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« Last post by LongWalker on Today at 04:15:40 PM »
Well, not exactly.
Yesterday morning I went to test-shoot a rifle a friend is trying to trade off. This one is a military rolling block carbine in 44-40, built on the No. 1 action, with markings from Mexico. (These were also used as guard guns in some prisons here in the US, but guard guns aren't as cool as veteranos of the Mexican Revolution.)
The rifle checked out OK. Chamber and bore looked good, some wear from cleaning from the muzzle. Action locked up. Ammo was an Ideal 42798 on top of a caseful of FFg. Brass was many-times fired, and full-length sized to chamber in the various 44-40s my friend shoots.
On the 4th shot, I got treated to a faceful of burning powder residue and smoke, coming out of the now-open action. The case ruptured and separated at the neck (we found the case neck in the chamber, didn't find the case head). After some research, we think the back-half of the case slammed back on the firing pin, knocking the hammer back and allowing the action to open. This failure mode has been discussed some over the years, but I've only seen something similar once before (that time, a case head separation in a roller in 43 Reformado).
No injuries, thanks to eye protection and a covid facemask. I suspect the case separation wouldn't have been as much of a problem in a Colt or copy, or a lever-action rifle: both do a better job of managing escaping gas.
I suppose there are two lessons here, in addition to the reminder to always wear eye protection.
First, particularly when full-length sizing brass, keep a close eye out for incipient cracks/case head separations. The repeated use of this batch of brass, full-length sizing each time, had weakened it to the point it was ready to let go.
Second, if you're going to shoot an old rolling block, it might be a good idea to check the amount of play on the pins, and possibly replacing them with oversized pins if needed. When I disassembled the action and put the pins in their respective hammer and block, I was able to feel some "wobble".