As previously stated, I do have a good bit of experience with this material, it's pretty tough. I've been using it for over a year, and even poured it into nerf shells when doing integrations for structural integrity, it's always done the job. It's not quite as rigid as the plastic used in nerf parts, but instead has a very slight flex under high pressure, making it un-shatterable, and I have yet to crack a piece under pressure. Although I'm also looking into other casting resins, incase I find something better, but I doubt I will.
Have you considered shrinkage for the part? I didn't see any information for it on the product page you provided. We are not dealing with super tight tolerances in most of these parts but I could see a little shrinkage resulting in a bolt sled not securly staying on its intended rails.
Also, it might be worthwhile to look into over-molding so you could have a metal or wire armature for the heavy stress points.
Shrinkage is next to non-existence for this material, as I can clearly attest by the other things I've made with it.
Running a metal wire or something of the like through the center is an interesting idea, however, because the sides of a boltsled are only 0.11 inches thick (just measured), I don't think it would be of any help. Say inserting a .05 metal rod in the center of each post, I doubt it would make any difference at all, and any thicker then that and it would compromise the outer walls of the plastic, and more then likely just pop out under stress. For thicker parts though, I can see this as a possibility, although it's something I would have to experiment with.
I wasn't so much talking about the components, as trying to push the conversation towards discontinued shells.
Casting a whole shell? Because of the size and complexity, the mold would have to be much larger, and multi layered to get both sides in full detail so it would look how it should and internals will fit into place correctly. Casting something like a Maverick wouldn't be too bad, but it would NEVER be cost efficient. I'd have to ask at least $50 for a shell that size, and around $150 for a shell around a crossbow size.
Of course, knowing how the prop community is about recasting, Hasbro might have some issues, but I wouldn't mind dealing with them.
I'm glad you brought that up. As earlier stated, it's not going to be a direct re-cast, but a modified boltsled, and in-since Hasbro hasn't made the longshot in a number of years, the parts won't be identical, and it will have a relatively small amount of castings, I seriously doubt this would be a problem.