Sharps 1874 40 90 case seperation

billomike

Good day all,

I recently purchased 100 cases of 40-90 SBN made from 348 Winchester cases. Loaded 90 grns of Pyrodex ffg against 430 gr paper patched, base cupped, .399" dia lead bullet. Bullet snug+ fit at muzzle. Bullet seated against rifling minus a few thousands inch. Mag large rifle primers. Loads for original Sharps 40-90 SBN model 1874 in excellent condition - both bore and chamber (no cast taken). The first trial shot - resulted in case seperation 1/4" ahead of rim - not complete, but pretty obvious circumference failer. The case expanded apprx .016" forward of the fracture compared to unfired loads. Shoulder dia normal. Primer slightly flattened and approximately .002" protruded beyond shell base.

I would certainly welcome opinions on the case failer.

Best regards all.

MIKE WISKEY

classic sign of excessive headspace but...........the .40/90 sbn can heaspaced on either the bn or the rim, it 'sounds like' the .348 brass was over worked or over formed

billomike

quote:Originally posted by MIKE WISKEY
classic sign of excessive headspace but...........the .40/90 sbn can heaspaced on either the bn or the rim, it 'sounds like' the .348 brass was over worked or over formed


Thanks for the feed back. Much appriciated. I agree. I suspect this to be the greater part of the problem as well, plus a new wrinkle that has made itself known. Given the two; both incipient and actual case seperation is an almost certainty.

Although the original 1874 is tight and the barrel is about 7 of ten, I overlooked the obvious: the breech block is excessively worn.
Given overworked brass and worn breechblock rails, something has to give. Now on a quest for a replacement breech block in good condition. That is going to be a real challange! Again thaanks for the help.

v35

If you back off your resizing die so the breechblock rubs the case head shiny, you will be headspacing on the neck and case separation may stop.