Very Poplar CZ 455 Varmint

[justin amateur]

Bet ya' thought I don't know how to spell popular, eh?
Nope, it's the wood used to assemble a diagnostic tool.
Couldn't figure out why my new 455 Varmint was so inconsistent off the bench.
Receiver is pillared and bedded, but groups just weren't as tight as expected.
In fact the first trips to the range, they were pretty sad. Happened to have a chunk
of 3"x3" poplar in the scrap box, and with some odds and ends off the work bench
and parts jars, assembled this...

Ran a 7/8 inch channel down the top center of the block of poplar.
Sanded to rough the inside of the channel, then epoxy bedded a 0.866 diameter CZ barrel in place.
Using metal plates, zip screws and some scrap leather, clamped the barrel in position.

Mounted my work bench vise on a couple chunks of 2x10's and clamped it on the shooting bench.

Ran a variety of ammo down the bore, Fed 36 gr cphp, CCI bulk Blazer, CCI SV, SK Pistol Match and Lapua Midas +
Problem isn't the barrel, the better the quality of the ammo, the smaller the groups. Midas+ produced 1/4 to 1/2 inch groups.
And that was on a day with wind gusts to 20. Had to wait for lulls to be able to shoot.

So much for the free floated barrel theory, CZ should of free floated the receiver and fastened down the barrel.

 

[BenY 2013]

Why not bed the barrel to its balance point in the stock? There was a thread awhile back where they did that with some very impressive results!

 

[T.J.]

Nice set up. You certainly eliminated a lot of variables, including the human factor. My 455 PT will not tolerate crap ammo.

 

[justin amateur]

I didn't want to complain about the barrel until I proved it wasn't something else.
Stock flex and barrel harmonics seem to be the cause of the spread.

Barrel bedding already done.
Epoxy mixed with wood flour at three spots in the barrel channel.

Tested with the Varmint 22WMR barrel, bedding dropped groups down to moa.
The 22lr barrel went to just a hair under moa. Still have to see what it does to the 17 hmr barrel.

 

[BenY 2013]

I see, that's odd. It looks like you figured it out! Good job!

 

[noeesp]

Nice work looks like your on the right track

 

[bunsen27]

What are you torquing the action screws to? Most CZ's respond well 18-25lbs with less torque applied to the forward screw preferred. Also you've bedded the barrel channel, did you bed under the tang of the rifle as well?

BTW, nice shade tree gunsmithing on the barrel block! Now you have a great way to test ammo as well.

 

[[email protected]]

I just bough a CZ 455 varmint evolution..hope it doesn't have that problem, but the stock doesn't come near touching the barrel

 

[justin amateur]

I'm torquing the barrel screws to 30 inch-lbs, stock screws to 28 inch lbs.
Produced the tightest groups from both the CZ 22lr and 22Wmr barrels,
also from my Lilja Varmint Taper 22lr. With the barrel and receiver
epoxy shimmed to fit the stock and brass pillared, tap any part of the rifle,
the whole thing hums. Very solid feel.

After testing ammo for 3 hours, the results were as expected.
The more the cost per round, the smaller the groups. No surprise there.

As for the free floated barrel theory...Pttttthpt! ;^)

Lock that barrel down, bed it in place, dampen the harmonics
and those rounds run the same trajectory again and again.
It's worked on the last 4 rifles I've tested and tweaked.

 

[Parkerized]

Just took a new CZ 455 Varmint tactical ( Varmint in a boyds stock from CZ) to the range today. Each 5 shot group had 2 consistent smaller groups a 1/2"+ apart. I have a 1/2 dozen CZ 452s and they all shoot better than this. This thread has given me a few more options to look into. Thanks.