Odd primer strike

[Willie T]

Just a WAG but I’m going with high pressure. Do you get the same ejector marks and blown primers with factory ammunition? Is it gun or ammo related? If ammo related: Ejector marks on case head and possible blown primers are pressure signs. The blown primers I’ve seen do not look like those but the soot on the case head and marked up case head sure make it appear to be blown primers. I’m assuming your powder charge is not above maximum per your post but check your load data again. Particularly that your data is for lead of the appropriate weight and pull some bullets and weigh the powder charges to rule that out. Double check seating depth to rule out deep seating raising pressure. Did you work up to the charge? Did you get pressure signs with a starting load? What diameter are you sizing the projectiles to? Do the loaded rounds pass the plunk test in the barrel? If that checks out, check to see how much pressure it takes to push the projectiles further into the case to rule out set back. If that checks out color the projectile on a round and chamber it to see if it is seating or moving into the lands when chambering. What is the case mouth diameter of a loaded round? Too much crimp can let the case mouth slip past the end of the chamber. In a cartridge that headspaces on the case mouth the case then can’t expand to let go of the bullet and manifests as high pressure. There are several possibilities. You have some things to work through but it should not take you long at your bench to figure it out.

Be careful and good luck working through it.
Willie

[justindad]

I just had a similar issue with a .357SIG. The extra primer dent is in the upper right of the image below. The pistol was a SIG P320 (striker fired), with a 3.9” barrel.
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This round was loaded with 10.9 grains of Accurate #9, CCI 550 (magnum) primer, and the boolit was a Lyman 125 grain 356637 hollow point. The rounds were as long as the could be and still fit in the magazine, and I can’t give an exact length due to a mold defect. I chrono’d these at 1,113 fps. Given the length of this boolit and resulting case capacity I might be near max load, but my Lyman manual 49th Ed shows 11.0 grains for a max charge under a 147 grain j-word.
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So I’m thinking the most likely culprit is too long of a OAL.
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