I have a couple of new M4 type AR’s that came with a half shroud BCG. I was thinking about replacing the bolt carrier groups with M16 BCG’s in the hopes that the added mass will slow down the cycling. I’ve had a few dropped extractions with the carriers that are in the M4’s. I also have a couple of older Colt AR’s with a BCG that is open on the bottom. One of the Colts has never been fired, and the other has been fired a lot. Both of the Colts have blocks in them.
I was just wondering if it is okay to replace the BCG’s in these guns, by putting M16 BCG’s in the M4’s, and using the bolts that came with the M4’s on the Colts. Are there any concerns about doing this? For what it’s worth, the Colt AR has been shot a lot with no problems and always works, so I’m not sure if there would be any benefit to putting a BCG with a half shroud in it or not. From the looks of it, all it would do is offer more protection for the firing pin. The firing pin on the Colts’ open bottom BCG is exposed.
IIRC, swapping the carriers doesn’t pose a porblem. Swapping bolts may cause you some head space problems, but I don’t think it’s a huge issue unless you have several hundred or thousands of rounds shot through a particular AR with the same bolt. I’ve never had occasion to swap bolts, however, I’ve heard that you want to keep one bolt with one gun regardless if you swapped carriers in the same gun.
For what it’s worth, the difference in weight between a typical shrouded AR15 carrier and an M16 carrier is 0.3 ounces.
From a cost/results staindpoint, you are FAR better to get a heavier buffer instead as the difference in weight is about 3/4 ounce per each step you go.
