Is there a formula you use for determining what handguard length you use? The AR I am putting together will have an 18" barrel. Thinking of going with a 16-17" free float handguard. I like the look and will not be using any irons.

A 15 inch or greater free float handguard should completely cover your gas block, if your barrel has rifle length gas.

I like a handguard that ends just before the threads begin.

Thanks for the information! The barrel I'm looking at is mid-length gas, so it should be covered easily enough.

The "formula" regarding the location of the threads was very helpful. I will contact the barrel manufacturer about that measurement.

Ya I have a couple of 13” hand guards on 16” barrels but my last one, I used a 15” and I just really like the extended rail.

I get a longer sight radius and more room to add my light where it needs to be instead of where it has to be. And I do like the way it looks.

I can see how it would help to have room for the light/accessories AND still be able to place your support hand where it needs to be.
Thanks.

Yes, but the part about sight radius is a moot point. Sights mounted on a handguard are not for precision work, so the sight radius doesn't matter. For an 18" barrel like the op has (mid length gas system), a 13"-15" handguard would be ideal.

When you get old and can't see the front sight until it's way out there, you'll understand....

When using a barricade for support a longer hand guard also let’s you spread out your points of contact without getting the barrel on the barricade.

I’ve used a 15” rail on an 18” barrel and didn’t feel handicapped. I’m not sure I could take advantage of anything longer.

15" handguard on an 18" barrel looks fitting too.

Ok buddy. You made me laugh. I guess I will wait and see.. Thanks