CZ-457 Accuracy: The Most Affordable Way to Accurize Your CZ

The CZ-457 rifle has rightfully earned the reputation of being a highly capable and accurate 22 bolt action rifle right out of the box. However, a higher level of precision can be achieved with a few budget-friendly modifications that will take the CZ-457 accuracy to the next level.

Tightening up the headspace using bolt shims is the most affordable way to improve the accuracy of your CZ-457 rifle. This modification will tighten your groups and make your rifle more consistent shot to shot.

It really is amazing how much the accuracy improved with this little modification that cost less than $15.

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How Bolt Shims Work to Improve CZ-457 Accuracy

It is no secret that headspace plays a huge role in rifle accuracy. On rimmed cartridges, such as the 17 HMR, .22 LR, and 22 Mag, the headspace is measured off the thickness of the cartridge rim. The tighter the headspace, the more consistent the cartridge will be positioned in the chamber, and the more consistent it will ignite the powder. Accuracy is a direct by-product of consistency and repeatability.

According to the Sporting Arms and Ammunition Manufacturing Institute, better known as SAAMI, the .22 Long Rifle cartridge rim thickness is .043″-.007″. That means that any rim that measures between .036″ and 0.43″ is within spec. That is a big difference. Now, if we look at the spec for a chamber, you’ll see that the number increases even more!

The chamber spec for a .22 Long Rifle is a minimum of .043″ and a maximum of .051″. Tolerance stacking can quickly become an issue here. Let me explain.

If a rifle was chambered to the maximum .051″ headspace and you are shooting factory ammo that comes in at the lower end of the .036″ rim thickness, you will have .015″ worth of “space” for your cartridge to move during the firing process. This will not only cause your accuracy to suffer, but you will probably experience the occasional misfire as the cartridge is slightly cushioned with that much movement in the chamber.

This is an extreme example but one that is entirely possible with some lower-end rimfires. Bolt shims are one way to tighten up that headspace and improve the accuracy of your CZ-457. Let’s take a look at how to measure the headspace on a CZ-457.

How to Measure Your CZ-457’s Headspace

Headspace is the distance between the bolt face and the forward stopping point of the cartridge. On the CZ-457, the recess on the bolt face will be the rear point, and the face of the barrel will be the forward stopping point. Measuring them is pretty straightforward but requires you to disassemble the rifle and remove the barrel.

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Take the receiver and barrel assembly out of the stock and remove the barrel. Removing the barrel on a CZ-457 is easy and is held in by two set screws in the front of the receiver. Using dial calipers or, better yet, a depth mic, measure the distance from the barrel face to the shoulder of the thread extension.

Next, measure the distance from the receiver face to the bolt face with the bolt closed in the locked position. A CZ-457 has a recessed bolt, so you will need to measure the center part that the cartridge sits up against. Take this number and subtract the barrel extension length from it. The result will be your headspace. Below are the numbers from my CZ-457.

Receiver to Bolt Face	1.236″
Barrel Extension	1.190″
Headspace	0.046″

The headspace on my CZ-457 was 0.046″, a good middle-of-the-road number that will give you ok accuracy. In a previous test, I found that CCI’s Standard Velocity Target ammo was the most accurate in my rifle. Therefore, I wanted to tune my rifle for that exact ammo. Using a set of calipers, I measured the rim thickness of the CCI’s at 0.043″.

By subtracting the rim thickness from the headspace, I get the desired shim thickness, 0.003″.

If you are interested in another way to measure headspace, Jack Behrmann wrote this article for Triggershims.com. They are the makers of the shims I use in this article

Installing the Bolt Shim

Install the bolt shim by disassembling the bolt and placing the shim between the bolt handle and the bolt body. In the above video, I show you how quick and easy it is to disassemble the bolt to do this. The bolt shim will go in front of your bolt handle and behind the bolt body. It essentially moves the bolt forward those few thousandths that you need to tighten up the headspace.

CZ-457 Accuracy: The Results

Drumroll, please… The results of this easy and affordable modification were substantial. My 5-shot groups at 50 yards shrunk an average of .200″ across four groups. My average 5-shot group size was right around 3/8″ or 0.375″, a true sense of the CZ-457 accuracy.

When I shoot measured groups, it is usually for hunting purposes. Your testing may vary from mine, but I use three group sizes; a 3-shot, 4-shot, and 5-shot group. This will give me real-world accuracy when I’m out in the woods hunting. This accounts for any fliers that are a result of ammo variations, which are out of my control. In the ideal world, the first cold-bore shot you take is all you need, but this is how I choose to measure my groups.

The below chart can be confusing at first. The important data is highlighted in green. The “Average minus Largest Spread” refers to the average taken with the largest spread in that grouping not accounted for. This data helps identify any fliers that may affect the grouping. As you can see, these fliers make a minimal difference in the averages as a whole.

The accuracy I am getting out of my CZ-457 American is a result of a combination of things; action screw torque, target ammo, picking the right scope, and, now, bolt shims. I’ve written about all of those items, and they are linked toward the bottom of the page. Altogether, other than the scope, I spent less than $100(if you included the cost of a torque wrench) to get my rifle shooting this way.

The Downsides of Using Bolt Shims

A bolt shim is an extremely thin piece of steel. This brings up the question of wear. How long will it last? I only have a few hundred rounds through my rifle at the moment, so I really can’t speak to the longevity of using bolt shims. However, triggershims.com notes that one of their customers has over 5-6 thousand rounds through his without any issues. Even if it theoretically wore out at that point, spending less than $20 every few thousand rounds is worth the increase in accuracy, in my opinion.

I’ve read concerns about the use of bolt shims affecting the safety of rifles. On the CZ-457, the safety mechanism is completely within the trigger. The bolt shim only affects the bolt body, which is forward of the locking surface. Therefore, the shim will not affect anything behind the lockup of the bolt handle. However, this post is informational, and you should use them at your own risk.