I picked up a very lightly used CZ 455 in a trade a couple of years ago. I finally took it to the range earlier this week along with a Savage MK II to see how it shoots. I tried 12 different types of ammo including CCI mini mag target, mini mag varmit, stinger varmit, velocitor small game, standard target, SK standard plus, rifle match, high velocity match, Eley target, Aguila target compition, incepter, and some Winchester silver tips. I shot five 5-shot groups at 50 yeards of each of these with the CZ and 2 or 3 of each with the Mk II for comparison.

Most of the CZ groups were running about 2 inches with a couple getting down to inch and half and some up to 3. Most of MK II groups were sub 1" with a few below a half inch. The CZ was clean when I started. The MK II had several hundred rounds from the a couple of weeks earlier and hadn't been cleaned yet. My $189 10/22 with tech sights shoots most ammo better than the CZ. Highly disappointing. Do I need to be looking to get rid of this thing, or any suggestions on getting it to shoot better short of pillar bedding or putting a Lijia barrel on it? Either of witch would probably cost more than I have in the gun.

There are several things I would check before getting rid of it, but occasionally CZ does put out a rifle that just won’t group well.  

-Mounting screw tightness.  Is it torqued properly?
-Barrel to stock fit?  Does the stock make contact anywhere with the barrel?
-Crown?  Is it clean or are there any burrs/anomalies?
-Leading in the chamber or barrel?  Give it a good, deep clean scrub with some lead and copper remover.
-Do you a bore snake camera that you can run down the barrel to check the rifling?
-Bolt face.  Is it square or are the anomalies on it?
-Barrel torque. Is the barrel at the proper torque?

That’s about all I’ve got for now.  Good luck on getting this shooting great.

-Mounting screw tightness.  Is it torqued properly? Installed the scope and rings with a Wheeler Fat Wrench per the factory specs for the rings. Checked at the range to make sure nothing was lose but didn't check the torque again.
-Barrel to stock fit?  Does the stock make contact anywhere with the barrel? I'll look at this.
-Crown?  Is it clean or are there any burrs/anomalies? Didn't notice anything on inspection with my Mark I eyeballs, but they are getting a little worse for the wear. I'll check again with some magnafication.
-Leading in the chamber or barrel?  Give it a good, deep clean scrub with some lead and copper remover. It was clean when I started, but I'll give it another good cleaning before trying again.
-Do you a bore snake camera that you can run down the barrel to check the rifling? I do if I can figure out where I put it and give this look.
-Bolt face.  Is it square or are the anomalies on it? I'll take a look.
-Barrel torque. Is the barrel at the proper torque? I'll check this and the action screws per the factory specs.

Thanks for the list.

GlockPride pretty much nailed it.

The action screw (action to stock) torque values are also important.  I have found that the torque values on my 22LR rifles seem to have more influence on POI than my centerfire rifles.  I have zero explanation for this, but I have found it to be true.  

You may have gotten a lemon.  It happens.  But factory CZ 22LR barrels are notoriously good out of the box.  Good enough that many of the shooters on RimfireCentral retain them...and those guys are infatuated with minutia and squeezing the last .001" of accuracy from their rimfires.

Lots of good points above.

I’ll add my thoughts...

headspace....The barrels on the 455 are swappable.  I only have the older 452 types with fixed barrels.   You may have to check to see if the headspace is set correctly.  I am not a 100% sure but iirc discussions on the 455 and 457 this needs to be done when changing barrels.  Perhaps yours is long.

I am spitballing there not having had that model.

changing ammo during a range session.   I am not that much an expert but some bullet lubes don’t play well together and mixing in copper and lead without a good cleaning can really foul accuracy.

Shooting 5-10 rounds for “score” then doing it immediately after with another ammo is not conducive to good grouping.   It may take twenty rounds for the new ammo and it’s bullet lube to coat the bore and settle down.  

I would clean the barrel to bare metal.   Use a copper solvent.

Shoot nothing but lead bullet ammo in one range trip.  
season bore with a sight in target with 10-20 rounds
then shoot ten rounds for score

patch the bore out

repeat above cycle with the next lead bullet ammo, this includes shooting 10-20 rounds to distribute the new bullet lube down the bore before shooting for score or group

If you group brands of lead bullets together sometimes you can shoot right away without reseasoning.  Like SK lubed bullets, (it’s the same  as Lapua and the older wolf but not the newer Eley made Wolf.  I will shoot SK rifle match, SK pistol match and SK Standard without a lot of “seasoning rounds” in between.   It’s all the same lube.

and so on.

Then clean the snot out of it and do the same with copper jacketed ammo.

Plus one on action screw tension.   My 452 varmint in .22 lr was fairly disappointing until I played with the screws.  The 452V is an odd duck though as that model had a barrel lug and a forend action screw.   That set up is a royal nuisance.  Many guys would remove the screw altogether.   The 455 and 457 varmints did not use that set up for good reason.   It can work but a guy has to shoot it and play with the action and barrel screw tensions.

I almost gave up on my CZ 452 varmint until I figured that out.

I'll add check the headspace to the list.

As far as mixing and matching goes I was shooting five 5 shot groups of each type of ammo. The groups didn't seem to be tightening up any with the later groups in a set. It didn't seem to bother the Mk II, and I was only shooting two or there 5 shots groups of each type with that one. I do understand the point though and will either clean between sets or not mix and match the next time I take it to the range. I've cleaned between small sets before when breaking in the barrel of a Savage 12 LRPV or working up handloads for it. The goups on the model 12 didn't start tightening up until it had a couple hundred rounds run through it.

Thanks again for the feedback guys.

One other torque to check is the grub screws that retain the barrel in the receiver. Had it been shot much before you got it? Some barrels take a good bit of shooting to settle in. My 457 MTR was pretty disappointing straight out of the box for a rifle with a "match" chamber. Somewhere around the 500 rd mark, it started shooting like I hoped it would all along.