fiftyohm Posted February 7, 2021 Report Share Posted February 7, 2021 Good afternoon. I have just completed a 308 carbine build. It's an Aero M5 receiver set and an Aero BCG. The barrel is a 16" Wilson Combat Match, with a 13.25" "intermediate" gas system. The rifle cycles properly, but the bolt does not lock back on an empty mag. The buffer is DMPS spec 3.84 oz., and the spring is standard 31T. Using NATO M80 147gr FMJ ball. Ejection is at about 4:00. I also have an adjustable gas block that is wide open. When closed at all, the rifle does not feed or even eject reliably. It struck me that with this barrel and gas system length, the dwell time is pretty damn short. I contacted Wilson Combat, and they said the issue was likely restriction in my adjustable port, and I should change it to a fixed unit. Something about that just doesn't seem right to me. Comments would be much appreciated! Quote Link to comment Share on other sites More sharing options...
DM15 Posted February 7, 2021 Report Share Posted February 7, 2021 I just joined the forum myself, so welcome. My first thoughts are does the bolt lock back by hand using the same empty magazine? If so about how much space is between the bolt and the bolt stop when held back with the charging handle? Quote Link to comment Share on other sites More sharing options...
fiftyohm Posted February 7, 2021 Author Report Share Posted February 7, 2021 So - great question. Yes it can be locked back by the charging handle, and the travel of the bolt is at least an inch past the point where the bolt catch clears the BCG. Thanks for your reply! Quote Link to comment Share on other sites More sharing options...
mtrmn Posted February 7, 2021 Report Share Posted February 7, 2021 Read through these threads and if you pay attention to details and do what they say you should have your gun fixed in short order. https://forum.308ar.com/topic/16857-308s-seemwellproblematical/ https://forum.308ar.com/topic/730-buffers-and-springs/ https://forum.308ar.com/topic/16799-gas-tubes-barrel-gas-ports-and-buffer-weight/ In my case, it was gas tube length that fixed my problem. Also make sure your gas port is big enough. Quote Link to comment Share on other sites More sharing options...
fiftyohm Posted February 7, 2021 Author Report Share Posted February 7, 2021 Thanks! BTW the gas tube is also the correct unit from Wilson Combat. It is sort of a proprietary length and only available from them. I'll read the other stuff again. Quote Link to comment Share on other sites More sharing options...
mtrmn Posted February 7, 2021 Report Share Posted February 7, 2021 (edited) The travel past the bolt catch doesn't sound right. You are aware that the bolt catch catches the front surface of the bolt locking lugs and not the bolt carrier right? The face of my bolt doesn't travel very far at all past the bolt catch, more like a quarter inch at most. Also Wilson Combat may have been hinting that the gas block/gas port alignment may not be correct and the block may be blocking part of the port. I am not an expert by any means, but I did learn a lot the hard way during my cheapass PSA build. Took several months and probably 2-300 rds of ammo just to get it running right. ETA: Then I found this place and those threads got me fixed quick. Edited February 7, 2021 by mtrmn add info Quote Link to comment Share on other sites More sharing options...
fiftyohm Posted February 7, 2021 Author Report Share Posted February 7, 2021 What I meant to say is that the BCG travel is substantially greater than sufficient for the mag follower to lift the bolt catch to lock the BCG open. Sorry if that wasn't clear. They, (WC), may also be doing a bit of ass covering. The barrel was dimpled, and it would take a much bigger idiot than me, (and that's saying something), to goof the installation of the gas block. I have removed it, and the carbon deposits are exactly concentric with the gas port on the barrel. Do you think that the combination of a 16" barrel with a 13.25" gas system might result in too short a dwell time, given the 3.8 oz buffer, and all the rest? WC is, in my experience, a pretty top-notch outfit. And the other components are from AP - perhaps not the most expensive, but certainly well regarded. It just seems that the physics of this 16" barrel with a 13.25" gas system is a bit marginal... And to all that have replied - thank y'all very much! Your hospitality here on this forum is really great! Quote Link to comment Share on other sites More sharing options...
shooterrex Posted February 7, 2021 Report Share Posted February 7, 2021 First off your buffer is to light. It should be close to 5.4 oz. If your bolt is going back that far past the bolt catch it is also to short. Where the buffer tube screws in to the receiver check to see if the bcg is hitting the receiver. A too short buffer will let it hit when it isn't supposed to. Your bolt is probably traveling to fast to catch the bolt catch. My 16" wilson 6.5 creedmoor barrel runs fine w/a fixed gas block. It has the same gas tube length as yours. Quote Link to comment Share on other sites More sharing options...
fiftyohm Posted February 7, 2021 Author Report Share Posted February 7, 2021 OK. So the locking lugs of the bolt have enough rearward travel to clear the bolt catch by about 1/4" before it reaches the limit. Seems that were the buffer any longer, it wouldn't clear at all, right? I understand that excess BCG speed can cause this problem, but it also seems like the gun is just barely running as it is. Wouldn't a heavier buffer, while certainly slowing down the BCG, result in even less travel? Examination of the buffer shows no evidence of contact with the end of the receiver extension. (Which is 7"). My next build is going to be a 6.5 CM, so your input is fantastic. Quote Link to comment Share on other sites More sharing options...
Armed Eye Doc Posted February 7, 2021 Report Share Posted February 7, 2021 Can you measure the size of your gas port? @98Z5V can calculate how large it should be and whether or not it is truly undergassed. As @shooterrex said, your buffer is too light for a normally gassed 308AR. Quote Link to comment Share on other sites More sharing options...
fiftyohm Posted February 7, 2021 Author Report Share Posted February 7, 2021 Yes I can. Let me get back to you tomorrow when I take the hand guard off and slide the gas block off the port. Is substantially smaller than the hole in the gas block. Love the Texas flag, BTW! Quote Link to comment Share on other sites More sharing options...
Armed Eye Doc Posted February 7, 2021 Report Share Posted February 7, 2021 24 minutes ago, fiftyohm said: Yes I can. Let me get back to you tomorrow when I take the hand guard off and slide the gas block off the port. Is substantially smaller than the hole in the gas block. Love the Texas flag, BTW! The best way to measure is with numbered drill bits. Quote Link to comment Share on other sites More sharing options...
shooterrex Posted February 7, 2021 Report Share Posted February 7, 2021 1/4" between bolt face and bolt catch is good to go. Somewhere I got the impression that it was more like an inch. I must have misread something. You probably need to open the gas port a bit and get a heavier buffer. Slash @ heavy buffers can fix you right up. You won't know about the gas port until you measure it. Quote Link to comment Share on other sites More sharing options...
dpete Posted February 7, 2021 Report Share Posted February 7, 2021 Or this buffer right here. https://www.kakindustry.com/lr-308-parts/308-lower-parts/lr308-carbine-buffer-heavy Quote Link to comment Share on other sites More sharing options...
fiftyohm Posted February 7, 2021 Author Report Share Posted February 7, 2021 Right. I should be able to get within a few thousandths. Thanks, Doc. BTW - were you ever associated with the U of H? I did some consulting for the Optho Dept. there about 10 years ago. Designed an automated phoropter for them. Quote Link to comment Share on other sites More sharing options...
fiftyohm Posted February 7, 2021 Author Report Share Posted February 7, 2021 Morning, guys. The gas port size is 0.070". Quote Link to comment Share on other sites More sharing options...
DNP Posted February 7, 2021 Report Share Posted February 7, 2021 (edited) That seems small and could probably open up a touch. And you have plenty of dwell time. I have a rifle length gas system on a 16” criterion barrel. @98Z5V is the gas port whisperer. He can apply his Ninja math skills and recommend a port diameter. Edited February 7, 2021 by DNP Quote Link to comment Share on other sites More sharing options...
DNP Posted February 7, 2021 Report Share Posted February 7, 2021 (edited) And bump up the gas before you replace the buffer. Though, they have found over and over on here that a properly sized port and a buffer in the 5.4oz range is reliable. With your adjustable block, you may be able to tune the port to work after you open it up a bit. I’ll put on my fire suit...my recommendation on the buffer may bring me some heat. Logical thinking doesn’t always work with these rifles, but the math seems to. Which is why they recommend what they do. Edited February 7, 2021 by DNP Quote Link to comment Share on other sites More sharing options...
fiftyohm Posted February 7, 2021 Author Report Share Posted February 7, 2021 Much obliged. Just messaged him. BTW - I recommend Nomex, DNP. Quote Link to comment Share on other sites More sharing options...
billymagg Posted February 7, 2021 Report Share Posted February 7, 2021 4 minutes ago, fiftyohm said: Morning, guys. The gas port size is 0.070". Thanks, your gas port needs to be opened up, especially if you want to run the heavy buffer. My 18", rifle gas, Wilson Combat shipped with a 3.8 oz, 2.5" buffer and the 40 coil flat wire spring with adjustable gas block.. my gas port was around .082, it ran fine, ejecting, locking back and picking up rounds off the top of the magazine, but is very lethargic on ejection... especially with the M80 ball. On the other hand if you run some 168 gr 308, it may function and lock back just fine?? Quote Link to comment Share on other sites More sharing options...
DNP Posted February 7, 2021 Report Share Posted February 7, 2021 Quote Link to comment Share on other sites More sharing options...
fiftyohm Posted February 7, 2021 Author Report Share Posted February 7, 2021 Billymag -Much obliged. I suspect you are exactly right. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted February 8, 2021 Report Share Posted February 8, 2021 (edited) Gas port is too small. I'll get into details later, unpacking the truck from a shoot this weekend. For that barrel length and gas system, you'd need to be in the 0.080~0.083" range for a gas port diameter. Wilson's Intermediate 13.250" gas tube puts that gas sstem between midlength and rifle length gas systems. Dwell time is weird on it, not what we're used to seeing. My $0.02. There shouldn't be any .308AR out there that's not running a 5.4oz buffer in it, with the correct spring. Ever. Unless you're a Race-Gunnner, making money from sponsors from all your Top 5 Finishes, and all those first place Race Gun trophies... Light buffers in .308ARs belong in tuned Race Guns, that only shoot one "pet" competition load, to earn you money on that Race Gun Circuit.. But, that's just my opinion, FWIW... Edited February 8, 2021 by 98Z5V Quote Link to comment Share on other sites More sharing options...
fiftyohm Posted February 8, 2021 Author Report Share Posted February 8, 2021 Time to buy a reamer! Thanks so much, '98! Quote Link to comment Share on other sites More sharing options...
98Z5V Posted February 8, 2021 Report Share Posted February 8, 2021 7 minutes ago, fiftyohm said: Time to buy a reamer! Thanks so much, '98! I'll answer your other post in detail, later. I'm still unpacking the truck... Quote Link to comment Share on other sites More sharing options...
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