300BLK not picking up the second round. Could use some help.

[Outer Rondacker]

I have a BCA side charging 300blk in a 16in barrel with carbine length gas port opened to 1/8 inch. I have tried three different kinds of ammo all full house loads and it keeps showing under-gassed. Dropping the brass at 4:30-5 o'clock and not grabbing the next round. I have tried three different mags still nothing. Two different weight projectiles and its the same. I have a stock PSA buffer spring with a buffer that weight is 3.00 at the post office.

I think I need a lighter spring and or buffer but I am having no luck finding anything in stock that I can justify buying. I have found many 70-120 dollar buffers that are lighter but its only a Bear Creek Arsenals. I was even thinking of cutting a few coils off the spring. Do you guys think this is the way to go or perhaps something else?

I should add I pulled it apart to make sure the gas port was clear and aliened. Looked ok but the SS gas tube hole was much smaller then the gas port and thought perhaps I should open that up a bit. I have checked the bolt and the pistons look good and stand on its own. Kind on a fence here since it was a gift from the kids since dad been talking about a 300BLK for months now. I have to make it work because they got it for me. Most online stuff states stock spring and buffer for a 223/5.56 should work. I even tried my buddies lower that is a S&W 223 stock and it did the same thing. Any help would be nice. Thanks in advance I am no expert when it comes to this kinda gun.

[Fitz]

Have you verified that the gas port , gas block , and gas tube are all clear and free of machining chips . you can put a fired case with primer still in case and with the bolt removed you should be able to blow on the muzzle end and losen gas block so you can rotate and make sure you are getting full flow. If you open up the gas port on the barrel I would suggest a adjustable gas block which is would be needed anyway if you run a suppresser .

[Outer Rondacker]

Thanks Fitz. I have taken off the gas block and cleaned the gas tube and checked the port in the barrel. Also blow compressed air down it. That is how I learned its 1/8 inch size. I then checked the gas block and its also 1/8th size. What is not 1/8 is the gas tube whole where it meets the block. It looks to be half that size. I pulled the T-10 screw on the back of the gas block to look down and see this. I have thought about just chucking up a 1/8th bit and seeing if I could open up the tube a bit where it meets the gas block. Not sure its a great idea. I guess worst thing that would happen is I need to get a new gas tube and block if I screw up. Ugg

Wish I had an extra spring to cut or weaker one to try but Im kinda on this one alone in my area.

[rancher1913]

first try a different bcg. sometimes the gas port internal to the bcg can get blocked.

[Outer Rondacker]

Ops sorry Ranch I forgot to mention that I did try another BCG. Same thing happened. I even used a different lower oh I think I said that already sorry if I did. Same thing happened.

[imashooter2]

If you tried 3 different factory supersonic loads, then I would guess the gas port in the barrel is not aligned with the gas block.

[BLAHUT]

You could order a new spring and have on hand, so you could cut loupes off latter ? If you are going to drill out the port start with a drill just a tad bit bigger than the hole that is there and try, then you can step it open more if needed ? Like you said, you may need to get a new gas block, its called a learning experience ?

[Outer Rondacker]

I have had it off and on over a dozen times. I feel it was aligned every time. I used the air method, pencil method, light down the gas tube method that one sucks by the way I feel pencil is the best but what ever. Ill give it another try who knows.

[Outer Rondacker]

You could order a new spring and have on hand, so you could cut loupes off latter ? If you are going to drill out the port start with a drill just a tad bit bigger than the hole that is there and try, then you can step it open more if needed ? Like you said, you may need to get a new gas block, its called a learning experience ?

Small confession. I have built many of this style gun years ago. Just never ever had an issue with undergassing well never ever had a 300BLK before or built one for that mater. Still does not mean I am missing something simple others have ironed out already.

I figured drilling the gas tube and not port would be my first steps. Just wanted to get some advice from others who might have played a bit more with such an item.

[BK7saum]

Are you absolutely sure it is undergassed?

Sometimes an overgassed AR will overrun the magazine and not pick up the next round.

1/8" seems a little large for a gas port. Without looking, don't they usually run 0.080"-0.090"?

Try a new or different magazine with a good strong magazine spring. Have you tried other magazines and have you tried firing one round to verify lockback?

[Outer Rondacker]

Are you absolutely sure it is undergassed?

Sometimes an overgassed AR will overrun the magazine and not pick up the next round.

1/8" seems a little large for a gas port. Without looking, don't they usually run 0.080"-0.090"?

Try a new or different magazine with a good strong magazine spring. Have you tried other magazines and have you tried firing one round to verify lockback?

I have tried other mags but not the one round looking for lock back. I will try that in the morning. I am going with undergassed as its dropping brass at 5 oclock area.

On another note my neighbor just called for eggs and he is going to bring over his lower in the morning with a h2 buffer in it to try. I will report back.

[BK7saum]

You are probably right with a 5:00 ejection pattern, it is likely undergassed, but I have seen instance where overgassed was overrunning the magazine. Just something to check off the list.

[36g]

Have you checked the barrel extension for any burrs that might be inhibiting the unlocking of the bolt?

[1Hawkeye]

Another thing you can try it to take one weight out of the buffer assembly. This will lessen the weight acting against the bolt carrier group during recoil yet allow the recoil of the buffer spring to propel the carrier group foward into battery just fine.

[Outer Rondacker]

Well good morning guys. As always I wake up before the rooster does and put on the coffee. The neighbor stopped in and had a cup while he picked up his eggs. Next we waited for some daylight and put the upper on his lower. He has a heavier buffer {H2}. First shot I had a mag with two rounds in it and the bolt didn't even pull the first round half way from the chamber. Second time I loaded up a single round as suggested by BK7saum to see if it would lock back on the bolt. Once again failure to extract the round. Only pulled it half way out the chamber.

So my thoughts and the neighbors is his weight was to much or the upper did not have enough gas. He has headed home to cook up some breakfast and I am going to do the same for the wife. I will return to the puter and gun room shortly after as this is really bugging me.

I did not know buffers came apart I will look into this after breakfast.

I really appreciate the help guys you never know when a simple thing can be overlooked and a Dhuaa moment happens. It think this is more then a dhua moment this time.

Edit: I found a Tubbs flat wire spring that is said to be lighter for 300BLK I might order. I honestly feel this is putting a Band-Aid on the issue. Others on the web seam to run with the same stock buffer and spring fine. Its been a long time since I have uploaded a picture I will see if I can get on for you guys of the gas tube in the gas block.

[beltfed]

Rough Chamber????
beltfed/arnie

[shell70634]

Could the gas tube have been crimped to much when it was cut causing a restriction?

[Outer Rondacker]

Ok guys, I have to step back. I had something happen in all my 39 years of reloading and shooting I have only heard about. Lets start with what I did next and if it had anything to do with the result.

I disassembled the buffer. Weight on one piece of steel was 279grains. I found a socket the same size and its weight was 139grains. That is a difference of 140 grains and converted to ounces is .32. The buffer weight was 3.00 before would now come in around 2.68 ounces. So I loaded a dummy bullet in the mag and a live one on top. Headed outside and let it fly. The bolt only came back about 1/4 of an inch and was locked up. Came inside dropped the lower and put the rod down the barrel to give it a few taps. Bolt opened and the brass fell out along with the primer in hand. The primer pocket is blow out. I have never ever had this happen. I spent the next hour inspecting the gun and decided to give it another go. Bang!! and the bolt is stuck again about a 1/4 of an inch open. Repeat but this time the brass is perfect.

This is Armscor 147grain said to be 2000 fps. This is the first time I have ever shot this ammo. I am totally out of blackout ammo at this point. I have put the buffer back to the way it was with its full weight of 3.00 ounces again and pulled the bolt apart to see nothing wrong. Pulled the gas tube and drilled that hair bit to match the 1/8 inch gas block and port on the barrel.

So was the round bad?

Was a lighter buffer a bad idea?

The more I try to fix the issue the worse I feel about it.

[1Hawkeye]

Here's another thing to check is the bolt carrier key straight and tight on the carrier? It sounds more like something is impeading the carrier travel if the gas system is checking out ok. Yes it sounds like that round had a bad pocket another thing is if you remove one of the weights don't replace it with a lighter one just leave that section out. Something else I just thought of have you tried more than 1 magazine if not mabe you have a bad mag.

[Gtek]

If you remove BCG and remove bolt, stick pinky in rear of BCG and engage gas tube. Can you feel it engage?

[popper]

OK, my guess, try a standard BGC. Side chargers use a bolt screwed into the front of the BGC and if too deep, would prevent the bolt from moving in the carrier. Second, check the tail of the bolt! It is the back seal of the 'cylinder'. Leakage there and no worky. The rings are the front seal. 147 gr @ 2k fps is a pretty hot load. Would work fine in my 16" carbine. Other thing to check is the length of the spring. Can you easily lock back the bolt, in the gun? GK had a 308 with a too long spring, wouldn't cycle properly - almost had to use 2 hands to lock it back as the spring got wonky and bottomed in the tube. Cut off a couple turns to make it fit. Of course the normal staking gas key check and length of the tube into the key. Use a pipe cleaner to check the key isn't clogged - I did have that problem once. Heavy buffer is to slow down bolt speed so it locks back. I use a heavy weight in a 10" pistol port BO. I've not used anything but 'proper' standard spring in any of my ARs.

[Outer Rondacker]

Spring is 10.25 inches. I thought the same thing about the bolt so I took out the charging lever off for one shot. Wasn't that. I did clean and relube everything one more time and hand cycle the bolt about a 1000 times. Honestly does feel smoother and softer but like I said. I am out of ammo and I can not find load data for the short fat 125g oldschool speers I have.

[Outer Rondacker]

Here is the last update. Thank you all I think I figured it out.

Grabbed a box of Winchester white box 125g running 2100 ish at the muzzle this morning at the not so local gun shop. Last night I stripped it entirely. Drilled out the gas tube and cleaned it all once again. Lubed the entire rifle with summit racing assembly lube. Plopped my butt in the chair and watched some TV just working the action over and over and over. Took it all apart this morning and cleaned it, applied the proper lube where needed.

Stepped outside, Loaded one shot in the mag and let it fly. Brass fell at 3 oclock and the bolt locked back. Then like a school kid I loaded two more giddy as I could be and dumped the two back to back with the final shot locking back the bolt. Repeated this test until I ran out of ammo. Box only had 20 rounds. I think I got it. Ran flawlessly. Now I can work on casting some projectiles for this baby.

I will also not buy another Armscor box of ammo ever again or Magtech. Not sure it was the problem but I am a happy camper. Called the kids and told them dad popped off a few 300BLK today and couldn't be happier.

If you guys have any suggestions of cast bullets and loads I'm in the market. Don't need smokers just plinkers.

[imashooter2]

Glad you got it sorted.

The Lee C312-155-2R is my choice. 6 cavity mold makes a pile quickly. I size to .310 and lube with White Label Carnauba Red. Feeds great, no issues binding in the magazines. My load is 14.5 grains of IMR 4227 and it gets 1,733 fps average.