Are there any best practices to go by when building an Aero M5 308 specifically for use suppressed? As of right now I have the receiver, and Aero M5E1 upper and a 15" handguard. I've thought about a barrel in the 18 to 20" range. Has anyone put together a similar rifle that works well?

18-20" is "shorter"?
shorter is like... 12-14"

what's your budget?

adjustable gas block for starters

Stick with Aero for the LPK and BCG. Ballistic Advantage barrels have worked great for me suppressed using Aero's standard carbine stock kit.

Agree on the adj. gas block, I went with SLR adj. gas bocks.

I've put together five M5 builds sticking to Aero/BA parts and have had minimal issues.

The two issues which were easily resolved included broken bolt catch which was solved by buying the DPMS LR308 bolt catch from Brownell's and sharp extractor edges that caused the fired case to stick to the BCG instead of ejecting. Happened with two of their NiB BCG's and was easily fixed in seconds with a few passes of a file.

I have a 12.5 aero m5 sbr and it has always run well.  I have a .308 specific buffer and a slrrifleworks.com adjustable gas block.  It's tuned to wolf steel. BA barrel

As it stands, it still needs a scope and plenty of rounds down range to get it proofed out, but this is one I just built.

Columbia River/Black Hole 18" barrel rifle gas system
DPMS LR308 based action.
Midwest Industries 15" M-lok combat handguard
Superlative Arms adjustable gas block
Seekins Precision adjustable stock on a rifle length tube/buffer.
Radian charging handle
Aero Precision NiB bolt carrier
Geissele SSA-E trigger group
MAID V2 grip
Dead Air KeyMo brake.

If you want a collapsible stock, I highly recommend an A5 length buffer tube so you can use the enormous range of normal carbine buffers to tune the recoil system.

And I like the Tubb flat-wire spring as well.

I own a 16" standard Armalite 10B that runs well as is straight from the factory.

I also have and 18" and a 21" (Noveske) barreled uppers I put together that are hammers. AR10's are heavy as hell. Everything is stock on my lowers except the trigger. I'm running Slash's buffers on my home builds. I did not use an adjustable gas block and prefer to set up rifles to run without them.

All AR10 platform rifles need to be built with minimum clearance upon full rearward travel of the bolt so it just clears the bolt hold open device. Experiment using quarters to reduce rearward movement until the catch just trips (1/8"+/-) the bolt catch. If you don't do this you will eventually break the bolt hold open latch. The BCG simply has too much mass to hammer at the part for very long before something has to give.

Thanks for all the input everyone. Please keep it coming. I'm leaning towards an 18" barrel and an adjustable gas block. I've got an aero handguard so not sure if the gas block will fit. I do plan on going the collapsible stock route and will likely go with a magpul ubr collapsible stock. As far as my budget, I'm still trying to figure that out. I do know that I'd like to spend $200 to $400 for a barrel. As far as the barrel, if I got the 18" or 20" route should I be looking for anything special as far as the length of the gas system?

I have a 14.5" pinned with a YHM something or other.

I put in an adjustable gas block and haven't had any issues.
I think I upgraded the buffer as well, but I dont remember what to. Either way its tubed to run fine.

It's no 1000 yard gun, but for me it's really a do all.

Nope, either one of those, stick with a rifle length gas system. The longer the gas system, the softer the gas impulse, and the lighter action components you can use which, in turn, provides less recoil and faster follow-up. Plus it's MUCH softer on brass and extracting the case, which is a boon for reloading.

I personally do NOT like the UBR after finally getting to hold one on a rifle. The cheek weld is static in relation to the length of pull and your head ends up falling in the gap. B5 weapon systems makes a collapsible precision stock if you are going to put a variable power optic on it which gives you options on both LOP and cheek weld height.

16” Criterion M118LR barrel, rifle gas
Superlative adj gas block
JP SCS

The softest shooting rifle I own

12.5’, set up for deer hunting, shooting 125 gr SST

I'm in the middle of building an Aero M5E1 in 6.5 Creedmoor. Why are you going with 308? I simply bought the complete 18" upper, and Aero adjustable gas block, an Aero assembled lower and I'll end up doing a Geissele 2 stage trigger, Raptor charging handle and Radian Talon safety. Im using a Griffin Tactical Comp Taper Mount for suppressor use. Normally I would build, but given how sparse build items are currently, It probably would have cost more paying $10 shipping on each and every item.

I'm building the gun in 308 as it seems like 308 would be better for a rifle that is specifically meant for suppressed usage. I've already got the upper receiver, a handguard, and a few other bits so I'm already part of the way towards having a complete upper. Having said this, I thought about picking up a complete Aero upper and then modifying it. I may still do that.