New MP15 5.56. The bolt assembly is a snug fit in the last ~1/2” of travel. If I slowly release the bolt it will stop short of it’s full travel. If I release it quickly it closes all the way. Is this normal?

Yes, let the bolt go forward under the full power of the spring, don't baby it.

Yes normal , like a pistol slide the bolt needs to be quickly released to go into battery

Instead of telling you what to do I'll try to explain why.

During the last half inch of BOLT CARRIER GROUP travel the bolt comes into contact with the inner rear face of the barrel extension. The inertia of the BOLT CARRIER causes it to continue forward, which in turn because of the cam pin and cam pin cut causes the BOLT to rotate and lock into the barrel extension.

What your doing is removing the inertia of the BOLT CARRIER

Don't ride the charging handle.

However, if the parts were near-perfectly spec'd and lightly lubed, you could walk the bcg forward. But most guns are as you describe thus the recommendation to let it fly. Just another reason for a side-charger model.

Flip open your rifle and put the muzzle on the floor holding it upright in your hand.


Pull the charging handle up with the other hand and you'll get some resistance until the bolt lugs come out of the barrel extension. Then it will come up easily.


Let it back down slow until it stops. Shine a flashlight down where the bolt goes into the extension and push slowly on the carrier. You'll see the lugs rotate as they go back into battery.



That's what's responsible for that resistance you're talking about.

2 of my 3 uppers are side chargers (not S&W obviously)

But a brass catcher and a side charger have their own issues.

I have no brass catchers and no issues, whatsoever, with my one Gibbz side charger.

Every semi-automatic, locked breach firearm I own, and there are many, encounters resistance as bolt lugs are cammed into place. Many can be "hung up" short of battery by carefully lowering the bolt carrier group. It has nothing to do with bolt carrier-receiver fit or the charging handle and everything to do with the sudden encounter with camming surfaces or locking recesses. That's why continued use will "slick up" a gun by self-polishing the surfaces. You won't fix it by changing to a side charger, but lubrication and shooting will.