.257 Roberts Improved questions

[toby]

Load them up 10 or 20 at a time use a heavy bullet 115-120 grainers make sure to seat them touching tight to the lands and use a fast burning powder, like 4895 or so at a medium velocity not high and not the lowest. Remember to only do this for fire forming????? after fire forming load them off the lands...IMO, I have had the best luck using this method.

[ElvenSoul]

This thread has got me wondering what became of my Uncle's 257Roberts...I know my Dad has his old 1903 Springfield.

[kendog4570]

The 257 Roberts and 257 Ackley Improved have the same shoulder datum, and use the same headspace dimension. This is true for most, if not all, of the Ackley Improved chambers. Not so with many other "improved" calibers. The shoulder angle is different, 21 deg for the 257 Roberts and its parent case the 7X57 Mauser, and 40 deg for the Ackley, but they headspace at the same point. Ackley designed them this way so one could use factory ammo in his chambers in a pinch. Your 28 deg shoulder might, as well. You may want to check with 257 SAAMI Go, No-Go, and Field gauges (also known as 7 Mauser) in your chamber and see what you find. Not the absolute answer, but if the gauges work (providing it was set up correctly originally) it might be OK. A chamber cast would be next.
If you are in the SF/Monterey Bay area I can help.

I did a little more research, and I stand slightly corrected on the improved headspace measurement. See the attached pdf file by Ackley himself from the 1960's on headspace. He is one of the Granddaddys of the improved cartridge thing. The last few paragraphs shed some light on this subject of improved chambers. Also interesting is the rimless cartridge datum info. You could set a mike to the dimension, use the jaws to scribe a line on the shoulder of a factory case, do the same on a fire formed case, and compare the two.
Ackley was one of the greats. Just don't read his comments on the then-new .223 Remington, and the AR-15 rifle. Lets just say he is not one of our friends.

[gunboat]

KD -- that is good info, what book is it from?

[subijitsu]

Yes, good article indeed. Thank you. Mr Ackley may have known a little about the subject I guess.

"Headspace for rimmed Improved cartridges, of course, is the same as for the standard versions but as a general rule for Improved rimless cartridges the headspace is .004 thousandths less than the standard minimum........The gauge for the Improved .257 would be 1.794 minus .004. This method is necessary because of variation in factory ammunition to ensure a crush fit at the conjunction of the shoulder and neck. This allows the fire forming of factory ammunition without loss of brass and with no danger to the shooter."

So what I am taking from this is that the chamber should be fairly tight with factory ammo before fireforming due to it being .004 under the minimum. So it would seem reasonable that if I were to buy factory ammo and it chambers a little tight I should be ok to fireform. If it chambers easily I may have an excessive headspace problem and need to buy new .257 brass, handload to the lands, and fireform from there. I can dig it.

[kendog4570]

KD -- that is good info, what book is it from?

This particular article is in Gunsmith Kinks. PO Ackley used to have the gunsmith column in Guns & Ammo (I think, or Gun World) way back when (early 60's??). He wrote a lot of articles on this subject. Check out his double volume of wildcats for some interesting reading.

[kendog4570]

Yes, good article indeed. Thank you. Mr Ackley may have known a little about the subject I guess.

"Headspace for rimmed Improved cartridges, of course, is the same as for the standard versions but as a general rule for Improved rimless cartridges the headspace is .004 thousandths less than the standard minimum........The gauge for the Improved .257 would be 1.794 minus .004. This method is necessary because of variation in factory ammunition to ensure a crush fit at the conjunction of the shoulder and neck. This allows the fire forming of factory ammunition without loss of brass and with no danger to the shooter."

So what I am taking from this is that the chamber should be fairly tight with factory ammo before fireforming due to it being .004 under the minimum. So it would seem reasonable that if I were to buy factory ammo and it chambers a little tight I should be ok to fireform. If it chambers easily I may have an excessive headspace problem and need to buy new .257 brass, handload to the lands, and fireform from there. I can dig it.

Given this information, I would check the throat datum on both a factory case, and a fire formed case and go from there. .004" is probably no big deal with factory new ammo. It is made to fit in all chambers, min. and max., and even if it has little or no feel with yours, it will probably still be OK.
On the other hand, if you resize any case .004" under minimum, it will stretch and fail in short order with repeated sizing/firing cycles.
Gunboat nailed it, just set your die up for minimum, but adequate sizing, and enjoy the rifle.