As more guys dive in to building their own DPMS compatible 308 AR another detail is becoming apparent. These weapons clearly function better out of the box with the chrome bolt carrier group than the phosphate coated counterparts. The reason is simple, lubricity. These weapons have a lot of bearing surface. Bearing surface equates to friction. This is also why these weapons need a lot more oil when new. Quite simply the chrome bolt carrier group moves much more easily than a phosphate coated one in the upper receiver.
I suspect DPMS has a break in process that starts before a weapon is fired.
Builds utilizing the phosphate coated bolt carrier group appear to be more prone to not cycling properly with a fresh build.
Now this is not to say the phosphate bolt carriers are bad. They are not. They just need a few boxes of ammunition through the weapon to get all the surfaces polished. Once broken in you would be hard pressed to see any difference in function.
If you already have a phosphate bolt carrier group I would suggest doing the following before heading to the range the first time. (It’s ok do this with the chrome version as well)
- Make certain the weapon is unloaded and gun safety rules are followed.
- Generously coat the bolt carrier with oil
- Coat the bolt lugs with grease
- Manually cycle the action 50 or so times or until you notice the action moving smoother. So not “Ride” the charging handle. Let the bolt carrier go with all the velocity and force it can generate. Make no mistake you will see and hear a difference after a short time.
- Once satisfied remove the bolt carrier group from the upper and clean everything.
- Inspect the bolt carrier group. You will probably notice areas of the carrier getting polished as well as the bolt lugs.
- When you get to the range oil and grease as in steps 2 and 3. At this point you should be good to go.
Keep in mind there can be a significant cost savings with the phosphate coated bolt carrier group. You just need to devote a little time and elbow grease before hitting the range.