I have a Fime Group conversion Saiga.I would like to add a KNS adjustable piston. I don't want to grind on my existing bolt carrier to remove the factory piston. Anyone know of a source for an interchangeable small bolt stem bolt carrier?

TIA

Bulgarian 74 or Polish Tantal carriers are your most likely surplus options.

Just be aware that there are wear matched mating surfaces on the bolt carrier for the camming channel. Mixing a mismatched bolt can introduce additional wear to the camming lug on the bolt if if was already well worn in to the channel on the Russian carrier. Doesn't affect headspace though.

So, I  should be looking for 5.45 carriers? I really like the idea of a new Toolcraft carrier,  as above.

Swapping the piston out is no biggie.  No grinding required, just a little precise drilling or milling…

You can use an end mill in a drill press, the rivet is obvious, clamp the carrier down good, just go deep enough to be able to unscrew the old piston.

You can just use a roll pin for a new piston, or whatever KNS suggests (never used one of the adjustable pistons myself).  No need to go full steel rivet and then sanding it down to the carrier to be perfect…

If you do it correctly, you can put the original pistol back in someday if you so desire.