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Posted: 1/7/2008 6:08:13 AM EDT
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Greetings I bought my first 16" DPMS M4 last year and it worked flawlessly. Because I can't leave well enough alone, I installed a Jewell trigger. These triggers are awesome and greatly improved overall accuracy. I had an above average armorer perform the install. I installed an A2 stock for my oversize cheek. I later noticed the hammer has a distinct half cock in it's travel. This is where the problems begin. I am a regular reader of this forum and I have read posts on low mag feeds, Short stroking and bolt binding and these are the symptoms I am experiencing. Typically, it occurs when I release the charging handle and send the round to carry into the chamber on it's own momentum. The bolt carrier never seems to close all the way and sometimes the round hits the ramp and jams. Sometimes the bolt will slam shut, but you can tell it is slow making it's lockup. Occaisionally when the bolt does shut it binds so badly that I can't pull the charging handle back to clear the misfeed. The key on the carrier seems to be mating with the gas tube without any interference. I have disassembled the Jewell Trigger and reinstalled using aftermarket anti-walking pins. The half cock on the hammer travel is still there, the odd shape of the hammer itself worries me. The stock hammer was smooth without the sharp cutouts. The anti-walk aftermarket trigger pins have reduced the half cock hammer travel problem but have not totally eliminated the problem. Is this normal? I carefully adjusted the Jewell trigger from the factory instruction manual, I called Jewell in San Marcos Tx and could not locate a tech to give advice. I tore down the lower receiver and rebuilt it with new DPMS parts. I inspected each part during the rebuild. Next I moved to the DPMS upper and replaced the bolt (new) and gave the bolt carrier group a look over. Everything is lubed. I replaced the buffer, tube and spring (new parts-DPMS). ammo and mags: I have used mil-spec mags and a colt (20 rd) (blocked to 5) mag. I have tried black hills and federal premium ammo. I am out of ideas. The good news is I now have enough parts to build another rifle. Is the bolt binding caused by low mag feed feed and\or short stroking? Has anyone had a similar problem that relates to jewell triggers? Should I focus on the upper receiver? what do I look for? Thanks in advance robo |
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Greatest hits, When the A-2 stock was installed, you did installed the correct longer spring and longer buffer for the longer tube, and did not use the carbine spring and buffer? With the B/C in hand, you have confirmed that the firing pin collars is either flush or just slightly below the ramp of the carrier when flushed out against the back of the carrier? On the jewel hammer, you have checked out the very top of the hammers contact pad (over the top of the edge) to confirm that it's not catching the FP collar back on the forward-stroke. If the hammer catches the FP collar on the forward stoke, the jam will be with the bullet just out of the mag with the tip of it just into the barrel feed ramps (read FA will be no help getting the B/C any more forward). You have set the trigger up for a break weight of 4.5 LB? Granted that the trigger can be set up lighter than this, it does start to have problems is not set dead-on with the less than legal CMP pulls limits (read you start bumping the trigger and the hammer is release before the B/C lock home and the safety feature of the system kicks in with the hammer catches the FP collar. Also to point out, if you are going to explore the lightest limits of what the trigger can be set, you have to tune the disco to not release the hammer until the trigger is dam near at rest (read if this is not done, then you bump the trigger during charging cycle, and the safety feature kicks into prevent hammer follow through). When you pull back on the CH, you should feel the hammer cock/cam back and go from behind the carrier to start riding the bottom of the carrier. From that point on/back the pull of the CH should feel constant. If the pull gets harder 3/4 of the way back, then you have either the hammer wedging or the recoil spring is having problems and has completely compressed before the end of the reward stroke. P.S. Welcome to the site!!! |
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Reinstall as many of the stock components as you can. FCS, stock, etc. Return the weapon to it's last known functioning state. Then change one component or group at a time. I doubt it is the upper, as it "worked flawlessly" prior to your additions of the trigger and the stock. Spare parts are never wasted money. I have spare parts for firearms I do not even own. |
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Yes sir. I did replace the A2 buffer and spring with the correct length, not the carbine versions. I have not confirmed that the firing pin collar is flush and just below the ramp, but it is now on my list. The Jewell trigger is adjusted to the factory limits to simulate a single stage trigger, but yes- It is less than 4.5lb. Your description of the malfunction is spot on. Sounds like I have some trigger adjustments on the todo list as well. Thanks for your input- robo |
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