S&W M76 Machine Gun Jams. Is it mags or ammo?

[Machingun59602]

I had several Suomi and Swedish "K" mags modified for my S&W M76 machine gun. So far 3 of the mags have worked and two have not. I still have one more to test.  I was told that 124 grain (9 MM) ammo works best. I purchased a bunch of Winchester NATO 9 MM 124 grain ammo. I was told that other types of ammo might work better. I am open to any suggestions. Is there a "best" ammo for this gun? What about the mags? Will some mags just not work? Or are jams just more common with "open bolt" machine guns?

[Lewisfan]

Gun should be reliable.  If some mags work but others do not, then it is most likely mag related. I don't recall the SW76 or MK760 series being finicky about ball ammo (115, 124, whatever). 

If mags are modified Suomi then it is likely that the amount of catch surface remaining on the mags may vary. This will affect how high the mag sits when "locked in". If the mag is canted, or not high enough for the bolt to strip the round reliably, then it could cause failure to feed. If you're getting empty rounds failing to eject, then you extractor could be dirty or weak / worn out.  Also - don't hold the mag when shooting. Hold the gun and let the mag hang there without manual pressure of any kind. You may be unknowingly introducing the canted mag by holding it (common mistake).  

The last thing to suggest is to pop the loaded mag on its back (primer side of cartridges) before inserting it into the gun. This is done to make sure that the loaded rounds are uniformly resting against the back of the mag. You'll often see the GI in movies tap the loaded mag against his helmet. Same thing. Don't hit it hard, just enough to help stack all of the rounds correctly inside the mag.

They are good guns. You may just have a few things to iron out. Issues are finite and fixable.  Good luck 

[Don.]

What kind of failures are you getting?  I’ve had mag issues when I first got mine and a ton of the $9 Suomi mags.  I’ve had to adjust the feed angle on some of the mags due to them being bent.  Usually it was one side that needed correction.

I’ve also had to replace the extractor a few times.  I’ve had a broken lip on the lower part of the bolt.  There’s more malfunctions that you could have, but we need an accurate description and pictures also help.

[ranger1385]

I have had the same issue.  The factory mag works great and the Suomi mags are hit or miss.  I figured it was the angle as well.  

[Rekraps]

Great points all. The S&W shoots well with 115, 124 and 147's. I hand fitted my suomi mags, (going slow on the removal of metal) until they just fit. If you're having feed issues, then as the boys above say, most likely its damaged lips leading to feed angle issues. There are plenty of NOS suomi mags available. Just buy some and do your own work. 

[Moose1]

In our group, there is about 5 of us that own SW76s.   Sound of the guys had issues with the mags, others would only work with pacific brand or size (124gr)     

I was luck, my 76 uses unmodify Suomi mags and will run on any brand or bullet weight.

My problem was with the trigger bar.     Once I found out what I needed to do, then it was back up.

Good luck.   Moose

[Rekraps]

Yep, the trigger bar is the #1 issue with this gun..... Andrewski says he fixes quite a few each year.