New builder for an AR 15

[Strickland]

I recently bought a new upper and lower set I was wanting to use a 20" barrel, is a rifle length gas tube, carbine length spring and buffer be compatible, I would like to use an adjustable stock

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[powermad]

For a rifle length system I would use an A5 with an A5H2 buffer if you want an adjustable stock.
A Carbine action will work but a rifle action is much smoother.

BCM has A5 action kits now too.

BCM MK2 Recoil Mitigation System - Mod 1 - T2

The BCM MK2 recoil mitigation system (RMS) Mod 1, T2 includes a MK2 T2 buffer, M16A4 action spring, M4 lock nut, MK2 receiver extension, & QD end plate.

bravocompanyusa.com

 

[ScatPackLife]

I recently bought a new upper and lower set I was wanting to use a 20" barrel, is a rifle length gas tube, carbine length spring and buffer be compatible, I would like to use an adjustable stock

I've seen 20" barrel ARs with adjustable stocks.

I built an AR with an 18" barrel, rifle length gas system, and a carbine buffer set up, it works fine. I do have an adjustable gas block though.

Not sure if you bought the parts yet but I recommend you get an adjustable gas block. I use them to n all my ARs.

 

[titsonritz]

For a rifle length system I would use an A5 with an A5H2 buffer if you want an adjustable stock.
A Carbine action will work but a rifle action is much smoother.

BCM has A5 action kits now too.

BCM MK2 Recoil Mitigation System - Mod 1 - T2

The BCM MK2 recoil mitigation system (RMS) Mod 1, T2 includes a MK2 T2 buffer, M16A4 action spring, M4 lock nut, MK2 receiver extension, & QD end plate.

bravocompanyusa.com

I would suggest an A5 system as well. I haven't got fancy with their MK2 version, yet.

 

[eldbillbo]

If you want to run a carbine stock and buffer system with your 20" barrel there is no problem with that they run great, Don't run a heavy buffer because you don't need that. Guys have been doing this for a long time. they just used to look weird before there were M-lok forearms. Don't buy into needing some expensive buffer system to run a 20" barrel with a carbine stock.

 

[Hueco]

I recently bought a new upper and lower set I was wanting to use a 20" barrel, is a rifle length gas tube, carbine length spring and buffer be compatible, I would like to use an adjustable stock

I did an A5 length tube, Sprinco green spring with my 20" rifle length upper. Suuuuper soft shooter.

 

[Yarome]

I recently bought a new upper and lower set I was wanting to use a 20" barrel, is a rifle length gas tube, carbine length spring and buffer be compatible, I would like to use an adjustable stock

Sure! One of my best shooters is a 20", carbine length tube w/H2 buffer and mid length gas. You might not need an H2 with rifle length gas, but what you're suggesting is certainly viable.

Is it an "ideal" config? Maybe not, but if that's the gear you already have... I don't see any red flags.

 

[powermad]

You can piece together an A5 action as well but it's only a few bucks cheaper than just getting a kit depending on what you have for spare parts or take offs.

The extension on a .308 is the same intermediate length as an A5 tube.
I had the tube and a green spring but getting an A5H2 buffer was almost impossible, always backordered forever.
I wound up buying the Vltor Emod stock kit just to get the buffer, only color left was forest green.
That's on my 14.7".

I wound up getting another A5H2 buffer and used the other RE and a Tubbs flatwire spring for my 18"
Just swapped that out for an A2 stock as I don't need to collapse it and I like the A2.

 

[collector rob]

I recently bought a new upper and lower set I was wanting to use a 20" barrel, is a rifle length gas tube, carbine length spring and buffer be compatible, I would like to use an adjustable stock

What you described is just like a Canadian C7A2.
20" flat top upper with a car style stock from the C8.

C7A2 Automatic Rifle - Canada.ca

The C7A2 Automatic rifle is the personal weapon used by the Canadian Armed Forces. It is hand-held, shoulder-controlled, and capable of single or automatic fire.

www.canada.ca