Just got the call that my form 4 came back for my first MG. It's an original gun in great shape, so I want to change out things like buffer assembly and upper so the originals stay in pristine shape.

I will probably mostly shoot the thing suppressed so I was thinking about going 10.5" Or 11.5" upper. My thoughts were a pigtail gas tube, and adjustable gas block. What buffer/spring should I run? I wanted to put a carbine stock on it but am leaning towards staying full length buffer system so it's smoother and easier on parts.

Built several ARs in various calibers for everything from hunting to 3 gun but want to make.sure I do everything right with the full auto stuff to preserve the gun

ODINWorks 10.5" ULTRALite Barrel
carbine length gas tube
H1 Buffer
V7 Titanium M16 BCG
SLR Adjustable Gas Block Titanium
Tubb's CS Flat Buffer Spring

Call BCM and order it all from them...this is what i did...i also added a SLR gas block...needed if your going to use a suppressor or your gun will run 1000rpm

ask BCM, buy it all from 1 place....i turned my A2 into a M4...i stripped my whole lower, and put it all in boxes.....get a geissele full auto trigger too!

PS- make sure whatever upper you buy is padded on the ejector flap.....mine left a mark on my brand new A2...i use electrical tape now

Mine

Thanks! I'll just take the ejection port cover off. Wouldnt have thought of that!

Is the guiselle SSF the only aftermarket trigger that works with full Auto? Anyone know of a place that has them in stock?

Arms Unlimited has them for $310.  That's a pretty good price.
Strike Industries makes a plastic port cover.  They work great.  I run them on all my uppers so I don't have to worry about running any of them on my A2 lower.
I recommend the A5 system for the receiver extension, spring and buffer.  I put one on mine and now I'm switching all my semis over to it.  Do some research before committing to a system, there's plenty of info out there on the A5 and why it's better, particularly when you'll be running multiple barrel/gas system length uppers on one lower.  The down side is that the A5 buffers are not "mil-spec" standard, but the spring is a standard rifle spring and the RE length is standard SR25/AR10.

I actually ordered the a5 system earlier after some research lol. Glad you like it, looks like that research didn't steer me wrong lol

When I got my M16, I ordered a 11.5 Bushmaster upper for it. It would run with the 11.5 with fixed stock but wouldn't run with the 11.5 and collapsible stock. I tried a bunch of different buffers and it would semi fine but no full auto.

I never did figure out what in particular was happening other than it was running too fast. It would fire one, maybe two rounds in FA, then it would quit with a live round in the chamber with a light primer strike. What I think was happening is the bolt was slamming shut so fast that it would bounce out of battery enough it impede the firing pin, either that of the hammer was riding the bolt home for some reason. Ended up buying a slow-fire buffer from Advanced Armament and problem solved. It runs around 600-650 RPM now.

What grip are you using  on the front.

I'd say get whatever buffer weight you want and stick with it (H2 or Vltor A5H2 would be a good choice). Then make sure all of your uppers work with it. If they are under gassed, open up the gas port. If they are over gassed, I use a BRT gas port insert. The Vltor should be accepting of a large range of gas port sizes. This way you can swap any upper with any lower and you don't have to buy a bunch of different buffers.

everything you see on my gun is BCM...its their front grip....im not sure if i like it or not.....for a front grip its great...just not sure if i prefer a horizontal grip instead..