Compass Lake NM Rifles?

[Danny]

Hi,
I am trying to figure out a problem with an AR that I built. If anyone here has a factory built Compass Lake AR with one of Frank's adjustable front sight bases on it, can you check to see if the front sight base is pushed all the way back against the shoulder of the barrel immediately behind it? I suspect yes, but knowing what others have would help.

Thanks,

Danny

[PhillipM]

Mine is against the shoulder. Krieger barrel if that matters.

[BigMo]

Yes- On mine it is.
Are you having trouble with the amount of gas you're getting?
Or in other words: Is the barrel port and front sight assy gas port not lining up?

[Danny]

Thanks for the help guys. That is the way I have set mine up, and assumed Frank did the same, but in my quest to find my problem, I am leaving nothing out of scrutiny. When I set up my A2 Bushmaster with a float tube (prior to this build), the front sight was not against the shoulder, but the starting point for the rifle was completely "Issue" with taper pins holding the front sight. Obviously, when the GI handguard cap was removed for installation of the float tube, there was space between the shoulder of the barrel and the front sight where the cap used to be. Frank, then, as I assumed (and as he should do) has located the barrel shoulder forward to take up space from the missing cap. I will post more on my issues in a while.

Danny

[Danny]

A few years ago, I used my AR at the National Matches. I popped some primers. I put the rifle away for a couple of years. When I went to use it again, I found that the bolt would not lock back on the last round. I cleaned the rifle thoroughly, especially in the areas around the trigger, the bolt lock and the buffer/buffer tube. I think that I probably changed out a bolt lock set, as well as stoning the back surface of the bolt lock to make sure it was operating freely. I cleaned out the magazine, changed the spring, and might have even tried another magazine. I put a new buffer spring in. Nothing changed anything. It was asked if I thought that my front sight and gas port were not lining up. That was somewhat of a thought, but knowing Frank's machining, I considered it highly unlikely. I can only assume that the issue is that I am somehow losing gas (least likely), or impeding bolt travel. I have come to the conclusion that I may be impeding/retarding bolt/buffer movement by greasing the buffer and buffer tube. Now, I have always done this in my Bushmaster, but that does not mean that it is proper or will always work. Someone also mentioned the vent hole in the upper buttplate screw. Neither of mine have that, but one lower works flawlessly. Through research, I have come to conclude (most likely) that this is a drain hole for battle conditions and not to relieve pressure between the back of the buffer and the closed end of the buffer tube. From memory, it seems that the clearance between the buffer and tube is enough to equalize pressure on both sides, and anyway, your shoulder covers the vent hole during firing. I am wondering if my greasing might, with no screw vent present, be overcoming the built in clearances, causing just enough pressure build up behind the buffer to impede some rearward velocity. I noticed something odd with my buffer that I will touch on in another post.

Once, in the past, with my Bushmaster, I was able to get the rifle to malfunction by greasing the bolt/receiver area like a Garand. I stopped doing that there, and my problems went away, though I continued with greasing the buffer/buffer tube. That is another reason why I think that greasing the buffer/buffer tube in this rifle might be part of or all of the trouble.


Danny

[Danny]

The only other thing that I have noted, in addition to the above, is an issue with my buffer. I do not know if it would cause a problen, but I have little else. I notice that when I close the upper and lower, as the rear of the bolt carrier bottom touches the buffer, sometimes it imparts a rotational motion to the buffer. This only happens with the buffer in certain rotational positions in the buffer tube. What appears to be happening is that the front face of the buffer has a high spot, or the face is not perpendicular to the centerline of the buffer. I am sure that if I were to put the buffer in the lathe and indicate off of the front face, I would find some runout.

Danny

[PhillipM]

A few years ago, I used my AR at the National Matches. I popped some primers. I put the rifle away for a couple of years. When I went to use it again, I found that the bolt would not lock back on the last round. I cleaned the rifle thoroughly, especially in the areas around the trigger, the bolt lock and the buffer/buffer tube. I think that I probably changed out a bolt lock set, as well as stoning the back surface of the bolt lock to make sure it was operating freely. I cleaned out the magazine, changed the spring, and might have even tried another magazine. I put a new buffer spring in. Nothing changed anything. It was asked if I thought that my front sight and gas port were not lining up. That was somewhat of a thought, but knowing Frank's machining, I considered it highly unlikely. I can only assume that the issue is that I am somehow losing gas (least likely), or impeding bolt travel. I have come to the conclusion that I may be impeding/retarding bolt/buffer movement by greasing the buffer and buffer tube. Now, I have always done this in my Bushmaster, but that does not mean that it is proper or will always work. Someone also mentioned the vent hole in the upper buttplate screw. Neither of mine have that, but one lower works flawlessly. Through research, I have come to conclude (most likely) that this is a drain hole for battle conditions and not to relieve pressure between the back of the buffer and the closed end of the buffer tube. From memory, it seems that the clearance between the buffer and tube is enough to equalize pressure on both sides, and anyway, your shoulder covers the vent hole during firing. I am wondering if my greasing might, with no screw vent present, be overcoming the built in clearances, causing just enough pressure build up behind the buffer to impede some rearward velocity. I noticed something odd with my buffer that I will touch on in another post.

Once, in the past, with my Bushmaster, I was able to get the rifle to malfunction by greasing the bolt/receiver area like a Garand. I stopped doing that there, and my problems went away, though I continued with greasing the buffer/buffer tube. That is another reason why I think that greasing the buffer/buffer tube in this rifle might be part of or all of the trouble.


Danny

Mine is a 2002 Bushmaster built by Frank, sold through the CMP. I had the exact same problem come up, the bolt wouldn't lock back and eventually I discovered the carrier key had come loose. Somewhere I read this is a common problem on Bushmasters of that era so I sent it to compass lake and they staked the screws.

[Jim in Salt Lake]

... I discovered the carrier key had come loose.

+1 on that. Have had that problem four times with different rifles (Armalite and RR National Match). When the carrier key gets loose enough, the bolt won't go back far enough to strip another cartridge from the magazine. It's something to look at every time you clean your bolt carrier. I keep a spare bolt carrier and bolt in my stool.

[BigMo]

FWIW:
I wouldn't bother looking at the buffer/spring and the greasing of it.
You'd have to pack ALOT of grease to get it to bind.

What I do is this:
-see if good factory ammunition solves it.
-Make sure your magazines are good quality and work. Test with known good ones.
-Switch out the bolt/carrier with a known good one.

#2 and#3 mean you have your answer.

I'll say this again, I grease my buffer tube/spring and you would have to stuff that puppy with a lot of grease before it bound up.

[Andouille]

The only other thing that I have noted, in addition to the above, is an issue with my buffer. I do not know if it would cause a problen, but I have little else. I notice that when I close the upper and lower, as the rear of the bolt carrier bottom touches the buffer, sometimes it imparts a rotational motion to the buffer. This only happens with the buffer in certain rotational positions in the buffer tube. What appears to be happening is that the front face of the buffer has a high spot, or the face is not perpendicular to the centerline of the buffer. I am sure that if I were to put the buffer in the lathe and indicate off of the front face, I would find some runout.

Danny

That's abby-normal, in my experience. You might as well do a thorough flush and clean of the buffer tube and spring while you're at it.

If you were blowing primers, something that happened to me once was that a primer got blown completely out of its pocket, and migrated back into the buffer tube somehow and was locking up the rifle. I would have thought that impossible, had I not done it myself. This in a "Leg" match and dang inconvient when you're chasing those last six points, I'm a-telling you.

In additional to what BigMo stated, switch out the buffer with a known good one as well. Inspect your buffer to see if the plastic tip (grasping at the unlikely here) has fractured

[Danny]

I talked with Bunny at Compass Lake a couple of days ago, and she gave me some unusual things to check that it could be. When I checked one of them, the diameter of the bolt stem, I found that it was undersized by pretty close to .010". It seems that after I popped the primers at the National Matches, I cleaned the $h!t out of the rifle because of the carbon from popped primers. It seems that I probably cleaned the tolerance off of the bolt stem while at it! I will replace at minimum the bolt and also the bolt carrier, in case I cleaned that too well, also. This cleaning seems to be what made the rifle start to malfunction "while it was in the safe", and also why none of the regular fixes had any effect, but I won't be sure till I try the rifle in the spring.

Danny

[Danny]

Ok,
I finally got out to test my rifle, and with my previously good loads. As a recap, this is what I changed:
Bolt Carrier
Complete Bolt
Buffer.

I fired 15 rounds today and the rifle functioned perfectly. It seems that the bolt stem being undersize was causing the problem by leaking gas.

Thanks for the help guys,

Danny