Had a kaboom with my reloads.

[markm]

After looking at your case photos...….what I am seeing (due to the flow of the brass) is "over-pressure" due most likely to bullet "set-back" during chambering. This bullet set-back would make your chamber-pressure increase dramatically.

I've found this not to be as significant of an issue as I had previously thought.

When I first tried loading 77 gr Sierra TMKs, I loaded to small batches of OTMs and TMKs to compare. Both had identical charges. The TMKs have a much different ogive and required the bullet to be set much farther into the case than the OTMs to achieve the same over all length. When we chrono'd the loads, they shot the same velocity.

Now if the round was really deformed with the bullet mangled somehow, yet still able to chamber... perhaps it could be the cause. But a 55 gr fmj set back simple doesn't take up anywhere near the case volume that a 77 gr does at correct over all length.

And then of course with more "jump" to the lands, you get more initial bleed of, and thus LESS pressure spike. I just don't see set back as a realistic cause of this.