I hope I don't go too far off the original subject.
I have an NEF Handi Rifle. Bought it in the late '90s I guess. It was a 223, heavy barrel 12 twist. I never got it to shoot well at all. First I noticed fired cases had a big bulge on the top side when they came out of the chamber, like an oversize chamber. But what made me give up was using an old Stoney Point OAL tool I could push 55 grain bullets completely out of the case neck without ever contacting the lands.
I was kind of obsessed with the idea of a single-shot break barrel rifle so Idecided to barrel-stub it using a new barrel blank. After I sawed off the barrel just in front of the hinge I realized I was holding a perfectly good 20-some inch 12 twist 223 blank in my hand. A quick look around found a K-Hornet reamer and I immediately envisioned a short, suppressed 22 K-Hornet hand loaded with 60 grain subsonics, like a hard hitting 22 LR, up to supersonic 35 and 40 grainers. Cool!
I threaded the stub internally like a bolt-action receiver and cut a shank on and threaded the sawed-off barrel. Chambered in 22 K-Hornet. Suppressed, scoped, look out varmints!
At first it was pretty dang cool but soon, as my brass got harder, I began having neck tension issues. Not enough tension, bullets would collapse into the case while handling rounds. I tried undersized expanders and mandrels. No good size was found. I had either insufficient tension or smashed, collapsed cases during bullet seating, even with a chamfer and a boat tail like a Hornady 40 V-Max. They collapse right at the shoulder.
I tried annealing the case necks and back to the original expander. No luck, about one out of three cases collapse when bullet seating. Too many to loose in my opinion. I actually resorted to super-gluing bullets for a little while there
I know others have good luck with the K-Hornet but I ran out of patience. It just sits in the safe these days.