The information I have shows minimum headspace for 22LR at .043 with max at .051. Other information I see shows No-Go gauge at .046 and Field at .049.
Information also shows that specifications for ammunition rim thickness is .036 to .043.
My measurement of rim thickness on various brands and styles range from slightly under .035 to .038. Nothing approaching .043.
There are articles about improving the accuracy of CZ 457 rifles by using shims to adjust the headspace. This is what started this quest.
My 457 shoots very well with most ammo. A .043 gauge alone and with a layer of scotch tape will chamber. Two layers of tape "no".
Question. There is a .007 range specification on rim thickness. By my measurement of 8 different varieties all are at the lower end of those specifications with the thickest at .038. Has anyone intentionally reduced the headspece below 043 via chambering or shims and what were your results.

I will tell you about my own experience with 22 rim fire.

I must have shot so many different rifles, using hundreds of different types of ammo from all over the world - currently I have over 80 different types!!

Rifles ranged from incredibly bad made Chinese ones, to the very best European manufactures can offer.

I have tried rim measurements, I have tried weight segregation.

Nothing really works.

There is no magic formula.

You can get fantastic accuracy, by using match rifles with match ammo from the likes of Lapua and Eley.

On the question of headspace, not sure if this is relevant.

I have several different types of 22 rim fire reamers.

Each comes with certain claims.

I have chambered rifles with them, using match barrels, generally from either Dan Lilja or match grade European manufacturers.

Our reamers are made to minimum specs.

And I chamber my barrels so that an unfired case from match ammo will just chamber.

Funny enough, only ammo that refuses to chamber are certain types from American, and South American and South African manufacturers.

From America it includes Federal, Remington and Winchester.

Playing with 22 rim fire is great fun, and very challenging.

My own limited observations with the performance of 22 rimfire ammunition is that ignition is probably the main driver of accuracy.
I have noticed that in most cases where a misfire has occurred and where the cartridge is rotated in the chamber to allow another firing pin strike, the bullet, from the cartridge when or if it fires second time round, invariably hits low.

Possibly this initial misfire and subsequent firing of the cartridge is due to a gap in the distribution of the priming compound in the rim of the RF case i.e. the case did not receive the correct dosage of priming compound hence distribution was not even and hence the combined pressure from primer and powder was lower than normal.

My own 22RF is a Geverm semi auto firing on an open bolt with the 'firing pin' a fixed ridge across the breech block face so the cartridge receives a heavy blow and double crush of the rim as the breech block slams a cartridge from the magazine into the chamber and fires it. Considering the long but smooth trigger pull, the ignition lag from when the trigger is pulled to the breech block slamming into battery, and the take down feature of the Gevarm E1 carbine, the accuracy from these guns when using good ammo is amazing. I think it is the solid ignition feature that contributes to the accuracy of these Gevarm carbines.

Recently I was trying out some Browning BPR ammo in my Gevarm, 40gr bullet at 1435fps. Online reviews of this ammo are almost all scathing of the ammo performance with misfires, blowouts, squib loads, poor accuracy, misalignment of bullets in the cases, etc. Some warned not to use the ammo in blow back semi auto rifles, only use in solid lock up rifles (if you must use the ammo altogether).

While I did not experience any of the first two adverse behaviours I did experience the rest. Yes bullet alignment in cases is poor, some okay but a lot had the bullet seated tilted. The Gevarm fired and ejected without fail but the sound signature of the ammo was all over the place from loud to soft and accuracy was poor. Some cases were badly blackened and often quite a lot of smoke came back out of the chamber when the breech block was opened and
back in the cocked position.
Back home I removed the bullets from a handful of rounds and while the powder charges were a constant weight the distribution of the priming compound was terrible, some had compound halfway up the walls of the cases and others had lumpy bumpy compound spread unevenly around the rim. I would conclude the inconsistent distribution and likely dosage of the priming compound is the cause of this particular ammunitions poor performance.

Just happen to be reading an old Gun Digest (1996 50th Annual Edition) and came across this so scanned a copy. Just what the OP needs.

Ive never done anything to a 22 but shoot them, never occured to do otherwise, this is a new one on me, seems like a waste of time for a hunting rifle anyway. Hmmmm?

First, to get it out of the way. Mr. A, you're right about hunting accuracy. Minute of gopher or ground squirrel is just fine.
But, and it's a big but, trying to shoot little groups can be, at least for me, somewhat addictive.
Every little thing seems to have an impact and there are lots of little things. Always looking for something that will make a difference.
Challenging is a nice word.
I was hoping that there was someone who had squeezed down the headspace and what results, if any, they had found.

I agee, and found your approach interesting, just never occurred to me...as I just fired factory ammo and picked the one that shot best in my 22 rifles! I suspect most folks did the same as me with the rimfires..Did a lot of testing with all manner of centerfires. Good post on your part.

I shimmed the bolt on a 513T, didn't seem to make a lot of difference, and I took the shim out.
A better shot than I might have seen a difference, I dunno...

Now that I'm thinking about it, there were two other guys who are better shots than I who tried it in 513T rifles.
One kept the shim, the other did not.

That gauge/tool was around a few years back----as you can see, it never went anywhere!

Hip

Eagle, I was unaware of the Gevarm E1 until you mentioned it. Fascinating little rifle!
I also remember seeing the Neil Jones tool advertised years ago. Be fun to mess with.

https://www.youtube.com/watch?v=kQW7Q0eqZpQ

quote:

Originally posted by Bill/Oregon:
Eagle, I was unaware of the Gevarm E1 until you mentioned it. Fascinating little rifle!
I also remember seeing the Neil Jones tool advertised years ago. Be fun to mess with.

https://www.youtube.com/watch?v=kQW7Q0eqZpQ

Yes the Gevarm is a great little rifle and has quite an ingenious step to set up for either high velocity ammo or low velocity standard or subsonic ammo. Often semi autos do not function reliably with subsonic ammo, those that do such as the Ruger 10/22 often have to use a nylon buffer at the rear of the action to cushion the breech block as it is slammed back after each shot. The spring and breech block have to be setup to allow standard or subsonic velocity cartridges to reliably operate the action while high velocity cartridges slam the block back with greater inertia than needed leading to wear and tear over time.

The take down Gervarm has a spring guide which can be inserted to the rear of the action for subsonic or inserted at the other end of the spring inside the hollow breech block for high velocity. The guide weighs 50 grams so while the spring 'weight' remains constant, adding the 50 grams weight of the spring guide to the breech block creates the extra inertia to overcome when firing high velocity cartridges.

The simple changeover process only takes about a minute or less and makes the carbine ultra reliable when shooting standard or subsonic ammunition, even when some of the latter is well below 1000fps in velocity.

Another little gadget to tinker with if wanting to narrow down accurate 22RF ammo, would be easy enough to make at home too.

I have a homemade rim thickness jig someplace, worked well enough but didn't improve my scores.