Help me troubleshoot

[rxer311]

Took out my newly renovated rifle today and I was having some intermittent problems with failure to eject.

It is a Rainier Arms Select barrel which is a stainless 5r 1:8 twist middy. It has been cut to 13.7" and has a KX5 pinned. Addax tactical chrome BCG. Standard Carbine weight buffer and spring.

I was shooting PPU 5.56 and Federal 5.56 55gr.

The first 30 rounds went through without a hitch. Then, I started having intermittent failure to ejects. Some would stovepipe, and others would stay stuck in the upper receiver and get jammed with the next round being picked up.

I didn't think that I was having any sort of gassing issue because every round that did eject landed in a perfect little pile at the 4 o'clock position. The other thing that happened is I had a failure to eject on the last round of a magazine but the bolt did lock back. This tells me that it is cycling fine.

I took out the BCG and was inspecting my bolt and it looked good. The extractor spring did feel really light. I could push on the extractor and easily push it in. I think this is the issue. I went to the local gun store and they also felt this was the most likely culprit. I added an O-ring to the spring and the gunsmith did a test fire (but only 3 rounds) and didn't have any issues.

I wasn't able to get back to the range to put more brass down range, but I am hoping this is now fixed.

Do you think I made the right diagnosis?

[Battle Cock]

The extractor spring would be my first guess as well. A damaged extractor would be my second. But, any guesses we can make here will only be guesses. Testing it at the range will be the only thing which will tell you if you've diagnosed it correctly.

[Eric]

The extractor, extractor spring (http://www.weaponevolution.com/forum/showthread.php?t=373) and insert would be a good starting point. While the O-ring might get it running, I would also replace the extractor spring. I would also detail strip the bolt, to include pulling the ejector pin and spring. Debris can get jammed in there which binds up the movement of the ejector. If that spring is in question, swap it out as well.

Did these problems start after the barrel modification?

[rxer311]

I had problems with this in the past for the first few rounds before the modification. It only lasted for 1 magazine and then 700 rounds later the issue never popped back up. Now after the modification of the barrel it started again...but very intermittently. I can go a whole 30 round mag without a malfunction and the next mag I might have 5 malfunctions.

[Iraqgunz]

I suspect the extractor spring is worn and you should replace. Also some food for thought. When you have someone chop the barrel it's also a good idea to consult with someone who understands AR's as it is usually a good idea to make sure you have a correct size gas port. It probably wouldn't hurt to replace that buffer as it is much too light. Your port size is around .080 and you could use an H2.

[rxer311]

With only chopping 3/4" from the barrel I really didn't think it would make a difference, considering I also used a KX3 which also causes back pressure. I contacted ADCO who did the barrel chop and they don't think I have a gassing issue since my bolt locks back.

I also did a test with 10 rounds, loading just 1 round in a magazine and it locked back every single time...but I only had one failure to eject.

[KevinBLC]

Off topic just a little, I'm wondering why you cut a barrel vs buying one that was already 13.7" Doesn't Rainier Arms offer a 13.7?

[Iraqgunz]

Be that as it may. I am more than certain that the gas port is larger than .076 and is closer to .080-.082 (at least the last few barrels I saw were) so I would be using a heavier buffer. I would also change the extractor spring as I mentioned.


With only chopping 3/4" from the barrel I really didn't think it would make a difference, considering I also used a KX3 which also causes back pressure. I contacted ADCO who did the barrel chop and they don't think I have a gassing issue since my bolt locks back.

I also did a test with 10 rounds, loading just 1 round in a magazine and it locked back every single time...but I only had one failure to eject.

[rxer311]

Even though it is a midlength cut to a shorter 13.7"?

[Iraqgunz]

I'm not sure how else I can explain this. The larger the gas port, the more gas flow. The more gas flow the more bolt carrier velocity you will have. To offset this and to slow it down you would want to use a heavier buffer. BCM 14.5" midlength barrels have a gas port of approx. 076. The RA barrels I have personally checked with pin gages measured out at .080-.082. I have tested BCM barrels using M193/M855 and they will cycle properly with an H2. So I am more than confident your weapon will cycle with an H2 as well.

If I was building this I would use either an A5 set up with the A5H2 buffer and green Sprinco spring or I would get a blue Sprinco carbine spring and an H2 buffer.


Even though it is a midlength cut to a shorter 13.7"?