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Posted: 1/21/2007 4:49:54 PM EDT
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Need some input to what fix I need to get my AR running. Gun is a dpms 16” barrel six position stock factory gun other than the modifications to the carrier and some clearance work done by M60joe for the RLL. Checked timing and operation of link appears to be working ok. 1. Pull trigger fires one round stops hammer has dropped new round in chamber may intermittently fire 2 or 3 rounds. It’s like it has a light hammer strike? 2. Remove fcg install select fire conversion retry, ran better 3 or 4 rounds but still will stop with new round in chamber hammer down. Remove bolt and inspect found 2 ring gaps lined-up cleaned reinstalled retry stopped a couple of times and started to run great about 300 rounds. I stopped because it fired when I let go of the trigger. ( I did not start with the select fire fcg because I knew there was a worn disconnector and it may cause problems but I had to try something) I will get the parts to fix before using again. 3. Reinstalled factory fcg and had the same problem basically a semi with a intermittent 2 or 3 round burst. What is going on do I need a stronger hammer spring? Sorry about the long post but I have a 3 hour drive to the cabin just to shoot full auto so I hate to get there and have this problem.  |
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Your description is a little confusing, but it sounds like one of your problems is bolt bounce, see this threadbolt bounce My head started hurting when you started describing switching out FC parts. I recommend you replace the complete FCG including springs with new stuff. CMMG has complete Full Auto LPK for about $70, get one. |
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Quoted: My head started hurting when you started describing switching out FC parts. Basically I changed fcg and it worked better but still did not work until I checked and adjusted the bolt rings. It runs ok in semi that’s why I questioned the hammer spring. With the factory fcg it will not run full auto. Sorry about your head I just wanted to give a complete description of what I did and the results. Some how the combination of messing with the bolt and fcg it worked Can you fix bolt bounce w/out reducing rate of fire |
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Yes, no, maybe. As stated, the hammer is striking the FP with it being blocked by the back of the carrier when the carrier bounces off the face of the barrel extension after lock up. The yes response is to retime the hammer/sear release so it strikes the FP before the carrier can bounce back. The problem to this Mac-jacking is that you will be walking a fine line in regards to timing around a specific ammo type/load. The NO response is that you just install a heaver buffer to control the carrier at lock up to prevent it from bouncing back open. The maybe response is that a standard H or H-4 buffer may all that is needed to solve the problem, and you may never notice a difference is cycle rate without a timer. |
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Thanks for all the info; this will be my plan for the next trip to the cabin. I’ll replace my hammer spring and make repairs to the fcg so I can have select fire. I’ll get a H2 buffer and a 9mm buffer install the H2 first and if it runs ok I’ll use the 9mm later possibly build a gun for it LOL. I did a search and found this chart for buffers; it seems that my gun is so close to running with just a hammer spring change I may not need to go to heavy with the buffer. If any one can make any other suggestions on parts I can take with me to try I just hate to drive 3 hours and not be able to get this gun running I would appreciate it. BUFFER WEIGHTS Standard Rifle - 5.15oz Standard CAR - 2.9oz H CAR Style - 3.77oz H2 CAR Style - 4.7oz H3 CAR Style – 5.6oz 9mm - 5.47oz, made of steel Special purpose buffers designed for suppressed SMG's or 9mm carbines using high pressure (+P+) ammunition 9mm A - 6.3oz CAR style buffer 9mm B - 7.1oz CAR style buffer 9mm X - 7.9oz CAR style buffer |
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I was haveing the same problems with light strikes and thought it was a worn hammer spring. I bought a few hammer springs and a H buffer. I tried the H-buffer first before I was going to change out the hammer springs and the rifle ran great on FA. 5 30rd. mag dumps and 3 mags in bursts all ran perfect! The H buffer stoped the light strikes and is runing great. I could tell it is running a little slower but not enough to really notice. Before you change out springs again just try different buffers. And the heavier you go it will go slower and slower. I was going to buy the MGI buffer but thought it would slow it down too much and did't want that. Good luck and keep us updated. |
To function test, Hold the trigger, Pull the Charging handle all the way back, then slowly ride the charging handle/the B/C all the way back forward. With the C/H ridden forward slowly, the hammer should not release. Now with the trigger still held back, pull the charging handle back just 2" from locked closed position, and let the charging handle go. With the B/C running forward loose a few inches under recoil spring tension alone (no mag in the rifle); the Hammer should be released off of the disco (via the link). If you are swapping uppers, then you may need to get a few tails in different thickness to adjust the link to each of them. If the link is set up to release the hammer with you riding the charging handle all the way forward by hand, then the RLL is set up to timing advanced per that upper combo. |
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I checked the operation of the link and found it to be working ok. The hammer was down so the link was tripping the disconnector. With the select fire parts installed gun ran ok don’t know if it was the hammer spring difference? Stock fcg no run, intermittently once or twice in 30 round mag may get 2 or three round burst. I have repaired the select fire control group and picked-up a H2 buffer and a 9mm. I plan to keep the select fire installed but out of curiosity will try the new buffers and I got a new hammer spring to see if I can get the stock fcg to run. It will be probably 2 weeks before I get back to the cabin to test; we sadly lost are local FA friendly range.  |
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Almost sounds like the link is kicking out to disco tune'd slot, and the trip/release is going advance (catching a upper/lower surface). On the mod'd burst kit (your select fire kit), is the disco tuned slot V'd or Square cut? Also, does this problem only happen on the select fire kit, or a standard semi FCG as well (safe-full only)? |
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