Assistance with under-gassed ar15 build?

[kmk1012]

So you have to kind of force it to lock back ?

It doesn't lock back when firing it. Operates normally when cycling by hand, meaning pulling the charging handle with an empty mag inserted, or pulling the charging handle and manipulating the bolt release to lock it.

 

[titsonritz]

Yes, it just seems like the bcg doesn't travel far enough back by just a fraction of an inch. This is while firing, I can manually pull the charging handle and manipulate the bolt release and lock it.

Have you tried another BCG? You might have a gas leak at the carrier key. As far as I know rifle buffers do not come in multiple weights like carbine buffers.

 

[kmk1012]

Have you tried another BCG? You might have a gas leak at the carrier key. As far as I know rifle buffers do not come in multiple weights like carbine buffers.

I haven't done that yet as there wasn't signs of any gas getting to the BCG before tonight. I realigned the gas block and found success for the cycling issue but just not enough oomph to lock it open.

 

[titsonritz]

It doesn't lock back when firing it. Operates normally when cycling by hand, meaning pulling the charging handle with an empty mag inserted, or pulling the charging handle and manipulating the bolt release to lock it.

What is your barrel length and gas system length?

 

[kmk1012]

What is your barrel length and gas system length?

18" with rifle length gas system.

 

[kmk1012]

What is your barrel length and gas system length?

I have two other rifles set up with this exact same system that run reliably, the only variable is the brand of buffer tube, buffer spring, and buffer itself. These loads as well as factory loads function in my other rifles and I tried to copy them for my son's rifle but haven't had much luck.

 

[titsonritz]

I have two other rifles set up with this exact same system that run reliably, the only variable is the brand of buffer tube, buffer spring, and buffer itself. These loads as well as factory loads function in my other rifles and I tried to copy them for my son's rifle but haven't had much luck.

Identical barrel? 18" barrels with with rifle lengths have a fairly short dwell time and can be finicky. The Crane MK12 SPR spec their GP size at .0995", I'm wondering if yours is smaller. I've seen 18" barrels with a standard 20" barrel GP size which is .093". I would measure the gas port so you know what you're dealing with.

 

[DirectDrive]

18" with rifle length gas system.

That could be why you're on the edge with that rifle's function.
18" with rifle gas you are losing 2" of "dwell" time.
I think if you get the carrier and carrier tunnel wet with CLP and feed it some full power ammo, it will loosen up and lock back.

 

[DirectDrive]

Agree that it would be good to know the gas port size.

 

[kmk1012]

Identical barrel? 18" barrels with with rifle lengths have a fairly short dwell time and can be finicky. The Crane MK12 SPR spec their GP size at .0995", I'm wondering if yours is smaller. I've seen 18" barrels with a standard 20" barrel GP size which is .093". I would measure the gas port so you know what you're dealing with.

Will do tomorrow, thank you

 

[kmk1012]

That could be why you're on the edge with that rifle's function.
18" with rifle gas you are losing 2" of "dwell" time.
I think if you get the carrier and carrier tunnel wet with CLP and feed it some full power ammo, it will loosen up and lock back.

I agree, it's been hand cycled several hundred times and is adequately wet. I'm not a noob at this just been stumped on this one rifle. I'm going to pick up a couple buffers in my way home from work tomorrow and swap them out in succession and report back. Thank you all for the assistance and I hope I find a solution.

 

[titsonritz]

Will do tomorrow, thank you

Do you have a pin gauge set? That is only way to get an accurate measurement, using calipers or drill bits won't cut it.

 

[titsonritz]

I agree, it's been hand cycled several hundred times and is adequately wet. I'm not a noob at this just been stumped on this one rifle. I'm going to pick up a couple buffers in my way home from work tomorrow and swap them out in succession and report back. Thank you all for the assistance and I hope I find a solution.

Where are you finding rifle buffers with varying weights?

 

[kmk1012]

Do you have a pin gauge set? That is only way to get an accurate measurement, using calipers or drill bits won't cut it.

No pin guage set, just me and my experience using calipers. I trust myself to at least get close. With a round hole it takes several averages to get what you get.

 

[kmk1012]

Where are you finding rifle buffers with varying weights?

My local gun shop generally has enough parts in stove to keep me busy. I'm pretty spoiled with Santiam Buyers in Stayton

 

[titsonritz]

No pin guage set, just me and my experience using calipers. I trust myself to at least get close. With a round hole it takes several averages to get what you get.

When talking about thousandths of an inches, close ain't close enough. I'll be down in the Salem this later this week and/or weekend sometime, I have my set with me, PM me if you want to hook up and do it right.

 

[titsonritz]

My local gun shop generally has enough parts in stove to keep me busy. I'm pretty spoiled with Santiam Buyers in Stayton

Point being I do not believe rifle buffers come in multiple weights like carbine buffers and you can not use a carbine buffer in a rifle RE.

 

[arrowshooter]

Pull down a buffer, take out all the weight, slap'er back together and it should run fine. I have had to do this with two RL gas barrels, but only for testing. Ultimately I opened up the gas port two steps on both then added weight back to the buffer as needed to smooth things back out. I also had an adjustable gas block standing by just in case.

 

[kmk1012]

Point being I do not believe rifle buffers come in multiple weights like carbine buffers and you can not use a carbine buffer in a rifle RE.

Ok, that's what my plan was. That's too bad as it would have been an easy swap. I'll look into why they aren't interchangeable as I thought they were.

 

[DirectDrive]

Ok, that's what my plan was. That's too bad as it would have been an easy swap. I'll look into why they aren't interchangeable as I thought they were.

They are two very different animals :


With some range time with full power ammo, I'd bet your rifle will start locking back.
However, it would be interesting to know gas port size.
I'm guessing it's .093 and in your configuration (18" rifle gas) it could stand to be slightly bigger.