After successfully seating and crimping cases ( thank for all the tips) I did some range testing. First couple of shots almost touching, then a flyer 4" away, then another near the first shots and then the gun jambs solid.

After hammering the lever open I checked the case which was a Federal. Other cases were Winchester. Now I know you're not meant to mix cases but I thought on a starting load it would be ok. I weighed the cases and found a huge difference. Winchesters were 170-171 grains and held 82 grains of water and the federals were 200-202 grains and held 76 grains of water.

I guess this is what caused the high pressure, but it was a starting load in my manual. has anyone had a similar experience?

Maybe w/ a load running near max. but it shouldn't have caused an overpressure load. What was your load?
I used to mix brass all the time for CAS when you could still use the .45-70. Now these were powder puff loads, 300gr lead bullet @ 1000fps, but your problem should not have been the cases.

quote:

Originally posted by jdl45:
After successfully seating and crimping cases ( thank for all the tips) I did some range testing. First couple of shots almost touching, then a flyer 4" away, then another near the first shots and then the gun jambs solid.

After hammering the lever open I checked the case which was a Federal. Other cases were Winchester. Now I know you're not meant to mix cases but I thought on a starting load it would be ok. I weighed the cases and found a huge difference. Winchesters were 170-171 grains and held 82 grains of water and the federals were 200-202 grains and held 76 grains of water.

I guess this is what caused the high pressure, but it was a starting load in my manual. has anyone had a similar experience?

What was that load, pray tell? It would have to be really hot to jam the rifle shut!

Possible double charge? That could get exciting with some loads.

The starting load used was 55 grains of AR2207, the max load is listed as 60 grains, with 300gn projectile. The rifle jambed at 55 grains with the Federal cases.

Time for a bit of detective work. There has to be a logical explanation for what happened, changing the brass with a starting load isn't enough to do it. But, if you think it through carefully, there might be enough evidence to figure it out. Two cases need to be examined, the first one where the POI shifted, then the second one, the jammer.
Were there other signs of overpressure on the second case like a flattened, cratered, or pierced primer? The double charge idea is plausible, but also powder bridging in your powder measure could have dropped too light a charge in one case and an overcharge in the next one. That is not a powder where bridging is usually a problem, but static or humidity can contribute to it. Is there any soot or powder fouling on the outside of the first case you fired just BEFORE the problem round? Do you use a mechanical powder measure, or do you dip? Do you use a loading block when you charge your cases to inspect the powder levels individually before seating bullets?
Another idea: Were they cast or jacketed bullets? Tell more about them please; brand if purchased, profile, construction, alloy if cast, gas check, etc. Back to the obvious change of POI with the shot before the one that jammed things up. Bridging isn't the only thing that could cause the POI shift and then pressure spike. I wonder if there is a possibility that something left in the barrel like a shed gas check or disintegrating bulley from a brittle alloy like linotype could have caused a minor obstruction and subsequent overpressure. Is there perchance a bulge in your barrel now? (With a tight cleaning patch, is there a place where it suddenly moves easier?) If there was a minor obstruction near the breech, it wouldn't necessarily banana peel the barrel like a muzzle obstruction would.