CZ Model 550 22 Creedmoor Build with Bonus Rockchuck Hunt

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Editor’s Note:  I remember the conversation like it was yesterday.  Cache Carlson was on the phone and he was telling me about his next build.  “I’m going to find a CZ Model 550 and do a .22 Creedmoor build with it as the donor rifle.  It will make a great rockchuck and predator combo.”  I could not argue with his logic.  In fact, I was planning my own build at the time, using a Howa 1500 donor rifle, so I understood the want for this dynamic cartridge, in a bolt-action rifle!   Everything fell into place rather quickly, so within a few months, I saw this build come to fruition and get out into the field in June of 2020.  I have personally witnessed the affectionately called, .22 Killmore, take close to 50 rockchucks and numerous other varmints.  Every single kill was the result of devastating destruction that was an instantaneous death, or as close as you could get to one.  The .22 Creedmoor is an excellent varmint round, for both small, to larger coyote sized animals.

Cache’s Article: 

When varmint hunting, small caliber bullets going extremely fast, most always results in quick, clean, kills and DRT animals.  With the push for small caliber rifles to shoot heavier bullets, I realized that those shooters had the right idea, but were pushing bullets that were much too heavy for the average varmint hunter.  Having a slightly heavier bullet, while still keeping the ballistic advantage of a light bullet out to 500 yards, was the real sweet spot for anyone looking at the .22 Nosler, .224 Valkyrie and the .22 Creedmoor.  Although the Nosler and Valkyrie, shooting 55-60 grain projectiles, have a decent following with the predator hunting crowd, running the ballistics on the .22 Creedmoor and a slightly heavier bullet showed that it would outperform the two with both speed and energy.

Looking at what was available at the time, I decided to work with one of my favorite bullets, the Sierra 64 grain Tipped Game King.  This bullet has a proven track record of accuracy and of shedding it’s energy on thin-skinned varmints.  With the help of our other Varminter brother, David H., we developed a load in QuickLoad that I used to create the first loads for accuracy testing.

Accuracy and Finding the Load for the CZ 550:

While doing my initial testing, I tried various powders, including Varget, IMR 4166 Enduron and H4350.  Varget came close to what I was looking for, but the pressures were too high to stay with the load I developed.  Overall, none gave me the accuracy, velocity and lower pressures I was looking for.   More research brought me to Reloder 17 powder.  The R17 gave me everything I was looking for and availability at the time was not an issue. 

Redding .22 Creedmoor 3-Die Set

Redding .22 Creedmoor 3-Die Set

Just a note on the reloading dies I am using.  Redding was kind enough to send us a full 3-die set for this reloading project.  Speaking for all of us here at Varminter, we love Redding dies.  They are very well made and are always consistent.  This is important when you create your own rounds, but even more so with “wildcat” cartridges, like the .22 Creedmoor.

My groups varied from 0.95″ down to 0.50″ in ideal conditions.  I settled on the load that gave me the 0.50″ groups at 3700 feet per second and proceeded to test bullet performance on some local rockchucks.

Although the CZ 550 I converted had a detachable box magazine (which are hard to find), I was able to still set the bullet depth at 2.095” to the lands, then back-off at 50 thousandths and have them chamber with no issues.

There was a slight feeding issue, caused by the slightly less taper in the case, not allowing the cartridge to load properly with the control-feed action.  This was resolved by modifying the magazine lips by slightly opening them (see image).

Reloaded Ammunition Component Breakdown:
Redding 3-Die Set (.22 Creedmoor)
Starline 6mm Creedmoor Brass – Large Primer (necking down is a very simple process and Starline holds up to the resizing very well)
Reloder 17 Powder
Federal GM-215M Primers

Initial Field Testing on Rockchucks:

I live in an area where hunting rockchucks is a short drive away, so on Saturday, June 6, 2020, I grabbed my .22 Killmore and my reloaded ammo and went out looking for some of these larger varmints!  My first kill was in a rocky area out in the desert near an alfalfa farm, where the farmer was having issues with the rockchucks coming in and eating/digging up his chip potato field.  The range on the first rockchuck was 150 yards and the results were devastating!!  At that moment, I knew this combo would work for my varmint hunting needs!  Through-out 2020, the .22 Creedmoor racked up dozens of kills, from rockchucks to coyotes.  Nothing lived after being hit with the 64 grain TGK out of my Killmore!

Rockchuck Hunt on Video:

I am good friends with a local rancher who grows crops and runs cattle in Idaho.  Every spring, he invites me over to his place to do some rockchuck management.  This time, Eric Mayer met me and brought his video equipment.  We were fighting very strong winds, with gusts up to 35mph!  I was shooting at distances that ranged from just under 100 yards, out to 300+ yards, with the average being in the 250 yard mark.  My holdover was minimal at all ranges and even with the sustained winds of 20mph and the frequent 35mph gusts, my windage adjustments never exceeded 2MOA.  That proves out how flat the trajectory is with this cartridge/bullet combo. 


Most of the shots on video are self-explanatory, but some stood-out and deserve a short synapsis.   One that comes to mind is at 4:56 in the video.  This was a large rockchuck, sunning himself on the top of some rimrock.  The distance was approximately 225 yards and I was battling the wind to stay on target.  As you can see in the video, the bullet impact launched the rockchuck about 20 feet into the air.  We found him piled up in nook around 12 yards away.  That is pure energy being released into the ‘chuck when the bullet hit (1237 foot pounds of energy).  The other that stands out, is at 6:32 in the video.  This rockchuck was huge and obviously spent his life gorging on the pasture grass where the rancher’s cows grazed.  If you watch the video carefully, you will see that the bullet completely opens up the rockchuck, causing immense damage, killing it instantly.  Again, every bit of energy from the bullet was released on impact.

Final Thoughts:

I shot more than 20 rockchucks that first full day out at the ranch.  100% of them were killed with this CZ Model 550 .22 Creedmoor build.  Fast-forward almost a year and this rifle has become my favorite rifle to take hunting.  There is a simple reason why.  The accuracy and ballistics make it a highly versatile rifle on all of the varmints I come across, or call in (coyotes).  I have made shots out to 487 yards and continue to push it to the ethical limits on extended range varmint hunting.  Anything in the 100 to 300 yard range has become a chip-shot, with my success rate being at least 90%.  If you are looking at a new varmint cartridge, I highly recommend the .22 Creedmoor.  My reasons for this recommendation are numerous, but the results in pictures and on the video(s) released, solidify my reason for making this suggestion.


.22 Creedmoor Rifle Information:

CZ Model 550 American – $550
22″ McGowan Barrel (5R – 1:8″ Twist) – $500

Zeiss Conquest V6 – 3-18x50mm  (30mm tube)
Warne 30mm Rings

Swagger Hunter 42 Bipod

Gemtech One Suppressor
Rauch Precision Suppressor Cover

Mad Dog Weapons Systems / Bruce Finnegan – Barrel Install/Work

Cache Carlson
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