thossoma@pm.me

So prior to the adjustable gas block I was able to get the bolt to lock back after shooting the last round from the mag because I drilled the gas port out with a #44 drill bit as suggested. But jamming still occurred pretty badly. It was also suggested that I dunk the BCG in a bath of oil then wipe it's face, slam it in and start shooting. I ended up purchasing the Adjustable gas block because of some other recommendations and installed it before test firing yesterday. I'm assuming that the oil bath is what actually made the gun start working properly and not the new gas block, but I do like the extra flexibility of having that anyway. I will continue to put rounds through it and make sure the bolt is dripping wet. Another question I have is about bullet weight as it compares to amount of gas going through the gas tube. Does a heavier bullet require more or less gas to cycle to bolt back? Or does it not even matter the weight of the bullet? The AR-10 world is so different then the AR-15 world. I built two AR-15's and have shot multiple different bullet weights through them without issue. And when I put the gun together I had no issues firing right out of the gate, different story with the AR-10. I'm glad that you guys were available to give me guidance and get it working for me.

Good to know! This would be my first time with an adjustable gas block. I have questions then... 1. Should I start over wide open and then watch where the shells fly? 2. Is 3:30 a good spot? Or what position tells me that I have dialed it correctly? 3. How many rounds would be considered a good break in period? Thanks again.

Got some news! I took some 5w30 oil and poured it into a ziploc bag and took my bcg and threw it into it over night. I also bought an adjustable gas block https://www.midwayusa.com/product/1094240120979. I wiped off the face of the bolt and threw it in. I adjusted the gas block all the way closed and fired shots one at a time and slowly adjusted the gas block open until the bolt locked back shooting the last round from the mag. Once I got there, I added a second round into the mag and made sure it would eject and load the rounds properly. I was able to successfully fire off 7.62x51 149 grain brass rounds and 308 WIN 150 grain wolf ammo without any jams or problems probably shot off around 20 rounds. I also tried 308 WIN 180 grain and it was having a problem ejecting the round completely out, it would pull it out of the chamber but it would be sitting on top of the magazine and not thrown out. I ran out of time to diagnose further, but I'm thinking I should increase the gas a bit more probably. The shells are landing at about 3:30. Thanks for everyone's help and suggestions! I greatly appreciate it!

I will give the BCG a good soak next time and spray it with oil as I shoot. I noticed a pattern on my shells from the last test. The two scratch marks on the neck of the shell. Does this mean anything or shed any light on any problem? Also, when I was shooting the steel casings and the shell was ejecting, it was flying to around 1 o'clock to 2 o'clock. Also, some of the primers look pushed out where the firing pin hit them. Looks to be just the brass. VF_280821153804.mp4

I put about 30 rounds through this trip. Should I just use something like REM OIL while breaking her in? And should I be spraying it into where the cartridge seats into the barrel and all over the BCG?

Another note, I am able to eject a round every time manually using the charging handle.

So the drill bits came today. I got it drilled out and did some test firing. The first thing I tested is I put 1 round in my magazine to see if it would lock back the bolt. I was happy to see that it did lock back and ejected the shell! I then put 3 rounds into the mag and fired again, Not the outcome I was hoping for this time around. It failed to eject the shell and jammed the next round into it. I tried this a few more times and received the same results about 80 percent of the time. There were a few times where it did eject the shell correctly and a few where it almost ejected it. I then decided to try some steel ammo that I had and it actually performed better then the brass surprisingly. I would say that it worked correctly about 75% of the time and only jammed a few times. It seemed like my ejector grabbed the steel better for some reason. So I'm open for some ideas on what to try next. I will say that I probably should have taken lube up with me when I went shooting, so that is what I will do next time. I did just freshly lube it up before I went shooting though. The first picture was the most common outcome for the brass. The ammo I used...

Thanks for the tips. I do have a drill press, would that be the smart choice? I've actually never removed a barrel from an upper before, shouldn't be too hard right? I did get my Sprinco orange buffer spring in the mail. Now I am just waiting on the #44 drill bit. So please tell me if I'm wrong, but I am going to be drilling the hole that is on the barrel, not the hole on the gas block. Also, worst case scenario if I go from under gassed to over gassed, I can always get an adjustable gas block, correct? Thanks.

Yes, sorry I mistyped. Thanks again for your help!

Thank you! I will find the #45 drill bit and get it done! I'll be in touch with the results. So apparently I am under gassed and need more to get the job done. It's not pushing my BCG back far enough to eject the old round and also lock back after the last round. Correct?

How about this drill bit?? .082". It's a #45 gauge drill bit.

So my current options for drill bits are using the 5/64 (0.078125) to make it slightly bigger, or using 3/32 (0.09375) to make it over the size you specified? As far as the scale, it specifies lbs.ounces.fractions of an ounce. So the picture shows 1.2.2. 1 pound 2.2 ounces. The display is just messed up. Not sure why it doesn't say lb.oz or something like that. Thank you for your attention to my rifle issues. I have purchased the orange spring and will report back after I do some test firing. And I'll wait to hear from you guys about the gas port drill size. I have been pretty liberal with the gun oil on the bolt especially. I'll keep that up.

Ok, here goes everything I got! 1. NOT an armalite system 2. Buffer weighs 5.3oz. my scale doesn't show last digit. https://www.midwayusa.com/product/1021956650 3. Buffer is 2.5" 4. Buffer tube is 7" 5. Buffer spring is this one ...https://www.midwayusa.com/product/1019426458 6. This rifle is carbine length with an 18" barrel 7. Gas tube is just under 12" 8. 9. 10. 11. Gas journal is .75" and port is just smaller than 5/64", but bigger than 1/16". 12. I will take photos of the malfunction as soon as I can get out and shoot again. Planning on this week Ammo I've shot is...(same results on both)

The buffer is just over 5 oz. The barrel is 18" 1:10 twist. .750 Low Profile Gas Block I will get the rest of the info soon...

Just built my first AR-10 / LR-308 from an 80% arms lower and a CBC INDUSTRIES Upper. https://www.cbcpfa.com/products/ar-10-upper-assembly-18-308-win-110-15-cbc-industries-keymod-ar-10-handguard-rail/ My buffer. https://www.midwayusa.com/product/1021956650 My buffer spring. https://www.midwayusa.com/product/1019426458 My BCG https://www.cbcpfa.com/products/ar10-bolt-carrier-group/ I use Magpul magazines. If I manually cycle the bolt with the charging handle, I can smoothly eject cartridges and load cartridges without issue. It will also lock the bolt back after the last round. When I start shooting, it is a different story. I put one round in the mag and put it into battery. After I touch it off, the bolt is still in battery and the round didn't eject (about 5% of the time it will eject in this scenario) and the bolt doesn't lock back. If I put two rounds in the mag, I will slam the first round in and touch it off and then look at the ejection port and find the second round pushing up against the spent round still in the chamber. So it tries to feed the next round, but failed to eject the last round.

On it! Thanks!

Here is some pictures

Wondering if this got solved. I'm having a similar issue where my bolt won't lock back after firing the last round from a mag, also it will eject the round only 5% of the time. If I cycle the bolt manually, it will eject and feed with no problems and lock back the bolt on the last round without issue.