Sizing .458’s down for Mauser model 71’s .454 bore?

[mkj4him]

I got this Model 71 Mauser 11.15x60Rmm that has a .454” bore per my chamber cast.
Dies are ordered and I have some 348 brass already formed. Question is should I be able to size my 380 grain .458’s down to .455 or .456” without much trouble? Don’t want to buy another mold.

[ascast]

Is that bore or groove diameter? I'm thinking that's groove. You might size them that much if soft. You might break your sizer. I'm betting you would not get a loaded round that big in the chamber. The best bullet for those is .448 or .446. Lots of people use the .439 which works well with soft lead and black powder.

[mkj4him]

.454” It is grove diameter. .446” is correct for the later model 71/84. The early 71’s had the larger size. Accuracy would suffer with .446” bullets.

[Larry Gibson]

Push size your bullets through a Lee .457 sizer and see if the chamber. If so, you are good to go.

[beagle]

I've successfully ran .458s down to .450" for sabots. An interim step helps as well as nose first sizing./beagle

[GregLaROCHE]

You should be able to do it if your lead is not on the harder side. I’ve done it with several intermediate passes. That’s why I like the NOE system. Just remember the more you size down, the shallower and deformed the grooves get. Not a problem if you PC.

[Gtek]

Might want to take that chamber cast and measure the OD of cartridge neck area of the chamber. A little math from there will tell you what booilt size you will need. These weapons were designed for a close to dead soft bullet and the bump up from Black Powder.

[mkj4him]

I powder coat. Chamber cast done per post.

[PositiveCaster]

I used to size .458” jacketed bullets down to .452” using a Lee sizing die. Worked like a charm using Imperial wax, lubed cast bullets will be a snap in that die, the only possible trouble might be closing lube grooves - that depends on the mould.



.

[mehavey]

.454” It is grove diameter.

Then +0.002 (0.456") would be fine -- after powder coating.

[mkj4him]

Thanks for helping. Currently waiting on Dies to arrive so I can try this

[Wayne Smith]

For those who do not want to compress the lube grooves simply lube first, the lube does not compress.

[GregLaROCHE]

If you use lube to size, be sure you can remove all of it before powder coating.

[44MAG#1]

I have sized 45/70 and 458 WIN Mag bullets that dropped .460" and 515 grains down to .452" for use in a T/C Encore 454 Casull handgun barrel and they worked very well.

[Fitz]

In my 45 raptor ,and 460 S&W I size down .459 to .453 powder coat first then size they seem to work just as expected . I use the lee sizing die .

[rockrat]

As said, lube your boolits first if you are sizing down a lot. I had to go to .448" for my 71/84. Lubed in a .461" die then a .457" lee, a .454" lee, then a .451" lee, then final size in a die I made from a cut down 30-06 die. Had to go so far so I could chamber a round. A .451" boolit wouldn't chamber

[GregLaROCHE]

With some of the extreme sizing I’ve tried, the boolits ended up with fins coming off the bases.

[mkj4him]

I resized some of the fire formed 348 win brass I had received. Clearly it wasn’t fired in a 43 Mauser.

L to R: 348 win brass as recieved, same brass sized in Lee 43 Mauser die, chamber cast of M71.

The inside neck diameter of sized case is .445 or so. So I need an appropriate bullet mold that will drop around .446 or even larger. My grooves are .454” so I’ll cast soft lead, powder coat and hope bullet expands into grooves at firing.
Anyone have suggestions? My ears are wide open.

[hpbear101]

I think you will find the chamber wont accept anything over a.449/.450 bullet. When I first got started with my 71 the first bullet I used was a Lee 45-70 405 hollow base, I sized it down to .451 in a lee push through. After loading the cartridge I removed the decapping pin from the sizer die and ran the loaded case into the sizer to swage the neck down enough to chamber freely. It worked fairly well.

I am currently working on a paper patch load and a heeled bullet load.

They are a lot of fun but kind of a pain to get going

[mkj4him]

Old west molds has their 43 Mauser mold available. Anyone use theirs and have any comments good or bad?