The First Problem: Suppressed AR’s have a lot of felt recoil, increased amounts of carbon build up at faster rate, slower on target for follow up shots and burn lubrication off faster.
The First Solution: Build an AR with a much smaller gas port size so that it can utilize the back pressure generated by the suppressor to cycle the weapon.
The Second Problem: Dedicated suppressed AR’s will not cycle enough to pick up a second round, making the weapon useless if the suppressor becomes damaged or removed.
The Second Solution: Find a gas port size that is just big enough to cycle the weapon without the suppressor, but small enough to not exhibit the issues listed in problem one. Then find a way to slow dwell time down in order for the extractor to remain on the casing as long as possible so that the ejector can remove the spent casing and pick up a new round.
Exhibit A: 10.5” upper that is setup specifically for suppressed use.
When I built the 10.5 upper some twelve months ago, I did not realize that I got it just right from the beginning (will explain what I mean later). Below are the specs on the 10.5 upper:
1. Noveske 10.5 N4 Light (with small gas port)
2. LMT Enhanced Bolt Carrier.
3. LMT Standard Bolt
4. M4 Upper Receiver
5. VLTOR CASV (Mid)
6. H2 Buffer
7. Tactical Spring Co CS Buffer Spring
8. SureFire MB556
9. SureFire K Can
10. PRI Gas Buster Charging Handle
Above upper has been through two carbine schools with about six thousand rounds through it. No issues shooting suppressed or none suppressed.
With the success of the above 10.5, I wanted to try and create a better mouse trap by using the new KAC URX II, Fail Zero M4 Upper Receiver, Fail Zero BCG and a Noveske 11.5” N4 Light barrel with a small gas port.
We ordered the custom 11.5 N4 Light from the good folks at Noveske and acquired the URX II and Fail Zero items. After machining down the Noveske GB to fit inside of the URX II, we assembled the upper. The lower used was the same one that I used on the 10.5 upper mentioned above. It had an H2 buffer and Tactical Spring CS buffer spring in stalled in it.
For testing purposes, I loaded up a PMAG with one round and installed the SF K Suppressor on the barrel. Fired one round. BCG locked back. SUCCESS! Wanting to see what I could get away with, I installed an H3 buffer. Loaded one round and got the bolt to lock back again! Cool I thought. Now let’s test this upper WITHOUT the suppressor on it (as I need the weapon to still cycle without the can on, but does not need to lock back). There is a VERY fine line here between the weapon extracting the round, picking up a new round, but not locking back.
With the suppressor off, I loaded one round into the mag and fired the weapon. No brass came out. Hmmm. I pulled back the CH and ejected the spent casing. I removed H3 buffer and installed an H2 and tried it again. No joy. Removed the H2 and went to an H buffer. Still no luck. Removed the H and installed a Car Buffer. Again, no luck. Now I am really wondering what is going on. The spring that is installed in the lower is a CS spring so I thought that was what was doing me in. I grabbed a standard SS carbine buffer spring and stayed with the Car buffer. Same result. The casing had to be manually removed. Grrrrrrr!!!
At the end of my rope with this configuration, I told Adam (board member that works in my shop part time) what was happening and he suggested that we install the LMT Enhanced Carrier that we used in my 10.5 upper. I said; “that won’t make any difference as it is actually going to remove more pressure and make it worse.” Boy was I wrong! This is where the story gets interesting and is the lesson on extractor dwell time.
I removed the Fail Zero BCG and installed the LMT Enhanced Carrier and Standard Bolt. I kept the SS buffer spring and Car Buffer. The suppressor is still off the weapon. I loaded one round and fired the weapon! VICTORY! The casing ejected from the weapon! With this success, I loaded up two rounds in the mag to see if the BCG would come back far enough to pick up and load the second round. Success again! Now I wanted to see how heavy a buffer I could get away with. I tried H, H2 and H3. All worked with the H3 pushing the envelope and only getting an ejection distance about two feet.
So how can this be? How can the LMT Enhanced Carrier make this big of a difference??? Remember that the gun would NOT EJECT the casing at ALL with the standard BCG, but with the Enhanced Carrier I could run all the way up to an H3 buffer and it would eject and pick up the next round. What is happening with the Enhanced Carrier has slightly angled cam area which helps with bleeding off excess gas (slowing everything down). This allows for more positive extraction which in turn allows the ejector to push out the spent casing from the weapon. Simply fascinating stuff and if you would have told me this, I would said BS!
Commonly, we have view the LMT Enhanced Carrier as a useful tool for helping bleed off excess gas on a suppressed weapon. I also now view it as a good idea for guns that are short stroking as well.
The last little piece of info I have gotten from this build is that a suppressor generates at least DOUBLE the pressure created by the cartridge. So if you have an AR with an above average gas port (BM, Oly, DPMS, all piston operated AR’s), you are going to get at least double the felt recoil (if not more)!
1. Noveske 11.5 N4 Light (with small gas port).
2. KAC UXR II
3. LMT Enhanced Bolt Carrier
4. Fail Zero Bolt
5. Fail Zero M4 Upper Receiver
6. SureFire MB556
7. SureFire K Can
8. PRI GB CH
9. SS Car Buffer Spring
10. H3 Buffer