I had, for a short while, two of them, along with six magazines, the owners' manual, the reloading kit (and it's manual) and a big pile of cases and primer parts.
I, too, looked at trying to convert 'em to .40-caliber blowgun ammo. (This was before the RAP-4 stuff came out.) I still have a dozen packets of .40 ammo that must now be five years old or more. It's pretty lumpy...
Anyway, the barrel would be easy. M85's are molded plastic, and the barrel has actual rifling molded into the bore. I figured I'd just order up a .400" reamer, or whatever the "proper" bore would turn out to be, and just shave those few thou out of there by hand.
The problem, however, is the case, always the case.
The cases use three pieces; the body, an "anvil", and a "cup". A primer fits over the anvil, slides into the cup, and the pair are then seated in the case.
When fired, the stud on the bolt- like a firing pin, but far too large to ignite a firearm round- slams the cup/anvil together, which ignites the primer. The force of the primer pushes the two pieces part like a tiny piston, and this supplies the energy to push the bolt back again. The residual gasses then flow out through thin holes, sort of like a venturi bolt, and blast the ball downrange.
Direct primer pressure on the ball- even "dampened" with a wad of TP or other buffer- almost always breaks the ball in the barrel. The speed of accelleration is just too high, even for those tiny, thick-shelled balls.
Original cases appear to last about six firings or so, before either cracking, or wearing to the point where the cup/anvil pop out of the case as it's fired, and are lost on the ground somewhere.
The gun can be dry-fired. It needs no projectile, since all the force needed to cycle the gun happens in the cup/anvil action. I fired mine- with wads of TP jammed in each case- a couple of times, just to try it, and wound up cracking two more cases, and losing at least three cups and anvils.
Now, all of these parts- cases, cups and anvils- could be made in bulk by someone with a CNC setup that could handle tiny parts. The "cup" is about 5/16" in diameter and 3/16" tall- the anvil fits inside that. The case could theoretically be made from aluminum- as in turned, rather than molded in some machine that'd cost $50K just for the molds.
But again, you'd have to use .40, or convince some encapsulator to invest in a couple hundred thousand in a run of .38 cal.
A determined person- or company- could produce new ammo, but I'd wager you'd have to invest about a quarter-million, and produce at least that number of rounds, and go into the deal knowing it'll be a break-even at absolute best.
For that matter, a determined individual could produce a handful of new from-scratch rounds, but you'd have to be pretty damned determined to make more than one or two magazinefuls- and the gun shoots at 20 BPS.
If you make some, I always thought one should look long and hard at redesigning it, somehow "capturing" the cup/anvil so it can't come loose or fly out. Maybe a two-piece case that screws together, or the cup's retained by a snap ring or something.
But that's a lot of effort and time to invest in a long-obsolete gun that most fields won't let you use anyway.
