Posted 18 June 2009 - 11:02 PM
Yep, it's a standard metric pattern charging handle like the one in the link.
To get it on the S12, first I cut a 1/8" wide slot on the left side of the receiver from the barrel trunnion back, the length of the handle from the driving pin to the end. The scope rail had already been removed. This slot was just about .010" above the guide rail for the bolt carrier, so the driving pin wouldn't drag on the rail as the handle was pulled to the rear. I cut an inlet into the trunnion that was wide enough for the charging handle, and flush with the receiver. It stops right at the last digit of the serial number. This puts the handle driving pin against the trunnion when fully forward. I took a piece of 1/8" thick flat bar that was 3/4" wide, and milled a groove in one side as wide as the base of the charging handle, where it is the widest. I then milled a short 1/8" groove in the center of the wide groove at each end that went all the way through. The wide groove was only deep enough to clear the thickness of the widest part of the handle, the "T" part. I then welded it to the receiver, using 1/8" pins at either end to align the plate (flat bar) with the groove in the receiver. I then had to tweak it straight from the weld distortion. Then I milled out the flat bar to the width of the narrow part of the "T" on the handle, checking for fit as I got close. Once it would enter, although with some bind, the machining was mostly done on the receiver, except to drill a spot for the detent plunger to lock the handle in the forward position. Then, the receiver and handle were tweaked and filed some, until the handle would slide freely in its track without being too sloppy. A small notch had to be cut into the bolt carrier, right above the guide rail slot on the left side, so that when it went forward it would not hit the drive pin on the handle. It actually clears the pin by about .010", to be sure it doesn't contact the pin and peen it over time. A small pad was then welded on the bottom of the bolt carrier under the left guide rail, as the carrier would drop off the rail when fully rearward, because of the clearance notch. The bolt carrier could conceivably catch on the end of the guide rail after travelling to the rear, and not go forward and chamber the next round. The pad keeps it in alignment, as it sits on the rear trunnion. A notch had to be cut in the left locking lug on the bolt head itself, to clear the handle driving pin, or it would drag the charging handle to the rear every time the gun was fired. The notch is only large enough to clear the pin, and leaves at least 2/3 of the lug in place. Since a shotgun is a relatively low-pressure weapon, this shouldn't be a problem. This, and the small weld pad, were discoveries made after actually getting the other part done. I was pretty much committed at that point, and so just continued on. If I screwed the gun up, it's mine. I then discovered that the handle hit the dust cover, and it had to be cut along the left side to clear both the track I welded on, as well as the handle itself. Since it was cut all the way to the rear, the back corner where it sits down in the groove across the rear trunnion was gone. This is what mainly keeps it centered on the receiver, this, and how it goes down the sides of the receiver a bit. The recoil spring rear piece also keeps it in line, but mostly keeps it down. I had to weld a pad on the rear left side of the receiver to stick up inside and make sure the cover was retained on the left side.
After about 100rds of test firing, a couple of observations have been made: The travel of the charging handle is limited, if you want the slot through the receiver covered. It's enough to charge the weapon, but with a full drum mag, it kind of barely seats the first round. Also, it won't eject a chambered round, as it only goes right to the ejector, but not past it. The FAL cartridge length is less than that of the 3" shotgun, apparently. There are 3 immediately obvious fixes for this problem; lengthen the slot and travelling track for the charging handle, provided you don't mind the open slot visible at the rear end, do this and weld an extension to the charging handle to cover the longer slot, or move the ejector forward some. Moving the ejector forward is the easiest, but may create problems with firing 3" shells. I haven't had time to look into it yet. It may be possible to move the ejector a small amount and get it to kick out a loaded round, and still eject fired 3" shells. Any future guns so modified can be done any way desired.
I will probably do this for customer guns in the future. First, I want to give it some time and use to be sure there aren't any unforseen problems that crop up. It won't be cheap, as it took almost 3 whole days to get the track right enough to work. Yes, it would be faster next time, but not necessarily a lot. I also had to make the track from scratch.
NRA Life, SASS #42701, Glock Armourer
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Posted 17 June 2009 - 11:31 AM
It is one of the coolest Saiga conversion i have seen. 
