the groove diameter can be a challenge.

Throat: That portion of the barrel that is forward of the chamber neck that has no rifling whatsoever. The throat is often as large as or larger than the groove dimension of the barrel. The throat may be cylindrical or tapered. The throat is way, way too much overlooked when it should be THE issue if the rifle has one. If your rifle has a throat, find out its dimensions. It is usually more relevant to fit the throat than the barrel.

Leade: The leade begins in that portion of the barrel where the rifling starts. The leade ends where the rifling reaches full height. Leades may have an abrupt or gradual taper. Cast bullets often do better with a more gradual leade.

The problem with the guy "slugging his bore" is he's not paying attention to factors that may be more relevant than the actual groove diameter of the barrel.

A checklist for those guys properly investigating chamber and barrel dimensionality:

When the barrel is slugged, does the slug drive through evenly or does it have tight and loose spots? Where are these tight and loose spots in the barrel? Oftentimes, they are under stampings, dovetails, or constrictions like thread choke in a revolver.

What is not only groove diameter, but bore diameter? Many cast bullets are bore riders (the front end of the bullet rides atop the lands and receives guidance from them) and proper fit of the bore riding portion of the bullet is needed for best accuracy. This can be as critical as matching or exceeding groove diameter, as a loose bore riding bullet is asking for a poorly supported bullet to shoot accurately. Oftentimes it won't. Bore diameter in odd land barrels is often most easily found with pin gauges or with bore riding bullets that have a known nose diameter.

Does the rifle have a throat? A slugging of the barrel won't tell you. A chamber cast or a pound slug of lead will tell you throat diameter and length. It is often critical to fit the throat, if one is present, and this is too much overlooked. If you have a throat........pay attention to its shape and dimensions. If you don't know, you're missing out on something important.

What is the largest cast bullet the rifle will accept in terms of neck clearance? In rifles without much of a throat, like Marlins, this gives you a safe idea of what is permissiable and possibly a smoother transition between case neck and barrel as the bullet exits. My 35 Remingtons, for example, will accept a cast bullet of up to .362" and still allow chambering.

What does the chamber look like? A chamber cast will tell you. Overlong necks and abrupt starts to rifling origins, for example, often doom cast bullet accuracy.

How abrupt is the leade? Leade angle can be critical to treating a cast bullet gently. Sometimes rifles can be made to overcome this, but everything else has to be right and if it's combined with something like an overlong chamber neck I'd rather hit my thumb with a hammer repeatedly than try to get it to shoot cast bullets. For example, in my no throat, abrupt leade 35's, a bore riding bullet of close fit to the bore helps mitigate some of these issues versus some of the alternatives. Microgroove 35's often like fat bore riders and proper fit is not easily found. Actually, good cast bullet accuracy is not easily found either if unsuitable designs are used.......and that might be most of those offered in that particular caliber! Surprisingly, all body, Loverin type bullets do less well for me sometimes. My 45-70 is rather the opposite. In some instances a reamer can improve an unfavorable leade or throat. Given the chances of reaming a non concentric throat or leade this job is best left to someone with experience.

Do yourself a favor. Do more than 'slug your bore" when investigating the suitability of your rifle for cast bullets. More dimensionality in your measurements will tell you the "why" of what will work and help you avoid making bad choices in cast bullet selection. More knowledge is better than a cursory approach to cast bullet fit.
 

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Discussion Starter · #3 ·
Boy, that looks kinda weird. The neck region of the case looks like it was tapered. But maybe that's the picture being deceiving.

It does help somewhat, so thanks.
 

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great topic, was wondering what I was missing with just "sluggin the barrel".. you state

Does the rifle have a throat? A slugging of the barrel won't tell you. A chamber cast or a pound slug of lead will tell you throat diameter and length. It is often critical to fit the throat, if one is present, and this is too much overlooked. If you have a throat........pay attention to its shape and dimensions. If you don't know, you're missing out on something important.
If I get an accurate throat diameter what will that tell me for bullet size? or does that just relate to the OAL and bullet dimensions.
 

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Boy, that looks kinda weird. The neck region of the case looks like it was tapered. But maybe that's the picture being deceiving.

It does help somewhat, so thanks.
Pleasure :)

What you see in the photo unfortunately is what it is.

DSCF2033 resized.JPG

Pictured now with a full length sized case and the 257-420 to help highlight all that room....But wait there's more.
 

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DSCF2050.JPG

Picture taken under different light cast, may help to see whats going on in there.
Is someone has the ability to take one of these images to add arrows or pointers for descriptive purposes by all means do it.
 

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Discussion Starter · #7 ·
Oh good grief. That barrel looks like tomato stake.

Mr, if a throat is present size the bullet to that diameter. Throats are almost never smaller than groove diameter in rifles so this is a more relevant dimension than groove diameter.
 

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wow learn something new everyday on this site. I guess I need some more technique on measuring the throat. i appreciate the information.
 

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I hope you guys keep adding to this thread .... text and pictures make good company too.

I'll be burning this onto paper for future reference:)


JD
 

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Discussion Starter · #10 ·
LFD knows why his rifle acted as it did with cast bullets. A guy who just "slugged his bore" (barrel) wouldn't have a clue.

"Hey!" He would say. "I slugged it. I know my groove diameter and allowed for that. How come it still won't shoot?"

Had Joe "Bore Slugger" bothered to get relevant information instead of just a slug he would know.
 

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Great Thread--

My eyes have been opened---keep em' coming. Being a "Bore Slugger" myself I can use all the additional info./help I can get. Thanks.

Steve
 

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This link helped me understand what 35Rem is talking about a little better. I don't reload yet (still buying equip.)so I needed to look at more info to make the "pound slug" clear. I have bought what I needed to slug some barrels, but now wonder if I need to or not. If I slug them and buy .002 over Cast Bullets have I wasted my time? Will I not be able to use them? I am so confused! :confused: :dontknow: This pound slug may be the best way there is, but others success with slugging the barrel was good enough for me...I think.
Firearm Chamber Specs
 

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Discussion Starter · #13 ·
The additional information is a diagnostic tool when things do not go as planned or anticipated.

I often take the path of least resistance myself and try a diameter that has worked in other rifles and go from there. If things aren't working out more information as to why is needed, which is where these suggestions come in. They are also useful avenues of exploration for those interested in the best possible results.
 

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IMG_20140608_140030817.jpg
Here's a chamber cast of a 32-40 I did awhile back. If you look closely at it there isn't any indication of a "throat" the rifling goes to the brass with an abrubt "lead" at the end. I was able to select my mold design with a little help from it. Not knowing much about the old chambering this helped me gain a little understanding.
 

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Is the cerro-safe (sp?) a one time use or can it be melted down and reused ?
 

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Discussion Starter · #16 ·
If you really look closely at Sparky's chamber/barrel cast, you will see what he means when he says the rifle has no throat......just a taper from chamber neck diameter to barrel diameter. If there was a throat....there would be some area ahead of the chamber neck that had no rifling, which is what the definition of a "throat" is. This is also called freebore.

I'm not sure I'd call the transition from neck to barrel a leade. Leade should commence somewhere beyond the neck recess, and there isn't even much of that in terms of a gradual increase. It looks sorta like the rifling goes to full height in a very short distance. However you choose to define it.....that's a very abrupt leade angle. In other words, the rifling goes from not being there to full height in a very very short distance.

Chambers/barrels such as this mandate that the cast bullet cannot have much full caliber bearing surface outside the case neck or otherwise the round cannot chamber as the rifling prevents the bullet from seating. A clever guy that wants a heavier bullet that does not seat so deeply in the case can work off the known dimensions of the bore (land to land diameter or distance) to create a bore riding design that allows more bullet weight and/or shallower seating in the case, freeing up some powder capacity. All assuming, of course, that the round is of proper overall length to function through the action. Most levers have a maximum they will accept in OAL. In the 336 this is 2.55-.257." If this is known, then an appropriate design can be chosen.
 

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It can be melted down and reused. It's kind of a hassle to use and there's a time factor for measurements. I've done pound casts (a bit rough in my opinion) also and I like the cerrosafe method better so far.

Thought I would add this after reading 35's very good comments. The mold chosen for the chamber does in fact have a sharply tapered nose and a bore riding front band. It's the only way the cartridge will chamber without resistance from engraving the bullet. The bullet shown in the pic is actually a 8mm and did not work well.
 

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Discussion Starter · #19 ·
photo-5.jpg

Okay, after all the excellent photos posted above how could I top that except to drag the overall photo quality down with something taken with my IPhone?

The following is a chamber cast taken of my BarSto 45 ACP barrel. In it can be seen what passes for a throat, which is a gap between the chamber ledge and the start of the rifling. The leade is that place from where the rifling starts to where it is full height, and with a casting can only be determined by measuring the depth of the groove left in the casting.

In any event, this barrel is different than that in my Ruger P97, which looks more like Sparky's 32-40 casting. This barrel allows a bit of bullet outside the case and in so doing is more tolerant, and in theory more cast bullet friendly, than barrels that having rifling right up to the end of the chamber. In pistols, though, other things like barrel/slide fit may be more limiting than how the barrel is throated. In rifles, it may be a major player in how the rifle shoots a cast bullet. Having a choice in terms of bullet seating possibilities widens the potential list of cast bullet designs that may be used.
 

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Discussion Starter · #20 · (Edited)
Now, let's contradict ourselves (meaning me) a little. I just said a gradual taper to the leade and a bit of a throat are more cast bullet friendly.

First, why is that so? And second, can that be overcome to some degree?

Relate to the sizing dies found in lubrisizers. They used to have no taper into the sizing section, and if the top punch and ram started it into the die crooked......it stayed crooked all through the sizing die. The result was a bullet sized off center. They now come tapered, as do the Lee push through dies you mount on your press. Much better.

Now, take a chamber and relate the same thing. Potentially, the gradual leade and throat allow a bullet to be centered before entering the barrel itself. Sounds pretty good and is the best theory we have, anyway. There is considerable reason to believe this is important.

Now.......are you screwed if you don't have it? Well, not if you know something more than just your groove diameter from "slugging your bore (barrel)".

With Sparky's rifle, we now know bore diameter and neck diameter of the chamber neck....so we can fill the chamber neck with a bullet that takes up the slop twixt chamber neck and case neck and leaves a closer tolerance fit. Since the bullet's sides and back end have less room to wander before entering the barrel, it has the potential to shoot better. Since his bore rider fits the rifling closely, the front end of the bullet steers the back half of the bullet "truer" into the rifling.

Contrast that with a bullet fired in the same chamber that has loose bore riding fit and too much chamber neck clearance. Worse results are to be expected, and you'll probably get them.

Chambers like this are exactly WHY measuring more than just a slug driven through the barrel is beneficial if you want a cast bullet to shoot well. With the considerable number of custom makers of cast bullet moulds out there, it is possible to make a reasonably poor chamber shoot quite well.

I hasten to add, though, that I nor anyone else can work miracles with cast bullets in a really bad chamber. You're better off throating it and saving yourself the aggravation and wasted time. In this instance LFD's chamber would be a great topic for discussion. There is a whole laundry list of problems with that chamber, and that opinion comes from just looking at a picture! Once we start measuring things the whole sorry debacle would be made very clear to everyone. Once you see what a bad and a good chamber look like, you have a perspective you didn't have before.
 
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