I posted this in "Troubleshooting", but maybe I should have posted this here.

I’m having an issue with an AR15 pistol build that “appears” to be under gassing.  

The upper receiver is a complete new BCA 10.5" 7.62x39 including BCG using a carbine length gas system, on the lower receiver I moved all the way down to a 3 oz. buffer.

I load a mag, chamber a round, and only half the time does the casing eject and the next round doesn’t load.  So, I wind up clearing the casing and manually chambering the next round.

I swapped on a Radical Firearms AR-15 16” 7.62 upper from my rifle on to the lower, and it runs through a mag just fine, indicating the lower was fine.

The conversation at the range then centered around the gas system, some thinking I need an adjustable gas block.

So, I come home and at least inspect what I have.  The alignment of the gas block to the hole in the barrel looks good and the tube looks fine.  A 3/32 (.094) drill bit fits nicely in the hole with maybe .002 of wiggle, so the gas hole appears to be a 41 (.096) or possibly 40 (.098) hole.

I’ve spent the last couple of days researching and this seems to be a common issue with the setup, and I’ve read a few times about gradually opening up the hole to even .125.

I’ve also looked for charts relative to hole size relative to barrel length, but couldn’t find one for 7.62.  Found them for others such as 5.56.

I’ve read the sticky “How it Works- The AR gas operation and how everything works in harmony”, it all makes good sense to me.  If I interpret the graph correctly, I certainly have more pressure that the 16” barrel that works, so I can’t explain why it isn’t working unless the gas hole is indeed too small.  But, I’m not in a hurry to open it up unless necessary.  I’ve also read through some other threads.

Anyway, if this rings a bell and you can offer guidance, suggestions, pearls of wisdom, and lead me to a solution I’d sure appreciate it.

Looking at this from the hole change point of view, this is what I'm seeing in opening up the hole.

Anyone that's done this have any input on how they went about it and what hole size the wound up with?

                     Gas Port Hole Size Increase
Drill     Hole       Area          Area        %         Cumulative  Cumulative
size     size        size        Increase    Increase        Area           %
#40    .098      .00754          -              -                 -               -
#38    .1015    .00809     .00055        7.3%        .00055          7.3%
#36    .1065    .0089       .00081        10%         .00136         18%
7/64    .1094    .0094      .00050         6%          .00186         24.7%
#34    .111      .00968     .00028        3%          .00214          28.4%
#32    .116      .01057     .00089        9.2%        .00303         40.2%
#31    .120      .01131     .00074        6.6%        .00377         50%
1/8     .125      .01227     .00096        8.6%        .00473         62.7%

Have you contacted the vendor to see what they say?  BCA is a total QA crapshoot, but most folks say they will work to fix what doesn't work.

Zero luck with getting a response from Bear Creek.

About 15 calls over a 2 week period and they didn't answer the phone once, customer service and sales.  I left at least 5 messages with name, phone, and issue and they have not called back.  I did a google on their quality, and one of the hits was the BBB website, and there are LOTS of complaints about them.  I was, well there ya go.

So, I figure I'm on my own.

Damn, that sucks.  If you had popped in here and asked about their stuff before you invested, we might have saved you some headache.  Don't be afraid to open up the hole.  You can always choke it back down with a gas block if you go too far.

That's kind of what I was figuring, if I go slow yet still go to far I can get an adjustable gas block.

I'd use a drill bit to determine the current port size and drill out with the next size larger bit. As said, you can always add an adjustable gas block to close off pressure.

I've got a KAK 300blk barrel that came with a 0.125" gas port. I added a an adjustable gas port to close things down because it was way over pressured.

Before drilling the gas hole, I would put in a Wolff extra power extractor spring.

Weak extraction will have the same issues you described.

Yes, I've seen that the adjustable gas port can be used should the hole get too big.

Thanks...

Thanks for the suggestion, looks like I can get one from Midway.  I'll take that with me to the range and try that, it'll take at least a week to report back...

Will it lock back if you have an empty magazine?    That's an easy way to check if it's extraction/ejection or under gassed in a lot of cases.    I fought this issue on a used 10.25 5.56 upper I bought used.    It had been run suppressed 100% of the time and had worked for the previous owner.    In my case it was under gassed and I fixed it by drilling it out.    

Yes, pull the charging handle back with an empty mag and it locks back.  Won't be at the range until next week to try a single round.

Thx for the reply...

Not directly comparable, but


I had a 12.5" Noveske Leonidas SBR. Factory upper. It would run with any 7.62 load I tried with the can on. Without the can it was only reliable with 147gr ball.

I would say go with adjustable gas to get the greatest flexibility.

I'm thinking he meant when you fire a round does it lock back on empty.  It doesn't sound to me that it would, but it is a pertinent question when it comes to gassing.

That is what I meant.   Does it lock back on an empty mag if you fire it w/ just the round in the chamber.   If it does you may have enough gas or are really marginal.    If it doesn't it's more likely gas.

Just to be clear, going back to the problem as stated in the beginning:

I load a mag, chamber a round, and only half the time does the casing eject and the next round doesn’t load.  So, I wind up clearing the casing and manually chambering the next round.

I never ran through a mag, a little more than halfway through and I tried a couple of other full mags and the changes described above to figure out what was different.  At that point it was time to look for help.

Trying a single round in the mag sounds like a good idea and provide information as you point out.

Another thought.  Lube the shit out of it for the test w/ something like CLP.  It'll spit out anything it doesn't need.  

Clean the chamber really good with a wire brush cleaner
Maybe case is sticky,
Are you using steel or brass ammunition

Actually this should be the first test of a new build.  See if it locks back on empty.

But of course,

Out of the blue this AM I have an RMA from BCA to send them the upper.  I would have preferred a conversation first, but...

And of course yesterday I ordered some number drills from McMaster-Carr to open up the gas port and from Midway the Wolff extra power extractor spring suggested above.

Ah well, I'll ship them the upper and see what they tell me.  But, if the lower feeds other uppers just fine is there anything else on the lower other than the buffer weight that could affect a working upper?

I'll keep this thread updated as this rolls along.

I would send the upper back for evaluation/repair/replacement before taking a drill to it.

OK,

So follow up to this issue...

As we discussed, I sent the upper back to Bear Creek Arsenal using their RMA process.  I expected at some point to get an email or phone call, but never did.  

Last week I suddenly received the upper.  I looked it over and someone had clearly reviewed it as there was excessive oil on the bolt carrier group.

But, no note, explanation, statement, or anything in the box.  Just the upper.

I sent them email and used their on line contact system inquiring what they had found or what had been done, but crickets.

My next move is to the range to try it out and see if it works.  Part of that will be using a magazine with a single round to see if it locks back after firing.  If it works, I guess I'll be dissecting it to see what has changed, notably if the gas port is larger.  If not, gradually open up the gas port I guess.

From my view, having an issue with something purchased new is one thing. It happens.  But, zero communication except the email with an RMA? Unacceptable in my view.  Needless to say, I won't be a Bear Creek Arsenal return customer.

Swap in a different carrier
look at the gas key alignment and staking
check alignment of gas tube to gas key

I purchased a BCA Upper.

The quality control was shit. I had to basically clean, remove rust, and rebuild the thing.

Issues:
-Barrel had surface rust inside the bore which thankfully cleaned right off.
-Muzzle Device wasn't really even torqued on properly.
- Their handguard requires shims. None were used. It was only torqued to 15-20 Ft LBs
-Barrel Nut was looser than a Hooker from the Philippines.
-Gas Block Screws were loose.
-Gas Block was oddly super oversized in regards to outside diameter. Replaced with a spare .750 Gas Block in order to better free float and avoid barrel whip. Used a drop of orange permatex on each screw and torqued to 20 inch lbs.


Observations:
-As a cost cutting measure most barrels are heavy profile.
-Most Barrels are Phosphated.
-BCA Upper had a very sloppy receiver to barrel fit.
-Staking on BCG was decent.
-Barrel on mine was dimpled but was not well done. I corrected it on my own.
-Upper was rather dry. They didn't use any oil during shipping

BCA is serviceable with basic tools, and your spare parts bin. But how much is your time worth?

Androcorp is the cheapest I'll ever go on complete uppers.

If you really want a BCA, buy the rebrand from Midwayusa. At least they take care of warranty bs.

'But, if the lower feeds other uppers just fine is there anything else on the lower other than the buffer weight that could affect a working upper?'

Yes, the recoil spring. It could be wrong for one upper and okay with another. However, in your case, I think it was a gas problem as you thought and they most likely fired it, took it apart, drilled out the gas port, fired it again with success and sent it back. Your concern about communications seems a little 'nit-picky' to me as long as they fix the problem.
I've had good results with Radical Firearms buying complete ARs, especially the 7.62x39. Making an upper from one maker work with a lower in another caliber from another maker is not always easy - they use different buffers/springs for different calibers, gas system specs and barrel lengths. Worst case if it still doesn't work for you, they might say sorry, it worked for us.

I don't agree at all that asking for communication from Bear Creek Arsenal is nit picky.  Simple communication could have answered the issue and sent me in a positive direction by telling me something about the lower they tested with for example.

If you don't want to interact and help someone having difficulty with your product, it's time to close shop and hang it up.

Especially on the lower end, some manufacturers use unaltered 5.5.56X45 barrel extensions. Such barrel extensions can be narrow and sharp for the larger diameter 7.62x39. My first 7.62x39 upper was pre '94 Colt flat top. I had feeding issues with the bolt not quite loading the round all the way into the chamber. I  noticed that the rounds would have two scrapes from near the tip of the bullet to the base of the shell. Colt used a standard 5.56X45 barrel extension with M4 feed ramps. I rounded and polished the sharp tops of the feed ramps and didn't have any more feeling issues.

Check your rounds after being fed into the chamber. If there are a pair of gouges, round the top of the feed ramps.

Scott

True.

for ex. My BCA 10.5" carbine gas 7.62x39 works great. Sorry, i cant help. I've not had trouble out of mine, so i not needed to look into it.

Mine has the FSB sight and a generic 3 oz carbine buffer.

Just a post to wrap up this dilemma.  It finally got warm enough today to go to the outdoor range I use for ARs.

Wouldn't ya know it, the upper works just fine, all spent casings ejected which was the real problem with the upper.  I put maybe 300 rounds through it and had maybe a couple of misloads after 250 that a quick yank on the charging handle took care of.

So, they fixed it, but I haven't a clue what they did.  The gas port hole measures the same so they didn't open that up.  Maybe the tube was clogged?  I can't detect what changed.

Who knows as they ghosted me on communication, but at least I have a working upper.