For the .17 WSM wildcats:
I've handloaded .22 WMR (.22 "mag") in the past, by pulling the bullet, adjusting or replacing the powder charge, and seating and crimping a new bullet in the case.
It is an inherently dangerous operation, due to all of the pressure required for the loading operations being exerted on the very part of the case that contains the primer compound to set it off: the rim.
I did have one cartridge detonate in my seating die.
Although that did not immediately stop me from continuing with my experiments, it did have a long-term impact. I eventually gave up on the process - luckily, fingers and eyes still intact.
I do really like the concept, and I had hoped that there would be a .22 WSM (or at least a .20 WSM) put out by Winchester/Olin. But the conversion is not something that's easily done at home, without taking on an unnecessary level of personal risk.
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On your .22-458 SOCOM:
This wildcat is designed to be made by necking down the .458 SOCOM cartridge to .224 caliber. It is similar to .223WSSM, except it has a .473 rim diameter. Overall length is chosen to fit AR15 magazines. Must have pretty good performance for varminting applications. I assume it must be a high pressure round (around 60K psi) … I think AR15 platform will be able to handle it (just like there are ARs in WSSM calibers). Shoulder angle is kept same (27degree). So here are some pros and cons of this concept that I can point.
Pros/advantages:
1) Expands AR15 platform hunting capabilities. Switching from .458SOCOM to this wildcat will only require barrel change (with proper gas system). So same rifle can be used both for close range hog hunting and varminting.
2) .473 rim will let to have relatively stronger bolt due to smaller rim compared to WSSMs.
3) .473 rim will also make easier chambering standard bolt action (short action) rifles in this caliber using conventional bolts. And in that case longer bullets (or not too deep set with more powder charge) can be used.
4) Will fit and feed from AR15 magazines (single stack).
Cons/disadvantages:
1) It will require a set of custom dies and some handloading skills to make the cartridge.
2) It also needs a custom reamer to chamber a barrel.
3) Will need some money to spend. Anyway, these are cons to any wildcat cartridge, right?
I think .223 WSSM load data can be used as a reference for load development.
Of course original .458SOCOM can be necked down from .452 all the way down to .172. However I thought .22 will be most suitable for varmint hunting use (maybe 6mm, too).
.458 SOCOM operates with a max pressure of 36,000 psi, to keep from battering the AR15 receiver and/or shearing bolt or barrel extension lugs. That is why it uses Large
Pistol primers, rather than Large Rifle primers. It's a matter of gas volume produced by the size of the powder charges in the case, more than anything else. As long as the case retains its capacity, pressures must be kept sedate.
Increasing pressure to "standard" bottle neck cartridge levels (50-60k psi) is extremely detrimental to long-term health of the rifle, and possibly detrimental to the well-being of your body parts. The brass case can handle it (with a rifle primer). The rifle cannot.
Keep it at 36k psi, or step up to an AR10/LR308.
Added to that...
A standard AR15 will not reliably feed a cartridge with that shoulder angle and size, shoulder location, and body diameter. Just as the cartridge starts to tilt and "pop free" of the magazine, the nose of the bullet will jam against the breech face and the side of the barrel extension.
Modifications to the upper receiver, barrel extension, magazine feed lips, and magazine follower may help, but a lot of fine-tuning will be necessary.
Also...
.458 SOCOM is based on a "lengthened" .50 AE case, that is then necked down for .458" rifle bullets (not .452" handgun bullets) and modified for the .473" rim. Being based on the .50 AE, the SOCOM has very thick case walls and exceptionally thick neck walls (compared to more 'standard' bottleneck rifle cartridges). Necking all the way down to .22 caliber is not likely to work well without multiple, small increments and repeated annealing steps. And the closer you get to .22 caliber, the smaller the increments will need to be. At a minimum, I would expect to need at least: .458 -> .400/.405 -> .358 -> .308 -> .277/.284 -> .257 -> .236/.243 -> .224" -> final sizing.
Even so, I would predict case failure and loss rates to probably be 30-50% (or worse). When you do finally get the cases necked down to .22 caliber, you'll have incredibly thick necks. Neck reaming AND outside neck turning are likely to be necessary to maintain concentricity and acceptable amounts of neck tension.
The cartridge, itself, could potentially be somewhat touchy about powder charge increases, as well. When you stick 49+ grains of case capacity behind a .22 caliber hole, chamber pressures can increase very rapidly with only minor charge weight increases (like reloaders of .17 Rem, .17-223, etc frequently see).
And, of course, .458 SOCOM brass is both expensive and difficult to obtain. Choosing an obscure cartridge for a wildcat parent always runs the risk of not being able to get brass. Choosing an obscure, expensive, hard-to-find parent cartridge is just asking for trouble.
I own a SOCOM, and I am in the process of building a .475 Tremor (.458 SOCOM necked up to .475 caliber). I have considered many wildcats based on the cartridge. ...But .22-458 SOCOM is not one that would be at the top of my list. There would be a
huge time sink and labor requirement for case forming, and many hours of troubleshooting and finessing just to make the rifle feed.
And, when it's all said and done, you have a "speed limit" - that 36k psi limit - constantly holding you back and keeping you from pushing the cartridge as far as other varmint cartridges would allow; and 30-50% of that expensive brass that you bought (and waited 6+ months to receive) will be in the recycle bin, because it failed during case forming.
.22-250 or .243 Win, in an AR10 or LR308 type rifle, would be a much better choice.
