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I've sifted through a lot of the posts here about the pros and cons of .375 vs 38-55 when considering a rebore and I've still not been able to make up my mind one way or the other. What I hope will happen here is that here within this one thread a few of you old pros will chime in with just the right info to push me off the fence one way or the other.
I already have a 38-55.....got a hyphenated hat too......and I've had a couple .375s but sold them both for one reason or another but,
I have this nice old Texan 30-30 that I really want to send to JES for a rebore. I just want to get all the facts together here so that I can feel confident when I send it off that I ask him to do what will make it the most useful for me.
As I said I already have a 38-55 cowboy that I can use to shoot lead bullets in, so if I want this one to use mainly for jacketed bullets should I just go for the standard .375?
Can the 38-55 be loaded up as hot as the .375?
If I go the 38-55 route, what bore size should I request so that I can shoot the jacketed bullets that are available in it?
If it sounds like I'm not really sure what the heck I want then you're reading this pretty close. ??? ::) :-\
 

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The 375W brass is a little heavier than the 38-55 brass. Some would say it will stand more pressure. IMHO the 38-55 will generate all the pressure you want in your Marlin Texan. Goat has one that JES did and his comments are very favorable. In real usage, from a pressure perspective, I don't think you'll gain anything with the 375W (in real performance) and chambered in 38-55 it will still shoot the 375W. JES can give you the right bore size and twist for jacketed and you will still be able to shoot cast if you choose to.

From pure nostalgia, the 38-55 gets the nod. Since you already have these, the 375W looks interesting - however the real difference between these two (in the same rifle) is the headstamp on the case. Twist and bore size you can work out with JES, regardless of which you choose. Good luck, cause either way, it will be a winner. From my own viewpoint, I wouldn't want to shoot cast, as, again from my viewpoint, you stand nothing to gain with jacketed in this round, other than higher cost of shooting. My last elk was shot with a cast bullet from a 32WSpl. You should expect no less from your cast loads. Again, good luck, enjoy, and let us know.

Jeff
NRA Life
 

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I am facing the same question with a pre safety 336 (wish it was a Texan!), leaning toward the hyphenated for the Lyman 284gr at .376".
 

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Send Swany a PM with the same questions..........he'll specify the bore diameter and twist that maximizes the round's abilities, then you can call JES and see if they'll do it the way he says. Swany is a retired Master Machinist and longtime benchrest shooter, and has some definite ideas about how to do it right.

I'm with Jeff on the 38/55 having all the thump you need. I used 38/55 starting load data in my 375 with 4198 and the 335-grain bullet, and it about backed me out of my teeth. A full charge would be more than I could enjoy for long. And off the bench it's downright rude! :eek:
 

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You have the 38-55 brass already, it's plenty strong for the loads you would use in a Marlin. If your blowing primer pockets on 38-55 brass, you way over pressure for the 375 anyway. DP
 

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Don,

I think you received good advise from everybody...........IMO....... They both are really equal to a handloader, so choose the one that makes you tingle.............The 38-55 gets the nod, for nostalgics...........

Tom
 

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sounds like what you "want" is a ton of money .... which just makes it easier to get what you "need" ..... :)

personally, I'm very sentimental toward .375 .....

Cheers,

Carl
 

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As much as I love the romance and lore of the 38-55, I really love my Marlin 375. It will do everything the 38-55 will do, and a bit more. That doesn't mean I don't still want to build a 38-55, but it does mean I can be patient while I look for a suitable donor rifle. I figure the 375 can keep on shooting those accurate little Hornady 220's, and the 38-55 will never see anything but lead. :)
 

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dpe.ahoy said:
You have the 38-55 brass already, it's plenty strong for the loads you would use in a Marlin. If your blowing primer pockets on 38-55 brass, you way over pressure for the 375 anyway. DP
I think you have it backwards. The SAAMI pressure for the 38-55 is a lowly 30,000 CUP, while for the 375 Win, it is 52,000 CUP http://www.leverguns.com/articles/saami_pressures.htm. Now if one loads their marlin to TRUE, 375 Win, levels, then do so at your own risk. I have pushed my 375 Win, 94 Big Bore, to 2250fps with a 250gr bullet. That level load would destroy a 38-55 brass, and possibly the Marlin along with it. Just for comparison, that's 30-06 levels of velocity with a 250gr bullet.

Now, no doubt, the 38-55 can be loaded to it's top level in a Marlin, you are going into uncharted territory, load wise. Now just because you chamber it for the 375, in a Marlin, I'm not sure if that fully qualifies it at a full blown 375 Win.

How many guys here load their 375 Marlins to 2480 fps with a 200gr bullet. That IS a published load from Hodgdon powders, in fact they list two loads with the 200gr over 2400fps, with the 220gr loads running well over 2200fps.

I say go with the 375, use 375 brass and load it to what ever Jess says is safe, but start with 38-55 loads. Now I might get flamed for my comments, but there is little doubt, the 375 Win was created for the stronger (than the Marlin action too) action of the Winchester 94 Big Bore, which was also chambered for the 307, and 356 Win. All of these are 52,000 CUP loads.

Using the 38-55 brass at TRUE, 375 Win load levels, is asking for trouble.
 

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38-55 brass will not let go at pressures above 30,000 cup unless you run it over the pressure of the 375. I have run it up in my factory MARLIN 375 and it has been reloaded without issue, pockets are still tight. Same with my 45 colt brass, loaded hot and fired out of my 454 Casull. Check with the makers, they don't use a different formula for each run of cases, 38-55 brass is not "weaker brass" than 375, merely drawn a bit thinner. I agree the Win. BB may be stronger, that was not what I said. What I said was, if you load hot enough to blow primer pockets in 38-55 brass, you are running higher pressures than the 375 is rated for by the SAAMI. As to the Marlin being strong enough to handle the 375's pressure, I don't think they would have put over 16,000 of them out if there were concerns on them being destroyed running factory loads. Just my opinion, mind you. Maybe Tom would comment on the strength of the M-375? DP
 

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JES bores the groove to a dia acceptable to use .375 bullets which is a win win either way. He chambers for 38-55 with that dia groove, which will accept most cast bullets of the right size. Next the twist is a little slower than factory .375 which gives you a pressure advantage when pumping it up with handloads. Less twist lower pressure.

Brass is the question when going on the upper end especially with the heavier bullets available. While not much difference in the new Starline here is a photo of the sectioned brass.

I do believe you would be better off with the 38-55 and I'm pretty sure you can shoot .375 in a JES rebore, ask him or others who have done that here.

I will tell you my 38-55 CB with the larger groove has seen some +P+ loads stabilizing that dang 220gn Hornady before it would quit keyholing. I don't publish that load and don't use it, but then I have and could. I have plenty of the proper size bullets in cast and jacketed for that gun. My current 250gn jacketed load is in the .375 win area and shoots fine with less pressure due to the larger bullet dia and slower twist.

Here is what you are dealing with brass wise.
 

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Good pic there swany. You can see the thicker sides of the .375 that some say don't make any difference, the thin .38-55 brass is just as strong.
 

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Discussion Starter #14
;)
Gentlemen, I'm accomplishing here exactly what I hoped for. I appreciate each and every post and hope they will continue within this thread. I haven't absorbed it all but I'm getting educated and sorting it out as I go.
 

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I am not that familiar with the Marlin 375's but weren't they built stronger than the regular 336's like the Win BB's were built stronger than the regular 94's to accmodate the higher pressure of the 375? I thought I read that somewhere but I bet someone here will know for sure.

If the Marlin 375's were built stronger I think it might be a problem shooting full 375 Win loads in a regular 336 action built for 30-30 pressures. If the 375's were built to the same specs as the 30-30's then I would think it should be no problem.

I just had an 1893 rebored by JES from a 30-30 to a 38-55 and Swany is right that JES bores to a .375 diameter. I don't think he has options for a larger bore. I have been trying .376 and .377 cast bullets to see if my rifle had a preference and both shoot great but I think the .377's have a slight edge.
 

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If your chamber is cut large enough that you split the side wall of 38-55 brass, using 375 brass might give you one reload before it would split. The chamber contains the pressure until you are so high on pressure you blow primer pockets. If you do not have enough pressure to "seal" the case wall against the chamber wall, you will have smoked case walls on the outside. Once the brass expands to fill the chamber, the chamber contains the pressure. As I said before, 38-55 brass is drawn thinner, the brass is not "weaker", just thinner. This allows a bit more powder to fit in a case if needed for a bulkier powder. Another way of looking at is, more case volume with the same weight powder charge= less pressure, or more of the same powder at the same pressure= more velocity. Just one of the benefits of an "improved" case, which when improved will give you thinner sidewalls where the brass stretches to fill the chamber. DP
 

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No one has said the sides of the case was going to split. What was mentioned before was someone was blowing primer pockets, which according to the real experts at Hodgdon, not we armchair experts, that when you have blown a primer, or expanded the primer pocket enough to loosen the primer, you have not only exceeded safe levels, you have gone far beyond them. Hodgdons data requires that the web area of ANY cartridge case not expand more than .0005", that's 1/2 of one thousandth of an inch.

Of course the case expands to fill the chamber, then the chamber contains the pressure, partially, the unknown here is the ability of the receiver itself, to withstand the pressure, on a constant repeated level of 375 Win loads. Like I said before, when Marlin says it in writing, I will believe it. Doing otherwise is at one's own risk.

I am fully aware that there are more than a few that have done this conversion, and no one has had it blow up on them, and hopefully never will. I would not load my Marlin 1895SS 45-70 to the Ruger #1 levels that are posted, just because it's the same chamber. Another example, is Marlins own design changes for the 450 Marlin, in the same 1895 receiver. It's said to be loaded to higher pressures than levergun loads for the 45-70, yet in order for them to produce it, they changed the barrel thread design to a stronger one than they use for the 45-70. Yes the chamber is one of the components that contains the pressure, once the case expands, the other parts, are the bolt assembly, the receiver where it supports the bolt, and the threads of the barrel. If the bolt holds up, the receiver holds up, the threads could still fail, little by little. Marlins own admission, is that the threads were made stronger to withstand the higher bolt thrust pressures. Granted, we are talking larger bolt faces, and with equal pressures, there will be greater bolt thrust from the 450/45-70 class cartridge. Ruger #1 load levels in the 45-70 reach 50,000 CUP, yet the levergun loads never exceed 40,000 CUP. In my mind, the 38-55/375 Win loads are like comparing the 450/45-70.

Again we are faced with the PSI/CUP faceoff, and there is no direct correlation to the two (SAAMI for 450 Marlin 43,500 PSI, 45-70 is 28,000. Hodgdons loads the Marlin levels to 40,000 CUP), yet Marlin did not feel comfortable with the standard design, the same one used on the 336, with the higher pressures of the 450 Marlin. So even if one wanted to TRY a direct number comparison of PSI to CUP, those numbers are very close, yet Marlin did not want the 43,500 PSI on the 1895 receiver, without some improvements.

Has anyone ever taken their factory Marlin 375 apart to see if there is any similar improvements not easily visible?

In the words of Jeff Goldblum in Jurassic Park, "You guys got so entangled with the idea that you could do it, that you never really thought about whether or not you should do it".

As for the thinner brass being just as strong as the thicker??? Since when is thinner brass, of the same type (ie cartridge brass, not soft vs hardened steel), stronger than thicker brass? We are talking basic metallurgy, and that just will not be the case. That's like saying 3/16" low carbon steel is just as strong as the same carbon level steel in 1/4". Sorry, not possible, not when comparing similar metals, which we are when comparing the rifle cartridges in question.

That thinner brass (38-55) will expand to chamber dia faster than the thicker 375 Win brass. And for the theory of case expansion, and chamber pressures, it get very complicated, depending on the powder used, brass, bullet weight, bullet design, and even primer used. Some powders reach full pressure much faster then others. A slow burning powder, could actually prove safer in this case than a faster one, since it will add a slight delay to the pressure peak. If the bullet has begun to move from the case, before powder pressure peaks, it will keep the pressure down. Yes slower twist rifling has been shown to keep pressure spikes down, a certain degree. Not sure if it's ever been noted just how much. Guys use the same philosophy with the 6.8 SPC to push it way beyond the factory velocity levels.

One last warning, then I am done. On straight wall cases like these, there are strong warnings given out by reloading suppliers, like Hodgdons. They say (told me personally, on the phone) one of the last things to show over pressure signs is the case head, because, being a straight wall (or close to it) case, the majority of the pressure is transmitted through bolt thrust.

Enjoy, shoot safe.
 

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;D We are agreeing on more than one might think. Maybe my wording isn't getting my points across, but not going to belabor this and run the thread into the ground. ;) ;) DP
 

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I am leaning toward the more generous 375 chamber, I will likely use only fire formed 30-30 brass and lead bullets with a 40 KPSI maximum.
 

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I measured some brass with a dial caliper to see what its running.
45 Colt,44 Mag-.012
357 mag,30-30,32 spl,35 Rem,375W-.010
8x57-.012
44-40,38-55 .008
You will notice that the 375w is 20% thicker than the 38-55.
As for my Marlin 375,My warm loads are 375W with jacketed bullets and the target loads are 38-55 with Cast.Works for Me.
 
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