Is a higher powered .22 Rimfire possible?

I was thinking about this question recently due to the British gun laws.

Here in the UK, all semi-auto rifles, which are called “self-loading” in British terms are classed as Section 5 (Prohibited) firearms. There is an exemption in the law that states “unless chambered for .22 Rimfire cartridges”. The description goes into no more detail than that. As such .22 Short, Long/LR and .22 Magnum are currently legal.

There are no further limits placed on the type of firearm, magazine type/capacity or fixed/detachable mag. The only other conditions are that it that it must be a minimum overall length of 24", with a minimum barrel length of 12".

This made me wonder if a bottle necked .22 Rimfire cartridge with a higher powder capacity was possible. I know that rimfire pressures are limited by the construction of the case.

That again made me wonder about the possibility of steel or stainless steel cases rather than brass.

An AR-15 type rifle chambered in this new calibre with 30 round magazines is the type of firearm I am thinking of. Unfortunately I doubt that anyone here would risk developing it, as the government would likely change the laws. It is still interesting to consider if it is theoretically possible.

i heard that .17 rimfires had hight pressures compared to .22
so maybe developping a “new” bottlenecked .22 could be possible

You need a balance of the case stiffness: the head of a bottlenecked cartridge must be robust enough to stand the gas forces (much higher due to the larger diameter in a bottlenecked case). On the other hand, it must be fragile enough to let the firing pin crush the rim in a way that securely ignites the priming mix. At the same time, the larger diameter can lead to an unwanted large mass of priming mix in the case.
Look at the .17 HMR cartridge for comparison.

Some years ago when The .17 Mach2 came out several companies came out with conversion kits for the Ruger 10/22. Volquartsen, E.A Brown and several others. It became immediately apparent that just swapping barrels wasn’t going to work. The pressures were higher, the velocity a lot higher and resulted in the bolt opening before the projectile left the bore leaving the base and rim exposed outside the chamber and rupturing the case. blowing the magazine out of the gun usually destroying the magazine. ( I have first hand experience with this) Two solutions to the out of battery firing was increasing the weight of the bolt and / or a heavier recoil spring. Volquartssen had kits made to correct the problem. But that didn’t solve the problems. On top of the mechanical issues Hornady , CCI was having problems with properly heat treating the brass as the bottle neck required another annealing step. (oddly Eley ammo for the Mach2 I or others have never had an issue with.) some cases were extremely brittle and the necks cracked after the round was loaded. I still have several boxes that have 20+ out of 50/box with cracked necks. Others were too soft in the rim area and the firing pin pierced the brass and vented gas out the breech area. Hornady acknowledged they had a brass production problem and ceasesd production for a while. I have a bolt Ruger 77/22 converted to .17 Mach2 and no issues. The rimfire problem with a high pressure round I would think would be a major obstacle to to a safe and reliable semi-auto/ self loading firearm.

The Savage .17 HMR uses a roller delayed bolt to deal with dwell time issues. Seems to work too FWIW.


17 Winchester Super Magnum runs at 33000psi: .17 Winchester Super Magnum - Wikipedia

The 22 Winchester Rimfire Magnum only runs 23200psi and the 17 Hornady Rimfire 26100psi

Thanks for the replies.

If Winchester would design a .22 Super Magnum and a magazine fed semi-auto rifle to shoot it, there would be a market here.

Are Rimfire semi-autos legal in Australia or New Zealand? If they are, they might sell there. As far as I know Canada has a limit of 5 round magazines for centrefire semi-autos, but not for Rimfire. Is that correct? If that is correct, could Canada be a possible market?

In Australia semi auto rimfire rifles are classed as Category C firearms which are available to Primary Producers (farmers) and professional pest control shooters. It is a limited market because many people who are eligible either think they aren’t or couldn’t be bothered with the paperwork.
There are also clauses in some states where firearms can be recategorised at the discretion of the authorities. Some firearms have been classed as Cat D (even harder to legally obtain) based on performance or look. Examples include “tactical trainer” 22 semi auto rifles that look like AR15s and the Franklin 17wsm semi auto rimfire - not sure if that was because of looks or the increased performance of the 17wsm cartridge.

Because of this, it’s likely a super 22 rimfire semi auto would be legal by the regulations but deemed illegal by bureaucracy that didn’t like the extra performance.

After reading all the replies above, my questions are:
What is “wrong” with the .22 Magnum cartridge?
What kind of “powerful” are you looking for, and why?
I have killed small game and pest animals out to 300 yards with one shot from an H&K Model 300, topped with a Schmidt und Bender 6 power scope, with the federal 50 grain Hollow Point.
In a defensive handgun, out to 10 feet the Federal 50 grain H.P would be absolutely devastating.

i think a rimfire version of the 5.56x45 so the 22 mag is out

In New Zealand semi auto rimfire 10 shot mag are legal, all centrefire semi autos are on the banned list, can obtain an exemption for professional pest control work
Cheers Tony G

My question was actually directed at Falcon.

But, but are you thinking something along the lines of a 5mm Remington Magnum necked up to .22, on steroids?

.22 version of the 17 WSM would be an obvious modern contender for this concept.

You could think political action would be easier than developing a very niche cartridge (essentially 5.56x45RF) with a gun and delayed action to boot.


It was an idea I had of something that would fit within the definitions of the current laws here.

It could probably never happen as they would likely change the laws again to ban the specific gun if anyone tried it.

The .17 WSM necked up to .22 would be possibility if someone was willing to design a semi-auto rifle to shoot it.

Any number of bolt action rifles, like the Winchester .17 WSM rifle, that way it does not scare anyone because of the way it LOOKS, and it shoots too many bullets too fast?

I think they did something in the past in Germany.
Otherwise I cannot explain the additional label; “mit verstärkter Ladung” (with stronger load)
Unfortunately, I have no more information.

Perhaps @JPeelen can help us out.

Sorry, Willem, no factual information.
I seemed to recall that Bundeswehr used for G3 .22 rimfire conversion kits a .22 l.f.B. that was stronger than the ordinary cartridge. But the Munitionsmerkblatt for the DM31A1 (which replaced older types) gives no indication in this direction.
Nevertheless, cartridges exceeding CIP limits could only be sold to Bundeswehr or Police. I still think that any kind of “hotter” load could be intended for making some .22 conversion kit work reliably. Of course, this is speculation.

H&K sold those conversion kitsin the US for owners of the civillian Model of the G3, and also for the G3.
I remember test firing several, and as long as we used the 40 grain high velocity rounds, but not any of the hyper-velocity rounds or rounds with lighter bullets, they worked.

5 rounds max for mags designed for semi-auto, centrefire, rifle.
10 rounds max for mags designed for pistols (Centre fire or rimfire)
No limit for mags for rimfire ammo. (Used in a rifle. Pistol mags are still capped at 10. )

The words designed for are bolded as 10 round mags designed for AR-style pistols CAN be used in rifles. (Until they say No…)

So, getting back to your comment, yes the idea was raised on a while back, but nothing came of it.