Thread: .17 Mach IV Barrel

Originally Posted by southernman

I had a Cz .221 for a while, bought it to convert to a 20 vartarg, sold as I bought a cooper single shot in 20 vartarg, you may need a .221 mag to get feeding correct on a CZ, I had troubles feeding a fireball round, with my .204 CZ,

Yes this was my first concern too and I found a few old posts on other forums that had mentioned problems feeding from a CZ 527 too.

So...I loaded 5 dummy rounds to test the .223 mag feeding into the 6x45 Rem barrel and was pleased with the result. See attached vid.
There seems to be .221 Fireball mags available from CZ USA too

https://youtu.be/Qfgst8Tw4Ms

Very nice. I can get away with firing 17 fball in my 17 mkiv. Have not shot it much at all this year. Its 42 degrees at the moment so still a bit warm cold change coming soon. I had feeding problems in my brno fox but tuning up the claw extractor fixed it, it was a .222

Originally Posted by Tuidog

Very nice. I can get away with firing 17 fball in my 17 mkiv. Have not shot it much at all this year. Its 42 degrees at the moment so still a bit warm cold change coming soon. I had feeding problems in my brno fox but tuning up the claw extractor fixed it, it was a .222

Sorry I have written that info around the wrong way... it is the .17 Mach IV that is longer than the .17 fireball not the other way around. The bolt on a Remington fireball will not close in a mach IV cartridge.

While you might "get away with" firing .17 fireball in your .17 Mach IV it is not good practice. The cartridge body is 6 thou shorter than you chamber so add 2 thou for the std head space clearance and you have a total of 8 thou of head space.. your brass will migrate forward or backward to match the mach IV chamber but at the cost of side wall thinning just forward of the base cup with the risk of case head separation especially if you reload your brass.
Im keen to see pics of your .17 fox if you have any?

Originally Posted by Wingman

Sorry I have written that info around the wrong way... it is the .17 Mach IV that is longer than the .17 fireball not the other way around. The bolt on a Remington fireball will not close in a mach IV cartridge.

While you might "get away with" firing .17 fireball in your .17 Mach IV it is not good practice. The cartridge body is 6 thou shorter than you chamber so add 2 thou for the std head space clearance and you have a total of 8 thou of head space.. your brass will migrate forward or backward to match the mach IV chamber but at the cost of side wall thinning just forward of the base cup with the risk of case head separation especially if you reload your brass.
Im keen to see pics of your .17 fox if you have any?

I'll take some pics for you. The 17fb ammo is a firm close in my mach iv. I had a heap of cases when I got the rifle (over 200)but the necks have been splitting or were already split they were formed from 221Fb.