Help diagnose this malfunction

[Climbhard]

My PCC is a 7.5 barrel on SBR lower with a Hahn block. I’m using a CMMG bolt with the weight removed and a JP ScS. Three tungsten and green 308 spring. I’ve played around with steel versus tungsten weights and lighter springs to no avail. Shooting 147 gr Berry over 3.1 gr of titegroup @1.160. I still get these occasional malfunctions. It’s like the bolts not fully stroking to get the case to the ejector?  Any other thoughts?

[Aircooled6racer]

Hello: I think you need to bend the ejector over a little so it hits the brass more. Also check to see if the bolt is rubbing on the top of the ejector. Your buffer setup is pretty stiff for that load. I would shorten your reloads to 1.145" and try it again. Thanks, Eric

[Climbhard]

The ejection is pretty weak. I didn’t think the top of the ejector might be dragging. I’ll look into that. 

[Aircooled6racer]

Hello: The ejection may also be weak since you are over sprung. Look for a shinny spot on the ejector and also check to see if the block is loose. Thanks, Eric

[L9X25]

The extracted case should hit the ejector before it can strip a new round from the mag.  Since the photo shows it is loading a new round, the bolt traveled far enough to eject the case.  

 

I would guess that the ejector is too far away from the center-line (or too low) and it barely hitting the edge of the case.  This would lead to occasional  problems like you have shown.

Edited December 7, 2017 by L9X25

[compshootfl]

In my opinion, you are a little light on the Tightgroup....move it up a bit. I really don’t think you will notice much more recoil.

[stick]

7 hours ago, compshootfl said:

In my opinion, you are a little light on the Tightgroup....move it up a bit. I really don’t think you will notice much more recoil.

I wouldn't bump up the load at all.  In my PCC, 3.0gr of Titegroup behind my 147gr bullets is 973fps for 143 PF.  I ended up at 2.5gr for my 147gr loads.  My gun cycles fine.  I don't think it's the powder.  however, I do think his oal is long at 1.160.  My loads are 1.135.

Edited December 7, 2017 by stick

[TRUBL]

You NEED to bend the ejector over towards the center more......the right side of the ejector should be touch or really damn close to touching that wall on the bolt.....dragging is ok.

 

As for your springs and buffer weights.......heavy buffers and 308 spring are the devil. Don't care what anyone says......it's a non-debatable topic.

[gerritm]

Same type of failures at a match last weekend with another shooter. Similar set up with .308 spring. Bumped his loads up and gun ran fine. Even had the weight out. Talked him into Taccom ULW light buffer like I run in all my PCC's & AR's.

 

gerritm

[jrswanson1]

I had this same problem.  I had to use a heavier buffer (7 oz) to get it to work properly.

[MikieM]

I agree as to the recoil impulse being too light. We run into the same problems with our 19 and 2011 handguns.

Increasing the powder charge is one way to fix it, but I would rather match the charge to the buffer spring based on power factor. This is, of course, based on the premise that your bolt and buffer are what we commonly use.

Edited December 7, 2017 by MikieM

[L9X25]

I had a rifle that worked perfectly, I varied the recoil spring weights from 8 lbs to 16 lbs, and went from one extreme of buffer weight to the other (JP SCS) and it never caused a jam.  It made the gun feel very different, but it never caused a malfunction.  If you are short stoking, you will not strip the next round.  If you are stripping the next round, the bolt has cycled far enough to eject the previous round. 

 

This is either an extractor that is not gripping the case properly, or an ejector that is not aligned properly. 

Edited December 7, 2017 by L9X25

[Climbhard]

Thanks for all th feedback. I got it running good now. Left the ammo alone because at 2.9 gr I was making 131 PF so the 3.1 I was loading would seem to be sufficient. I bent the ejector in towards the center to where it was just lightly riding on the inside f the channel in the bolt. Then ended up settling on three steel weights and one tungsten and the black spring. Cases eject about 10-12 feet dead right and double taps at 5 yards are about 1 inch apart. When I run it with the suppressor on double taps are almost in the same hole. That’s some real fun right there.  Here’s a picture.  I’ve since replaced the fast fire with a Holosun. 

Edited December 7, 2017 by Climbhard

[Aircooled6racer]

Hello: So your buffer weight was too much and the spring was too strong. Try the green spring with the 3 steel weights and 1 tungsten. It will feel great and work well. Thanks, Eric

[Climbhard]

I’ll no doubt play around with it a little more but I think I need to shoot it more as is to get a little more experience with it. I’m new to the platform. Bending the ejector in toward the center of the bolt I think was key to the ejection problem (along with being over buffered).