One of the benefits of this forum is that you can admit to mistakes...no shame in that, but I have something that baffles me.
I wanted to try a Lyman 311359 in my SKS. I discovered an unopend 4 lb. metal can of SR-4756 on my shelf and found a suggested load of 17 grains. The boolits were gas checked, sized to .311, coated with Alox twice and loaded with no problems. Out to the range......
Loaded one cartridge, just to see if the bolt would retract fully upon firing and lock. Fired the gun, bolt never moved. Humph. Grabbed the carrier handle and could NOT open the bolt. Finally ended up smacking the handle against the wooden bench smartly and it opened. Case appeared normal. Second round, same thing. Normally you can pull back on the handle and there's a small amount of "play" before the lugs begin to unlock. Not this time...the handle wouldn't budge until struck. All shooting stopped immediately.
This happened with BOTH of my SKS rifles, a Norinco "paratrooper" and a Yugo, both normally good shooters with either surplus or reloads. Now, I can see the powder being too fast would cause function problems (wrong pressure curve) but locking the bolt? What in the world happened here?
Edit: I may have answered my own question. Although I have over 40 years of reloading behind me, this is the first time I've seen actual overpressure signs. I re-examined the fired cases and every one of them has a flattened, cratered primer. On top of that, one primer FELL out of a case while I was examining it. From this I suspect that the load was way too fast (hot) and jacked the pressure up to the point where the case expanded and stayed glued to the chamber walls. I would also suspect that these cases (Winchester) now have enlarged primer pockets and are probably useless. If I had been using a j-word, the results could have been disasterous. Too bad I didn't have my chronograph set up......I bet that little boolit was really moving!
It's a constant learning game and I've learned the following:
1.)I was using a powder that I had never used before. More caution/research should have been called for. This particular can of powder is OLD. The price tag says $13.75! I smelled it immediately upon opening and no laquer smell, but no red dust or signs of deterioration although it could be simply dry.....and changed its burn characterisics.
2.)Never accept someone's load data as gospel...especially off the internet.
3.)Examine the ENTIRE case...I was concerned about possible chamber roughness, never thought to look at the primers.
In short, I made several "newbie" type mistakes and got away with it. So, I think I'll junk these cases and start over. Maybe a nice, soft load of 2400.........