.22 LR rim thickness

A friend was recently experiencing spitting from his fairly new Marvel Conversion. (He's awaiting a call back from FCW as timing has not been good with "everyone" out of town to the matches. FCW has been great, just bad timing for speedy reply. No complaint.)

We have also measured rim thickness on a variety of brands. Our findings provide a range of .037 - .044 with Ely CMP bulk in the .037-.039 range and Federal GM Match and SK Pistol Match Special being in the .042 -.044 range.   Most brands seem to be in .040 +/- .001 range. 

The ammo which caused the most problem was CCI SV #0035 which is the 50 rd packaging. That lot measured in .044 - .045 range. Other varieties of CCI SV #0032 (100 pack) Green Tag and CCI Pistol Match measured consistently .040.

Our guess is that the .044 - .045 rim thickness ammo is holding the breach (slide) back slightly thus permitting some blow by when it fires. Any other thoughts? It is not lead, just gas, oil etc smacking the wrist. Accuracy is still good considering the ammo.

FWIW, our means of measuring was having flat upper "side" of dial caliper resting on brass case, then bring moving part up to bottom of rim. Perhaps not ideal since the rolled edge of where the barrel of the case meets the rim may vary giving a false reading, but this way it was a consistent way to measure.

Another issue, while I'm at it. After cleaning gun, almost always the 1st shot extracts and ejects, the second shot jams going into battery. It appears the first shot's slide action is enough to eject, but shy of coming back far enough to clear the rim of the follower round to push it into battery. After 2 -3 shots it's pretty much 100%. Various mags reveal the same condition. All using std 9 lb spring as recommended.  Other than lighter recoil spring, taking some tension off the sear spring disconnector finger, lightening spring in mags, hotter ammo or just shoot the gun dirty, we're open to other's experiences/suggestions.

Newer CCI splits rims in my MG2. Older CCI fine. Haven’t measured the rim thickness.

On conversions is not picking up next cartridge usually dropping recoil spring 1# cures the problem in my experience.
Jon

Spitting in a 22autoloader is usually from a case failure or excessive blowback from the bore after case extraction.  So I’d first pick up as much spent brass and see if there are any case failures in the rim area.  It happens and that is an ammunition issue.  If they don’t have case failures, then you have excessive blowback of debris which is an ammo problem.

Thanks Jon and Ashley.

Case in 22lr should not split and rim thickness should matter at that level of thickness and variation. Could be bad ammo I had a bad case of CCI SV. 

More important make sure you chamber and barrel are supper clean. Carbon can build up about an cm from the breach and cause those sorts of problems.

Both my Nelson Conversion and my S&W M41 (Alex Hamilton relined barrel or Clark barrel) will not pick up the second round after they have been cleaned and I shoot CCI SV from 2014 - 2018 production lots in them.

Since the phenomena is so consistent and I never have the problem again until the pistols get cleaned I don't worry about it. It will either happen in practice or Slow Fire so no big deal for me.

I'll go between 600 to 700 rounds between cleanings.