KAC NT-4 QDSS Review

General Firearms NFA
1

I purchased a KAC NT-4 QDSS suppressor back in January of this year and I finally received it sometime in September. The first time I went to the range I fired about 300 rounds of 5.56 mm 75gr TAP. On the second outing I fired about 200 rounds of BH 55gr red box. Here go some of the things that I noticed when firing. I know that most people probably already know this, but in case you didn’t here goes:

  1. The gas blow back that comes out of the ejection port sinks like shit. Thank God for the PRI Gas-buster.

  2. Lube does last as long when firing suppressed.

  3. The can gets HOT and the rifle will get hotter than normal.

  4. 5.56 suppressed is still loud.

Know to the equipment:

LMT 10.5" upper
LMT FA BCG
KAC FH
KAC NT-4 QDSS
LMT BUIS
KAC RAS w/ SAS lower
Aimpoint M3 on Larue mount
SF M951C

LMT lower
LMT 2-stage trigger
LMT SOPMOD
H Buffer
Larry Vickers 2pt sling

Slip 2000 lube

Ammo:
Hornady TAP 75gr 5.56mm
BH 55gr red box

KAC NT-4 QDSS

What came in the box: Can, shim kit, KAC FH, small bottle of Rocksett and owners guide.


Pic of baffles

On my first outing I fired 300 rounds of 5.56 TAP at 50 yards and 100 yards. The accuracy of the rifle didn’t change with the suppressor on at 50 yards but it did open up and shot lower at 100 yards. After shooting the 300 rounds and letting the suppressor cool down I was able to remove with out using any tools. One thing I did notice was that the rifle started short stroking right around 200 rounds. I added more lube to the BCG port holes but it didn’t get rid of the problem. The other thing that I noticed was that it sent a lot of carbon fouling into the magwell which tarnished the ammo (see pics below). When I got home and started to clean the rifle I realized that running a suppressor on a SBR gets the BCG, bore, and everything else extremely DIRTY!!

On the second trip to the range I fired a string of 200 rounds of Black Hills 55gr Red Box. On the second trip I made sure that the BCG and the buffer tube spring where generously lubed. I didn’t try to readjust the zero for the 55gr, so I don’t have an accuracy report, but it shot well enough for 50 yards. Removing the suppressor the second time was a bitch. I had to use my Leatherman and Slip Carbon Killer to get it off. Clean up was much easier this time around, but I still had some short stroking issue.


Pics of FH after second outing


The threads that you see in the pic are supposed to help breaking up the carbon fouling when removing the suppressor



Pics of carbon fouling on mags


Top row is BH red box that was left in the last mag and bottom row was all of the ejected rounds from “tap rack bang” when it was short stroking


Same ammo, primer views


Rifle and rig

PROS:
-Easy to make follow up shots
-Quiet enough to use with out hearing protection
-Reduced recoil (not that it was a problem before)
-QD mount is easy to use with bare hands or when using thin gloves (flight gloves)
-GWOT tested and approved

CONS
-weight (lighter can available from other manufactures)
-QD lever can be hard to move after a long string of fire
-rifle gets very dirty and lube won’t last as long
-can gets HOT!!! (this is with all cans)

Overall this is a great can. If I could afford more I would buy more. I think the fact that this is the main can for SOCOM and the SOPMOD program speaks for itself.

One thing I would like to ask.

If any one knows of a lube that is aqueous based and that will not burn up from the heat of firing suppressed, please IM, post, or email me the name brand.

Marco

2

Marco,

Did your rifle short stroke without the suppressor? If not, it shouldn’t be short stroking with the suppressor because the can creates more back pressure. Maybe it’s overgassed with the can on. Try putting a H2 buffer in it and see if that helps.

I use a H buffer in my 10.5" w/ NT-4 and I have not had one problem. I’ve put around 900 rounds through the combo in two days without cleaning. I just relubed it generously with CLP after day one (500 rnds).

3

Thanks for the write-up/review.

Nice pics too.

4

It never short stroked before; the only thing I ever had was FTF, but that was due to the magazines. The carbine had about 1000 rounds thru it before I got the suppressor. I currently do have a H buffer, but I’ll give the H2 a try.

5

Cool pics and info.

I too just got my first 5.56 can. I was amazed at how dirty the ejected brass was compared to the same rounds fired unsupressed.

I’m running my can on a 14.5. When I get my next mount, I’m going to try it on a 20 inch rifle for comparison.

The gas in the face was negligible to me. I completely forgot about that aspect until I started smelling it a little.

6

If the thing started to short stroke at the very end of 200rds, I would bet that all your lube was gone, and being quickly replaced with carbon and gunk.

Might try to coat it more than normal, but expect to get some carbon and slip2000 back on your glasses and face. :frowning:

Or plan to run 300rds and lube after each 150rds and see how it goes.

7

My LMT 10.5 behaves the same way after a few hundred rounds with the suppressor attached. I have an SWR Specwar2 and am running the upper with a Colt M4 bolt group on a Colt M16 lower with H2 buffer and standard carbine spring.

It will run 100% with the suppressor attached, no matter how many rounds or how dirty. If I remove the suppressor, the upper begins to choke with FTFs and with the bolt getting stuck with a round partially pushed out of the feedlips. I think this is due to the extreme amount of fouling in the upper causing alot of bolt drag. The fouling robs all of the inertia from the bolt group, causing inadequate energy to strip rounds from the mag. The quick addition of some lubrication to the bolt and it no longer chokes.

I think the increased bolt velocity with the suppressor attached allows the bolt group to overcome the dirt/grime in the upper.

Re-lube your bolt group when you remove the suppressor and see if it helps.

8

What are those two small latch/lever things at the mounting end? It looks like they rotate? Is that a locking device or something?

9

It’s one big latch that rotates and keeps the large retaining pin from going up.

10

Got it, thanks.