MGC M725... Tweaking for consistent Automatic Firing

Post by Jez_JRP

Exactly what it says on the tin I'm asking on behalf of a friend who just bought one, it's doing his head in - the problem is that it won't fire more than 3-4 rounds on full auto without a stoppage.

As far as I know the rounds are properly loaded (the thing works flawlessly on semi auto), so can anyone recommend any tuning procedures, adjustments or modifications to allow consistant auto fire?

Thanks in advance

Post by Claymore

The ejector can get burrs on it so stops the gun from ejecting well and gets jammed, get him to have a look at this first and make sure it moves freely

Post by Mark

Jez_JRP wrote:

Exactly what it says on the tin I'm asking on behalf of a friend who just bought one, it's doing his head in - the problem is that it won't fire more than 3-4 rounds on full auto without a stoppage.
As far as I know the rounds are properly loaded (the thing works flawlessly on semi auto), so can anyone recommend any tuning procedures, adjustments or modifications to allow consistant auto fire?
Thanks in advance

Hmm, I think that the problem is either the auto sear,the magazine spring or bolt "bounce" In semi, the bolt is usually fully seated before the disconnector allows the hammer to fall. In the full auto position the hammers fall is controled by the auto sear as the disconnector is held back by the selector. If the full auto sear is out of "time" it can drop the hammer befor the bolt is full closed. If the hammer falls before the bolt is closed it's momentum is lost and that causes misfires.
Bolt bounce is when the acceleration of the bolt/cartridge hits the breach hard enough to cause the bolt to spring back just when the hammer falls.
If material is added/removed to/from where the bolt carrier contacts the auto sear then its timing ( in relation to when the hammer falls) can be adjusted.
Bolt bounce can be addressed with the addition of weight to the bolt carrier that will slow the bolt down.
As for the magazine spring/follower these magazines need to be de-burred as the undersides of the feed lips are full of sharp little burrs. These burrs/sharp edges dig into the cartridges and can cause the gun to jam. If the feed lips are de-burred the cartridges slide out somuch better with much less friction.

Post by khyle

Thanks for posting this thread, Jez.

Gentleman, thank you all for the replies. As you might have guessed, the M725 in question is mine and now that my forum account's active, I might as well post here

Mark, thank you for your advice. Based on your post, I think it's highly likely that the problem in question is the auto sear since it's only on auto that the rifle misfires. That is - it'll fire anything from one to even ten rounds without a problem and will then chamber a round and the hammer will fall (at some point during the cycle since the action will be fired off) but the cartridge will not fire or cycle.

So from what you've told me, it seems that the auto sear is the problem, so I'll look into fixing it. I don't suppose you'd be able to tell me the part number of the offending item is by any chance? I'd not totally broken the M725 down yet, so it'd help me greatly if I knew which part I'm after.

Post by Mark

Khyle wrote:

Thanks for posting this thread, Jez.
Gentleman, thank you all for the replies. As you might have guessed, the M725 in question is mine and now that my forum account's active, I might as well post here
Mark, thank you for your advice. Based on your post, I think it's highly likely that the problem in question is the auto sear since it's only on auto that the rifle misfires. That is - it'll fire anything from one to even ten rounds without a problem and will then chamber a round and the hammer will fall (at some point during the cycle since the action will be fired off) but the cartridge will not fire or cycle.
So from what you've told me, it seems that the auto sear is the problem, so I'll look into fixing it. I don't suppose you'd be able to tell me the part number of the offending item is by any chance? I'd not totally broken the M725 down yet, so it'd help me greatly if I knew which part I'm after.

First off, I would like to welcome you to the forums Khyle!
The auto sear is part # 235 on my MGC parts list.

Post by ljerr2

I'd check the easiest things first. A little trip up can cause a malfunction in full auto. Check the magazine lips like Mark said. I have several of these models and multiple magazines. Some needed filing.
Next I'd push out the rear receiver pin and look down the breech area and see if the firing pin/detonator is completely centered. Check and adjust as necessary. Sometimes I think these get overtightened and cause the pins to be off-center and drag on the cartridges. Also, while you have the reciever open, pull out the bolt and check the ejector and the other lever on the other side (can't remember what it
s called) and make sure they are not hanging up. This happens after time, esepcially if you have some jams I think.
As always, make sure your cartrdges are properly lubricated. I use a little silicone grease on the cartridge o-rings.
Do these easy things before you go removing material from those metal parts and I bet you'll be happy.