Question on a BCM bolt assembly in a older BCG

**Hank6046** · 01-29-21, 10:44

Does anyone have experience or knowledge on the pro's and con's of replacing (upgrading) a bolt assembly on an existing bolt carrier group?

I have an old Tactical Ambush BCG (company doesn't exist anymore to my knowledge) in my spare parts bin with maybe 2k rds through it and am thinking of upgrading it with a BCM bolt assembly and firing pin and wanted to know thoughts.

I originally bought it for a PWS DI upper (14.5" Carbine Length) I had and ran it for some time, however, if I was shooting certain types of ammo I would see double feeds and light primer strikes. I then replaced the BCG with a Fail Zero Nickle Boron (it was 2015) and a H buffer haven't had an issue since. I'm wondering if I were to replace the bolt assembly and firing pin, if it would help as a spare when and if I needed it to be.

**Clint** · 01-29-21, 10:58

Sounds like several possible issues with double feeds and light primers.

FP protrusion should be checked at a minimum, but the carrier and gas key bores may be out of spec if it was short stroking.

Might not be worth the trouble.

**TomMcC** · 01-29-21, 11:00

I've replaced a bolt in an older carrier and replaced an updated carrier onto an existing bolt. The two I did worked just fine. Of course, the things I replaced seemed to be in spec.

If you do replace the bolt, I would try and go right to the problematic ammo and see how it flies.

**Hank6046** · 01-29-21, 11:25

Originally Posted by Clint

Sounds like several possible issues with double feeds and light primers.

FP protrusion should be checked at a minimum, but the carrier and gas key bores may be out of spec if it was short stroking.

Might not be worth the trouble.

Yeah, I was assuming that there was more gas coming out of the carrier then usual, however, it always seemed fine running Wolf Gold 55gr and Adcor 62gr. The issues came mostly from winchester 55gr whitebox and some Federal/Lake City 55gr I used at a class once. I was hoping that slowing down the buffer would help in the double feeds while a firing pin would aid in primer strikes. This doesn't solve the extra gas of the carrier key, but I couldn't pin point that as the main issue.

**Hank6046** · 01-29-21, 11:30

Originally Posted by TomMcC

I've replaced a bolt in an older carrier and replaced an updated carrier onto an existing bolt. The two I did worked just fine. Of course, the things I replaced seemed to be in spec.

If you do replace the bolt, I would try and go right to the problematic ammo and see how it flies.

I believe, that the Tac Ambush had the same specs as Spikes at the time, which was better then most, but either way I'd feel better with replacing the bolt assembly with a BCM. I have an ALG defense, Geissele and a Mid-West carrier for spares as well, but as it was a problem child before, and I have to constantly tinker with things, I wandered if it was worth doing.