Just installed an MGI buffer into a new build and after about 100rds I got one or two weak primer strikes.  I also noticed the rate of fire as changing dramatically during my range time.  I pulled out the buffer and saw that the roll pin holding in the rubber bumper was actually walking itself out.  It was binding against the spring that surrounds the buffer shaft.  I knew then why the changing rate of fire cuz' the spring was getting hung up on this protruding roll pin.  
    Would that also cause a couple of light primer strikes??????????  The build is new as well but all the parts (bbl/upper/lower) used in it are relatively new and worked flawlessly on my other gun.  I'm wondering if the spring gets hung up enough the force coming back to the extension isn't enough to really seat it nicely.  Any thoughts............

the buffer tube should be screwed in far enough for the end of the tube to protrude over the shoulder of the buffer retaining pin and hold it in place.

sounds like the buffer tube isn't positioned properly.

   It's no the tube retaining pin I'm trying to describe.  It's the roll pin on the buffer itself.  The pin that holds the end rubber bumper inside the MGI RRB.   When it walks out the spring cannot compress and expand freely over the buffer shaft..  Does that help..?   I wish I had my camera handy...

Tweak just nailed it.                                                                                                                                                   Yes, it seems tha the three weak hits I had were all during FA.  I would fire some short bursts and then realize that the hammer was down on a live round.  I punched the roll pin back down and had no problem for about 100 rds.  Then when I got my last weak hit I pulled out the MGI and found that the pin had come out again.   I think it's got to be the culprit but I thought I would ask the experts for any other areas I need to look......  I expanded the roll pin slightly and punched it back in.  Haven't had the opportunity to test it though.............Thnx

As for the light strikes, It could be that the roll pin binding is causing the hammer to come down on a unlocked bolt (lack of locking force).

If staking in the roll pin does not solve the problem, you may want to check the auto sear release timing.    The auto sear should be releasing the hammer when the carrier gets around .083'ish off the barrel extension.  To figure out the timing gap, use round feeler gauges, or drill bit (mic'd) to determine the release gap of the sear.

Depending if this upper/BC combo is working on other lowers, either adjust the auto sear on the lower for the correct release, of if it a upper only problem (carrier), then adjust the carrier trip point (read helps to have a factory rig that is totaly in spec to solve the problem).

Quoted: Boog, pretty sure he's talking about the 1/8" spring pin that retains the anti rebound buffer on the rear of the buffer itself not the buffer retainer. I know, we get that one A LOT.

OOOPS!!



that's what I get trying to respond too quickly when I'm late for a meeting.

my bad.

Tweak, don't feel so bad,
I have trying to use wireless hot spots to get on the net.  When I do seem to find a connecting, it's like watching ice melt waiting for the pages to load.

Hey Tweak....... I would lose my friggin' mind if I lost my dsl for a week.  Thnx for the input.  The MGI weighs in a a whopping 7.2oz.  I've staked the roll pin on both sides and will test it this weekend at work.  I'm thinkin' the roll pin binding the spring has got to be my problem.  I'll re-post with results... thnx
   

May as well check the auto sear release gap before you go out as well.

Again, just use the back end of  two drill bits (one mic'd @ .080 and one mic'd @ .100) to check the release gap (placed  the ejection port, and between the barrel extensionface and the carrier face).  With the trigger held back and you riding the charging handle down, the hammer should be released off  the sear with the.080 bit/gap, but not on the .100 bit/gap.

If the hammer is released with the carreir .100 or father off the barrel extension, then the problem is too advanced of a release timing, and not failure to lock up or bolt (carrier) bounce.  With the added slowing cycle function of the MGI buffer, the carrier will be traveling even slower than norm, and the hammer is going to follow/strike the back of the carrier (firing pin still blocked) before the action has even begun to lock up (read hammer down on a unfired round in the chamber).

Cool technique Dano523... I'l give it a look.   Is there a esay fix if I find a problem with the gap?

Quoted: Cool technique Dano523... I'l give it a look.   Is there a esay fix if I find a problem with the gap?

The correction is easy (read many areas that can be used), it's the part where you figure out wither the lower or upper is out of spec, and which unit/part needs to be brought back into spec that gets a little harder.