Here is a stray project:

EAA Biathlon rifle in 22 Magnum rimfire. Rim size is approx .291", cartridge length 1.35".

Start with Hornet brass, turn from rimmed to rimless, base diameter is 0.294". Trim to 1.050", neck to .224 caliber, go with K-Hornet profile. Essentially a shortened K Hornet, computer suggests I give up 4.0 gr water capacity, meaning I can get a 50 gr HP to go 2100-2200 fps from the 19.5" barrel .... a lot more than the 1600-1700 listed in the charts for the Mag ....

Modifying from rim fire to center fire will be a challenge, but the project rifle is $275 and has that nifty biathlon action ....

Marty,
i've got some 5.7x28 if you want to start from there.


but that action isn't hardened... just about no rimfire is, and I doubt anything but the sear and cocking piece are harder than 20-22...

now, if you had a 17 barrel.......

jeffe

maybe I am totally wrong, but I thought that the 22 rimfires were .223 bore diameters. I know the hornet was originally .223 and is now .224.

Am I wrong about the rimfires? Just wondering.

Sounds a little like the .22 Cooper to me.

Jeffe - I have 5.7x28 here, thought about a shorter version, also looked at cutting it off and sticking a 7mm in it (Lilliput version of 30 Carbine I guess)

DigiDan - 22 Cooper? I have the 22 CCM, but that is rimmed straight case. Other Cooper I do not have in my files?

HL

The 22 Long Rifle/Rifle/Short rimfires use .222" heeled (same diameter as outside of case) bullets, but the 22 Magnum rimfire uses .224" bullets that fit inside the case like the centerfire cartridges.

Marty, that's it. Think it is the "Cooper Centerfire Mag", no?

The twist is going to be 1-16" so 50 gr bullets should still work but barely. 40 grains will work great; the 35 gr V-Max even better.

I think HL is right about the bore diameter but if you cut the chamber for the right size neck that shouldn't be a problem. The .224 bullets will swedge down .001 just fine as long as the case can release them.

quote:

Originally posted by HL:
maybe I am totally wrong, but I thought that the 22 rimfires were .223 bore diameters. I know the hornet was originally .223 and is now .224.

Am I wrong about the rimfires? Just wondering.

Yep. The 22LR barrels are 0.222 to 0.223 groove dia (rifling), but the 22magnum barrels are 0.224 just like the centerfires - which makes sense since they launch the same jacketed bullets.
My personall choice for a project of this type would be for the 5.7x28 round straight out of the box. SS-196 is one of the latest loadings for this round and is loaded with the 40gr V-Max so your barrel twist would be just about right. It (loaded rounds) might be a tad longer than the 22 magnum factory round, but the choices would then be to short chamber and shoot a short wildcat off of this case or single load and still eject the empties.

I wouldn't worry about the receiver all that much as the 5.7x28 is designed for a blowback action and is not factory loaded above pistol pressures - about the same as the 22 mag maybe a WEE bit more, but not much. Besides the 0.310 head dia will keep bolt thrust managable and low.

quote:

Originally posted by tiggertate:

I think HL is right about the bore diameter but if you cut the chamber for the right size neck that shouldn't be a problem. The .224 bullets will swedge down .001 just fine as long as the case can release them.

Having chambered a 22LR rimfire barrel to shoot a jacketed wildcat (22 Epperson Cricket - necked down 25Acp) I can address this directly.
Yes SOME of the available bullets will...some won't.
I found that no matter how light the loading the Rem 45gr HP bullets would result in blown/loose primer pockets. All the V-Maxes I've tryed from 33gr to 45gr perform great even with full (acp) cases of bulleye (of course that's not but about 2.5 grains)

When trying to swage bullets into a smaller bore you DO have to pay attention to the bullets resistance to being squeezed down. The "softer" varmint bullets will let you get away with this the harder ones will most definitely NOT.

I did a web search on the 5.7x28 FN.The chamber pressure is listed as 345 MPa.MPa -P.S.I.=MPa x145.0377 = P.S.I.(345 x 145.0377 =50,038 P.S.I.).

The 5.7 FN pistol is a delayed blowback.

WC

The thought had crossed my mind to heat treat the action to allow higher pressure, but I also need to see how it locks up (don't have one yet, just doing some research)

Also thought about the 5.7 and loading 77SMK seated BACKWARDS .... looks like a truncated cone with a realllly long boat tail

The Cricket is was gave me the idea, if I could get longer 25 ACP brass, I would make a longer version of the Cricket to be honest ...

First need to take some 5.7 brass and see if it will fit the mag. That will be all telling. If not, then I need to look at other options, or just go back to messing with my 50BMG .... see my other post in this forum ....

quote:

Originally posted by Wildcat Crazy:

The 5.7 FN pistol is a delayed blowback.

WC

True, the Fiven-seveN IS a delayed blowback design...but the P-90 submachinegun is NOT. It's a straight blowback action.

quote:

Originally posted by MartytW:
The Cricket is was gave me the idea, if I could get longer 25 ACP brass, I would make a longer version of the Cricket to be honest ...

First need to take some 5.7 brass and see if it will fit the mag. That will be all telling. If not, then I need to look at other options, or just go back to messing with my 50BMG .... see my other post in this forum ....

I cut down 5 pieces of 5.7 brass to 25ACP length, inside reamed using a modified 0.281 chucking reamer (profiled to provide a thinner mouth and rounded base interior), and then necked the resulting case down to 22cal. . The result was a test cartridge I called the Fat Cricket. 0.030 larger in body than the 25ACP or the Cricket, but the same over all length. A lot of work for not much gains, but then again I din't have a 22 Magnum action to try it on...but the same technique would work in what you are trying....But it might also be easier to just extend the throw distance of the bolt to accept this new parent round too.

5.7x28 is too fat to fit the 22 Mag magazine of a Marlin, and I do not feel like messing with the magazine. Had it fit, cutting off the 5.7 below the shoulder and fitting it with a 7mm held promise for a 7mm Whisper type round but alas.

Going to ask some brass maker guy I know about long rimless 25 ACP brass, he'll probably just moan at yet another wacko idea from me ....

That or turn the rims off Hornets ....

quote:

Originally posted by MartytW:
5.7x28 is too fat to fit the 22 Mag magazine of a Marlin, and I do not feel like messing with the magazine. Had it fit, cutting off the 5.7 below the shoulder and fitting it with a 7mm held promise for a 7mm Whisper type round but alas.....

I'm "overcoming" this issue too since I'm using the Rom M1969 action for my project. But I'm getting away from the removable mag and looking at a non removable mag utiliizing the existing magwell which is already wider. My other approach is to look at machining a whole new trigger group and housing. Which would allow me the additional option of a double stack mag.

quote:

Originally posted by MartytW:
Going to ask some brass maker guy I know about long rimless 25 ACP brass, he'll probably just moan at yet another wacko idea from me ....

That was pretty much the responses I got to that idea. Even thought of getting some 5.45x18 russian brass, which is only about 1 or 2 mm longer than 25acp.

quote:

Originally posted by MartytW:
That or turn the rims off Hornets ....

Yep. there is always that. Or order some 5mm Craig (Centerfire version of the 5mm Rem Mag rimfire) brass - some of which is already turned from Hornet.

Vibe, I was particularly interested in your experience re different 224 bullets in a 22rf bore. I have a BSA Martini 'thick side' with a rf barrel, converted to Hornet. I use Sierra 40grain HP bullets in this. I believe these are a relatively hard bullet (don't seem to do much splat damage to rabbits/hares). But I bought some 45RemHP recently to try. Your experience gives me pause for thought. Have you tried any other than the 45RemHP and the Hornady V-Max bullets for 'size'?

quote:

Originally posted by trepur:
Vibe, I was particularly interested in your experience re different 224 bullets in a 22rf bore. I have a BSA Martini 'thick side' with a rf barrel, converted to Hornet. I use Sierra 40grain HP bullets in this. I believe these are a relatively hard bullet (don't seem to do much splat damage to rabbits/hares).

I had been tempted to try the Sierras and Noslers - These look to be closer to the "Varmint" soft jacketing built bullets and with your results I might just try a box and see.

quote:

Originally posted by trepur:
But I bought some 45RemHP recently to try. Your experience gives me pause for thought. Have you tried any other than the 45RemHP and the Hornady V-Max bullets for 'size'?

No. Like you the experience with the 45HP sort of put the brakes on trying other things. But I have used the Hornady line bullets which include the 33,35, and 40gr V-maxs, the 45gr "Hornet" and the 222 "Jet" (also 40gr I think) all with good results.