Let me see if I can describe this since it is fairly complicated and tech support at Bushmaster hadn't seen it before.
I mounted a Bushmaster ORC Upper on a Bushmaster National Match lower. When I took it to the range I started with M855 to get it on the paper and had no issues feeding, firing or ejecting; however, when I moved to hand loads that fired fine in my National Match upper the issue started.
- The load is 69 grain Nosler BTHP Competition with an OAL of 2.25.
- The load fit in the magazine fine and feed from the magazine without issue
- When I attempted to fire I felt and heard the firing pin fall but the round misfired, there was a very light brush on the primer
- I attempted to eject the round but the charging handle would not move to the rear and I had to tap it with a small rubber mallet to get the round to eject; this happened every time I tried to fire this load.
- I removed the bolt and firing pin and inspection didn't show any damage to the pin so I went back to M855 and it function correctly.
- I tried dropping the magazine and feeding the round into the chamber through the ejection port by hand and it fired correctly.
- Also tried a hand load with a 55 grain VMAX and it had the same issue, I went back to the 855 and it fired and fed correctly
The part that has me puzzled is the failure to extract the round after the misfire? The only thing I can think of is the hand loads OAL is causing an issue when fed into the chamber, the closing of the bolt jams the bullet into the rifling and after the initial closing the bolt recesses a small amount; because the bullet is stuck in the rifling it pulls the primer away from the bolt face slightly causing the misfire and making the round hard to extract?
I mounted a Bushmaster ORC Upper on a Bushmaster National Match lower. When I took it to the range I started with M855 to get it on the paper and had no issues feeding, firing or ejecting; however, when I moved to hand loads that fired fine in my National Match upper the issue started.
- The load is 69 grain Nosler BTHP Competition with an OAL of 2.25.
- The load fit in the magazine fine and feed from the magazine without issue
- When I attempted to fire I felt and heard the firing pin fall but the round misfired, there was a very light brush on the primer
- I attempted to eject the round but the charging handle would not move to the rear and I had to tap it with a small rubber mallet to get the round to eject; this happened every time I tried to fire this load.
- I removed the bolt and firing pin and inspection didn't show any damage to the pin so I went back to M855 and it function correctly.
- I tried dropping the magazine and feeding the round into the chamber through the ejection port by hand and it fired correctly.
- Also tried a hand load with a 55 grain VMAX and it had the same issue, I went back to the 855 and it fired and fed correctly
The part that has me puzzled is the failure to extract the round after the misfire? The only thing I can think of is the hand loads OAL is causing an issue when fed into the chamber, the closing of the bolt jams the bullet into the rifling and after the initial closing the bolt recesses a small amount; because the bullet is stuck in the rifling it pulls the primer away from the bolt face slightly causing the misfire and making the round hard to extract?