Knight's Armament SR-15 E3 Legacy 16" & SR-15 E3 CQB SBR 11.5" malfunction suppressed
Purpose of this post is to ask for malfunction diagnosis confirmation and advice on how to setup these guns to run.
My particular gun consists of a complete Knight's Armament Company SR-15 E3 CQB SBR upper (with carbine action spring and H2 buffer) on a lower I built out from a S&W stripped lower. The specs are 11.5" URX 2 upper with the E3 bolt and barrel. My gun serves as a training platform and HD rifle... My plan is to always run it suppressed, using my newly acquired SDN-6.
My buddies gun is a complete factory KAC SR-15 E3 legacy carbine (16") that is bone stock as far as operating / internals are concerned. My buddy wants to run his both suppressed and unsuppressed and have it be 100% reliable both ways.
Yesterday our plan was to zero 4 rifles (I also brought along a 20" rifle and he a 16" SR-25 ECC), shoot a few types of HD ammo into water jugs to recover and analyze the bullets, function test his Glock 21 with a factory threaded barrel and his MK23 with a Ti-Rant 45. We also brought out a chronograph to compare velocity deviations from the 11.5" / 16" / 20" rifles and some commercial .308 ammo vs. some milsurp 7.62 ammo. Unfortunately when zeroing the KAC SBR gun and his 16" KAC gun with SDN-6 suppressors mounted we had a plethora of stoppages from ejected / partially ejected brass getting caught on the bolt on its return stroke jamming up the action... I was shooting Black Hills 50gr TSX in the SBR and 75gr Hornady TAP T2 in the 20" rifle, he was strictly shooing TAP T2 in his SR-15.
At first we thought it was a fluke, but after the 6th or 7th same type of stoppage in about 30-35 rounds we decided to step back and verify the fundamentals. Mags were ruled out, ammo was ruled out, and so was proper weapon control / handling. After deciding to shadow the person shooting to watch the ejection pattern of the brass it was determined that both guns were suffering from too much gas. This resulted in the guns cycling so fast the brass was hitting the upper receiver in front of the brass deflector causing the brass to bounce off almost perfectly forward (12:00 - 1:00) and right next to the open ejection port... Removal of the suppressor confirmed the brass hit the deflector properly and slid off at the deflector a few feet from the gun (3:00 - 4:00). We were able to repeat this with both guns...
At this point we finished zeroing the other two rifles (the 45 degree offset sights messed with us on the SR25 and by the time we realized the way to zero them it was getting dark), tested the MK23 (ate everything we fed it and asked for more) and finally we collected a Black Hills 50 grain TSX all copper slug with a water jug test right before nightfall, then packed up and headed home.
Now today after thinking about my next course to remedy my SBR's gas problem I have installed an H&K 416 action spring and kept the KAC H2 buffer. As long as I can get it to run 100% reliably with the suppressor attached I will be happy. I decided to swap in this spring as I have a few new ones laying around in my parts bin and I don't have to wait to order one from SpringCo. Referencing rsilver's action spring analysis, the H&K Spring is 34% stronger than a Colt Carbine spring versus a SpringCo red which is 32% stronger with regards to mechanical force at 6.902" length. I will visit my local range and run a few hundred rounds of XM193 through it very soon to verify ejection and function.
My buddy wants his to run 100% both ways, no suppressor and with it attached. I informed him he may need a switch block or adjustable gas block to achieve this but I'm in uncharted waters here as this is my first time shooting /troubleshooting with suppressors. So, gentleman, please add some value to this thread if you have already blazed this trail... Please no speculators and internet spinsters. I will update my findings with my own SBR setup after I hit the range (may have time to today). I'll let my buddy (who is a member here) chime in with his findings when he can.
Pics of the stoppages... (my gun only but they look identical to what was taking place on his 16" KAC)
http://img841.imageshack.us/img841/2310/0005kc.jpg
http://img442.imageshack.us/img442/5812/0006xp.jpg
http://img36.imageshack.us/img36/7474/0007px.jpg
http://img837.imageshack.us/img837/9354/0008jz.jpg
http://img6.imageshack.us/img6/8724/0009sa.jpg
http://img834.imageshack.us/img834/8540/0010rry.jpg
http://img338.imageshack.us/img338/139/0011xp.jpg
http://img151.imageshack.us/img151/3896/0012yo.jpg
And a few of our setup that day so we don't end on a negative note... :)
http://img39.imageshack.us/img39/8356/0004nc.jpg
http://img23.imageshack.us/img23/203/0003hy.jpg
http://img171.imageshack.us/img171/2411/0002dq.jpg
http://img32.imageshack.us/img32/7024/0001lf.jpg