Hey guys, sorry if this topic has already been done before, but I can't seem to find a consolidated source for my questions.....

I'm planning on my first pistol build, from a 80% lower from Tactical Machining.  I am planning on building this pistol just for a range toy, and because AR pistols just look so damn nice.

I understand that shorter ARs have cylcing and reliability issues so I've done a little research into piston setups and would like some advice.

1) for a pistol, would you even recommend using a piston build?

2) what piston system would you recommend?

3) besides milling out the 80% lower, would i need any for work on the lower to insure a tight fit to an upper?

4) are all uppers recievers the same?  that kind of recoil buffer tube would be ideal for a piston setup?

5) 1/7 twist would be ideal for a short 7.5"-10" barrel right?

6) does it matter if I use a full auto carrier?

I have so many more questions, but will limit myself.   If you have any constructive advice I'd really appreciate some of you hands on experience!

No.

The one Gene Stoner built into the bolt carrier.

It's all in the radius at the back of the lower where the lug from the upper fits in.

Define "are they all the same"?  As far as fit, quality, or what?

Just use a full length pistol tube not one of the reduced length systems.

Not really, all depends on what you are shooting.  Twist rate is twist rate, barrel length is almost meaningless.

If you want a recommendation on what to put together that will likely run well, just get a quality 11.5" barrel and run it with a full length pistol buffer tube, and probably an H buffer.

Here's a similar thread of someone building an SBR, but the barrel length question would be the same as for a pistol.
http://www.ar15.com/forums/topic.html?b=6&f=51&t=344937

Thanks for the input...can you go into why you would not recommend a piston build?

For my last build I went with a BCM upper with BCM auto carrier-very good rep and good quality and a good price. For barrel I went with a centurion 1:7 cold hammer forged since I won't run any thing less than 62gr and for my "pet" loads being in the 68-72gr area. No complaints and it shoots great. I did end up putting in a H3 buffer since I had the classic cycling issues(needed to slow it down).
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It's not "necessary" but there are commercial SBRs and AR pistols with a piston, like the LWRC PSD. No problems here at all.

If I was going to build an AR pistol with a 7.5" bbl I would definitely go for a piston, as I actually did.

I spent a lot of time researching my build and decided that going with a piston upper would save me a lot of hassles. Pistol length gas systems are more likely to be problematic than longer gas systems and they run much dirtier than longer bbls (10.5"+) with carbine gas systems. This is my opinion based upon all the posts I read and my desire to not need to tweak the pistol to get it running reliably.

I built a 7.5" 5.56 using a Rainier 1/8 SST Ultra Match Barrel.
BCM Upper Receiver
BCM FA BCG
Spikes carbine length Pistol Tube
H2 buffer. Carbine spring

It has been very reliable.
The Ranier barrel uses a small gas port, which I had doubts about, but has run great. Smaller port that runs means less recoil and less crud in the works.
Dave N