Wont Cock with top cover down

[FKpt.Fritz]

Well exsactly what it says. ive come this far and now been halted by this. i am useing a AR15 trigger an a pirate verson two peice fireing pin. it fuctions fine with the top cover up just a little binding towards the rear but with the cover down i cant cock it back at all. is it rubbing on the AR15 hammer? that would explain the other binding. my charging handle fits losely could that be the problem? the bolt has some resistance in the rails, i can move the bolt easly with my hand but i have to push it and use some force to, could this be the problem?

-joe

[JBaum]

Wow, where to start.

With the trigger grip off the receiver and the recoil spring out, the bolt must move freely in the receiver. Not simply move if you push it hard enough, but smooth enough that the bolt, when unlocked from the barrel, will fall out if you tip the muzzle up and have the stock out of the way. The MG42 bolt is supposed to recoil fully rearward. If you use some of that energy because the rails are too tight, there may not be enough energy to advance the feed system the first half step, eject the empty shell, cock the hammer, or push the bolt rearward far enough to compress the recoil spring so that the spring has enough stored energy to push the bolt fully forward, lock with the barrel extension, advance the belt for the second half step, and strip the new cartridge. No resistance on the bolt movement (with the trigger grip off and cover open) isn't a goal, it's required.

Before you close the cover, do you push the feed lever to the left so that the roller on the bolt housing goes into the slot of the feed lever in the cover? If not, the feed lever is smashing down on the roller and won't let the bolt move.

Does the feed lever move freely in the cover? Take the cover off the gun or open the cover, and wiggle the feed lever back and forth. Does it move without resistance? Do you have the pivot points lubed? How about the feed pawls, do they move OK?

Do you have the retaining spring on the rear end of the feed lever seated in the slot on the cover pin that the feed lever pivots on at the rear of the cover? Try to lift the feed lever off the cover without pushing in on the catch spring. If it lifts, you don't have is assembled correctly, and there isn't enough room for the feed roller on the bolt to move rearward because the feed lever in the cover is slanted down at the rear (with the cover closed) and there isn't enough room for the roller to fit as the bolt moves rearward.

A loose charging handle wouldn't work with the cover closed or open if it were binding. You say it works fine with the cover up, and not with the cover down. Therefore, the cover is the problem.

"is it rubbing on the AR15 hammer?" Is WHAT rubbing on the AR15 hammer? The bolt has to cock the hammer, so it has to rub on the hammer to do that. If there's something else rubbing the hammer, you have a problem.

[FKpt.Fritz]

Wow, where to start.



Before you close the cover, do you push the feed lever to the left so that the roller on the bolt housing goes into the slot of the feed lever in the cover? If not, the feed lever is smashing down on the roller and won't let the bolt move.

Does the feed lever move freely in the cover? Take the cover off the gun or open the cover, and wiggle the feed lever back and forth. Does it move without resistance? Do you have the pivot points lubed? How about the feed pawls, do they move OK?

Do you have the retaining spring on the rear end of the feed lever seated in the slot on the cover pin that the feed lever pivots on at the rear of the cover? Try to lift the feed lever off the cover without pushing in on the catch spring. If it lifts, you don't have is assembled correctly, and there isn't enough room for the feed roller on the bolt to move rearward because the feed lever in the cover is slanted down at the rear (with the cover closed) and there isn't enough room for the roller to fit as the bolt moves rearward.

A loose charging handle wouldn't work with the cover closed or open if it were binding. You say it works fine with the cover up, and not with the cover down. Therefore, the cover is the problem.

"is it rubbing on the AR15 hammer?" Is WHAT rubbing on the AR15 hammer? The bolt has to cock the hammer, so it has to rub on the hammer to do that. If there's something else rubbing the hammer, you have a problem.

alright i can get it lose enough to fall out that isnt a problem i wasnt sure. the lose handle doesnt bind i took it all apart again so that is not the problem. when i say rubbing on the hammer i mean the bolt hitting it to much...i know it is supposed to rub against it but wasnt sure to what degree. thanks for the help. also top cover functions good but needs lubricating along the feed rail. i am not sure what else needs done but i will continue to tinker with it.

[sdk1968]

he gave you just about all the possible answers there.

so im gonna ask you the dumba$$ question....

is this happening with NO belt involved?

[FKpt.Fritz]

yes no belt. and i think i found the problem to. the top of the rollers on the bolt are hitting the top of the receiver right before it hits the feed trey. i now have 2 options i can eigther grind the rollers down about a mm or 2 or gring the reveiver a mm or 2 still trying to decide so far im thinking the rollars.

[JBaum]

Grinding the top of the rollers off would remove the hardened outer surface and you may end up cracking a roller, which could cuase the gun to blow up when a chip from the roller gets stuck, or you could wedge the bolt and have to cut it out of the receiver. The rollers aren't the problem. The receiver is the problem. Put in another bolt, and the problem is still there.

If you do it carefully, you could used an abrasive wheel on a Dremel tool and grind the inside of the receiver until the rollers don't bind (a little weld slag maybe?). I'd recommend solving the problem, rather than just fixing the symptom.

[Karbinator]

Maybe a reweld that shrunk in that area? There were many guys having to spread the rcvr
due to binding (back in the day) . If it's really a mm or so, I would come up with a way to spread that sucker
somehow, and fiddle 'till it rolls in smooth....rather than grind anything. Certainly not grinding parts off the bolt !
A real Kaboom can leave you in the ward.
Hmmm....I wonder how many wives recieved the dreaded visit/offical letter saying their husband/son died in battle when it
was really a catastrophic failure of the weapon?

[FKpt.Fritz]

how could they onlu harden the surface? i thought if you hardened something you had to harden the whole thing.

i did a combination of all the above. i took some off the receiver, i managed to bend the reciever just by mm and i pushed the rails further into the coner (turns out the rails were at a angle because of the receiver) i also had to take some off the bolt to get it running perfectly. so now eigther the bolt is hardened all the way through. or i need to reharden the surface. i may be able to do this or if i cant i have a few friends who do alot blacksmithing (have a shop and everything, they build muzzleloaders and stuff) and they would know how to.

[JBaum]

The key to successful hardening for some applications isn't to harden the entire part, but only the surface where it wears. If the entire part is hardened, it becomes brittle and will chip. If it's just the surface that is hardened (sometimes to a depth of 50/1000" for example), the part is still flexible enough internally to absorb an impact, and the hardened surface resists wear.

There are several ways to harden a part. I'm sure you've heard of case hardening. The part is only hardened on the surface, not completely throughout the part. Other hardening methods include quenching, which changes the molecular structure on the surface, but not completely through the part. Hardening the outer surface only is discussed in the MG42 armorer's manual. It's especially important for hammers, disconnectors, ejectors, and any part that takes an impact. If it were fully hardened, it would be beaten to pieces sooner than softer steel with a hard surface.

Going into great detail of the several ways it is accomplished is beyond me (I'm not a metallurgist), but that's the ideal way to harden such parts. Fully hardened parts can shear off more easily than parts that are only surface hardened. Soft steel is better for some things, hard steel for others. Softer inside with a hardened surface is the goal for this application.

[Bil]

I don't follow,is it the RAILS that it is rubbing on? And is it tight top-to bottom or side-to side? Thr receiver can be spread easily using the rivet buck or similar device,just put it between the rails and turn the screw.Go a little wider than you think is right,the metal has some memory and will return a bit.I had to do this on my re-weld,it had distorted just a little.Then some filing and polishing of the rails and the bolt slides like John describes.Good luck! ---bil

[FKpt.Fritz]

alright i think i know what needs to be done to harden the bolt back. it was the rails it was rubbing against and the reciever above the rails in the center. i fixed it by binding the low spot in the receiver up alittle, grinding a bit off the roller (very lilttle and i did it before i read the responses to the thread because im a moron) and used a screwdriver and hammer to beat the rail into a better fit along the side of the receiver (the top of the receiver being bent was not allowing the rail to fit smoothly along the side of the receiver) the combinations of all of this fixed it. now the cocking handle is jamming on the ar15 hammer....

[FKpt.Fritz]

well i test fired it!!! it worked!!!!! i had some serious reloading problems and cartridge jams so ill need to figure out whats causeing them.

[sdk1968]

with as much as you were talking about going on there... its just gonna take some polishing and fine tuning to get it to smooth out.

go slow and dont grind anything else off of the bolt.. polish up on the charging handle and plate for it, this is a place lots of people get binding.

[FKpt.Fritz]

i switched bolts.. the one i messed up is a M53 bolt now im useing my MG42 bolt. everything is working did some more fitting today it now works flawlessly without a belt its ready to try again i have a feeling its still not going to cycle rounds.