I Need to do a 'Ned Roberts'

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My Ruger M77 .257 Roberts needs reloads, and my brass has all been shot multiple times - I've had 2 case neck splits, in spite of re-annealing at 3 and 4 reloads. I recently tried necking down a few once-fired 7x57 Mauser rounds, knowing that that is how the .257 bob came into being. I checked SAMMI case specs first, and then went ahead with these cases. After resizing, I measured the case length (.005" - .008" longer than trim-to length) and the neck wall thickness (uniform at .015").

I trimmed, reloaded, and they seem to function OK. My load is IMR 4350 - 40.0 gr./CCI 200 LRP/ Nosler CT Bal. Tip - 95gr. I have read (elsewhere on this forum) that the 7x57 has slightly less case capacity than a .257+P, and I am wondering if I need to adjust the load downward. My current load shows no signs of high pressure, although it's not a mild one. It also delivers about 1 moa with .257+P brass.

Since new Roberts brass is nonexistent out there right now, I bought 50rd. of Winchester 7x57 Mauser to resize and load. Is there anything more I need to know about the process of resizing and using this brass in my Ruger M77 Roberts?
 
I managed to score two bags of 'Bob' brass a couple years ago so I am sitting pretty good for now. Sizing sown the 7x57 doesn't sound too complicated.
 
Amazing fertilizer...

It always amazed me at the incomplete knowledge that swirls and swirls...

Yes, the 7x57 was made from the 8x57 as was the 7.65x53 Belgian and a several others. Somehow the 6.5 Swede is not the same exactly... ??? Rim/base is larger, slightly. But supposedly you could make workable cases from '06 military cases.

H. Donaldson stated that Mr. Roberts longed to be a competitive shooter but his eyes were not good enough so he "fiddled." Remington picked up his creation, 7x57 to .257 and "factorized" it.

THEN: Remington wanted something "new." Fred Huntington had had the .243 Rockchucker out for some time... .257 Roberts necked to .243... Remington called it the .244 Remington, then the 6mm Remington, then the .244... etc.

Second point here, 6mm Remmie was made for the current pressure standard, approx. 55 K CUP so no concern about +P anything and when you neck a case up you thin the neck slightly and should never have to worry about reaming. Always an exception but I cannot fathom it. 6mm is not going to be found in the once fired bins line .243 WCF or .308 but sometimes it is there and sometimes cheap... Luck. Happy trails.
 
I am not exempt, I form 257 Roberts from 30/06 cases, same for the 6.5 Japanese/257 Roberts. Care must be taken when 'doing' the necks, one does not want thick necks in chambers that are not generous.

Case capacity? I use commercial cases, I use military cases, if I thought the +P weighed less because it was thinner? I would choose the case with the thickest case head. If the object was to use the case with the largest case capacity I would size the cases available then fill with lead shot, powder or water (with a primer installed) then weight the filler. I have 257 Roberts cases with military arsenal head stamps that go back to the early 40s.

And I have 257 Roberts Ackely Improved, not a problem, when I want more case capacity I use a case with more capacity. After I shoot a +P case it becomes a once fired case, and another head stamp that allows me to sort cases, it is nice to be tumble a tumbler full of brass then sort and get the cases back in the same box they started in. And I still have the orange and green R-P unprimed/new cases for the 257 Roberts.

F. Guffey
 
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