What's the difference in FCG and bolt carriers?

[Lone Eagle 839]

I had a bud give me an unmolested Bulgy bolt carrier/piston for a spare.  I dropped it in my Arsenal Saiga, and I have to push the Arsenal hammer down just a shade for the carrier to clear.  I don't have a Tapco FCG, and my spare Bulgy FCG is buried in the storage shed.  So, the questions are:

 

1.  What's the difference in the hammers, Arsenal, Tapco, factory Bulgy?

 

2.  The carrier was from a Bulgy '74 kit(bud took 2 kits and built 1 for a BFPU look).  My bolt fits and functions in both carriers.  If I remove the hammer, it actually runs smoother than the stock carrier.  Is the x39 version a different dimension then the 74 version?  I can't see any noticeable differences with them side by side.

 

I can get pics of the two carriers if needed.

[thebuns1 4,323]

If I remember correctly, only the Bulgy '74 carriers will work with the Saigas. The carriers in the SLR-107, 106, and milled receivers are heavier AKM style and won't work. Your SGL 21 has the '100 series bolt stem, and therefore fits in the '74 style carrier.

[Lone Eagle 839]

That's the carrier I have.  Guy gave it to me because I wanted to polish it up and have both the stock carrier(which I plan on refinishing this spring) and a polished carrier for when I order my wood stock.

 

I got to wondering if maybe Arsenal  hammers were slightly larger than the original.  I know the early Tapco G2's had to be "shaved" on the side that rides the bolt for some rifles to cycle.

 

With the carrier on the rails, it hits the top of the Arsenal hammer just enough to prevent it from going into battery.  I just barely have to move the hammer for it to clear(maybe 1mm tops).  Is it possible Arsenal shaved the bottom of the import bolts a touch when they ground off the auto sear trip tab or used an oversized hammer?  I can normally spot this stuff by looking at it, but I may have to put the calipers on this one.

[mancat 2,368]

The geometry of the entire AK-74 FCG is actually different than the Tapco G2. The G2 is modeled after the AKM FCG. The AK-74 FCG has a much higher hook on the trigger, and the hammer face is shallower overall. The AK-74 carrier has a much more angular contoured hammer reset surface at the bottom of the bolt tail retainer, and doesn't protrude as deep into the receiver as an AKM carrier would. This means that when an AK-74 carrier and FCG are matched together, the carrier doesn't push the hammer down anywhere near as much as it would in an AKM.

 

It never seems to lead to problems with people using the G2 components in an AK-74 or Saiga, because the AK-74 carrier is still capable of depressing the hammer enough to properly reset it and engage the disconnector, even without using the AK-74 long-hook trigger.

 

Even using an AK-74 hammer with the G2 trigger/disconnector works fine, despite the lack of the longer trigger hook that the AK-74 hammer is designed to work with.

 

If you really want me to I could lay out all of the parts for a comparison.. You'll notice the difference side by side.

 

The AK-74 carrier, as Captain mentioned, is otherwise 100% compatible with the Saiga. With minor modification it will even work with the Saiga BHO, since the BHO function is just a modification of the auto-sear trip ramp on the carrier - on the Saiga carrier, the ramp is milled into a 90-degree L shape which catches on the BHO lever. The AK-74 carrier's ramp will just press the BHO back down under the recoil spring force unless modified.

Edited January 17, 2014 by mancat

[mancat 2,368]

BTW are you putting the carrier in without the bolt when testing? The carrier can hang up on the hammer if installed without the bolt. The bottom lug of the bolt holds the hammer down a small amount as the bottom of the carrier begins to contact the hammer near the trigger hook area.

Edited January 15, 2014 by mancat

[Lone Eagle 839]

BTW are you putting the carrier in without the bolt when testing? The carrier can hang up on the hammer if installed without the bolt. The bottom lug of the bolt holds the hammer down a small amount as the bottom of the carrier begins to contact the hammer near the trigger hook area.

 

Duh-oh!!  I'll try it with the bolt in it tomorrow.

[Lone Eagle 839]

Thanks for jogging my brain, Mancat.  Went right into battery with the bolt in, and actually a little smoother than the factory carrier.