Oh, I know the history of the 10mm MP5. Its just they have historically been impossible to get parts for (and thus supidly expensive.) The 'in stock' part is what surprised me (plus not much more $ than 9mm kits.) Looks like someone is making aftermarket barrels finally. Though I wish they had used the proper metric muzzle thread vs stupid SAE I guess thats not too big a PITA if only using the 10/40 specific 3-lug adapter.