I am building my 2nd franken rifle.  I buy a piece here and there, taking my time, lots of research.  

So I had a free day today and put everything together.  No scratches, nothing flew across the room, everything fits the way it should.  EXCEPT!!  the rear takedown pin will not engage.  I can clearly see that the upper hole does not line up.  I can punch it in, but I also have to punch it out.

Do do I drill out the upper rear hole?  I ussume that would be preferred vs messing with the lower.

What's the hives opinion on the zero fail / nickel boron bcgs?  

Upper list:
PSA A4 blem upper
YHM LW free float 4 rail handguard
Low profile gas block (stainless)
WOA fluted SDM 16 barrel

Still need:
Bcg
Charging handle - BMC gunfighter or raptor type most likely
Optics - I have a Bushnell trophy hunter 4-12 600 DOA.  I may use that.

Lower list:
PSA blem lower
Geissele ssa-e trigger
Generic parts kit
Moe odg grip
Moe odg rifle butt stock

Thanks for the feedback!

does the pin slide in and out freely by itself in the upper or lower separately? If not start by deburring the pin. its the cheapest part to replace. slowly whittle it down w/ some emery cloth and see if that makes an improvement.

if it does move freely in both and scuffing it down a little doesn't help take a small rat tail file to the upper and just slowly pass it through once or twice then try again. don't get in a rush and slop something up.

My shooting friend has a Fail Zero BCG and has no problems with it, but I have seen some negative comments on the web about them. I have a WMD Guns BCG and it is flawless.

FWIW please do not call your gun a franken gun. All AR's except Colt are basically franken guns. You home built AR is no different than any sold on the market other than Colt.

Vince

I would just hammer it in and out.. you will see over a few times cleaning it that it will fit just fine.

Tap the pin out with a punch is not odd for some builds. It will loosen up over time.
If you really really need it loose fitting, slightly fit the hole within the rear  take down lug of the upper receiver. A small pass of a file will open up the hole...but I would not mess with it.

I have that problem with my forward pin. I have to tap it out. I haven't decided if I'm going to do anything about it yet.

Before any filing, check that the rear lug has enough clearance.

"Back in the day" it wasn't uncommon to "fit" the rear lug on the upper to the lower. That was when the only lowers available were Olympic Arms.

Olympic Arms lowers were so out of spec you needed a fine tooth rat tail file to fit uppers.

......

Don't alter anything, just keep tapping that pin in and out for a while.  It'll "break in" in a relatively short time, and it will lock up so smoothly you'll wonder why you worried about it now.

Rock River has their upper and lower receivers machined for that kind of "initial interference" fit on purpose; when they are broken in, they go together as smooth as melted butter.

Again, this is NOT a problem, just a minor hassle.

This. It will slide in and out easier the more you clean it/take it down. This isn't even a problem.....if it was loose than that's a different story.

This.

I built a rifle for my buddy with spikes upper and lower and both of his takedown pins need tapped in and out. He started bitching about how f'ed up it was so I offered to trade him any upper and lower For his...I know guys that would kill for that kind of fit. He kept it and now it's like butter.

Thanks for the feedback.

This is what I gleemed from the responses.

1.  All AR rifles except colt are franken rifles so I will drop that.

2.  Enjoy the tight fit.  Because the bitch will loosen up.  ;-)

3. Fail zero type bcg is basically just another bcg.  Some good, some bad.

4. File down the pin.  Not the receiver.

Thanks!

Now to find a SS flash hider/ brake..

DO NOT mess with that takedown pin.  Just put up with tapping it in and out for a while - it won't take long for it to fit like it was all made of the same piece of WIN.  It won't "loosen up", it'll stop being "too tight" and you'll be able to get the pin in and out easily, with a very snug, "perfect" fit.

This may be what you seek OP...http://www.seekinsprecision.com/parts-and-accessories/muzzle-devices/ar-atc-muzzle-brake.html