The .303 has an actual diameter of .311" which might be good for air/spud use of .308 diameter bullets. (many rifle calibers use .308" too)
Although the copper jacket will no doubt be tougher to go through rifling than even harder type lead.
There are molds for .308" as well as .311"(3o3).
.243 is .244".
On my drill bit chart, a size "C" bit is .2420" and a "D" is .2460".
An "N" bit is .3020" and a 5/16" is .3125"
The smaller sizes are good if you wanted a precision bullet mold because a reamer in a drill press, mill or lathe would give it better consistency.
(edit: few more bits for .308,.311 like 19/64th (.2969),"L","M" if reamer is used. drill bits tend to make oval scratchy holes...)
Or even maybe polish the mold holes larger with a dremel or hand drill and abrasive polish/grinding compound.
Although, If the projectile came out a few thousandth (or even .010) over it would be easy to press through something to shave a little off.
I'd go for a homemade mass production mold myself (with precision).
Haven't done much lead mold work though.
Seems more practical for both air/spud use projectiles and cost-wise.
At $75 for a surplus barrel, whole rifles used to go for that not long ago.
One disadvantage to firearm barrels is that combined with spud equipment one could run into legal snags which could become lengthy and costly, maybe painful to sort out. (so...careful storage is in order(?))
That's why I avoid them and prefer black powder muzzle loader stuff.
Definately
never mount a silencer to one
ever...Bad idea.
BTW, I found .50 BMG surplus barrels for 150-200$ USD online one time...
Started daydreaming of getting a manufacturer's liscense...(legally) (so no zip gun discussion)...It would be simple to build a solid block, and rather than break open, a simple hinge that swings the barrel open to one side (rather than forward, rather than a locking bolt).
Single shot . 50 BMG designs go for over $1500(++and+),
and Many use those barrels and look a little home-workshop crafted.
Many people are unaware, I read somewhere in USA it's not illegal to build a firearm as long as it's not full-auto or a shotgun with less than 18" barrel. And one's self-made gun cannot be sold or transfered without going through legality paperwork. (not too interested much myself but it was interesting, still I would double check that).
Oh, on the "magnum pellets", I wasn't stating they won't get stuck in co2 power, just that even co2 power would be viable for use in firearm barrels was all.
silly mood last night...Had to drop off my woman till next weekend..was already bad mood...I have GOT to get better work this week!
8)