.257 question

[TxMedic]

My grandpa gave me a custom built .257 Roberts on a Mauser action. Problem is, I don't know if it's a Roberts or a Roberts Improved...grandpa's memory has slipped and he isn't sure. I vaguely remember him talking about get shells hand loaded since the shells were "necked down". How can I figure out what I have and will if hurt to shoot factory .257 Roberts shells?

[Cajun Blake]

do a chamber cast using cerrosafe

[TxNurse]

To make brass for an "improved" chamber, you shoot a regular cartridge in the gun to fire-form the "improved" brass. You then use the correct "improved" dies to reload. You can always use the parent shell in the improved gun if you do not have reloaded "improved" cartridges. You lose a little velocity because of the reforming of the brass. Accuracy is usually not affected. So, if you shoot a regular .257 Roberts shell in the gun, and look at it afterwards, you should be able to tell if it has a different shape coming out than what it had going in.

[TexMax]

Edit: was wrong on that one


But since i opened my yap already can someone give a quick rundown on how the roberts is able to chamber with the 'improved' variants having a steeper shoulder. My brain tells me it would work the other way around. Does it headspace forward of the shoulder the first shot?

[Rubi513]

To make brass for an "improved" chamber, you shoot a regular cartridge in the gun to fire-form the "improved" brass. You then use the correct "improved" dies to reload. You can always use the parent shell in the improved gun if you do not have reloaded "improved" cartridges. You lose a little velocity because of the reforming of the brass. Accuracy is usually not affected. So, if you shoot a regular .257 Roberts shell in the gun, and look at it afterwards, you should be able to tell if it has a different shape coming out than what it had going in.

This

[Cajun Blake]

Edit: was wrong on that one


But since i opened my yap already can someone give a quick rundown on how the roberts is able to chamber with the 'improved' variants having a steeper shoulder. My brain tells me it would work the other way around. Does it headspace forward of the shoulder the first shot?

b/c the parent case has slightly smaller dimensions than the blown out Improved case . Improved cases will not fit an a std 257 Roberts chamber - see pic below

I shoot a Cooper 257 AI and it is one bad mutha ... zero recoil, flat, and deadly

[TexMax]

Eh i know the dimensions are different. It's just not clicking for me how exactly the round seats in the chamber. My assumption is the bullet just gets pushed into the lands or spaces mid way up the shoulder somewhere. I'll have to read more i'm slow sometimes

[Cottonfish]

Theoretically, the two cases share the same datum line on the shoulder where the headspace occurs. In actual application, fireformed .257AI cases have necks that are several thousandths shorter than the parent .257R case, which tells me the datum lines may be slightly different, but not enough that the Roberts case won't chamber easily in the AI.

Several things you have to be aware of........use only new, unfired brass for fireforming - fired Roberts brass tends to be work hardened and will crack rather than fireform properly. The newly fireformed brass is unique to that particular rifle's chamber, and likely won't match another AI rifle. The best fireforming method I've found is to load a 100gr bullet over a medium load of faster-burning powder like IMR3031, with the bullet seated out to contact the lands. That holds the cartridge case against the bolt face for proper fireforming. You can also shoot factory ammo as noted above, the result should be a fireformed AI case ready for reloading. Get a good neck-sizing die (I have a Redding), you should only have to neck size for the next several loadings, and trimming is almost eliminated.

Like CB said, a good idea is to have a gunsmith make a Cerrosafe cast of the chamber to see exactly what you're dealing with, unless you have some fired brass out of the gun to examine. The sharper 40 degree shoulder of the AI is easy to differentiate over the standard Roberts case profile. My guess is that your grandpa says "necked down", meaning the .257 Roberts is derived from a 7x57 Mauser parent case necked down to .25 caliber, and would mean you have a standard Roberts. You'll enjoy it either way, they're both excellent cartridges, short on recoil and long on performance. Get into handloading for it, the combinations of bullets and powders that are available will drive you to distraction..........

I'm on my second .257AI, a Remington 700 short action with 24" Shilen barrel. Another TBH'r has my first one, a Ruger M77 with a Douglas barrel, and it apparently sees a lot of use. My Dad has an original Ruger M77 MkI in the standard Roberts, it's a really soft shooter. I find myself doing a lot more hunting with the .257 than my heavy-recoiling 7mm Mag these days. Just used it to take a 250yd doe, and a 140yd pig down in Encinal last week..

Stu

[TxNurse]

Eh i know the dimensions are different. It's just not clicking for me how exactly the round seats in the chamber. My assumption is the bullet just gets pushed into the lands or spaces mid way up the shoulder somewhere. I'll have to read more i'm slow sometimes

If you chamber a standard cartridge in the improved chamber it headspaces where the shoulder meets the neck, unless it is a rimmed cartridge like 30-30.

[TxMedic]

Thank you all for the clarification and advice! I can't wait to go hunt with it!

[Artos]

Eh i know the dimensions are different. It's just not clicking for me how exactly the round seats in the chamber. My assumption is the bullet just gets pushed into the lands or spaces mid way up the shoulder somewhere. I'll have to read more i'm slow sometimes

First, Just think of taking a standard roberts and sticking it into an improved chamber/gun. Forget the bore/grooves/lands...all of this change only happens in the chamber.

A 'correct' AI chamber will have a bit of shoulder chamber crunch to snug the standard Roberts into place and should feel a little resistance when closing the bolt. When you go BANG, the standard Roberts brass ends up conforming to the size of the bigger AI chamber...think of it as blowing up a balloon inside a square box until it fills up the corners & you were then able to remove the box and the balloon held it's square shape. This is really the easiest way I can describe.

Obviously, after you do this...your improved Roberts will never be able to fit into a standard/factory Roberts gun/chamber because it is now too big.

got it??

[TexMax]

Thanks guys. The idea of fire forming wasn't troubling me. Just the technicalities of it. Yall answered pretty much everything i was curious about. I wasn't too far off

[TxMedic]

Now, I can't find Roberts ammo! Any help appreciated!