first AR15 build: need help with upper

[hava982931]

So I thought I would get started on building the upper today, having completed the lower last week.

Right off the bat, a little problem. When attaching the barrel extension to the upper receiver, the barrel doesn't go into the receiver more than about 1/8" or so. Kept trying to push it in, banged on barrel lightly with rubber mallet, sanded down opening of upper receiver a little bit, but it still won't go in, much less line up the tab on the barrel with the notch on the receiver.

What am I doing wrong here, if anything? Any replies appreciated.

Thanks!

[uxo2]

pics..
could be off spec parts

[edgerly779]

You need a good set of calipers to check id of receiver and od of barrel.Harbor freight has a digital on sale often for 10-12 bucks. If you were in sfv I could look at it.

[NewbieDave]

Pictures would help... my guess is one if not both are off spec.

I've noticed these types of problems are popping up more in the last 4-5 months because of Q&A issues. Everyone's jumping the bandwagon on AR has caused manufacturers to push out parts at a faster rate... killing good Q&A testing.

While you getting pictures... be good to know who manufactured your receiver, barrel & extension.


dpc

[hava982931]

Ok, will put up pics later tonight. In the meantime, the upper is a JD Machine Tech flat top upper, purchased in Jan 2013. Barrel is a BCM with the following specs:


M4 Feed Ramp Barrel Extension (USGI)
USGI 1/7 Twist Rates
USGI 5.56 NATO Chambers
Mil-Spec 11595E - Barrel Steel (CMV)
Chrome Lined Bore and Chamber
Manganese Phosphate Barrel Finish
USGI Government Profile Barrels
HPT (High Pressure Test) Barrels
MPI (Magnetic Particle Inspected) Barrels

I will see if I can pick up some calipers later today. I really doubt that the barrel would be off spec. Most likely the upper?

[isplice]

Just assembled a JD Machine upper today (upper was bought Dec. 2012). The anodizing is way too thick. The barrel was a Daniel Defense. A brake cylinder hone took care of the problem. I'm betting you are having the same problem.

[hava982931]

Should I just try sanding down the internal diameter of the upper by hand? I don't think I could do much damage to it doing it by hand.

Just assembled a JD Machine upper today (upper was bought Dec. 2012). The anodizing is way too thick. The barrel was a Daniel Defense. A brake cylinder hone took care of the problem. I'm betting you are having the same problem.

[isplice]

You could try it by wrapping some wet and dry sandpaper (320-400 grit) around a suitable round object, like a broom handle or 3/4 in pipe and only sanding the area where the barrel extension goes. Keep checking the fit often and you'll eventually get it. Just go slow and straight.

[savs2k]

Just give it a good smack. I installed my brothers noveske in a dd upper last week. It was the tightest fitment I've encountered in a couple years. I had it mounted to my vice and all my weight didn't move it. Gave it a few solid blows with a dead blow and I was able to push the rest of it in

[isplice]

Just give it a good smack. I installed my brothers noveske in a dd upper last week. It was the tightest fitment I've encountered in a couple years. I had it mounted to my vice and all my weight didn't move it. Gave it a few solid blows with a dead blow and I was able to push the rest of it in

Tried that with mine. No joy. Hence the hone.

[jameshenry]

A little lube might help.

[Akers]

Had the same thing with a Palmetto barrel into a JD upper. Had to get another upper and it fit perfect.

[generalpetres]

just goto autozone or any local auto store and buy your self a brake hone, they are cheap and will make sure your sanding is going to be concentric. once you get it put it in a drill and slowly sand it down and periodically check your progress you want it to be snug, you want to take off just enough. its easier to remove material but harder to put back on so go slow.

[FeuerFrei]

OP,
Please use some good anti-sieze grease and try again before you sand/grind etc..
I use Loctite 38650 Copper Anti-Seize Lubricant.

[hava982931]

See picture attached. This is about as far into the upper receiver as the barrel will go.

Will try the brake hone. I don't think any amount of grease or lube will fix this.