if i rechamber my 17rem to 17-223 can i fireform 17rem factory brass

dilrkilr, unless I'm mistaken, the .17 Remington is longer than the .17-.223, so you wouldn't have much luck rechambering your rifle without having the barrel set back. Not sure what rifle you have, but if it's factory, you'd probably want to consider a custom rebarrel over rechambering. In either case, not sure why you'd want a .17-223 over a .17 Remington in the first place. You won't see any difference in velocity and it's not any more efficent, but you will have the expense of the gunsmithing work, combined with the cost of specialty dies.

I know some guys haven't been real happy with Remington brass, and several have tried forming .17 Remington brass from IMI .223 brass, etc., but it generally leaves the necks short. If your motivation for wanting the .17-.223 is simply because of the availability of .223 brass, I'd have to say it wouldn't be worth it to me. I use factory Remington .17 brass, and as long as I don't go "full house", they'll last several firings.

If it were me, and I was going the route of rebarreling my factory Remington BDL, I'd look real serious into a .17Mach IV. Everything I've ever read indicates it's about the most efficent .17 caliber available because it generates plenty of velocity, but at modest pressures.

Just outa curiosity, what is the parent case of the Mach IV?

.221 Fireball.

I also shoot 30 grain Bergers out of my REM Mdl 7 but I do not like the MEF's for coyotes. I use there plain spitzers. I have killed numerous dogs with the 17 and that is the only gun I use now for daytime calling. Amazing little rifle.