Lower to Upper clearances (problem?)

[KS63]

Let me first say that this is my first AR build. I'm a machinist and I'm a prick about tolerances and fit and finishes. My so called "problem" has to do with my front takedown pin notch inside width on my lower. Colt prints spec .500" -.004"(.496"). Mine measures .503". It's a Tactical Innovations T15 BDX billet lower mated to a Vltor MUR 1A upper. The Vltor pin boss measures .4965 hence the horizontal .00065" clearance. I can grasp the lower and upper at the barrel nut and and rock it visibly side to side. How do yours match up? I'm sure the rifle will function just fine, but I'm just looking for your experiences with this.

I've checked other brands of lowers with my upper and they all fit relatively snug, but my lower on the other Vltor and upper manufacturers fit loosely. I can make this work if this is normal. What are your thoughts and experiences? Thanks for your time.

[J]

On a non-factory rifle, it is always a crapshoot. Some uppers and lowers fit nice, others not so much. If you use different pins/lpk, you can get even further off. I wouldn't use it for a 500+ yard bullseye tack driver with those tolerances, but as a carbine you will be more than happy. You will get minute of man at that range, but probable not bullseye accuracy. Of course many things like barrel, load, bullet, bolt, trigger come in to play there too.

You can get "acurizing" wedges. I'm not sure they really "acurize" as they claim, but they are essentially a polymer rubber-like wedge that fits in the lower to create resistance and force the pins to ride at the top of the holes and eliminate slop.

[TheBelly]

On a non-factory rifle, it is always a crapshoot. Some uppers and lowers fit nice, others not so much. If you use different pins/lpk, you can get even further off. I wouldn't use it for a 500+ yard bullseye tack driver with those tolerances, but as a carbine you will be more than happy.

You can get "acurizing" wedges. I'm not sure they really "acurize" as they claim, but they are essentially a polymer rubber-like wedge that fits in the lower to create resistance and force the pins to ride at the top of the holes and eliminate slop.

Pit has been my experience that those wedges do not contribute a significant amount to practical accuracy.

[J]

Yeah. Hence the very last sentence of my post.

[SAnd]

Call Tactical Innovations and see what they say. If it's that far out they should replace it.

Can't hurt to try.

Good Luck.

[BPTactical]

Now you know what you pay for with a Colt, LMT, Noveske etc.
This is a great example.
Will the rifle function well? Yes, it will probably outshoot any of us on any given day.
Realistically the majority of Aluminum forgings are made in a handful of forges, maybe 5-6. The rough machining is contracted out then initial QC takes place.
That determines the fate and where they end up.
Very few manufacturers actually fully machine their own receivers, Saber, LMT, Black Rain come to mind.

[ray1970]

Personally, I think you might have C.D.O.

It's kind of like O.C.D. but the letters are in the right order.

[KS63]

I hear you BP. These guys say they do 100% of the machining in house. When I asked them about Colts blueprint tolerance, they said their print says .500"-.5004". So technically to them, my lower is in spec. My Vltor upper fit perfectly in an LMT, LWRC and a S&W lower. I stuck a piece of paper on both sides of the pin and its tight, roughly .003" thick. Perfect. My backup plan is picking up a Noveske Chainsaw lower. Like you signify BP, I hope Noveskes specs are better because their stuff is still going through the Fowler digital height stand. I was trying to give the Little Guy a chance and gambled wrong I guess.

[KS63]

Personally, I think you might have C.D.O.

It's kind of like O.C.D. but the letters are in the right order.

Haha! When it comes to precision machining and tolerances/fitment, complete OCD!

[Great-Kazoo]

Call Tactical Innovations and see what they say. If it's that far out they should replace it.

Can't hurt to try.

Good Luck.

They will say it's the upper and not their lower TacIN has always been good CS wise. They took care of an issue i had with some browning bbls, didn't care how many rounds fired they wanted to make it right.
FWIW: Both my Colt & LMT Factory AR's have some slop. Fortunately i am not That Anal and only concern myself with COM out to X yards. I have also seen "on line" (surprise) a co. that was offering "shim" kits to eliminate s-s play between upper & lower. IF TACIN does not help you this could be Plan B.

http://triggershims.com/ar_15_shims.html

http://www.midwayusa.com/Product/148...-package-of-10

brownells stocks the PC kit.