http://www.akfiles.com/forums/showthread.php?t=70602

Retrieved: 12/08/2013


TRX
07-24-2010

The standard AK uses the pressed ridges in the gas tube to hold the piston steady. The Valmet and variants use a smooth gas tube and there's a star- shaped section behind the piston head to keep things centered up. In a Galil it's usually called a "sand scraper", though since it's a Valmet design, you might as well call it a "snow scraper." Doesn't scrape anything either way, it's just to guide the piston.

The AKM uses a rear sight block with a half-round pin to lock the gas tube in place. The Valmet/Galil/R4 have no rear sight block; the ears of the front trunnion are notched at the inside, and the longer gas tube has a machined end with little ears that fit in the grooves. It's all held in place by the top cover; there's no separate gas tube retainer.

The Galil is wider between the trunnion ears than an AKM; you can't open it up enough to fit a standard Galil tube in there. You could machine the Galil tube or make another one, and saw or file the matching grooves in the ears. The only hard part would be modifying the gas tube; easy if you have a mill, possible with some patience and a file if you don't.

The bulged-trunnion guns, like the Yugo and PSL, have the same distance between the ears as a Galil. You can just file the grooves in the ears and slide a Galil gas tube in.

Though some of the drawings make the ears on the gas tube look triangular, the ones on my Galil tube are square.