CentralNChunter

30 rounds of success. 20 rounds shot relatively slow fire in five shot groups and 10 rounds shot rapid fire (as fast as I could). I replaced the AIM BCG extractor and springs with the DPMS upgrade assembly LR-308 GII. The AIM ejector had what I felt like sharp edges. I slightly beveled and polished the ejector edges just to be sure it wasn't binding in its bore. I ran the gas block adjustment screw in and started backing it out a half turn at a time until the bolt locked back correctly on an empty mag. I then turned it out a quarter turn, hoping this extra gas would keep it functioning after being shot awhile and running "dirty". I'm thinking of turning it back in a quarter turn though as I'm not sure that quarter turn is needed. What do you all think? The brass is ejecting at 3 o'clock, landing (4'-6'?) away, in roughly a 2' radius. 10 shot rapid fire vid: https://www.dropbox.com/s/z084k8b3gsweifs/308AR 10rd Rapid Fire.mpg?dl=0 While shooting the five shot groups, I got one cool screen shot of a case ejecting. Seems pretty good to me, but being 308 AR inexperienced, does this ejection/deflector contact look correct for the 308 platform?

I think I have one last issue to work out, one that seems to be somewhat common on some DPMS/PSA guns from my limited search. That would be the good 'ol failure to eject. As I was testing for feeding issues, I turned out the gas screw a half turn every 5-10 rounds. That may have made it worse, but I'm not really sure with the limited rounds used. Ejection pattern is around the 3 o'clock range. I found the AIM bcg extractor cracked. I went ahead and ordered a Gen 2 DPMS extractor (supposedly backwards compatible), ejector & spring. Reviews I read were pretty positive on this part fixing ejecting issues of others. I emailed AIM, but as this was a Christmas gift, ordered 6 months ago, I don't really expect them to do anything about it, unless there was a known issue of a run of bad extractors in their bcg's. Looks like I won't have to work this Saturday, so maybe I can get back out to the range with the new parts and see how it goes. I'm going to run the gas screw in until the bolt doesn't lock back on an empty mag, & start turning the screw out from there. Question, does the average (if there is such a thing) 308 AR have a 2-4 o'clock ejection pattern similar to AR15's? video of failure to eject: https://www.dropbox.com/s/gdte6tcjv5u1ag3/Failure to Eject vids and pics.mpg?dl=0

Failure to Feed issue is resolved. 98Z5V, I wasn't butt hurt, but could not let the out of spec assumption pass without responding. I come from a QA Lab background. My point was even if you think a part is crap, it is not crap until part dimensions are compared to print spec's. Yes, the receiver set and bcg were purchased because they were on sale / cheap, as Christmas gifts from the wife. If the only option was a $300+ receiver set and $250+ bcg, well I wouldn't have attempted a AR308 build as I have no real need aside from just wanting to put one together. From Christmas gift parts, friend giving me a $250 Midway gift card for my birthday, I have very little out of my pocket invested ($300? don't remember what it tallied up to). I will note (attempting to) dealing with Thunder Guns has not been a pleasant experience. I emailed them with a video, pic's and CAD drawing of my mag catch slot in relation to the receiver top deck and pivot/take down holes. They would not respond to email, but requested I call 9am-4pm for further assistance. I work from 6:30-4. With 10 minutes of lunch break left I called, 2/3 of that time spent on hold. As my break ended, the third person to come to the phone, the resident "gunsmith". I thanked him but informed him my break was over and hung up. I called at 4:15 but was told by the person that answered, everyone else had already left. I emailed again and got the same please call response. I machined part of the mag catch slot higher and made a new mag catch. My catch even has full engagement with the button, unlike the three threads the DPMS catch had. I moved the magazine up 0.040" Shot 30'ish rounds without any failure to feed. Had failure to eject but will expand on that next. Mag catch was machined from some mild steel flat stock I had on hand. The threaded stud was from a grade 8 screw. The end that went into the catch was turned down to 0.125" and high temp soldered to the catch. I believe this fix's that issue. It looks a little like butt now, but once the gun is determined to be reliably functional, I'll likely Cerakote the gun in some camo pattern.

Before I went to email Thunder Guns I wanted to verify my measurements. I wasn't sure which print I looked at for dimensions (and posted the wrong link when I intended to post link to print in first post) I looked at the few DPMS pattern prints Google pulls up. On one my slot is 0.010" higher (sketchy looking print and not sure how accurate). Couple other prints my mag catch slot is 0.008"-0.012" lower than print spec. Called a friend and his PSA G2 mag catch slot is 0.015" higher. Not sure if 0.015" would cure my issue or not. Sure wouldn't hurt, but if I were to make a mod to the receiver and make a new mag catch I would likely go 0.040" higher for starters. survivalshop, I'm not sure a different mag catch would help. I can't imagine how the Armalite catch would hold the mag up higher any meaningful amount. There is zero play between the upper and lower. I machined the trigger pocket to just fit the upper. To break them apart it takes a light tap with my palm to the buffer tube to separate them. Gap between upper/lower: At front 0.004", at rear 0.002". Not sure If I got the dimensions you requested, but here goes; from top deck of lower to top of cartridge rim is 0.4195". From deck of upper to bottom of barrel extension is 0.1595"

I have not tried a different bolt. I have a friend that owns a PSA & another that has DPMS but would be unable to get up with either until the 2nd Sat next month. Per the dimensions found online from another guys DPMS bolt, mine is the exact same diameter, which I believe would be the measurement that matters for this issue. 98Z5V , if you have DPMS pattern print specs that is different than what I have came up with, I would be glad to accept a copy to compare to my parts. Sounds like I didn't use the brand or retailer you are partial to. From what I found on the web, my parts are in spec for DPMS pattern, but as you stated in another post, 308AR is not standardized & companies can make whatever they want. Survivalshop, I'm at work now but will reply to your questions as soon as I'm able.

Before someone goes to correct me that only Armalite is AR 10, the title " DPMS style .308 AR10" is a copy and paste from Thunder Guns LLC were this 80% was purchased. Mine is a DPMS "High" pattern. https://www.thundergunsar.com/ar10-receivers/upper-receivers/ The issue I am having: When the bolt pushes a round from the magazine, as the bullet starts up the feed ramp the bolt slips over the case head and jams (bolt over brass). I think it's mostly, if not completely happening when the round being feed from the magazine is on the RH side of the mag. Magazines tried: PMAG M3 20rd, Lancer L7AWM 20rd. From the spec's on this drawing: https://www.thundergunsar.com/ar10-receivers/upper-receivers/ The location of the mag catch cut in the lower is the exact distance down from the top of the lower and height as shown on print. Someone on the Practical Machinist forum posted his DPMS bolt (dia over opposing lugs) .891" which is what mine measured. From spec's I can find my parts seem to be in spec. With the mag catch pushed in, the PMAG can be inserted 0.053" deeper and the L7 0.063" deeper. If nobody has any other solution (besides modified mags as I want the ability to use off the shelf unmodified mags), I have the idea of cutting the mag catch slot 0.045"-0.050" higher and making a new mag catch. This would move the magazine up enough to solve my issue. I think. Is there a solution I'm not seeing? Billy Parts: Thunder Guns 308 DPMS style 80%upper/lower, BCM charging handle, AIM AR 308 BCG, PMAG, Lancer L7, barrel made from Begerra blank & BAT Machine barrel extension.