Mixing Buffers, Springs, and Gas Systems

[DMW1116]

I’m digging into my first full build and am considering a couple options. One is an SPR. Several 18” barrels have mid-length and some have rifle length gas systems. If I go with the SPR option I’d prefer a fixed stock. If I were to go with a barrel with a rifle length gas system, would a rifle length buffer tube and spring be necessary?

 

[InTheSwamp]

I’m digging into my first full build and am considering a couple options. One is an SPR. Several 18” barrels have mid-length and some have rifle length gas systems. If I go with the SPR option I’d prefer a fixed stock. If I were to go with a barrel with a rifle length gas system, would a rifle length buffer tube and spring be necessary?

Those are relative to the buffer tube you're using, not the barrel.

 

[DMW1116]

Right, but can I take a rifle length gas system upper with an 18" barrel and put it on a lower with a carbine length buffer tube and spring?

 

[InTheSwamp]

Right, but can I take a rifle length gas system upper with an 18" barrel and put it on a lower with a carbine length buffer tube and spring?

Yes, you can.

 

[InTheSwamp]

This is my 20" rifle length barrel with a carbine tube lower...

 

[Varminterror]

If I were to go with a barrel with a rifle length gas system, would a rifle length buffer tube and spring be necessary?

No, not necessary.

There really isn’t any reason to try to coordinate gas system length with buffer length.

All we are doing is balancing gas and mass - and the “balance point” is not a razor edge, it’s more like an 8 lane super highway.

 

[DMW1116]

Ah, good to know. I'm looking at a couple of paths for completion, but I can go with the planned lower parts and decide on the barrel and caliber later.

 

[powermad]

My 18" is rifle length gas with a .0995 gas port.
I used an A5 for a bit, rifle spring and rifle weight buffer (A5H2).
Don't really need to collapse the stock so used an A2.

I don't have a carbine action in anything, either A2 or A5.