7x57 for Brazilian 1908

A few weeks back I picked up a Brazilian 1908 -- you know, the full-length South American Mauser in 7x57. The shop had some 139 grain PRVI, so I bought a box to see if it was accurate and to for brass to reload.

After cleaning cosmoline and giving the barrel a scrub, I was greeted with 16 inch (!) 100 yard groups. I was afraid of this due to the bullet weight and seating depth of the PRVI factory loads. I don't think I've ever shot a group so large. I couldn't even really tell whether the group was centered above or below point of aim.

Graf's had .284 174 grain PRVI flat-base soft points. These are long bullets with a long bearing surface. I loaded these up to a ridiculously long OAL (almost a whole caliber-length was exposed beneath the cannelure) over 33.5 grains of IMR4064. My final group (six shots) was half the size of the original groups -- around 7", with all but one within about 4". Even with the limitations of the inverted V sights, I think this can still be tightened up a bit.

Original military loads used a relatively heavy, long bullet, which I was trying to get closer to by choosing the 174-grains bullets. I also have some 150 grain bullets around, but I was hesitant to use these after seeing how poorly the 139 grain performed. I know that my next steps are to play with charge weight and seating depth, but do any 7x57 or military Mauser aficionados have any experience with a similar situation?

 

With groups that size it sounds like you picked up a 7.92mm Mauser instead of a 7mm Mauser.
7.92 was adopted by the German Military between 1903 and 1905.

 

What did the bore look like?
Have you slugged it?

If you were able to seat a 174 grain bullet as long as you described, it sounds like the throat (at minimum) may be gone.

 

My 09 Argentine and ruger will shoot that 139 ppu under 1moa. Either you have a 8x57 barrel of something is very wrong.

 

What is your long col I'll load my hot loads with a 140 bullet at 3.200" with that rifle you can use the upper side of the load data

 

I thought the 1909 Argentine Mauser was chambered in 7.65x53 Argentine. I've never seen one in 7x57.

In any case, I don't think it would be possible to put 5 out of 6 shots into a 4 inch group while shooting .284" bullets out of a .323" bore. You'd be lucky if you put them into a four foot group.

Let's give the OP a little credit here and assume that he has a 1908 Brazilian Mauser in 7x57. They were never made in 8mm Mauser, just 7mm, 30-06 and 7.62x51.

@ NuclearMeltdown
With the improvement you already got from heavier bullets seated long, I'd try some 175 grain round nosed bullets (longer shank than the Prvi spitzers) and seat them even longer to "chase the lands".

I've got an 1895 Chilean in 7x57 that was hopelessly inaccurate with all the spitzers I tried, but it shoots OK with 175 grain Remington RNSP's seated long.

In addition to a badly worn throat the crown was nicked, so I had to recrown it.

 

This is a 7x57 without a doubt. There is no chance of a rebarrel in a different caliber because it is in original configuration (it had been in the same shop since it was imported ~20 years ago, and I took the cosmoline off a few weeks ago), and Brazilian 1908s were in 7x57. Also, it passed the "bullet test" for the crown before I bought it. The crown did not "swallow" the bullet. On top of that, had it been an 8x57, the once-fired brass would have been a dead giveaway.

Troy, I loaded the 174 grain bullets to 81.5mm, which divides out to 3.209". This fit in the magazine, but I don't think I could use the magazine if I loaded it out more than another 1mm or so. Here's a photo of the PRVI 174 grain beside a 150 grain .284 Core-Lokt, which I can also try:



When the 174 grain bullets (on the right in the above photo) were loaded to 3.209", I had about a caliber's worth of bullet inside the neck of the case. Troy, when you load a 140 grain bullet nearly as long, how much bullet did you have in the neck? It must have been enough for tension and to keep the bullet concentric. I didn't think that a bullet that light could be loaded that long, but it sounds like yours works.

The bore shines -- not mirror bright, but enough to show that it's never been heavily corroded. Rifling is clearly defined throughout. It has not been slugged. The only noticeable deficiency I can find is that the rifling at the crown is not as sharp as I'd like to see (overzealous use of a steel cleaning rod, perhaps?), but I've shot better with worse crowns. This photo shows the condition of the crown with the fouling from today's shooting.



As far as the throat goes, I don't think that it's so much the throat being gone (I assume you meant shot-out) as much as it is being an extremely long throat designed for the original heavy round-nosed bullets. That's why I chose the long OAL. I'm not set up to do a chamber cast, but don't think any spitzer bullet could touch the lands because of the long throat designed for long, heavy, round-nosed bullets from way back. As a side note, that style of bullet is still available, but I passed because of cost. They could also be cast, but I'd like to stick to jacketed bullets.

To summarize, factory 139 grain loads seated to standard length gave terrible results. Switching to my loads cut the group size in half so far. My last group put five shots into four inches, with one flier spreading the group to seven inches. The bore is in good shape, and I cleaned out cosmoline and old copper fouling before my first shots.

Nosler and Hodgdon show different maximums for this weight of bullet. 33.5 grains of IMR 4064 was quite comfortable recoil-wise in a rifle this heavy. I'm just shooting water jugs and steel gongs, so I don't need killer performance. Just looking for some reasonably accurate groups for recreational shooting.

For IMR 4064, I saw last night that Nosler shows a maximum of 39 grains:



While Hodgdon's is significantly lower at 35.2 grains (perhaps for 1893 and 1895 Mausers?):



I tend to avoid maximum loads, but I do have some wiggle room to play with charges from my starting point. Also, I'm using a Lee three-die set and have not used the crimp die.

I suppose what I was asking was, in anyone else's experience, what factors in handloading have shown the greatest improvement in accuracy in a situation like this? Charge weight? Seating longer or shorter? Adding a crimp? Just looking for a little direction before randomly changing factors.

 

It's a custom in 7x57 Ackley improved.

I've seen all kinds of stuff done to rifles to pass them off so never really know until every thing is checked.

 

I'd have to check how much bullet is in the case, there up the neck some so are probably çaliber or less of tension. I've done it with .002-.004" of neck tension , these were for hot loads were powder was into the neck some. 50gr imr4350 with a 140. Rem brass the pup have more case volume.

it's very common for 7x57 to have very long throats the old round nose bullets need the room, by if your ammo in concentric the jump shouldn't hurt your accuracy.

 

Swampman, you replied as I was typing my last response. I appreciate your direct response to my original question.

It sounds like the search may be on for an affordable round-nose projectile. A quick search at Midway shows very little in the .284 round-nose bullet department. They list these Hornady bullets as (unfortunately) discontinued, but these may have done the trick:



Also, I looked at post #3 here, where a photo shows how long the throats actually are: https://www.milsurps.com/showthread.php?t=54922

 

Brownells stocks Norma Oryx 7mm 170 grain bullets. These aren't a round nose per se, but a semi-spitzer with bonded construction.

https://www.brownells.com/reloading...ter+(in)_1=0xzzx284&avs|Bullet+Style_1=Bonded

 

IMHO I would either have the muzzle recrowned or counterbored to eliminate that area first. Nice rifle! The South American Mausers are some of my favorites.