Hammer follow

[mtnlvr]

I'm hoping to get some ideas on where to focus next on a firing issue with my project...now my New Year's Resolution to get running this year!

Background...my father began this semi auto conversion German MG42 reweld build a number of years ago and got it to the point where it would fire a round but wouldn't eject or feed another round. Now I'm trying to smooth / tune it to run safely and reliably.

I got it to feed / eject nicely, but what I've found is that the hammer has a tendency to follow the bolt requiring me to operate the charging handle to reset the hammer.

The FCG is the AR15 variety which I've tuned such that the hammer and disconnect or clearance is around 0.002".

The manual cycling function checks I've done show no apparent issues, the trigger, hammer, disconnector, etc seem to function properly every time. It's with the speed of live fire that the hammer follows the bolt.

So, why does the hammer not stay hooked on the disconnector?

One thing I've noticed is the hammer spur striking the rear lever of the disconnector. I've ground a bit off of the hammer spur and reshaped the disconnector to get a little more clearance but it's still making pretty solid contact. I tried to insert pics but they wouldn't show.

Any ideas on what to try next? Is this the bolt moving too fast causing the hammer to float and slam into the disconnector?

[blackreichswehr]

just what type grip handle set up are you using?








just what type grip handle set up are you using, OEM W/box, BRP design,etc. something completely home made ?????

[mtnlvr]

I'm not sure of the make of the grip stick. Here's a pic of it. Never mind my trigger travel limiter.

Here's a pic looking into the grip stick showing where I've relieved the disconnector (blue marker) and the fresh wear from firing a few rounds.

Here's the hammer spur. I've removed some of the spur (also blue marker) which shows where it is contacting the disconnector.

[blackreichswehr]

check and see if the hammer tail is bottoming out, that can cause hammer follow or not resetting. i'll follow you along and see if we can fix this. it's going to like a doctor telling you what's wrong on the telephone.

[mtnlvr]

Yes...the hammer tail (or spur as I called it) is bottoming out on the tail of the disconnector with pretty good force. If you look closely in the pics, I've already clearanced the hammer tail and disconnector some but it is still contacting with force. The pics show

How much further down should the bolt move the hammer beyond the point of catching the disconnector? It's difficult to measure, but this setup seems to only move the hammer ~.020" beyond the point of catching the disconnector. This is using a method of measuring that has probably .020" of error. For what it's worth, my AR15 seems to move the hammer closer to .050" beyond the disconnector catch point...very close to making the hammer tail contact the disconnector. It too shows signs of wear from contacting the disconnector.

Maybe I need to get the bolt to move the hammer further.

[blackreichswehr]

yes, you are getting hammer drag. in your 1st, top photo, hammer face to left-- you need to radius the 90 degree a little @ a time-- and check. as well, radius the bird beak face just a little @ a time-- you 3rd photo that looks like you have Prussian blue on. if this was here in front of me , I could fix it. hope this helps you. if this has confused you or you don't get my drift, let me know and I will try to explain myself better.

[blackreichswehr]

and one more thing, a Wolf extra power spring might help?

[mtnlvr]

To clarify, radius the 90° refers to corner #1 in the attached image right? That will reduce the amount that the hammer is moved by the bolt (to catch the disconnector). Will I have to figure out a way to increase hammer travel then?

And radius the bird beak, that would be corner #2 in the image right? What does that affect other than hammer to disconnector clearance?

As for extra power spring, are you talking hammer spring? Or disconnector spring?

[blackreichswehr]

as I stated, it's like doctor on the phone. yes to #1- yes to # 2 -- extra power hammer spring. just look at the areas I mentioned. if you feel there not the problem, don't mess them up. look else where, fire control group, bolt height, rail system. bolt extension rearward--it's there somewhere. this is always a major problem , trying to fix a thing somebody started and walked away from.

[mtnlvr]

While waiting on the hammer spring I noticed the bolt has some roll to it...it rides a little higher on the left. Digging a little deeper I found the recuperarator wasn't able to lay flat in the corner. There was a bit of a weld that needed cleaning up. There's also a ~0.40" dent or deformation near the ejection port that needs addressing as is pushes up on the recuperarator causing it to sit high. I'll have to rig up some tools to reach in and push the dent back down. Maybe this will allow the bolt to ride a little lower.

[blackreichswehr]

any luck yet? did you happen to check disconnector spring --broken by chance or upside down. just thinking, sometimes its overlooked. you also said, ejection problems-- is the bolt going reward enough, caused by to much spring tension, ie, the coils impacting other or just by site the spring appears overly bound? this could cause your disconnector to not be retaining the hammer also. heck who knows? check it out.

[blackreichswehr]

there is one thing I over looked,( very important) did you or your father headspace the bolt and barrel? if not, do.

[mtnlvr]

I will be making a couple tools to press the dent out from under the recuperation tonight. Not sure I'll actually get around to trying it or not though.

I did pull the FCG out and looked things over. I did verify that the disconnector spring is intact and not upside down.

I'm pretty sure the bolt is travelling far enough. My father had some extraction issues but those seem to be in the past. Brass ejects with authority so I would think with the feeding reliable, that the bolt would be well beyond the minimum travel required for the hammer / disconnector interaction, but I'll pay attention to that .

What does headspace have to do with hammer follow? I'll have to check with my Dad on whether he used some gages or what.

[blackreichswehr]

headspace has nothing to do with hammer follow. as with any firearm before firing one round, this must be checked, your not making a toy. think about it, its your face, possible even your life, this will have to be your call. I have witnessed an out of battery explosion, it wasn't pretty--the fellows face and arm sliced open with hunks of brass, i'll call him lucky, because it could have been worse.

[mtnlvr]

I never interchange the word toy for a firearm.

Thanks for the clarification. The only headspacing I've done is using the various manufactured factory rounds in 8mm and 308 I had laying around and verifying that they allow lockup of the bolt into the barrel outside of the receiver.

I made up the tools, but never got a chance to work on the dent in the receiver. I spent the evening digging out my sump pump pit in the basement to replace the old busted up basin. Lots of fun.

[www.Prussia.us]

Just a quick note on the headspace, you would be surprised how many barrels/bolts match up just fine and how many do not, once put to the gauges.

What is the diameter of the exit hole on your booster?

[mtnlvr]

I've been using the original one that is 12.6mm for both 8mm and 308. According to my notes I also have an 11.5 and a 13.0mm. Am I right in thinking I should have a smaller one for 308?

[mtnlvr]

Another unsuccessful day at the range. After pressing the dent out and dressing down a few receiver welds from under the recuperator, I got the recuperator, rails and bolt to ride a little lower. The top of the bolt extension is no longer scuffing along the receiver. Bolt runs extremely smooth when the hammer is out of its way.

I also tried the extra power hammer spring which did not help. Thanks for the suggestion though.

I really feel that the bolt should be either moving the hammer further, holding it down for a longer time, or not move the hammer so abruptly as the bolt is passing over it to battery. The bottom of my bolt has a speed bump of sorts just before the hammer slot in the extension. I've increased the height of this bump in hope of increasing disconnector lock up time. I'm thinking it's got to be a little bigger and more gradual. I'll try to post a pic later when I get home from the range.

[mtnlvr]

Here's my bolt showing the "bump". It seems like the bump should be stretched and made extremely gradual so when the bolt is driving forward, the hammer is eased downward by the bump so the disconnector can catch it, not abruptly lowered how it is now potentially causing the hammer to float and its tail to slam into the disconnector. Of course I can't seem to find any information about how abruptly a hammer should be moved.

Does that make sense?

Can someone else with a similar built bolt post a pic of the bottom of theirs?

[mtnlvr]

Last night it dawned on me that I may have introduced this hammer follow by adding the material to the bottom of the bolt (the bump). Manual bolt manipulation has the trigger resetting in two places (right at the start of bolt movement and at point of ejection) with the middle section being incapable of reset (as depicted in the above pic). I added the material to the bolt to solve a reset problem but in hindsight, I believe the problem at that time was the bolt riding too high. With the bolt riding high, combined with a first time MG42 builder, I thought that the trigger should reset as soon as the bolt moves the hammer.

Can someone confirm that their hammer doesn't reset until the last bit of rearward bolt travel?