Worked with some 7x57 brass Saturday

[PJGunner]

I worked with some 7x57 brass yesterday which included tumbling with the brass placed in the tumbler the night before, resizing and the usual chamfering after trimming. This set of brass, 40 Remington and .35 Winchester has been loaded five or six times, I've lost count so just call it five. Loads for this brass were well above published maximums as I strive to find the true potential of a cartridge handicapped by SAAMI keeping standard pressure low due to weaker rifles.
First, only five Remington cases needed trimming and 6 for the Winchester. This was a surprise and Ken Waters commented several time in his Pet Loads articles on the 7x57 on what a notorious case stretcher it was. Primer pockets are only slightly loose and I probably should anneal the necks. I have to wonder? :?: Brass fired in the Ruger #1 and M70 FWT stretch noticeably but almost none at all in the Mauser. :?: :?: :?: Brass fired in the #1 and M70 show a slight but noticeable bulge on one side of the cartridge case. So does brass fired in almost every rifle I own. I believe that the case sitting in the chamber will expand and slightly bulge at what would be the top of the shell. On brass from the Mauser that bulge is either non-existent or so slight as to be negligible. Chamber dimensions are extremely tight, match grade according to my gunsmith who built the rifle. Is this the reason cases do not seem to stretch when fired from that rifle? He's also done a .308 for me but I haven't shot it much. IIRC though, that bulge was also minimal in that rifle. Could very tight chamber be a way or prevent case stretch?
Anyone else looking into this????
Paul B.

 

[ShadeTree]

Short answer is yes. For the same reason neck sizing only, all but eliminates having to trim the necks, but you run into other issues with that. With a standard full length sizing die even if you just bump the shoulders back .002, if when formed to your chamber the case grew in circumference to being very tight in your die, then the die squeezes it slightly smaller at the bottom of the press stroke. That brass being squeezed down has to flow somewhere and the only place it can end up is at the end of the neck.

 

[PJGunner]

That's absolutely true however some cartridge cases stretch more than others. I also shoot rifles in 6 MM Rem, Ruger #1B with Ruger's oversize chamber and a .257 Roberts in an M70 FWT and have little stretch from the 6MM and quite a bit from the .257 Bob. Both cartridges are bases on the 7x57 case. I'll have to do a run on that custom .308 I have and see if it's very tight chamber makes a difference vs an M70 and a Ruger RSI. That is if I can ever find the time. :roll:
Paul B.

 

[ShadeTree]

Paul, I have a set of old very well used, Pacific dies for 30-06 that were given to me because they wouldn't size brass down enough for some guns with brass that was fired in those particular guns. That die set works out perfect for 1 gun in particular that I have with a generous chamber.

I use them for that rifle because brass lasts longer. Never kept any detailed records of case growth and neck trimming compared to using newer dies with that chamber, but it's less. My thoughts is it's the same as a minimal sized chamber and a standard die within normal tolerances, the die is barely nudging the brass at all tight points, but I could be wrong.

 

[PJGunner]

I loaded up 36 rounds of that Remington brass, 18 with the 150 gr. Nosler Partition and 18 with the ABLR. Stared out with 44.0 gr. and in half grain increment up to 47.0 gr. for testing in my Mauser. I'll be watching that brass for stretching. Maybe I'll even get unlazy and set up the chronograph. :lol:
Paul B.