• KAC QDSS-NT4 Pinning Question

Posted: **Thu Jul 16, 2009 1:20 pm**

Does anyone know how far forward I would need to "shim" the NT4's QD flash hider to pin on a Colt 14.5" LE6921 barrel to make it a legal 16"?

Also what would you recommend I use to shim it forward? A couple peel washers? I don't know if you could do two crush washers... Maybe a combo of the two? Thoughts?

Thanks in advance!

ETA: NM, I just found my old thread where I basically asked this same question. Looks like I need to have my gunsmith make a custom shim to bring it forward enough. I do plan on putting the silencer on this pinned flash hider too.

I never plan on taking off the flash hider once it's on, so if I can make it 16"+ in length, I won't have to SBR my lower. I think it's kind of silly to SBR a 14.5" barrel that has a flash hider on it that can be made to 16"+ length. Especially if you never plan on taking the flash hider off.

Posted: **Thu Jul 16, 2009 3:19 pm**

I get 15 7/8" with our M4QD or the Triple Tap with no shims - I used a Colt M4 barrel and our M4 SR16E3 barrel for measurements, and putting a .22cal cleaning rod down the barrel to the bolt face.

Posted: **Thu Jul 16, 2009 5:50 pm**

Alright. I have a brand new QDSS-NT4 on a form 3 to my SOT right now, so I'm not sure how long the standard QD flash hider will be. Maybe if I just use a single crush washer, it will be 16"? Wishful thinking probably...

ETA: Will those two mentioned flash hiders work with the QDSS-NT4?

Posted: **Thu Jul 16, 2009 6:37 pm**

To do this properly you need to grind a single shim/precision washer to the right thickness and they pin/weld.

Posted: **Thu Jul 16, 2009 6:49 pm**

Alright thanks.

You know I'm going to have to wait on the form 4 anyway, so I guess I should just nut up and SBR the lower at the same time.

I'm probably going to shoot the NT4 mostly on my RR (M16A1 with 6933 11.5" upper), but I wanted to also be able to throw it on my LE6921 upper which I am planning on putting on an extra LE6920 lower. So like I said, might as well SBR the 6920 lower I guess... Just seems kind of silly, but I guess I could put my 6933 upper on it then as well if I really wanted to.

Sorry I'm thinking outloud now...

Thanks for the replies!

Posted: **Sat Jul 18, 2009 11:31 pm**

Yup, never understood the complete idiot who decided a 16.1" bbl was the shortest bbl length to be legal. What a hack of an idea.
What I really don't get, is the ".1" added onto the 16".
What the F is that all about anyway???