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Posted: 8/11/2014 1:04:52 PM EDT
So I took the new MK18 clone pistol build out for testing and it would not lock back on the last shot. Did the one round in the mag test to 4 different P-mags with the same outcome. Have a standard buffer and spring. Should I go to the Sprinco Blue buffer spring and H2 buffer ?
The 10.5" MK18 clone upper 
Product Description A2 Flash Hider 1/2-28 Threaded Muzzle M16 BCG HP/MPI Tested with Viton O-ring 5.56 NATO Chamber 4150 CrMoV (Chrome Moly Vanadium per MIL-B-11595E) w/ F-Mark Front Sight 1/7 Twist w/ M4 Feed Ramps Carbine Length Gas System QPQ Corrosion Resistant Finish Standard 2-Piece Quadrail Dry Film Lubed Upper w/ T-Markings Forward Assist & Ejection Port Assembly Standard Charging Handle Made from 7075 T6 forging Sling Swivel on Front Sight Base |
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Posted: 8/11/2014 1:16:04 PM EDT
[#1]
What ammo? Cleaned chamber thoroughly upon receipt? BCG taken down, cleaned, and well lubed? Any ejection issues? Ejection direction?
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Posted: 8/11/2014 3:13:44 PM EDT
[#2]
Good ammo, cleaned and lubed on the generous side. If you have a different BCG, try it. You are losing gas somewhere or the gas port is too small. Oh and try a good metal mag, as some guns have had issues with certain generation/model type Pmags generally something to do with a nub on the back topside of the Pmag.
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Posted: 8/12/2014 6:14:25 AM EDT
[#3]
I'm assuming the bolt catch works fine when had cycling?
Are you using good NATO ammo? |
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Posted: 8/12/2014 7:55:22 AM EDT
[#4]
Cleaned and lubed her up. Was shooting some Rem 223 and WCC 74, LC 70 stamped 5.56 for the test. Bolt stop is a little wobbly, have another so will swap it out in the next test. Will be getting a H2 buffer and Sprinco blue spring coming in to see if that helps.
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Posted: 8/12/2014 3:04:28 PM EDT
[#5]
Who makes the upper? What is the port size? The port may need to be opened up a bit.
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Posted: 8/12/2014 4:45:47 PM EDT
[#6]
Quote HistoryQuoted:
Who makes the upper? What is the port size? The port may need to be opened up a bit. Got it from ACI a forum dealer, here is their ad http://www.ar15.com/forums/t_7_22/1319519_MK18_Clones_on_SALE__10_5_Upper_Complete_w_BCG_and_Rail__450.html The barrel has a .750? Gas Block Journal. Have to get in contact with ACI for the gas port size. |
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Posted: 8/12/2014 4:57:14 PM EDT
[#7]
Quote HistoryQuoted:
Cleaned and lubed her up. Was shooting some Rem 223 and WCC 74, LC 70 stamped 5.56 for the test. Bolt stop is a little wobbly, have another so will swap it out in the next test. Will be getting a H2 buffer and Sprinco blue spring coming in to see if that helps. I'm amazed every time a likely undergassing problem arises, folks want to try a heavier buffer or spring. That can only compound the problem. - OS |
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Posted: 8/12/2014 4:59:55 PM EDT
[#8]
You aren't running a BAD Lever are you? If so try taking it off and see if that helps...sounds crazy i know but i've had this happen to me before I just had mine on there a little tight.
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Posted: 8/12/2014 6:17:54 PM EDT
[#9]
Quote HistoryQuoted:
Got it from ACI a forum dealer, here is their ad http://www.ar15.com/forums/t_7_22/1319519_MK18_Clones_on_SALE__10_5_Upper_Complete_w_BCG_and_Rail__450.html The barrel has a .750? Gas Block Journal. Have to get in contact with ACI for the gas port size. Quote HistoryQuoted:
Quoted:
Who makes the upper? What is the port size? The port may need to be opened up a bit. Got it from ACI a forum dealer, here is their ad http://www.ar15.com/forums/t_7_22/1319519_MK18_Clones_on_SALE__10_5_Upper_Complete_w_BCG_and_Rail__450.html The barrel has a .750? Gas Block Journal. Have to get in contact with ACI for the gas port size. My DD 10.3" barrel has a gas port of approx .083 to .086. That is what was reported on a few posts from old threads. My 10.3" runs pretty much anything I put through it and I believe Tula was the only ammo that did not lock back on the last round. Other option would be that you are using some older 20rd Pmags....those has a history of not locking back and I have had that happen on another rifle (18" with rifle gas). |
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Posted: 8/12/2014 9:20:03 PM EDT
[#10]
Talked to the guys over at ACI and going to run it on another lower this weekend. 30 round p-mag loaded 5 rounds and ejected all rounds, just no lock back. The bolt catch seems a bit wobbly
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Posted: 8/13/2014 10:25:55 AM EDT
[#11]
Gas port hole is .0785
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Posted: 8/13/2014 11:25:54 AM EDT
[#12]
That's what my 10.5 was, I upped it to .081" and it's flawless now.
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Posted: 8/13/2014 2:32:52 PM EDT
[#13]
Aeroprecision 10.5" barrel i have runs a .077 gasport / carbine buffer and spring, and it runs everything I have with no problem...silverbear, Speer, Hornady, m193, Fiochi , Federal, Winchester, Remington, MK262 with no problems
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Posted: 8/13/2014 3:06:18 PM EDT
[#14]
The heavier H2 buffer is going to exacerbate a short stroking problem.
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Posted: 8/13/2014 3:22:02 PM EDT
[#15]
Quote HistoryQuoted:
The heavier H2 buffer is going to exacerbate a short stroking problem. Oh so true, and the OP hasn't mentioned what buffer he is using. So OP what buffer are you currently running? |
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Posted: 8/13/2014 6:14:32 PM EDT
[#16]
Quote HistoryQuoted:
Oh so true, and the OP hasn't mentioned what buffer he is using. So OP what buffer are you currently running? Quote HistoryQuoted:
Quoted:
The heavier H2 buffer is going to exacerbate a short stroking problem. Oh so true, and the OP hasn't mentioned what buffer he is using. So OP what buffer are you currently running? Stock buffer and spring with KAK super sig buffer tube. |
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Posted: 8/31/2014 7:19:25 PM EDT
[#17]
Tested the upper today and the bolt locked back on the last shot in 2 pmags, 2 metal mags. So I think it was the Tactical Link that was on the other lower that caused the issue. Thank You Jason at ACI for your GREAT CUSTOMER SERVICE and QUALITY UPPER !!!!! By Far My Favorite !!!
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