Adco assembled 2 AR10 upper receivers for me. I did not send the A2 Mid Length handguards. The uppers  were assembled with triangle front band. Now I can not get the handguards on, they are about 1/4 inch too long. I never had this happen before. Any help/ Thank You!

you know that for AR-10, there are 2 standards for the gas port location that are commonly used.

yours probably uses the more-common AR-15 gas port locations, which does not allow AR-15 drop-in handguards on a AR-308.

you need a barrel that uses the Armalite AR-10 gas port location.  That will allow you to use AR-15 drop-in handguards.  Faxon is one mfr that uses the Armalite AR-10 gas port location for their AR-10 barrels (308, 6.5CM).  it's about 1/4", 3/16" difference.  just fyi, the Armalite AR-10 "carbine" handguard length corresponds closely to the AR-15 mid-gas length.

I made this same discovery years ago.  It's discussed often enough in the AR-308 threads, forums.

what brand of barrel are you using?

Shave off slowly and equally at both ends?

Doubt that will work.

I used a Faxon barrel for mine.

Darn!!!! I am using Ballistic Advantage barrels. I have Faxon on other guns and they are ok. Now what to do?????

there's no way you're going to be able to use drop-in handguards with a BA AR-10 barrel.  You're just going to have to remove the handguard cap, barrel nut, and use one of the many available brands of free-float rails, take your pick.   That's the bottom line.  In a nutshell.

You could convert one of your Faxon-barrelled AR-10's to accept the drop-in handguards by disassembling them, swapping the barrel nut and handguard cap over to the Faxon, etc. if it's a mid-length gas port.  As long as it's not a pin-&-weld set-up.  Also depends on whether the Faxon AR-10's gas blocks are pinned on, or regular set-screw/clamp.  details.

or just go out and buy a Faxon mid-gas AR-10 barrel for your Aero M5.  Swap out the BA barrel for a Faxon.  Swap over the barrel nut, HG cap, gas block, muzzle device.  At least, the Faxon barrels are reasonably priced, as far as AR-10 barrels go.  You'll need to replace your AR-15 mid-length gas tube with a Armalite AR-10 carbine-length gas tube, available from Fulton (I think), and direct from Armalite.  The AR-15 gas tube is a skosh too short, it'll work, just not optimal.

I think Wilson Combat also uses the Armalite AR-10 gas length standards for their AR-10 barrels, 308 & 6.5CM.

chalk this up to a learning experience to the AR-10 world.

just my opinion.

Thank You for your help. I also have a Brownells 308 barrel that mid length handguards work ok,,,but they are discontinued. How much longer are Armalite AR10 carbine gas tubes vs an AR15 mid length gas tube? Thanks!!

AR-15 mid-length gas tube about 11-3/4"
Armalite AR-10 carbine gas tube about 12"

I say "about" because that's what I measured from the ones I've bought, not sure what the actual spec is.

I'm guessing your Brownells 308 barrel was probably manufactured by Faxon.  Faxon gets a lot of those contracts.

here's what a too-short AR-10 gas tube looks like:


compared to normal:

Thank You everyone for your help. Anderson has the 12 1/16 gas tubes. I do not have the tools for AR10's so I sent 2 out to be assembled. I am really surprised the builder did not know any of this. Looks like it is time to invest in AR10 receiver blocks and barrel nut tool.

to be honest, I don't think you can fault Adco for this.  Since you didn't provide them the handguards, they had no reason to verify the length.  You sent them your parts, and they assembled them as requested.  I would wager that the assembly work they did was up-to-par.

At least, there wasn't any machine work involved, cutting, or welding, so everything is reversible and can be un-done.  I'm assuming this isn't a pin-&-weld project.  But you're out the money for labor expended, and round-trip shipping.  Could've been worse.

Actually ADCO has done a lot of work for me and I have no complaints. I reached out to ADCO first and they got back to me immediately, It is 100% on me, I am learning just as everyone else.