Hello,
This is my first post and is about my first AR15 build. I am excited that there is a strong community with knowledge and experience!
My question is very specific. It is about the Brownells "retro" BRN-10 "Portuguese" handguard. This product is supposed to mimic the Portuguese contract AR10 handguard and I wanted to use it (for cosmetic choice) on an AR15 platform with a mid length gas tube. Confusingly, Brownells seems to imply that this product is compatible with the AR15 platform.
I assembled my upper from a receiver and barrel, torquing the barrel nut, etc. I have a standard delta ring and a standard end cap held by the FSB. I measured the gas port location to barrel and it is the correct 9" for mid length. The barrel is 20" and does have the correct mid length gas system. Unfortunately, it seems that the length of this "mid length" handguard is just too long to slip into the delta ring, maybe 0.5" oversized. Has anyone had any experience with this product? Or, has anyone had experience with 2 piece handguards that are nominally for a retro AR10 build and have tried to use them for the AR15 platform?

Confusingly, Brownells offers a rifle length BRN10 handguard. They specifically note in their BRN Proto rifle, which is retro 5.56 AR15, that they use this rifle length furniture that is from their BRN10 retro rifle. Therefore, this one is "interchangeable" between 308 and AR15 (??). I naively assumed that all of these 2 piece handguards are interchangeable. Am I incorrect?

If you tell me "you're not depressing the delta ring enough it should fit" I did purchase the delta ring tool to help and it'll be here soon.
Thank you

Hand guards are gas system length dependent. Rifle length will not fit of mid length and so forth. Where on earth did you get a 20” barrel with a mid length gas system?

Hi Jupiter,

To be honest I went for a pretty strange build! It's actually a 7.62x39mm barrel 20" with indeed a mid length gas tube. I measured the gas port to barrel and it is the correct mid length gas system. This is why I chose that Brownells "Portuguese" contract-inspired mid length 2 piece handguard. The handguard is too short for an AR15 rifle and it's not a carbine length so I do believe it's mid length. But, I'm not sure if it is compatible with an AR15 mid length 2 piece setup, because that product is nominally for a retro AR 308 build.
I realize that most 20" AR15 barrels correspond to rifle length gas systems (and thus rifle length handguards), but I decided to do something a bit odd for fun!

Thank you

Well, I can't give you anything definitive, but everything I'm seeing says that mid-length is mid-length, whether it's 5.56 or .308.  So length shouldn't be an issue...  

Keep us posted if you make the handguards work, I was kind of considering a 5.56 build with these, so I'm interested in whether it works.