AR Sponsor
Posted: 4/22/2015 1:02:17 PM EDT
|
I just built a 16" mid length carbine. It is a 16" BCM upper with a Aero Precision lower. It has a Rainier Arms bolt carrier, BCM gunfighter charging handle, 37 coil carbine buffer spring, Spikes Tactical T2 carbine buffer. The lower was built with a standard CMMG lower parts kit.
My problem is the bolt does not want to stay open after last shot or on an empty magazine. When comparing to other AR's I have built using the same components the bolt is not going back far enough for the bolt catch to contact the front of the bolt and stop it. It won't work with a empty mag or when pulling back the charging handle and engaging the bolt catch. The bolt catch moves freely and it is working but the bolt just doesn't go back far enough to catch the front of the bolt face. By the way the buffer tube is a mil-spec tube. Any Ideas? I think I have tried everything. |
|
Quoted:
I just built a 16" mid length carbine. It is a 16" BCM upper with a Aero Precision lower. It has a Rainier Arms bolt carrier, BCM gunfighter charging handle, 37 coil carbine buffer spring, Spikes Tactical T2 carbine buffer. The lower was built with a standard CMMG lower parts kit. My problem is the bolt does not want to stay open after last shot or on an empty magazine. When comparing to other AR's I have built using the same components the bolt is not going back far enough for the bolt catch to contact the front of the bolt and stop it. It won't work with a empty mag or when pulling back the charging handle and engaging the bolt catch. The bolt catch moves freely and it is working but the bolt just doesn't go back far enough to catch the front of the bolt face. By the way the buffer tube is a mil-spec tube. Any Ideas? I think I have tried everything. Was the spring installed on the bolt catch? Was the gas block properly aligned? |
|
First off, pull all the way back on the charging handle, and look where the bolt face stops against the back edge of the ejection port window. The bolt face should stop 1/8" to 1/4" in front of the back of window edge. Also, when you are pulling back on the charging handle, the last inch of pull should not increase in tension that the middle to back of pull. If it does, then either the spring is coil binding out, or you have FCG wedging going on instead (disco spring not installed large coil side down into the trigger tail, or the hammer tail too long)
To weed out problems with the charging handle itself, with the CH pulled all the way back, push back on the bolt face itself and see if the bolt will go back any farther. If it does, then you the CH is defective. Next, need to check the depth of the receiver extension void. The Carbine spring should be around 10.5" long, and the depth of the carbine receiver extension should be 7" from the lip of the tube, to the back of the inner void. If your butt stock system uses a butt stock bolt, then make sure that the butt stock bolt is not too long, and now protruding into the back of tube void to limit the buffer (instead of the buffer bumper being able to contact the inner void back wall cleaning instead). Now shotgun the upper open and insert a empty mag. The catch tab should cleaning catch the back of the follower, and raise the catch all the way up. If the you have a know good mag with a strong follower spring and the catch is not binding in the lower receiver (just spring tension pulling it back down), then chances are when you install the bolt catch, you did not clean out the bottom of the spring channel and crap in the bottom of the channel has the spring over compressed. As for the ST-1 buffer, bring me up to speed why you went with the heaver buffer. The standard weight buffer should work fine, and the heaver buffer is reserved for ammo heaver than 62gr (slower burning power, which will increase port pressure, causing the bolt to unlock too soon, and the heaver buffer is used to slow the unlock back down to normal). Hence during live cycle, if the rig should be using a standard weight carbine buffer, and you slap a H series buffer in it, you chance the bolt unlock too late now, and the rifle short stroking instead. |
|
To answer a few of the above questions. The buffer spring is correct. It measured 10.5" and had 37 coils.
The bolt face stops about 3/8" in front of the catch. That is as far back as I can get the bolt and carrier. Basically the carrier will pull back far enough for the catch to contact on the front of the carrier but not the bolt face. When looking down the receiver extension it looks to me like there is a ridge about 1/2" from the bottom inside the tube. It looks like the spring could possibly bind up on this but I am not sure. Also when comparing this mil spec buffer tube to a commercial tube it is a good 3/4" or more shorter. I realize these two types of tubes are different in size but are they supposed to be that much different in length? My next possible fix is that I have ordered a new buffer tube to try. It is a Vltor 6 position mil spec made from 7075 and is 8.1" overall length. This was the longest 6 position I found and I'll see if that fixes the problem. Everything else you guys mentioned above I checked out and I am hoping this new buffer tube is the fix. Thanks for all the advice and I'll let you know how it all worked out. |
|
By the way I measured the inside of the buffer tube from the lip to bottom of the tube and it is less than 7". It is about 6 5/8" to 6 3/4".
I am beginning to think this buffer tube is the problem. I should know tomorrow as my new buffer tube should be here in the mail. |
|
Quoted:
By the way I measured the inside of the buffer tube from the lip to bottom of the tube and it is less than 7". It is about 6 5/8" to 6 3/4". I am beginning to think this buffer tube is the problem. I should know tomorrow as my new buffer tube should be here in the mail. What you got was a receiver extension tube for the bb airsoft rifles, and why the depth of the void is not deep enough for an actual AR-15 rifle instead |
|
Quoted:
What you got was a receiver extension tube for the bb airsoft rifles, and why the depth of the void is not deep enough for an actual AR-15 rifle instead Quoted:
Quoted:
By the way I measured the inside of the buffer tube from the lip to bottom of the tube and it is less than 7". It is about 6 5/8" to 6 3/4". I am beginning to think this buffer tube is the problem. I should know tomorrow as my new buffer tube should be here in the mail. What you got was a receiver extension tube for the bb airsoft rifles, and why the depth of the void is not deep enough for an actual AR-15 rifle instead Well I got the new buffer tube on and that was the problem. This new Vltor A5 tube is longer and the gun functions with the bolt stop correctly. In the Vltor instructions it says to use only the Vltor buffer and spring. I am using a carbine spring with a Spikes T2 buffer. I haven't shot it yet but I would assume the setup I have will work. The previous setup worked perfectly except for the bolt holding open. I fired 70 rounds through the old setup with zero malfunctions and very good accuracy. I'll take this new setup out and try it later. Thanks for all the help, it was much appreciated. |
|
Quoted:
By the way the buffer tube is a mil-spec tube. Quoted:
By the way the buffer tube is a mil-spec tube. Quoted:
Quoted:
By the way I measured the inside of the buffer tube from the lip to bottom of the tube and it is less than 7". It is about 6 5/8" to 6 3/4". I am beginning to think this buffer tube is the problem. I should know tomorrow as my new buffer tube should be here in the mail. What you got was a receiver extension tube for the bb airsoft rifles, and why the depth of the void is not deep enough for an actual AR-15 rifle instead Where did you get the buffer tube from, OP, and what led you to believe it was mil-spec? I'm not criticizing. I just want to know what to be wary of when I shop for stuff. |
|
If you bought the Vltor A5 receiver ext, you cannot use a standard length buffer or standard length carbine spring as the A5 uses it's own proprietary buffer and rifle length spring. You will end up damaging your lower receiver.
If you bought this |
|
I found that out after I bought the buffer tube. I have ordered the proper spring and buffer to put in it before I fire it.
If anyone knows however could this buffer tube be used with the rifle length spring and a Spikes T2 buffer? Why would the lower be damaged using a different buffer? The only difference between the Vltor buffer and the Spikes would be the weight and length. Vltor makes lighter buffers to help tune the gun should it need it. |
|
Quoted:
I found that out after I bought the buffer tube. I have ordered the proper spring and buffer to put in it before I fire it. If anyone knows however could this buffer tube be used with the rifle length spring and a Spikes T2 buffer?Nope Why would the lower be damaged using a different buffer? The only difference between the Vltor buffer and the Spikes would be the weight and length. Vltor makes lighter buffers to help tune the gun should it need it. It's the length difference of the buffers as the buffer acts a stop for the bcg, too short and the bcg collides with the rec. ext. ring and will likely cause a crack. |
|
Quoted:
Well I got the new buffer tube on and that was the problem. This new Vltor A5 tube is longer and the gun functions with the bolt stop correctly. In the Vltor instructions it says to use only the Vltor buffer and spring. I am using a carbine spring with a Spikes T2 buffer. I haven't shot it yet but I would assume the setup I have will work. The previous setup worked perfectly except for the bolt holding open. I fired 70 rounds through the old setup with zero malfunctions and very good accuracy. I'll take this new setup out and try it later. Thanks for all the help, it was much appreciated. Quoted:
Quoted:
Quoted:
By the way I measured the inside of the buffer tube from the lip to bottom of the tube and it is less than 7". It is about 6 5/8" to 6 3/4". I am beginning to think this buffer tube is the problem. I should know tomorrow as my new buffer tube should be here in the mail. What you got was a receiver extension tube for the bb airsoft rifles, and why the depth of the void is not deep enough for an actual AR-15 rifle instead Well I got the new buffer tube on and that was the problem. This new Vltor A5 tube is longer and the gun functions with the bolt stop correctly. In the Vltor instructions it says to use only the Vltor buffer and spring. I am using a carbine spring with a Spikes T2 buffer. I haven't shot it yet but I would assume the setup I have will work. The previous setup worked perfectly except for the bolt holding open. I fired 70 rounds through the old setup with zero malfunctions and very good accuracy. I'll take this new setup out and try it later. Thanks for all the help, it was much appreciated. As stated above, DO NOT shoot a rifle with the A5 buffer tube and Spikes buffer. You WILL damage your lower, on the first shot. The buffer is what is supposed to stop rearward travel as it bottoms out against the back of the tube. If you use a buffer that is too short, it will no longer be able to stop rearward travel and instead the bolt carrier key will run into your lower receiver. This will crack the lower, damage the key, break the key off, or all of the above. |
AR Sponsor