257 Roberts vs. 257 Roberts+P

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Bucksnort1

New member
I'm helping a friend with advice and by donating loading components and equipment so he can begin loading for 257 Roberts.

After searching my loading manuals for recipes for his bullet weights, I come across 257 Roberts +P recipes. I know there are handguns that shoot +P cartridges so I know these are more powerful but this is the first time I have seen a rifle cartridge in +P.

I am curious about a rifle cartridge in +P. Do you need special cases for these?

I'm sure someone will provide some history.
 
If you look at the SAAMI standard, you will find the +P version of the cartridge has 10% higher pressure than the original load. However, when you scroll down to proof pressures, you find, just as with 38 Special, the original proof load has been declared obsolete and the +P proof load is used for all .257 Roberts chambers. This means any gun that is up to modern standards will handle both. And with +P being the only proof load level, there is no need for separately stamped +P case heads to prevent accidental chambering in a gun that is not rated for +P, as they all are so-rated at this point in time. You may get a somewhat shorter case life from the +P loading, but otherwise, no issues.
 
Unclenick or ???, is a small ring Mauser rifle in good condition that is chambered for .257 Roberts strong enough to safely handle +P loads?
 
Not an expert, but I would think a small ring Mauser 98 should be able to handle it. Without examining the gun in question", should" is as far as I'm willing to go.

In this case, +p is 10% over industry standard WORKING pressure, not proof pressure, and not close to that.
 
Examine the back end of the bolt to determine if it is a 98 action or an older 93/95 action. If the striker cocks on opening, it is probably a 98 action. The earlier designs cock on closing. The older designs are good to about 46,000 PSI loads.
 
Thanks for the feedback.
It cocks on opening so probably is a 98.
Are they rated for the 58,000 PSI that Nosler assumes for their +P load data?
It handles Barnes' max loads of 42 grains of H4350 with their 100 grain TTSX nicely.
Is there a significant difference in how Nosler 100 grain E-Tips start into the lands, spinning and traveling down the barrel compared to Barnes TTSX/TSX?
If not I seemingly should be safe up to 42 grains, but ???????????????
My 1:10" twist barrel isn't fast enough to stabilize Barnes 115 TSX.
Anyone out there with a fast twist 25 cal. barrel want a box of 47 TSX cheap?
 
It's not the gun design, but the steel quality that matters. In a thread on this subject here in 2016 (I am on a machine that won't let me put up a link easily), it was pointed out that Kimber had re-chambered a bunch of '96 Mausers in 308 Win among several other modern rounds. At the other extreme, Spanish small ring Mausers were famous for poor heat treatment and their ability to shatter.
 
SAAMI 257 Roberts MAP is 54,000 in psi and +P is 58,000. In CUP they are 45,000 and 50,000, respectively. So, 7% difference in the generally more accurate piezoelectric transducer. It's not a lot, and the +7% is well within SAAMI's variation allowance for the standard load, so you would think, especially if you load carefully for less pressure variation than SAAMI allows for, it would be OK. There are just two problems with this: we don't know what the receiver was subjected to since it was last proofed with it's original cartridge. You are, I assume, not in a position to measure pressure.

So, short of identifying the gun as a known safe make, or of access to an x-ray or a penetrating fluorescent liquid exam of the steel for cracks, you'll have to depend on visual examination. I would be checking for hairline cracks after every shot during load workup for pressure from the lowest starting load, and after every group during development for accuracy, then whenever cleaning after that.
 
No visible identifying marks on the exposed portion of the action. What should I look for on the portion of the action currently hidden by the stock to possibly identify the maker and year?
 
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