Bushmaster ORC Upper Issue

[hinton03]

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?

 

[rbernie]

Sounds like the handloaded rounds aren't resizing properly and you're getting chamber bind. Check yer die setup.

 

[dogmush]

Full length resize, or just the neck?

It sounds like the brass is a smidge too big for the chamber, is getting stuck not quite in and with the bolt OOB a little bit. Since the round is jaming in the chamber, it's sticking on the chamber walls.

 

[hinton03]

RCBS 223 dies with full length resizing.

I will try taking out the bullet seater and giving the die another 1/4 turn to see if that helps.

 

[MachIVshooter]

Sounds like the handloaded rounds aren't resizing properly and you're getting chamber bind. Check yer die setup.

Yup. Bolt is not going into battery because the case shoulders are too wide or too far forward.

The mark you see on the primer is due to the free floating firing pin of the AR.

RCBS 223 dies with full length resizing.

I will try taking out the bullet seater and giving the die another 1/4 turn to see if that helps.

The seating die is not for resizing. That would be the decapping and resizing die. You should be bottoming out on the die. If you are, and are still having this issue, switch to a small base die.

You issue could very well be that you're crushing the shoulder with the seating die, expanding it. You should not be pushing into the crimping part of the seating die if the bullets do not have a cannelure.

 

[hinton03]

Duh, I knew that; thanks for catching my error; I normally leave about a Nickel's worth of space between the bottom of my sizing die and the case holder I will crank it down until they barley touch.

Thanks again.