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Wraith
July 21, 2005, 07:04 PM
Can anyone explain to me how the cam system on a belt-fed gun works? I understand in theory but don't grasp how the cam grabs the belt. Does it have spring loaded claws? Is the cam basically the same in a cloth-belt weapon?

Pictures? Links? Descriptions? :confused:

Thanks!

shaggy
July 21, 2005, 07:51 PM
You've basically got it - spring loaded feed pawl in the topcover grabs the belt and pulls it in. On the 1919, there's a spring loaded 'stop' on the trunioun to keep the belt from sliding back out. I'll try to get you some pics later tonight or tomorrow.

shaggy
July 21, 2005, 08:24 PM
Kind of a crappy pic, but...

http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=40010

1919 on the left, MG42 on the right

The 1919 has a large single feed pawl in the topcover, while the '42 has two sets of two feed pawls. If you look at the 'pathway' that goes horizontal across the topcover near the pivot, thats where the feed pawl travels in - its all the way to the left.

On the '42 look to the 'hump' that extends out from the left side of the topcover. You'll see two 'claws'. A little to the right of them (further inside the topcover) are two more 'claws'. When one set is out, one set is in, and as the gun fires they move back and forth.

Wraith
July 21, 2005, 11:41 PM
Those are some nice play things you got there! :D Thanks.

Now are the claws mechanically actuated by the cover or is that part of the cam? Or do they just graze over the ammunition? On the MG-42 the bolt pushes the next round down into the chamber whereas the 1919 extracts the round from the belt when the bolt opens... is this correct? If so, how is the round extracted?

Thanks again for the pictures, I really appreciate it! :)

shaggy
July 22, 2005, 08:08 AM
Lets start with the 1919...

If you look at the topcover, you'll see a slightly angled arm. At the top of the angled arm, there is a small circular post that protrudes out about .25" Now look at the bolt and notice the trach thats cut in it running top right to bottom left. The post on the arm in the topcover rides in that track. When the gun is fired and the bolt moves back and forth, it causes that arm to move back and forth (left to right) as it rides in the track. That arm, in turn, moves the feed pawl back and forth (left to right). The feed pawl is spring loaded so it can ride over the belt of ammo as it moves from the right to left, but locks down and holds the belt secure and pulls the belt in as it rides back left to right.

If you look at the bolt, you'll see "7.62" engraved near the top (to the left of the charging handle). Just to the left of that you'll see a part that looks to be a backwards, upside-down "L". That part pivots up and down along the left side of the bolt. It has a claw that extends down and grabs the rim of the next round in the belt. As the bolt recoils, it pulls the round out of the belt and and drops it down a "T-slot" into the bolt face. The bolt then slams home, chambering the round ready to fire again.

I'll have to explain the '42 later, but as you can probably see the track on the '42 is in the topcover whle the post is on the bolt.

shaggy
July 22, 2005, 09:03 AM
The '42 operates similarly. The post on the bolt actuates the track in the topcover (it pivots near the back of the topcover). As that track moves back and forth, it moves the feel pawls back and forth which pulls the ammo in the weapon. Rather than pulling the ammo out of the belt as on the 1919, the MG42 pushes the ammo through the links or belts. If you look to the front top of the bolt, you'll see a ridge on the '42 bolt head. That ridge extends up, and as the bolt slams home it pushes the ammo through the link or belt. Unlike the 1919, the MG42 has a feed tray upon which the ammo sits. Notice the slot in the feed try. The ridge on the bolt runs through that slot and pushes the ammo through the hole in the front of the tray. There's a spring loaded plate in the topcover that pushes down on the ammo, which keeps it in line with the hole in the feed tray (so the ammo doesn't point up and slam into the front of the feed tray instead of pushing right through).

Wraith
July 22, 2005, 03:05 PM
Cool. Now all I have to do is build my own. ;)

Seriously, thanks for explaining that. :)

kozak6
July 22, 2005, 03:34 PM
Here's a couple of animations, if it helps.
http://people.howstuffworks.com/machine-gun10.htm

Victor Romen
August 4, 2005, 12:05 PM
Here are some good animations as well.
http://www.coz-fx.com/animations.htm