I was hoping I could i pick your collective brains for some more advice gentlemen.

I understand that a .22WMR barrel should a .224 barrel like a centrefire and not a .223 like a .22 LR.

How critical is the twist?

The normal twists for .22 CF are easily available (ie. 1-7" to 1-12")whereas the recommended 1-15" and 1-16" twist barrels are special order propositions which will take something like 6-8 months to get as Walther in Germany doesn't make them.

Has anyone built a 1-12" twist WMR, can anyone see any issues with one so built?

Cheers,

Amir

See the page marked 18.
Notice the twist is called out to be 16" or 406.4 mm.

This is the SAAMI standard for the .22WMR

http://saami.org/specification...I_Rimfire.pdf#page=8




There is also a similar standard by CIP for the .22WMR.

When the 2 standards conflict the American standard takes precedent because it is the original standard.

The rate of twist for most .22 rimfires and the .22 Hornet is 1 turn in 16".

I have no idea what to recommend to you. I know the accuracy of the Federal 50 grain lead bullets is terrible in the 16" twist of my rifle.

At one time the Anschutz 54 Sporter was sold in this caliber. I would try to find out what Anschutz did to make their .22 WMRs shoot so well.

CIP standard here

http://www.cip-bobp.org/homolo...22-win-mag-rf-en.pdf

quote:

Originally posted by curveball:
See the page marked 18.
Notice the twist is called out to be 16" or 406.4 mm.

This is the SAAMI standard for the .22WMR

http://saami.org/specification...I_Rimfire.pdf#page=8




There is also a similar standard by CIP for the .22WMR.

When the 2 standards conflict the American standard takes precedent because it is the original standard.

The rate of twist for most .22 rimfires and the .22 Hornet is 1 turn in 16".

I have no idea what to recommend to you. I know the accuracy of the Federal 50 grain lead bullets is terrible in the 16" twist of my rifle.

At one time the Anschutz 54 Sporter was sold in this caliber. I would try to find out what Anschutz did to make their .22 WMRs shoot so well.

CIP standard here

http://www.cip-bobp.org/homolo...22-win-mag-rf-en.pdf

Thank you curveball, I did some research into what Anschutz would have done to make their rifles shoot well and discovered that the CIP and SAAMI chambers are very different to each other.

The CIP chamber is cut tighter but has some sort of leade or freebore whereas the SAAMI chamber does not.

he second is whether to go with a CIP or SAAMI chamber.

Comparing the two the CIP chamber seems "tighter" in all respects promoting accuracy but has the overall case length as almost 2-3mm longer and a throat whereas the SAAMI spec chamber has no throat and seems looser.

Given that I am hoping for more accuracy than I am seeing at the moment which of the two chambers would be the way forward?

I reproduce both sets of standards for you convenience, I have put the CIP dimensions on the SAAMI print where applicable but please note the throat and what looks like freebore on the CIP print that is absent on the SAAMI print.

Rimfire manufacturers don't bother to differentiate between barrels for the .22 LR and those for the .22 WMR. The barrels for revolvers with interchangeable LR/WMR cylinders are all the same. If you can't find a 1-16" barrel in a .224" diameter, then one in .223" diameter would do just fine. Some rimfires even use .222" diameter barrels. A 1-14" barrel should also work just fine for the WMR.

"Tighter" is nearly always better when it comes to chambers. Assuming the rifle you are building is a bolt and not an auto/pump, then slight resistance upon chambering isn't a problem, anyway.