AR Sponsor
Posted: 4/13/2025 4:25:24 PM EDT
|
I have an LR-308 that I built a while back. I had DPMS receivers, so I tried to stick with DPMS parts as much as I could. Off the top of my head, all parts are DPMS except for the Faxon barrel (16" midlength), JP adjustable gas block, Rise trigger, Aero rail, and AAC 51T flash hider. Right after building it, I set the gas so it just barely locked back on an empty mag unsuppressed using Tula 145 grain .308, which I figured was lower powered than most. The gun runs fine with Tula, but it has trouble extracting any brass case ammo I've used (everything from Hirt to FGMM). it basically leaves the empty case in the chamber. I've tried 2 different enhanced extractor springs without any luck. So basically, garbage Tula ammo works suppressed and unsuppressed. No other ammo functions reliably. I do not have any steel case other than Tula to try out, so everything else was brass case commercial or surplus. I recently decided to add an o-ring to the doubled-up extra power extractor springs and the rifle is now extracting about 50-60% of the time with brass ammo. It was rarely extracting brass ammo before i added the o-ring. Today I tried it suppressed (762SDN6). It runs with Tula, but PPU 175s were still causing problems. When it works, it ejects cases at about 2:00, but otherwise does not seem over gassed. Cases only eject 2-6 feet. When a case does fail to eject, I can drop the bolt back down and it will grab the case and pull it out without any unusual effort. In other words, the cases do not appear to be sticking in the chamber. I measured some different unfired cases and all the ammo appears in spec. The Tula has the same case head dimensions as the various brass stuff. The DPMS extractor does not look damaged, but at this point I am thinking of trying a different one (or even a whole new BCG), since all signs appear to suggest that the extractor (or BCG in general) is the issue. Does this sound right to you guys? If so, what aftermarket extractor (or even entire BCG) would you recommend that I try to see if I can get this rifle functioning with brass case ammo? |
|
Quoted: You could try a JP enhanced extractor for .308 (fits DPMS bolts.) Or the whole enhanced high-pressure JP .308 bolt, which can be used with 6.5cm barrels as well if you ever wanted to change calibers in the future. Thanks! Those parts are on the pricey side. I think I'll try just the extractor for now and see if that helps any. ETA: I went ahead and ordered the JP extractor, but I'm open to hearing any other suggestions you guys might have. I'm getting pretty frustrated with this gun and really want to get it functioning 100%. |
|
Quoted: ... Faxon barrel (16" midlength), JP adjustable gas block ... ... trouble extracting any brass case ammo I've used (from Hirt to FGMM) ... it basically leaves the empty case in the chamber. I've tried 2 different enhanced extractor springs without any luck. So basically, garbage Tula ammo works suppressed and unsuppressed. No other ammo functions reliably. I do not have any steel case other than Tula to try out, so everything else was brass case commercial or surplus. ... what aftermarket extractor (or even entire BCG) would you recommend that I try to see if I can get this rifle functioning with brass case ammo? You optimized a mid-length gas system rifle to fire garbage ammo. Stick to garbage ammo. If you want to optimize function, change to a rifle-length gas system. |
|
Quoted: Not with a 308, but with a 7.62x39 I had very similar issues. I had to put in a heavier buffer to slow down the cycling speed for it to not skip over the full power ammo when extracting as it was coming back so fast. Just my $.02 Quoted: Not with a 308, but with a 7.62x39 I had very similar issues. I had to put in a heavier buffer to slow down the cycling speed for it to not skip over the full power ammo when extracting as it was coming back so fast. Just my $.02 Interesting. I would think that an adjustable gas block would solve this, but a heavier buffer is easy enough to try out. Thanks! Quoted: Quoted: ... Faxon barrel (16" midlength), JP adjustable gas block ... ... trouble extracting any brass case ammo I've used (from Hirt to FGMM) ... it basically leaves the empty case in the chamber. I've tried 2 different enhanced extractor springs without any luck. So basically, garbage Tula ammo works suppressed and unsuppressed. No other ammo functions reliably. I do not have any steel case other than Tula to try out, so everything else was brass case commercial or surplus. ... what aftermarket extractor (or even entire BCG) would you recommend that I try to see if I can get this rifle functioning with brass case ammo? You optimized a mid-length gas system rifle to fire garbage ammo. Stick to garbage ammo. If you want to optimize function, change to a rifle-length gas system. I'm not sure I'm following. Wouldn't I need a barrel longer than 16 inches to use a rifle-length gas system? As far as the garbage ammo thing, all of my AR15s work fine with both steel case garbage ammo, as well as full power NATO stuff. Are .308 ARs more picky? (Sorry if I'm ignorant. This is my first and only .308 AR.) |
|
Quoted: Interesting. I would think that an adjustable gas block would solve this, but a heavier buffer is easy enough to try out. Thanks! I'm not sure I'm following. Wouldn't I need a barrel longer than 16 inches to use a rifle-length gas system? As far as the garbage ammo thing, all of my AR15s work fine with both steel case garbage ammo, as well as full power NATO stuff. Are .308 ARs more picky? (Sorry if I'm ignorant. This is my first and only .308 AR.) I have seven 16" MLG .308 builds and they all function fine with various ammo. I'm sure the new extractor will solve your problem. While you might not "see" the problem, I believe the actual extractor you currently have is at fault. It's not the MLG system per se. |
|
Quoted: I have seven 16" MLG .308 builds and they all function fine with various ammo. I'm sure the new extractor will solve your problem. While you might not "see" the problem, I believe the actual extractor you currently have is at fault. It's not the MLG system per se. Quoted: Quoted: Interesting. I would think that an adjustable gas block would solve this, but a heavier buffer is easy enough to try out. Thanks! I'm not sure I'm following. Wouldn't I need a barrel longer than 16 inches to use a rifle-length gas system? As far as the garbage ammo thing, all of my AR15s work fine with both steel case garbage ammo, as well as full power NATO stuff. Are .308 ARs more picky? (Sorry if I'm ignorant. This is my first and only .308 AR.) I have seven 16" MLG .308 builds and they all function fine with various ammo. I'm sure the new extractor will solve your problem. While you might not "see" the problem, I believe the actual extractor you currently have is at fault. It's not the MLG system per se.  I hope you're right about the new extractor. I'll make sure to update this thread after I get it in and test fire the gun. |
|
Quoted: Interesting. I would think that an adjustable gas block would solve this, but a heavier buffer is easy enough to try out. Thanks! I'm not sure I'm following. Wouldn't I need a barrel longer than 16 inches to use a rifle-length gas system? As far as the garbage ammo thing, all of my AR15s work fine with both steel case garbage ammo, as well as full power NATO stuff. Are .308 ARs more picky? (Sorry if I'm ignorant. This is my first and only .308 AR.) You are definitely NOT ignorant. You've tuned your carbine to optimally work with steel case cartridges for those time - pressure curves (chamber and port pressures, unsuppressed and suppressed). A 308 Win / 7.62mm NATO cartridge has twice the powder and bullet weight than the average .223 Remington / 5.56mm NATO cartridge. Delta did much of the initial trial-and-error work in military working rifles, Knight's finished it and put it into production:  16-inch barrel with rifle-length gas option above. |
|
Quoted: Interesting. I would think that an adjustable gas block would solve this, but a heavier buffer is easy enough to try out. Thanks! I'm not sure I'm following. Wouldn't I need a barrel longer than 16 inches to use a rifle-length gas system? As far as the garbage ammo thing, all of my AR15s work fine with both steel case garbage ammo, as well as full power NATO stuff. Are .308 ARs more picky? (Sorry if I'm ignorant. This is my first and only .308 AR.) I realize you mentioned that you were using mostly DPMS parts, what style buffer & tube are you using? |
|
FWIW.... steel cased ammo does not "release" from the chamber walls as quickly / readily as brass cased ammo. So you did unwittingly tune it to steel cased ammo. And yes... LFAR's are more fussy in general. Can you post some pics of the fired brass ? Looking for scuff marks on the cases. |
|
Quoted: As far as the garbage ammo thing, all of my AR15s work fine with both steel case garbage ammo, as well as full power NATO stuff. Are .308 ARs more picky? Not necessarily. You just got lucky with your 5.56 ARs. I've shot .223/5.56- Herter's is one of them that comes to mind- that wouldn't run in any 5.56 rifle I or my associates owned- ARs, XCRs, Galils, etc... 308/7.62N rifles have never been known to be kind to garbage ammo- ARs, FALs, M14s. Hell, I've had issues with G3s not running on bottom-of-the-barrel ammo, and those are known for being able to eat almost anything. I learned long ago that paying for quality ammo means paying for a far lower likelihood of issues, which translates to a more enjoyable and productive use of limited range time. |
|
Quoted: I realize you mentioned that you were using mostly DPMS parts, what style buffer & tube are you using? Quoted: Quoted: Interesting. I would think that an adjustable gas block would solve this, but a heavier buffer is easy enough to try out. Thanks! I'm not sure I'm following. Wouldn't I need a barrel longer than 16 inches to use a rifle-length gas system? As far as the garbage ammo thing, all of my AR15s work fine with both steel case garbage ammo, as well as full power NATO stuff. Are .308 ARs more picky? (Sorry if I'm ignorant. This is my first and only .308 AR.) I realize you mentioned that you were using mostly DPMS parts, what style buffer & tube are you using? DPMS. I assume that the buffer weight is whatever they shipped their finished guns with. CDNN bought out all of the LR308 stuff after DPMS went under. That made it easy for me to avoid any compatability issues. |
|
Quoted: FWIW.... steel cased ammo does not "release" from the chamber walls as quickly / readily as brass cased ammo. So you did unwittingly tune it to steel cased ammo. And yes... LFAR's are more fussy in general. Can you post some pics of the fired brass ? Looking for scuff marks on the cases. Attached File I didn't think to save any of the Tula cases. Edit: sorry for the quality, but that was the best one my phone took. Edit 2: I cleaned my camera lens and wiped down the brass with Hoppes. Attached File |
|
Quoted: DPMS. I assume that the buffer weight is whatever they shipped their finished guns with. CDNN bought out all of the LR308 stuff after DPMS went under. That made it easy for me to avoid any compatability issues. Carbine or rifle extension? If its carbine it uses a shortened (2.5") buffer that is only 3.8oz. I would recommend a short buffer of 5.4oz at least. |
|
Quoted: https://www.ar15.com/media/mediaFiles/128932/PXL_20250415_024811178_jpg-3517060.JPG I didn't think to save any of the Tula cases. Edit: sorry for the quality, but that was the best one my phone took. Edit 2: I cleaned my camera lens and wiped down the brass with Hoppes. https://www.ar15.com/media/mediaFiles/128932/PXL_20250415_025832243_jpg-3517072.JPG |
|
Quoted: Carbine or rifle extension? If its carbine it uses a shortened (2.5") buffer that is only 3.8oz. I would recommend a short buffer of 5.4oz at least. Quoted: Quoted: DPMS. I assume that the buffer weight is whatever they shipped their finished guns with. CDNN bought out all of the LR308 stuff after DPMS went under. That made it easy for me to avoid any compatability issues. Carbine or rifle extension? If its carbine it uses a shortened (2.5") buffer that is only 3.8oz. I would recommend a short buffer of 5.4oz at least. It's a carbine buffer/extension and the buffer is shorter than a 5.56 version. I have an extra buffer. I'll see if I can pull it apart and add tungsten. Otherwise, I'll look for a heavier one for sale. |
|
Quoted: You need to polish the chamber. Tony Quoted: You need to polish the chamber. Tony I've never tried that. I found another Thread describing it and I'll give it a shot. Quoted: Polish the chamber and the JP extractor should put it to bed. Had to do the same with mine years ago. I'm thinking a patch with JB bore paste wrapped around a .38 bore brush and chucking the rod in a drill. Does that sound like a decent way to polish the chamber? Quoted: Quoted: https://www.ar15.com/media/mediaFiles/128932/PXL_20250415_024811178_jpg-3517060.JPG I didn't think to save any of the Tula cases. Edit: sorry for the quality, but that was the best one my phone took. Edit 2: I cleaned my camera lens and wiped down the brass with Hoppes. https://www.ar15.com/media/mediaFiles/128932/PXL_20250415_025832243_jpg-3517072.JPG That was my first thought when I looked at the photo. I put on my reading glasses and inspected the primers. They look much less dramatic in-person than the way they appear in the photo. |
|
Quoted: Interesting. I would think that an adjustable gas block would solve this, but a heavier buffer is easy enough to try out. Thanks! I'm not sure I'm following. Wouldn't I need a barrel longer than 16 inches to use a rifle-length gas system? No, 16" rifle gas is available in .308 |
|
I decided to look at the brass closure and the majority have these scrapes on the sides of the cases. I'm not sure what this might indicate. Attached File |
|
Quoted: No, 16" rifle gas is available in .308 Quoted: Quoted: Interesting. I would think that an adjustable gas block would solve this, but a heavier buffer is easy enough to try out. Thanks! I'm not sure I'm following. Wouldn't I need a barrel longer than 16 inches to use a rifle-length gas system? No, 16" rifle gas is available in .308 If the JP extractor, heavy buffer, and a chamber polishing doesn't solve my issues, I guess a new barrel will be in my future. |
|
Quoted: I decided to look at the brass closure and the majority have these scrapes on the sides of the cases. I'm not sure what this might indicate. https://www.ar15.com/media/mediaFiles/128932/PXL_20250415_213005475_jpg-3517552.JPG I think those eye-brow marks might occur during feeding, chambering. From the machined edge where the feed cone blends into the chamber. maybe try un-loading an un-fired round that was fed semi-auto, i.e. not the first round off the top of the mag, that will have different dynamics than a semi-auto cycled round. see if that un-fired round has that eye-brow. if not, then that eye-brow occurs during extraction/ejection, and my theory is toast. I used to see that on some calibers semi-auto, other than .308. remedied by polishing the entrance to the chamber. Sometimes it's just a machined chamfer or bevel, those are the worst offenders. The sharp edge snags the brass as it tips up into the chamber. just my 2 cents. |
|
Quoted: I'm thinking a patch with JB bore paste wrapped around a .38 bore brush and chucking the rod in a drill. Does that sound like a decent way to polish the chamber? No. Spend the money for a proper flex hone or find someone who has one. I may have missed it, but does the rifle have mid-length or rifle-length gas? If it's rifle, Faxon barrels use the longer 15.5" gas tube. Using the shorter 15 3/8" tube will cause early unlocking. I ran into that problem. I'm not sure if mid-length tubes are all the same or not. |
|
Quoted: I may have missed it, but does the rifle have mid-length or rifle-length gas? If it's rifle, Faxon barrels use the longer 15.5" gas tube. Using the shorter 15 3/8" tube will cause early unlocking. I ran into that problem. I'm not sure if mid-length tubes are all the same or not. yeah, Faxon LR-308 barrels use the Armalite AR-10 gas-tube length, different than AR-15 gas-tube lengths. The AR-15 ~11.75" mid-length gas-tube corresponds to the Armalite AR-10 12.0" carbine gas tube. |
|
Quoted: I think those eye-brow marks might occur during feeding, chambering. From the machined edge where the feed cone blends into the chamber. When machining a barrel, I have found it best to cut a radius at the entrance of the chamber for smoother feeding. Tony ETA: You can still do it after the extension is installed. Use a #425 dremel wheel to break that sharp edge left by conventional mil-spec type barrel making.  |
|
Quoted: yeah, Faxon LR-308 barrels use the Armalite AR-10 gas-tube length, different than AR-15 gas-tube lengths. The AR-15 ~11.75" mid-length gas-tube corresponds to the Armalite AR-10 12.0" carbine gas tube. Quoted: Quoted: I may have missed it, but does the rifle have mid-length or rifle-length gas? If it's rifle, Faxon barrels use the longer 15.5" gas tube. Using the shorter 15 3/8" tube will cause early unlocking. I ran into that problem. I'm not sure if mid-length tubes are all the same or not. yeah, Faxon LR-308 barrels use the Armalite AR-10 gas-tube length, different than AR-15 gas-tube lengths. The AR-15 ~11.75" mid-length gas-tube corresponds to the Armalite AR-10 12.0" carbine gas tube. @rpoL98 It's a Faxon midlength gunners profile barrel. I am 95% sure that I am using a standard midlength gas tube. Are you saying that that might be too short? ETA pic of tube in the receiver. Attached File ETA2: the more I think about it, I may have bought a special gas tune for it. I honestly can't remember. |
|
Quoted: @rpoL98 It's a Faxon midlength gunners profile barrel. I am 95% sure that I am using a standard midlength gas tube. Are you saying that that might be too short? ETA pic of tube in the receiver. https://www.ar15.com/media/mediaFiles/128932/PXL_20250418_012627221_jpg-3519406.JPG ETA2: the more I think about it, I may have bought a special gas tune for it. I honestly can't remember. that's the correct-length gas tube. this is what an AR-15 gas tube looks like when paired with a Faxon LR-308 barrel: 
|
|
Quoted: That was my first thought when I looked at the photo. I put on my reading glasses and inspected the primers. They look much less dramatic in-person than the way they appear in the photo. Quoted: Large firing pin hole and unlocking early. Common. |
|
Quoted: that's the correct-length gas tube. this is what an AR-15 gas tube looks like when paired with a Faxon LR-308 barrel: https://i.imgur.com/0S79ZsY.jpg Quoted: Quoted: @rpoL98 It's a Faxon midlength gunners profile barrel. I am 95% sure that I am using a standard midlength gas tube. Are you saying that that might be too short? ETA pic of tube in the receiver. https://www.ar15.com/media/mediaFiles/128932/PXL_20250418_012627221_jpg-3519406.JPG ETA2: the more I think about it, I may have bought a special gas tune for it. I honestly can't remember. that's the correct-length gas tube. this is what an AR-15 gas tube looks like when paired with a Faxon LR-308 barrel: https://i.imgur.com/0S79ZsY.jpg Awesome. Thanks! 
|
|
Just wanted to update this in case someone else might have similar issues. The JP extractor appears to have cured the problem. The gun is functioning great. One weird thing is that the last round is sometimes not ejecting. After the bolt locks back, the empty case is often laying on top of the empty mag. However, it falls out when you drop the mag, so it hasn't caused any issues. I did already buy a .308 flex hone, so I will probably polish the chamber, anyway. |
AR Sponsor