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6/21/2017 8:25:40 PM
Posted: 4/19/2012 1:28:35 PM EDT
I am putting a 13" troy alpha rail on my psa 16" midlength upper. Everything is going on easy and lining up as it should, however, once I tighten down the three screws that hold the rail to the bbl nut, the rail "pulls" away from the upper a little bit. There's not a huge gap but enough that I can see daylight between the rail on the upper and the rail on the free-float tube. I'd like them to fit together flush. Any ideas? Thanks.
Link Posted: 4/19/2012 2:23:24 PM EDT
Due to variances in both parts, 100% tight fit, no gap installation is almost guaranteed not to happen.
Small gaps between the upper and rail are to be expected due to tolerance stacking.

I think you have to live with it as is.


Link Posted: 4/19/2012 2:45:46 PM EDT
Thanks zman. Anyone else?
Link Posted: 4/19/2012 4:30:56 PM EDT
There is a small gap between my upper and Alpha rail too. Like, maybe the thickness of a credit card.
Link Posted: 4/19/2012 4:53:43 PM EDT
Thanks Blah. Thats about the same size of gap as on mine. I reckon I'll just have to deal with it. I appreciate the responses.
Link Posted: 4/19/2012 5:53:35 PM EDT
Theoretically you could cut the face of the upper back a few thousands with a lapping tool to make it fit closer. If you cut too much the barrel extension will insert too far into the upper. Alternatively you could cut the inside of the barrel nut so that the teeth are closer to the upper. A combination of both these methods might cut your gap in half.
Link Posted: 4/19/2012 5:56:03 PM EDT
Same gap on my 13" alpha. It's normal, don't worry about it.
Link Posted: 4/19/2012 6:18:40 PM EDT
Originally Posted By sigluvr:
Same gap on my 13" alpha. It's normal, don't worry about it.


This
Link Posted: 4/20/2012 9:00:11 PM EDT
Originally Posted By KentuckyWindage82:
Originally Posted By sigluvr:
Same gap on my 13" alpha. It's normal, don't worry about it.


This


same. mega forged upper.
Link Posted: 4/20/2012 10:46:06 PM EDT
I installed the 13' alpha rail on a spikes upper & lower 14.5 build and mine has the gap too. it's not enough for me to worry about
Link Posted: 4/23/2012 1:08:31 PM EDT
[Last Edit: 4/23/2012 1:09:37 PM EDT by captkirk32]
Same size gap on mine as well. 13" Alpha against a S&W MP-15 upper.
Link Posted: 4/23/2012 1:12:40 PM EDT
It probably just depends on the upper. I have a Troy 13" Alpha Rail on a Vltor MUR, and it fits like a glove (no gap at all). I also have a 12" Battlerail on a Vltor MUR that has a perfect fit. But like everyone has mentioned, different parts won't always be exact matches. I wouldn't be worried unless the gap is glaringly wide, which it sounds like it's not.
Link Posted: 5/19/2012 4:50:32 AM EDT
Did anyone have an issue with the Alpha rail working its way off the barrel nut when you tighten it down? I can't get mine to stay on the barrel nut...
Link Posted: 5/19/2012 5:08:10 AM EDT
I've installed two Alpha rails at this point. WhIat worked well for me both times was to use an optic mount to align the rail to the reciever before tightening the screws.
Link Posted: 5/19/2012 5:36:38 AM EDT
Originally Posted By CaptnBill:
I've installed two Alpha rails at this point. WhIat worked well for me both times was to use an optic mount to align the rail to the reciever before tightening the screws.


I did the same thing. I just couldn't get the rail to stay flush with the upper.

Spooky-Is your rail moving a little on the bbl nut or coming completely off? BTW, when I saw spooky130, I expected to see a different bird in your avatar. Either way, both badass birds.
Link Posted: 5/19/2012 6:03:45 AM EDT
Remember the alpha installs by pulling away from the upper and engaging the barrel nut "wings", so that gap is natural.
Link Posted: 5/19/2012 8:25:32 AM EDT
Originally Posted By bandit175:
Originally Posted By CaptnBill:
I've installed two Alpha rails at this point. WhIat worked well for me both times was to use an optic mount to align the rail to the reciever before tightening the screws.


I did the same thing. I just couldn't get the rail to stay flush with the upper.

Spooky-Is your rail moving a little on the bbl nut or coming completely off? BTW, when I saw spooky130, I expected to see a different bird in your avatar. Either way, both badass birds.



I was able to pull it completely off. I found some YouTube videos that showed how to install it correctly. I was putting it on a 9mm upper with no gas tube - the barrel nut was just torqued on and not aligned for a gas tube. Without aligning for a gas tube as the rail was designed it pushed itself off the barrel nut when tightening it up. I aligned the barrel nut for a gas tube and now it is very tight and has no movement.

I joined here before I was assigned to an airplane - ended up with the one in the picture instead of the screen name... Too lazy to change...

Spooky

Link Posted: 5/19/2012 4:35:03 PM EDT
this is absolutely true.. specially for after market self build.

however, when i wrote about UTG pro rails.. fanboys(not anyone this thread) immediately pointed out there was 1/16" gap between the rail and the upper receiver rail.. :)

Originally Posted By thezman:
Due to variances in both parts, 100% tight fit, no gap installation is almost guaranteed not to happen.
Small gaps between the upper and rail are to be expected due to tolerance stacking.

I think you have to live with it as is.




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