Warning

 

Close

Confirm Action

Are you sure you wish to do this?

Confirm Cancel
PSA
Member Login

Site Notices
Posted: 12/13/2004 5:33:13 PM EDT
I bought and installed one of these a couple weeks ago. Everything was really smooth (great trigger by the way) until I had a hundred or so rounds through it... then I started getting an occaisional failure to fire (weak hammer strike) which has progressed until now I get several failures from each magazine... upon inspecting the assy., I noticed that the very top of the hammer looks to have 10 or so horizonal striations (tiny grooves) peened into the face of it....
these were not there when I installed the trigger... so the very top of the face is obviously striking something... it would also seem that the hammer face is not as hard as it should be...

With the Upper off the lower, I "dry fired" the unit and the hammer sure doesn't fall with near the force that the GI spec one does... which is to be expected with the lighter springs (springs are installed correctly with the "roller" part of the hammer spring bearing against the front of the inside of the lower.

Anyway I bought it from Georgia precision and have a call into them about it but no one has returned my calls as yet... any ideas?


Gun runs fine with the BM trigger group but accuracy sucks a big one due to the enormous amount of effort required to work the trigger.  Gun shoots just under 1" with the Jewel

Link Posted: 12/13/2004 5:35:16 PM EDT
PS ammo has nothing to do with the problem, LC, Black Hills, Winchester same ole same ole
Link Posted: 12/13/2004 11:08:13 PM EDT
The carrier, if the marks are on the face of the hammer’s firing pin contact pad, is causing the dents/marks as it comes back and resets the hammer.  Although the finish should be scraped off, the surface should not of dented.

If the dents are on the very top of the hammer, then chances are it's the firing pin collar that is being caught by the hammer as the carrier moves back to close/lock. If hammer firing pin binding is the case, then it may be as simple as this slowing the carrier/feed to the point that the bolt is not fully locking up*. Hence, the firing pin is not completely reaching the primer at hammer strike (firing pin can only bottom out in the bolt when the bolt is fully locked closed).


Now it the bolt is fully locking up,

 When you first set up the FCG the hammer spring is new.  Over time, the hammer spring will take a set.  In taking a set, the spring has lost some of the original tension.  Now if you are using a trigger break gauge to set the trigger break at a pre-determined break weight, then you can add more tension back to the hammer spring by simply moving the spring leg up the star a few notches. But, lets take this one step further and just guess that you want to set the trigger at the lightest break weight possible.  When setting the FCG down to the 2 lb light set, you give up hammer speed, and with the hammer already lightened, mass too.  The spec for protrusion on the firing pin for full protrusion out of the bolt is .032 to .038 (standard FCG).  With the Jewel FCG set this low, you need to confirm/tune the firing pin to the max protrusion within spec.  To do this is as follows,

Use #400 sandpaper and clean up any milling/end burs on the back of the bolt (were the firing pin collar bottoms out). To do this, just roll sand the bolt with the paper on your thumb to allow the paper to contour to the back angle.

Now with the bolt back surface clean of end burs, insert/bottom out the firing pin in the bolt (out of the carrier) and check the protrusion. Using the measurement that the pin comes up short on bolt face protrusion (under .038), set back the firing pin stop collar the same amount to bring the firing pin up to the needed length to allow the lightened/less applying force hammer to reliably ignite the primer.

To add, while you have the firing pin chucked up in the lathe/drill, bevel the front and rear edges of the firing pin collar.  This allows the hammer to glide more freely over the hammer on both the rearward and the forward stroke.



*Now to add before Tweak chimes in,
The non-shrouded AR-15 carriers are the evils of the world.  In Tweaks eyes, Colt was in league with the devil when they invented the safety device. The fact that many other manufactures have just went on to copy the design must be that they too worship the wrong Gods. His directions will be to either change out the non-shrouded carrier to a M-16 shrouded one, or to use RRA's new shrouded carrier if there is concern on using MG parts in a Semi auto rifle.

Myself, since I always love a challenge, I just re-work the hammer and firing pin collar.  First step is to check the collar against the carrier ramp.  If needed, the firing pin stop collar outer edge is turned down to be flush with the start of the carrier ramp. Next is to bevel/relieve the top of the hammer’s firing pin contact pad to allow the firing pin to make contact with the hammer away from the top edge and glide down the retained hammer. This may sound simple, but you have to remember that the top edge of the hammer is the cam point, and if you remove/bevel too much from it, then the carrier will not lower the hammer to the point that the disconnector will engage and retain it during re-charge. If in question on the amount to bevel, take a few strokes, smoke the surface with a sharpie maker and test cycle. Once you have confirmed that the firing pin collar is contacting the hammer pad just below the top edge on the forward stroke (into the bevel), you are done.
Link Posted: 12/14/2004 3:39:00 PM EDT
Call Jewel direct.     I   put one in my varmint ar a couple of years ago and had the same problem .     After talking to one of their guys they sent me a new spring.  No more problem.   Very nice folks to deal with.
Link Posted: 12/15/2004 7:14:37 AM EDT
The Jewell has a safety notch to catch the hammer if the disconnector doesn't.  If you have too little sear engagement or too low a second-stage weight, the hammer may follow the bolt down and be caught in the safety notch (similar to a half-cock notch).  When you pull the trigger, the hammer falls but doesn't have enough energy to ignite the primer.  The instructions that come with the Jewell are less than clear, so take a look at these: http://www.highpowerrifle.com/Jewell.htm   The Jewell works beautifully when properly set up, but is easy to misset.  Don't take the adjustments right to the edge - always back off a bit from what just works to have a reliable trigger.  I had to readjust mine after ~1000 rounds as it wore in, but it's been totally reliable for >15,000 rounds.
Link Posted: 12/15/2004 8:19:49 AM EDT
Thanks Ronemus!  That's just what I was looking for!

Steve
Link Posted: 1/8/2005 6:06:01 PM EDT
I meant to update this thread long ago.  Thanks for all the help guys.  Turns out it was the overtravel adjsutment needed tweaking.  I had set the overtravel to bare minimum and the gun worked fine for a few hundred rounds until I started having the problem that led me to post here...

After following the link that ronemus pointed to (great instructions there by the way).  I was able to determine that the overtravel adjustment was the problem..... half a turn with an allen wrench and the gun hasn't skipped a beat over the last 500rds or so.

Dano also had some excellent ideas, and in fact the top of the hammer was being stuck by the firing pin retainer.... I followed his advice, smoothed out the nicks on the top of the hammer and it hasn't done it since.

THANKS GUYS!!
Top Top