.308 build problem

[gun'sRgood]

I put a .308 together and can not figure out why this issue. It will pull off the first, and perhaps the second cartridge, go into battery and fire. Then the next cartridge will not go fully into battery. I have a .308 that functions and I'm comparing it to this build. It seems there are several differences that I do not understand. The gas tube lengths are different. There are no burrs, dents or problems with the tube. The bolt from the working .308 will jam in the new, or green build. The bolt from the new build works fine in the silver or working model. There is a "slot" that is different in length between the two. That's the cleaning rod with the black marker. I'm getting all sorts of advice that now makes it worse. I'm nowhere near a gunsmith. The closest guy says the buffer spring needs a rung or two taken off. The first two pics I'm trying to show the bolt going into battery and "camming" over. The "nick" on the green one is where the bolt from the working one is jamming. [?] Thanks in advance.

 

[BreechFace]

Do you know how to or have you performed a lock back test?

 

[BreechFace]

Nevermind on the above post, you have issues with your upper.

Out of spec upper receiver or headspace out of spec.

Based on your "nick" on the green upper receiver it looks as if your milled portion of the upper is out of spec and the cam key can't rotate in the space.

Is there corresponding marks on your cam key that you can see that would verify it contacting your upper?

 

[gun'sRgood]

Thanks Sir. I have the .308, silver upper, that runs fine. When I take this bolt out and try it in the green upper it jams and that's the nick. When I dry test the green with it's bolt it seats and "cam's" over. I'll try that video. Hope that makes sense.

 

[gun'sRgood]

Nevermind on the above post, you have issues with your upper.

Out of spec upper receiver or headspace out of spec.

Based on your "nick" on the green upper receiver it looks as if your milled portion of the upper is out of spec and the cam key can't rotate in the space.

Is there corresponding marks on your cam key that you can see that would verify it contacting your upper?

BTW, thanks for your help.

 

[gun'sRgood]

This is the bolt that seems to function as it goes into battery and cams over. However it jams with the second or third round. The gas tubes are different. I'm told that the silver one is short but it works. The "channel" to the right of the gas tube is where the nick is caused by the bolt from the silver upper. What is that channel called and why is it longer than the one in the green upper?

 

[BreechFace]

This is the bolt that seems to function as it goes into battery and cams over. However it jams with the second or third round. View attachment 978682 View attachment 978683 View attachment 978682 View attachment 978683 View attachment 978684 View attachment 978685The gas tubes are different. I'm told that the silver one is short but it works. The "channel" to the right of the gas tube is where the nick is caused by the bolt from the silver upper. What is that channel called and why is it longer than the one in the green upper?

The channel you are referring to is where the cam pin rotates into as the bolt locks and unlocks. It appears as I said before that your green upper channel is milled shorter.

If you measure the distance from the barrel extension shoulder to the front edge of the channel on both uppers with a caliper or some measuring device it would be helpful in determining if the upper is out of spec.

To me it appears that your cam pin as it is trying to rotate in the channel is being interfered with its travel by the out of spec location of the channel, hence the damage done to the green channel and why it won't go into battery.

 

[BreechFace]

There has been in the past a lot of hinky stuff going on with gas tubes (DPMS vs Armalite pattern) in AR10's with companies. Some barrel gas block journals are in different locations causing a need for different length gas tubes. AR10's are different animal in regards to consistency in design from manufacturer of parts to others.

 

[BreechFace]

Do you have a picture of the cam pin's on the BCG's wonder if there is any scoring on the front corner of the cam pin where it looks as if it is contacting the cam pin channel in your upper.

 

[MistWolf]

First, yes! Perform a lock back check. In situations like this, always start with a lock back check. Use a mag you know will lock back when empty. Load it with one round, chamber it and fire. Whether or not the BCG locks back will narrow things down.

Second, DO NOT cut any coils from the action spring.

Third, it's not certain you have a headspace problem. It's more likely that the longer gas tube interferes with the gas key, preventing the bolt from going fully into battery.

Fourth, do not use military ammo for testing purposes. Us commercial ammo. Military ammo is loaded to lower pressure and may not generate enough to operate your AR.

 

[gun'sRgood]

The channel you are referring to is where the cam pin rotates into as the bolt locks and unlocks. It appears as I said before that your green upper channel is milled shorter.

If you measure the distance from the barrel extension shoulder to the front edge of the channel on both uppers with a caliper or some measuring device it would be helpful in determining if the upper is out of spec.

To me it appears that your cam pin as it is trying to rotate in the channel is being interfered with its travel by the out of spec location of the channel, hence the damage done to the green channel and why it won't go into battery.

I can't get my caliper inside to get an accurate measurement. The damage to the green upper was cause from the bolt from a .308 by Black Rain. The black Rain upper is milled for that bolt. Thanks for staying with me. Your input is very much appreciated.

 

[gun'sRgood]

First, yes! Perform a lock back check. In situations like this, always start with a lock back check. Use a mag you know will lock back when empty. Load it with one round, chamber it and fire. Whether or not the BCG locks back will narrow things down.

Second, DO NOT cut any coils from the action spring.

Third, it's not certain you have a headspace problem. It's more likely that the longer gas tube interferes with the gas key, preventing the bolt from going fully into battery.

Fourth, do not use military ammo for testing purposes. Us commercial ammo. Military ammo is loaded to lower pressure and may not generate enough to operate your AR.

Thanks. I will. The range is an hour away. But I think I'll find something much closer. This is driving me nuts and I can't tell you how much you guys staying with me is appreciated.

 

[gun'sRgood]

There has been in the past a lot of hinky stuff going on with gas tubes (DPMS vs Armalite pattern) in AR10's with companies. Some barrel gas block journals are in different locations causing a need for different length gas tubes. AR10's are different animal in regards to consistency in design from manufacturer of parts to others.

I'm hearing more and more of this kind of thinking. This upper cam from a company that no longer exist. Folks are telling me there's a reason for this. Thank you sir

 

[gun'sRgood]

Do you have a picture of the cam pin's on the BCG's wonder if there is any scoring on the front corner of the cam pin where it looks as if it is contacting the cam pin channel in your upper.

I will soon. Appreciate your thoughts!

 

[Riomouse911]

I also was thinking the two may be from the different spec (DPMS VS. Armalite) when I first saw the post. This is the cause of several poor reliability or non functioning issues among my friends who pieced together AR 10 pattern rifles rather than buy a complete one.

Check to see what type or brand of parts are recommended from the manufacturer and stick to those, if their call is not the same as what you've installed then you very likely have your issue identified.

This incompatibility is probably the cause of the damage to the upper from the Black Rain bolt:

I can't get my caliper inside to get an accurate measurement. The damage to the green upper was cause from the bolt from a .308 by Black Rain. The black Rain upper is milled for that bolt. Thanks for staying with me. Your input is very much appreciated.

Stay safe.

 

[gun'sRgood]

I also was thinking the two may be from the different spec (DPMS VS. Armalite) when I first saw the post. This is the cause of several poor reliability or non functioning issues among my friends who pieced together AR 10 pattern rifles rather than buy a complete one.

Check to see what type or brand of parts are recommended from the manufacturer and stick to those, if their call is not the same as what you've installed then you very likely have your issue identified.

This incompatibility is probably the cause of the damage to the upper from the Black Rain bolt:



Stay safe.

After reading your reply I called BSF and chatted at length about the thoughts provided to me here. Your thoughts concerned me as the serial number on this gun is 00006. And the company is now out of business. I re-drilled and made sure no burrs were present in barrel -by BSF-, gas block and tube, also bought from BSF. I was about to retest when I found the first round was now acting like it was the second. As in, not being striped off and put into full battery. i tried two other mags with the same problem. Then I tried the same mags on a .308 by Black Rain. I no fan of Black Rain but everything has always worked. [Except for the incredibly lousy trigger it came with!] Then I took the new Green upper and put it on the BR lower. Everything seems to work just fine. Rounds strip off, manually eject and puts the next fully into battery and locks back after the last round. So I think I'm chasing the wrong problem? Why would this be happening? Thanks you sir. BBQ and beer anytime your around.

 

[MistWolf]

What did you re-drill?

 

[gun'sRgood]

I took off the gas block and noticed that the tube did not have a clear opening to the block. I found that the hole in the block is just under the threaded mount hole. That is both in size and in physical space. I took a bit that would not affect the threads but fit inside the hole in the block. I set this in my mill and with just a "tap" the edges of the tube now are the same as the hole in the block..

Here's the strange part: When I put the gun back together It would not strip the first round off the mag. It used to do this. I tried a different mag. Then I took the green upper and put it on the Black Rain lower. Now the green upper strips the round and puts it into battery, it will pull the round and grab the next round and put it into battery. When ejecting the last round, it locks back. I'm I looking at the wrong problem? If so, what stops a mag from working in the green lower? Sorry guys. I don't mean to be stupid or so darn ignorant but your tutelage has been wonderful . If there's something I can do to help repay your assistance just let me know. Thanks all!