AR Bolt Carrier Issue with Geissele Trigger

[Fire4Effect]

I recently built a new complete upper receiver with a JP FMOS Bolt Carrier and JP Enhanced Bolt. I installed the completed upper on a Daniel Defense lower from a factory Daniel Defense MK 12 rifle. A Geissele SSA-E trigger was installed in the Daniel Defense lower.

The rifle shot perfectly with a Geissele SSA-E trigger, but I wanted a lighter trigger and installed a Geissele National Match trigger.

After assembling the upper and lower I did a function check. With the hammer uncocked the bolt would only retract about an inch then would not retract further. If I cocked the hammer manually the bolt carrier cycles fine.

Upon inspection it appears the hook under the face of the Geissele National Match hammer is hanging up on the tail of the JP FMOS Bolt Carrier. I compared the tails of the JP FMOS Bolt Carrier and the Daniel Defense bolt carrier and there is a slight difference. The hook under the shorter hammer face on the Geissele National Match hammer is captured at the rear of the JP Rifles bolt carrier as the BCG retracts. The Daniel Defense bolt carrier appears to cycle fine with the Geissle National Match trigger.

I sent the National Match trigger back to Geissele and they inspected and found it in spec. They feel that their National Match trigger is not compatible with the JP FMOS Bolt Carrier based on my experience. Both of these products have been on the market for a long time and I am surprised this is the first time an incompatibility issue has been raised.

I sent the JP Rifles FMOS Bolt Carrier back and they determined it was in spec. They concurred there in a slight difference in the rear of the bolt carrier where the hammer is hanging up.

I have two choices:

Go back to the Geissele SSA-E trigger and run the complete JP rifles enhanced BCG.

Install the Geissele National Match trigger and run the enhanced JP bolt in a MIL-SPEC bolt carrier. It looks like there are not many options to buy a stand-alone bolt carrier. I see LMT has one or I could just buy a complete BCG from Daniel Defense or BCM and keep the bolt as a spare.

Anyone have an opinion about utilizing a LMT, Daniel Defense or BCM bolt carrier with a JP Rifles enhanced bolt. Wish I could utilize the JP Rifles bolt carrier. The machine work is stunning and it glides in my BCM upper.

 

[jelenko]

How about removing a little material on the bolt carrier where it's catching on the hammer?

 

[Fire4Effect]

How about removing a little material on the bolt carrier where it's catching on the hammer?

That’s the problem. JP Rifles has removed material from the bolt carrier that the hammer needs to ride on.

 

[jelenko]

there are not many options to buy a stand-alone bolt carrier.

I've used 4 bolts from these guys - they work perfectly and have held up well.
https://www.unbrandedar.com/product/m16-bolt-carrier-group-nitride/

 

[jelenko]

That’s the problem. JP Rifles has removed material from the bolt carrier that the hammer needs to ride on.

Would there be a way to shape the leading edge so it didn't hook on the Geissele HSNM hammer?

The JP bolt carrier actually moves with less resistance than the one from Daniel Defense?

 

[Fire4Effect]

Would there be a way to shape the leading edge so it didn't hook on the Geissele HSNM hammer?

The JP bolt carrier actually moves with less resistance than the one from Daniel Defense?

I don't see how. If anything material needs to be added.

 

[ronemus]

There is plenty of material in the JP carrier to round the edge that is catching the National Match hammer; the carrier overrides the hammer for a considerable distance, so the location of the edge is not critical. Care with a Dremel and/or files can make it functional.

There are so many aftermarket parts available that it would be prohibitively expensive for a manufacturer to test all possible combinations. Each manufacturer will certainly test the complete rifles it sells, but you're on your own when you start substituting parts. Usually it works, but "enhanced" parts are a crap shoot since the don't follow the AR-15 design drawings.

 

[jelenko]

"enhanced" parts are a crap shoot since the don't follow the AR-15 design drawings.

+ a bunch.

 

[Fire4Effect]

There is plenty of material in the JP carrier to round the edge that is catching the National Match hammer; the carrier overrides the hammer for a considerable distance, so the location of the edge is not critical. Care with a Dremel and/or files can make it functional.

There are so many aftermarket parts available that it would be prohibitively expensive for a manufacturer to test all possible combinations. Each manufacturer will certainly test the complete rifles it sells, but you're on your own when you start substituting parts. Usually it works, but "enhanced" parts are a crap shoot since the don't follow the AR-15 design drawings.

Actually there is not. I worked with JP Rifles for several weeks before posting here. In addition, the face of the National Match hammer face is reduced considerably from the SSA-E hammer face.