Had several malfunctions today. I’ll start by posting the gun specs
Factory DD MK18
H-Buffer (standard issue)
SF SOCOM556-RC
USGI Mags w/ SS +10% springs, Magpul followers
~1500rnds, last ~200 suppressed
Freedom Munitions .223 55g FMJ
Zero malfunctions, until today
Seoncod time out with my recently approved SOCOM. Loaded 25 rounds into a mag and started firing… then “click!” Looked at the bolt carrier and saw the bolt was slightly out of battery. I tried to clear the malfunction with the changing handle but the carrier would not move. After considerable foce (and im a strong guy) I finally cleared the malfunction and kept shooting. A few rounds later I had a failure to feed. Cleared that, then immediately heard “click!” Again, the bolt was out of battery and required some muscle to get the carrier to move. Followed again by another failure to feed (this time I decided to take a picture). 10 more rounds no problem. I put the gun on FA and ran the gun the last 7 rnds no problem.
I kept the 4 rounds and took a picture of 'em.
I’m going to forego giving my thoughts and just see what you guys think first.
My thoughts, captured more eloquently. H buffer is kinda the bare minimum reciprocating mass for a lot of unsuppressed setups with smaller gas ports to run really well - in this case it’s probably too much gas volume at too high a pressure. I’d probably look at trying an H3 right away to see how much that helps, that said an upper like that is probably a candidate for AGB and/or A5H4 type of buffer setup to make it run happily.
I figured the excessive carrier velocity caused the failure to feed. What concerns me is the bolt out of battery, and the considerable difficulty it took to move the carrier. Any idea what, exactly, is going on with this? Why would that happen, and what happening?
Thanks for everyone’s input. I actually have an A5H3 system I could use, but i’m trying to say with carbine system IF I CAN. I really like shooting NTCH. I’m going to order an H3 buffer tonight, and maybe consider one of Clint’s gas block inserts.
I’ve seen this before. As others have said, you’ll need to bump the buffer weight up as the DD barrel is over gassed. I run an adjustable gas block on mine for this reason.
Did the cartridges that got stuck have any dents in the case? I’ve seen where some get slightly chewed up due to the same malfunction, but end up feeding and then lead to an out of battery / stuck BCG.
It all varies of the type of ammo you’re using. If you’re using a 556 round and its not Lake City brass, I know a lot of people get tired of hearing about Lake City brass. But with that being said Lake City brass is the only 556 cartridge in 55 62 and 77 grain that has a consistent gas pressure when shot. you can buy Lake City brass from Lake City or American Eagle Lake City sells its excess brass to American Eagle who then marks it up. try some Lake City XM 855 with your SF SOCOM suppressor and let me know how it works out for you brother.
I have shot a similar setup as you, with the exception of the barrel. My 556-RC has run just fine on my LMT 10.5" and my Noveske 10.5". I have used an H, H2 and every weight A5 buffer with no problems. I currently use an A5H4. Your problem leads me to believe that you problem is excessive carrier speed due to oversized gas port, as others have said. If I were you I would definitely try an H3 buffer.
I have shot many as well. Could be as easy as a buffer fix as firefighter 37 had stated. I actually have a full rear kit with an H6 buffer I’m asking 110 for shipped. So if you know anyone or you yourself are in need let me know. Is brand new, only out of packaging to show the full kit. It is mil spec not commercial, is the exact kit made for colt that the army uses.
I’m with black22rifle on this. It’s a known fact the DD MK18 are over gassed due to an incredibly large gas port. I would get an insert and bring it down closer to NSWC spec and then reassess. Its not the ammo, its not the buffer system, and its not because of the can. Its because the DD gas port is something like .086" as opposed to the engineered/tested .071" of the NSWC gas port. Putting the can on exacerbates the issue, but its not the cause.
I think gas port size depends on when the barrel was made. I literally just installed a DD 10.3" barrel dated 07/2014 about a week ago and i measured the port size to be .0785" (#47) drill bit. I have installed a Govnah gas block but havr not shot it yet, I am waiting for a SBR tax stamp.
I don’t know about 086" but previous posts I have read have said that DD 10.3" barrels were .082"
Interesting because I believe someone at DD recently stated .082 and when I measured one with a pin gage set it was at .081. In any case it is overgassed.
I wonder if Clint has a port reducer that will work for this set up?
Some would say a higher weight buffer. Try an H2 or H3 weight buffer. On my old units new M4’s had more open gas ports and H6 buffers. But that was only to shoot a wide variety of pressure rating and grain. It also depends on the twist ratio if it has a direct gas port or is a piston driven system. In my unit the new M4’s were ambadextrious but the sheriff’s department had the short stroke piston M4’s. So there are a lot of variants you have to start somewhere and work your way up if he’s using a wide open system in a lower buffer weight trying to switch to a more consistent pressure ammo like lake city xm855 just to test to see if the buffer weight is alright would be a better start and cheaper. if it still hang fires where goods jammed up then I would switch the buffer wait out to around a H4 or H5 maybe even H6. At this point without actually having the rifle physically in my hands the best I can do is guesstimate if it were physically in my hands I could tell you the exact problem with it.
Chances are they would not do that for free though munch, DD has a rather high end barrel. They may replace it but question is will they do so for free. LoL just trying to give him some easy fixes to at least try. Chances are he knows someone that has a higher buffer weight than his own and he should be able to temporarily Frankenstein that part to see if it will fix the problem.
Why wouldn’t they? If spec is .070 and it is measuring .082+, and resulting in repeated malfunctions…I don’t see a reason why they shouldn’t fix it. OP shouldn’t have to spend more money on a $900 upper to get it to run properly.
That is true, I must have missed something in the conversation. Had no idea that was a problem. So ya as long as he has physically not altered the gas block and ports they should replace it free of charge. Well also pending on how long he has had said upper.
Clint’s port kit would be a very good option. I ended up using it on a very overgassed midlength DD barrel and made a huge difference. I got the gun to run with a .070" port. Wouldn’t cycle steel case ammo but ran everything else very well.
