Removing Cerakote for Barrel Mounting

[Frankly]

So I had an Aero Precision upper Cerakoted and they did the inside where the barrel extension slides in. I have a new Faxon pencil barrel I want to use and it is such a tight fit that I can only "get the tip in"  about 1/8". There is no lip of paint build up and the Cerakote guy did an otherwise good even job (except he hasn't yet returned my call with my complaint.... going on 48 hours.).

 

I'm not super experienced but I tried some other barrels and they were also tight, one went about 1/2" with full hand pressure, the others were only 1/8". I've built several naked guns with tight barrel to upper fits that needed some thermal expansion/contraction (heat the upper, freeze the barrel) and some good wacks with a rubber mallet/wood. But nothing to this degree. I fear bending the pencil barrel or having it seize partway in. 

 

Right now I plan to return it and have the guy make it right, if I can not use a mass market quality barrel then it's no good to me and he needs to fix that. 

 

BUT... if I have to, what is the best way to open up this upper throat without introducing some sort of cant or warp? I also would like to understand this better in case the seller offers to fix this, the last thing I want is a sloppy fit. 

 

I imagine there is a drill chuck wire brush out there, any advice what size and kind to get? Or are we looking for a gunsmith with a lathe? Or just start over with a new upper (which might be cheaper in the end). 

 

Frustrated because it would probably be my best build yet and it does look great but cripes!

 

Thanks

Edited July 25, 2019 by Frankly

[Frankly]

Well... in case nobody answers here's what I found with more search engine diligence. It might help somebody here down the road.

 

From places like AR15.com so probably not the most reliable expert opinions but most people said that doing the frozen shrunken barrel and heat expanded upper was the way to go. Freezing the barrel 24 hours gets it as small as possible whilst heating the upper with a heat gun or torch isn't as large a gain (Steel versus Aluminum). Others used Scotch Brite on the  barrel extension and others used a progression of 200-400-1000 grit Aluminum Oxide on the receiver throat. Most used a rubber mallet and wood block but sparingly, not full force. The few with calipers reported 0.003" difference being too tight and how far the heat/freeze technique moved. 

 

Some Benchrest National Match shooter claimed to be the world's expert on this and tried to hold court. Other guys argued for loose fits. Some people typed in ALL CAPS. The rest of the gun internet is scary. 

 

All these guys mentioned only being able to get their barrels inserted halfway with hand pressure, versus mine that will go the first 1/8". My experience with calipers is limited but I found a 0.009 difference between barrel and receiver so I have a lot larger move than the guys above. 

 

My dealer finally came around and said that properly applied Cerakote was no thicker than anodizing so don't blame the Cerakote. But he did say that about half his Aero uppers ran tight and he did the heat/freeze technique when needed.

 

Looking closer, I suspect that the Cerakote must have gathered at the front of the receiver throat. Perhaps I caught the Monday hungover shift? But I'm going sand off as much as I need to get my barrel inserted halfway, freeze and heat, and lube the extension with lots of Aeroshell. I'll have the rubber mallet ready and can also use the barrel nut to pull it tight. I hope it's not such a big move that the receiver cracks but if I can get the barrel extension half way in I should be safe.

 

Also learned that heating and freezing parts is used in the Aerospace industry so it's definitely legit. 

 

Thanks for the help! Har Har 

 

 

Edited July 28, 2019 by Frankly

[mpom]

Suspect no responses because its so rare that anyone finds a 0.009" difference in the dimensions you referenced. If it doesn't work out, I would test fit the barrel extension to

as many upper receivers as needed till you get an acceptable fit before Cerakote is applied.

Good luck,

 

mark

[Frankly]

Turns out it really was a fat bead of paint. Only a few seconds of sanding cleared it up. Achieved the nice tight fit as desired. Such drama, thanks for reading.

[mpom]

Nice! Glad it worked out for you.

Mark

[jon49erfan]

I had this same problem with an anodized upper. Could only get a BA barrel about 1/3 of the way in a Seekins upper. I froze the barrel for about 2 hours and it went in significantly further and a few taps with a dead blow seated it. On the plus side, no loc tite on the extension was needed.