AR Setup

So I'm putting together another AR and plan to use rifle length gas (18" barrel) with standard carbine buffer/tube/spring. In my research, there seems to be all kinds of results on this setup. What might be any possible issues? Is a adjustable gas block advised? Will be shooting 55 and 62 grain out to 400 yards.and would like it to shoot smooth as possible.

An adjustable gas block is always advised

Approach the build one step at a time in other words use stock parts for buffer tube , spring, buffer and shoot and adjust gas block .

If you like it good , if it doesn’t run perfect then only change 1 part at a time and retest

Maybe you’ll end up swapping in a heavier buffer or spring or lighter buffer and heavier spring ....

1 part at a time

https://geissele.com/rifle-parts/lower-parts/buffer-tube-parts.html

Springco blue spring and H buffer.

Geissele stuff is great but their buffer parts aren’t compatible with other milspec parts

Thanks for all the suggestions. Ill try the standard carbine buffer and spring then go from there. Being fairly new to AR builds (this will me my 5th) just wondering what heavier buffers (h1/h2,etc..) do to cycling process?

Heavier buffers will slow down the cycling.

Doesn't an AGB eliminate the need for trying to find the perfect balance of spring and buffer weight?

Nope , it regulates the gas which imparts recoil and inertial forced upon the buffer/spring combo selected by the user.

The gas block doesn’t change the mass of any moving part therefore if the user selects a lightweight (skeletonized) bolt carrier to reduce the amount of reciprocating mass to influence felt recoil then the gas block is operating to adjust the gas flow (timing) of this setup.

Gas blocks should be a standard option in 2020 for any AR15 - base model, premium model, elite ultra premium model...

The tuning of felt recoil and “twang” of springs and force imparted on BCGs happens within that system away from the gas block function.