Headspace Shims

[cewrx7r1]

I read on another forum about using shims to move the bolt forward to reduce headspace.
This helps accuracy by reducing shell movement when hit by the firing pin and improves ignition.

My rifle is an 453 American 17 HMR:

I noticed that when I pushed on the rear of the bolt when a live round was chambered, there was noticeable foreword movement.

From http://www.mcmaster.com/ I ordered 1 packet of 98126A129 which contains 10 spacers, 18-8 stainless steel,
.001" thickness, 5/8" ID and 1" OD for $11.88 including shipping.

Using scissors, I cut 4 of them down to about 11/16" OD.
Each time I added another spacer, I would chamber about 5 rounds to check for play or being too tight.
It could have taken a 5th spacer but then some rounds would have been tight.

Warning: do this without the firing pin and spring in the bolt. That way you can not fire a round and any bolt closing tightness is not from the spring.

See example below.

[ls1man]

Hi, I was reading your post about the shims to remove bolt looseness against the shell.
Very interesting for sure.
couple of questions I've got if you have the time:
Have you checked to see if accuracy changes in any way yet?
What holds these spacer shims against the boltface?
Thanks in advance for any other information.
I have a CZ 452-2E in 17 hmr and I really am impressed with the gun.
It's only the second non-american gun I've ever owned.
The first is the CZ 83 in 380, I have nothing but good things to say about this little pistol, it functions flawlessly.
While everyone else is producing plastic and aluminum alloy guns the 83 is still all steel. I love the accuracy it has also.
 

[cewrx7r1]

On my first only test I only shot 50 rounds due to it being so hot outside and test was not conclusive.
The only obvious thing was that the gun was shooting higher. But thinner air due to high Houston air temps could have caused that instead of better ignition.

Have to wait to a cooler day when it is not uncomfortable to be shooting.

The picture is not my bolt but one from a posted 452. See the "washer" shim to the left of the bolt handle?

[ignantmike39]

any updates?

[cewrx7r1]

I can not tell if it really made any difference. But any improvement is an improvement.