View Full Version : Modern pressures for .257 Roberts???

zeke mccune
08-18-2009, 12:16 PM
Hi Gang:

I would like to know if anybody loads this cartridge to modern pressures, 50,000-55,000 psi. in modern rifles. The pressures that reloading manuals give are very low. The highest that I saw was 47,600 psi. In a modern gun, one could load this cartridge much higher. Is because the brass is too thin? If so, switch to 6MM Remington or .257 plus P cases for higher presssure loads.

Any suggestions for improving this round. After all, the .257 Ackley is loaded to very high pressure using .257 Roberts cases so it must not be a case problem.



Larry Elliott
08-18-2009, 05:24 PM
I had a .257 maybe 25 or 30 years ago before people loaded or headstamped .257 cases +P. There's no problem in loading the .257 to higher pressures as long as you know and understand how to tell if things are getting overdone. The same applies for the .222 Rem and .250-3000 Savage in strong modern bolt actions.

As I remember I was using slower powders than most of the manuals list for the .257. With 100 gr bullets something like one of the 4350's or RL-19 would probably be good, and with 115-120 gr bullets one of the 4831's or something similar should work. The Hodgdon Extreme shortcut 4350 and 4831 will likely work better than the older longer granuled powders too.

If you can find Winchester .257 cases or 7x57 cases they're thinner (hold more powder) and harder than RP cases. That's been true since Jack O'Connor was loading for the .257 60 years ago, and the last cases I had for a 7x57 a few years back were thinner and hard enough to hold stiff loads for more than 3 or 4 loads.

08-18-2009, 06:31 PM
You really have to watch for the +P cases if you begin your loading with them its ok but DO NOT try to stick a "load" from non+P cases in +P cases.

08-19-2009, 08:20 PM
From most of the +P brass I have come across, most manufs headstamp the +P to designate a different load, not that the brass is any different.

Nosler has some good loads on their site, and my Lyman 49th has +P loads.

08-22-2009, 08:06 PM
In modern rifles you're fine. The story goes that old mausers were chambered for the 257 and the pressure had to be kept down to a safe level. Makes sense. I load +P Winchester & Hornady brass with 46 - 48 grains of 4831 and 117 grain Sierra ProHunter's with no problems. Action is Interarms Mark X "mauser". Guns&Ammo ran a good story on the 257 in this September's issue. Try to get a copy of that; good reading.

Big Al
08-22-2009, 09:18 PM
Short of having and Oehler Model 43P, how would you know what the pressures are? I have the reamers for just about all the Roberts and the ACKLY deviations and have never known the pressures for any of them.

Treated like any other ctg you could load for (watching for pressure signs) why would this even concern anyone?

If the Question is about the brass thickness, I can see no difference.

If your action is suitable, there is no issue at far as I can think of. I do have one M-70 that is over 60 years old and it is as stock will shoot anything I have loaded in it, of course it on it 7th barrel. That darn .257 sure is and addictive son of a gun.:D

jackie schmidt
08-23-2009, 12:52 PM
keep in mind, this chambering dates back to the 1920's.

The whole "plus P" concept has it's origins in handgun field, mainly revolving around the 38 special. For years, 38 ammo was loaded with a rather low pressure because of the millions of old handguns that were never designed to handle the pressures that the case could safely generate in a modern firearm.

The ammo manufacturers finally recognized the fact that modern handguns chambered in 38 special could handle much higher pressures. It is written on every +p ammo box, "for use in modern firearms", or something to that affect.

Also, keep in mind that there was a large amount of brass available for the 7x57 Mauser, (the parent Case), that dated back to the late 1800's. The quality and strength of much of this brass could be considered suspect.

But, with modern cases, in a modern Rifle, there is no reason you can't treat the 257 Roberts like any other modern chambering.

A few years ago, I got into a arguement with a shooter about so called 'modern' cases and older ones. His contention was that the 7mm Mauser case was a weak case. We took a new 7mm Mauser case, sectioned it, and then a 6mm Remington Case, and sectioned it. They were identicle inside. Aside from the neck, you could not tell the difference in the construction of the two cases..........jackie

08-29-2009, 07:58 AM
When the .257 roberts came out there were many rifles in 7x57 around which were not intended for high pressure, i.e. Remington rolling blocks, M93/95 Mausers etc. These were prevalent and affordable. Many had bad bores from corrosive primers. Gunsmiths could turn out a hotrod rifle by going to .257. Today, you can load a 7x57, for a modern rifle, to just about equal a .280 rem. Beat the hell out of a 7mm-08. A .257 can be loaded to just shy of a 25-06. As for brass: The basic .473 rimless case doesn't need any introduction, it started it all.

Joe S
08-29-2009, 09:30 PM
SAAMI pressure max for the 257 RBTS is 45K "CUP" the +P version is 48K "CUP" this is not a psi measurment.
SAAMI PSI max pressure is 54,000 and thre +P is 58 K. The 58K load is not far from most modern cartridge loadings.
All manuals I know of load to the SAAMI specs -both std and +P- and are not as wimpy as they may seem.

brian roberts
09-04-2009, 06:25 PM
there is a seperate entry for, ".257 Roberts +P" and they have the explanation for the loading, and the pressures they're loaded to, along with the customary precautionary statements. You should have no problems. ;)