Bolt Shims

[Grimmy]

Me and another member of our gun club have a CZ Varmint MTR .22 cal.
He installed bolt shims in his and hopes it will improved the guns accuracy.

Are bolt shims really necessary in a MTR since it has a match grade action to begin with?

 

[CharlieNC]

You can find authoritative yes and no answers. A definite maybe. Your test results are the only one which matter.

 

[grauhanen]

What is it that bolt shims are expected to do to the rifle that will affect accuracy?

Slight alterations of headspace will not change how the ammo performs. When ammo performance is not meeting expectations, find better ammo.

 

[Liven The Dream]

It's fun to play with our Toy's.

 

[jepp2]

Are bolt shims really necessary in a MTR since it has a match grade action to begin with?

Actually the barrel has a match chamber (subject to varying opinions by others). The action is exactly the same at the cheapest 457 (American synthetic).

I would suggest you follow the technique that Lilja provide to determine the barrel shims needed with their barrels when you install them. But they intentionally make the shank length longer and exactly 1.200". I measured the factory MTR barrel and my action, and the headspace was exactly what I desired.

I have used bolt shims mostly on my 17 HMR barrels. It resulted in the case head not ballooning out after firing which it had been doing. Here is the Lilja directions.

Drop-in barrels do not require any special gunsmithing. Directions for installing the barrel are furnished with each barrel. These instructions can also be found directly below. If you do not feel qualified to install your new drop-in barrel we can do so for a $50 charge. Here is a link to our Facebook page with a video helping explain the process of measuring your headspace. https://www.facebook.com/580697272005364/videos/338760933509372/

Installation Instructions​

2. First you will need to measure your headspace. The most accurate way to do this is by using a depth gauge, and measuring from the receiver face, to the bolt face recess while the action is cocked. Let’s say you get a measurement of 1.235” and you want your headspace at .043”. That means you need a shank length of 1.192”.

(1.235 – .043 = 1.192)

2. Every barrel will have a shank length of 1.200”. So now we know to shim the barrel .008” to obtain proper headspace.

(1.200 – 1.192 = .008)

2. Now that we know how much we need to shim the barrel, we can use a .005” shim and a .003” shim stacked together to obtain headspace. You can use any combination you’d like, but try to use the least amount possible.

2. Slide the .005” and .003” shim onto the barrel shank, making sure they are fit up tight against the shoulder of the barrel.

2. Slide the new barrel, with shims up firmly against the shoulder into the new action, being careful to align the ridge of the cuts for the set screws at the 6:00 position. Tighten the two set screws equally, pulling the barrel into the receiver. Recommended Torque is 35-40 Inch Pounds.

The receiver stock screws are a T-27 Torx HeadNote: We turn the barrel shanks slightly larger than the original CZ dimensions on this diameter. We’ve seen a couple of receivers that had a slight burr where the angled tapped holes break out into the receiver bore. This little burr prevented the barrel from sliding into the receiver with our close fit shank. So if you find the barrel difficult to slide in place initially, check for these burrs.We offer a .043” Go Gauge made by Pacific Tool and Gauge. Please note that it is not necessary to use a Go Gauge to get correct headspace using this method.

 

[Topwater]

One of our gang bought and installed a shim in his CZ 457 MTR. Between that and playing with the torque on stock bolts, he claims group reductions approaching .5 moa. Has anyone else had similar success ?

 

[Shifty6br]

I had to use shims on a 17hmr barrel similiar to jepp2 above. I was experiencing fail to fire (light primer strikes) and bulged sometimes split case heads on the ones that did fire.

I did notice an improvement in group size as the rounds were getting properly headspaced with the shims, but I am not 100% certain if the results would not have been same had the barrel been headspaced correctly from the get go, so I will leave it as a solution rather than an accuracy improvement in my particular case. I purchased the barrel from rf central and I believe it is a 455 era bbl, hence the slight offset.

Either way I can attest the shims did solve my problem 100% and am having a grand ole time with the. 17.

 As far as will it improve overall group size...well one would have to tinker and determine accordingly to their own setup.

 

[tmwinds]

Before shimming a bolt you must identify if a problem exists and if so, what is the problem and what is needed to correct it?
Just arbitrarily placing shims in a bolt can create more problems than it solves.

 

[PWNolan]

Before shimming a bolt you must identify if a problem exists and if so, what is the problem and what is needed to correct it?
Just arbitrarily placing shims in a bolt can create more problems than it solves.

Yep! Agree!

These shims are great if you have an old rifle with excessive headspace and subsequent ignition problems. Otherwise they're just snake oil

 

[Liven The Dream]

Well to add to the Snake Oil story .
Had a MTR played with Screws , Trigger Spring and lots or Ammo .
I but a Lilja Barrel on that Rifle with Shims set Head Space at .042 . Boy it loves SK Std.Plus .
Took that MTR Match Barrel and Installed on a different 457 Action used Shims.
Installed in a Chassis .
Shoots better groups with Ely Match than Lilja Barrels Rifle ?
Go Figure! Love to play with my Toys.

 

[holstil]

Bolt shims and barrel shims two different/opposing things (in case someone doesn’t know).
Good idea to know head space, ammo rim thickness and firing pin protrusion before using.

 

[Tacoma]

I tried some bolt shims in a CZ 457 after installing an aftermarket EABCO match barrel. The EABCO barrel was giving me excessive head space per my measurements. ( 0.045 to 0.046") even though it shot very well.. I figured I'd shim the bolt to get into the 0.042/0.043" range that my CZ-s usually like to see if that would further tighten my groups.. After installing the 0.003" shim, I got hard/crunchy bolt closures on several brands of ammo that I had not felt before. I realized no improvement in accuracy with the shim so pulled it out after two range sessions.

 

[mrh1958]

If your head space is in spec you wont gain any accuracy from shims, ignition is more important.