Thread: .17 Mach IV Barrel

Right time for another one..
This time a little fast mover for the CZ 527 switch barrel.
This is another great condition but used S/S 1-9" twist barrel that also came with some Redding dies, 150 brass and 3 boxes of 25gr projectiles.



There was a gap in my arsenal, I was also considering a .20 Vartarg but I have never owned a .17 centerfire and I guess its time.
I can see a real neich for this cartridge with some of my 200 yard + hare shooting jobs over newly planted maize crops they destroy in a few short nights.
With all the larger dairy farms shrinking to lots of lifestyle blocks and housing the .223 can be a little too unsafe but with projectiles half the weight and 1000fps faster there is less chance of projectiles not exploding completely on impact.

The .17 Mach IV

Students of history are quick to point out that while the .17 Remington is considered the most popular .17-caliber cartridge, the .17 Mach IV beat it to market by about 8 years.

Introduced by the O’Brien Rifle Company in 1963, it wasn’t very far behind the introduction of Remington’s aggressive little .221 Fireball.
This in fact was the basic case for the Mach IV, all you have to do is neck down the .221 Fireball to .17 caliber and voila, you have the .17 Mach IV!
After its first fire form the overall length stays the same (1.400"), but the shoulder angle changes from 23 degrees to a more traditional bench rest short-cased 30 degrees.

Although printed load data for this is some what on the snow flake side the Mk 4's claim to fame was 4000fps with 25gr projectiles.

Much later to the party in 2007 Remmington released the .17 Remington Fireball as a response to the .17 Mach IV wildcat that had gained popularity in the states with varmint hunters.

Although both the .17 mach IV and the .17 Fireball were both based on the .221 Fireball cartridge they are not identical.
For liability and various other reasons Remington made the .17 Fireball cartridge a fraction longer in the body with a shorter neck and thicker at the base and shoulder diameters than the .17 Mach IV.
Intentionally this means the .17 Mach IV cartridge will fit in a factory chambered .17 fireball but the .17 fireball factory rounds will not fit in the .17 Mach IV wildcat chamber.

While this factory clambering enabled many non hand loaders dabble in this little varminting hotrod most hand loaders still preferred the .17 Mach IV with its longer neck and the availability of quality Lapua .221 fireball brass over the very underwhelming Remington brass that was fast getting a bad name for stretched primer pockets after only a couple of moderately charged loadings.

Factory loads drive a 20 grain bullet around 4,000 ft/s. Velocity is close to the .17 Remington but with significantly less powder, and therefore less heat and fouling. There are also many more published hand loading options for the .17 Remington Fireball that push the variation of .17 bullet weights now available.

Nice, I've got a Mack IV on a Sako l46, my most accurate small game rifle, mostly I shoot the 25gr v-max at 3750-3800, it gives five shot groups at 300m about 1.5-2" on a calm day, bit tougher todo on a blustery day, there is no doubting, a hit on a rabbit, the thuwk is very noticeable.
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,

My Mack iv load is 19gr benchmark lapua brass, WSR or CCI 400, with the 20gr v-max, 18.5 gr for the 25gr bullets. I drop back 1/2 grain with Remington brass.

Wingman where do you buy 221 Lapua brass in NZ please?

Belmont Ammunition are the Lapua agents but im not sure if they have current stock. Sportways often hold a bit of Lapua brass too for a slightly inflated cost. I Think they have some norma .221 FB brass in stock now

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?

Couple photes of my sako L46 in Mack IV, just cause.

Oooo thats nice... the more photos on this thread the better!

What are your thoughts on barrel length? The one Barrel I have is currently 24" long but I will cut to optimal I think

The Sako is 24", it too long with suppressor, ok with out,
I cut my 17 hornet to 20", ( from 24") good length, but I wish I had gone to 18", much handier, especially if on a bike or vehicle.

I think, .17 fireball, I would go about 18-20" if fitting a suppressor, 22" if not, no longer, maybe 20", kind off, depends on the type of small game shooting, your doing, shorter if your a walk abouts, kinda guy, longer barrel, for set up and snipe.

Well I managed to free up some workshop time yesterday evening and fitted up the .17 barrel to the CZ 527 action.





The barrel is 24" long and stainless steel with a bore that looks like new. I had it soaking in copper solvent for a few hours and none at all came out so it seems to be well looked after or it has possibly only run the molly projectiles it came with..

It was going to be a precise machining task for the simple reason I had to head space it without a chamber reamer as I dont have one or dont know anyone with one.
After closer inspection it had had an extended tenon bush fitted threaded in 1"-1/8x14tpi Whitworth which is a BSA .222 CFE thread but under the bush it is s M20x18tpi Sako Vixon tenon and this is what it was originally chambered in .17 Mach IV for and fitted on.





The CZ 527 thread is a shoulder less M25X1.25 which locks up on the rear face, this meant I could just turn the entire knox and tenon bush down to 25mm and clear off all the old thread, shorten off the rear contact face closer to the required headspace and re-thread it for the CZ.
I made up some go and no go gauges to work with my FL sizing die dimensions and took very light cuts from the rear face until it fitted up and head spaced perfectly.









I left the barrel at 24" for now just to see what velocity it could achieve but Im certain Ill cut it back to 20-22" once Ive had a play.
I had to make up a thread collar for the suppressor to square up against a shoulder for my M14x1mm suppressor as the barrel was only a fraction over 14mm out at 24". Will get away without it once trimmed back.

This afternoon I started working up some test loads for a ladder test with both 20gr V-Max and 25gr Molly coated Berger hollow points.



I started a grain below book max loads with ADI BM-8208 and worked up in 0.2gr increments until I started to see pressure signs on the primers. The velocities change very fast in these small cartridges with only very small changes in powder weights.
I found a couple of good velocity nodes for each bullet that I can start the paper work with and also noted max loads not to exceed.

Max load for the 25gr V-Max gave me 4200fps and the 25gr moly Bergers gave me 3900fps..

Nice write up, I assume that's a typo that the 25gr are doing 4200, 20gr I can see at about that. not 25gr.
I have struggled with both my chrony's, to get consistent readings, on the 20gr weight, I gave up fiddling with settings, after a while, point and shoot to 250m, explosive results on small game, a ground squirrel, rat or magpie, simply disappear, and rabbits, hares are just a smoking ruin.
Mostly I prefer the 25gr, bit better at long range,
Anyhow, nice info, and enjoy your rifle.

Umm yes a typo.. it was meant to say 20gr V-Max @ 4200 not 25gr as per the first paragraph

I got into a bit of 100 yard paper work this afternoon, Im still not really set up to load for .17 cal so I need a few more tools to get all my new Lapua brass cut to length etc but I ran some fresh necked down Remington brass for the test.

First thing I noticed is that it has a long throat so bullets can be seated a long way out.

The first 5 rounds Berger 25gr Hps and 20gr VMax were seated with about 80% neck contact which meant quite a bit of jump.

Berger 25gr


V-Max 20gr


The last and best group were 25gr Bergers seated way out with only about 30%neck contact. This group measured 9.3mm ctc!



Something tells me this barrel isnt fussy, it will shoot anything. I still have some Hornady 25gr HPs and some 25gr VMax (probably my go to bullet) to test but I think Ill just load everything with about 50% neck contact.

HAPPY DAYS!