I like wildcats.
And being an avid predator hunter, I've gravitated toward 'hotrod' type cartridges...fast & flat is where it's at!!! Maximum point blank range and terminal performance on critters are key elements for a 'hotrod' to improve upon, over factory available cartridges. Ideally, the performance gains should justify the extra time, effort & expense of wildcatting. That's never set in stone, we all like what we like...
Several years back, I built a .22-243Win. The 1:7.7 Krieger launched 75Amaxs nearing 3500 fps, and they sure can fly at that launch speed! But then, I saw a friend's (slow twist) .22-243AI, and couldn't stop wondering what that "Improved" case could do with a faster twist??? So, built a .22-243AI on a 1:8 Brux, and that has been my 'favorite' predator cartridge for a while now. Fireforming brass on summer 'chucks & LR steel targets was good fun, and the AI'ed case allowed for another 100+ fps gain over my previous straight .22-243Win. A longer throat & full case of slow burn H1000 allows my .22-243AI to run 'cooler', mitigating throat erosion for this overbore cartridge. Have a coyote killin' friend who swapped a new barrel on his .22-243AI after 1500 rds of 80Amaxs, and it still shoots under well 3/4moa as a fireforming barrel. Lots to like about the .22-243AI!
So, where's this all going, you might ask???
Well, the same 'wildcat' itch has begun to fester & I kept looking at all this SAUM brass & those Redding 7SAUM dies...wondering "what if"...
What if I necked a SAUM case down to .224?
That question has been bouncin' around in the brain bucket for a few years now. Well, a wild hair grew from my azz, and decided to spend some time on what this monster might behold???
First thing to consider is: bullet integrity. My .22-243AI is throwing a 75Amax @ 3600fps from a 1:8 twist barrel, generating ~324,000 RPM. Needless to say, that is ALOT of spin! Every bullet handles RPM differently, depending on its design & construction. Going over the edge on RPM may result in bad things happening, from inconsistent penetration, "splashing" on animals, to outright "poofs" where the bullet never even makes it to the target. So, keeping a bullet intact & happy is of paramount importance! With the huge increase in case capacity, a .224 caliber SAUM is prolly gonna push a 75-80 fast enough to make 'em quit...
So, easy answer to address excessive RPM? Slow down the twist rate! Let's assume 3750fps as an MV for a 75gr bullet from this .224 caliber SAUM wildcat. From a 1:8 twist barrel, that 75gr bullet would be spinning over 337,000RPM!!! NOT GOOD, that number kinda scares me. I sure don't wanna invest all this time, effort & expense to start blowing bullets up after only a few hundred rounds down the pipe. And I sure don't want the bullets that can handle that stress to be "splashing" on a coyote!!! The whole idea is to kill them with extreme prejudice & authority where they stand! Otherwise, this just ain't worth it. BUT...if ya drop down to a 1:9 twist, that 337,000 RPM magically drops to 300,000. Still ALOT of RPM, but despite a 150fps gain in MV, its actually considerably less RPM that my present 1:8 .22-243AI. That bodes well for keeping bullet jackets intact, and coyotes in the dirt. Me likey...
However, there are some things that need to be checked to insure a given bullet will fully stabilize from less twist. Enter: Berger's wonderful Stability Calculator!
http://www.bergerbullets.com/twist-rate-calculator/
Given that same MV of 3750 fps, a 75gr VLD is "marginally stable" from a 1:9 twist barrel, with a factor of 1.2. That is @ sea level & 30°F, atmopsherics toward the lower end of intended use. Given the conservative MV estimate, I'm OK with a stability factor of 1.2, so that finalizes the twist rate for this .224 SAUM @ 1:9...
Now, what brass should I use? Necking down from .300SAUM is not practical, especially given that there is 7SAUM and 6.5(SAUM) 4s brass on the market. Just happened to have some brandy new Norma 7SAUM brass, so let's go with it! I used bushing I already own, and got brass necked down in three steps. Before doing so, I did remove the stem from my Redding Type S FL 7SAUM die, so it would not interfere with the decreased neck ID. A bit of Imperial Sizing Wax, and here we go!
1st bushing: .291
2nd bushing: .270
final bushing: .258"
That was easy!
(.252 bushing at right will be final tension bushing, as you'll see later)
I decided on that last .258" bushing, as it would allow for a close fit for getting that necked down brass onto a .224" mandrel. Turns out, my K&M ExpandIron only had to open the necked down brass about .001"...nice!
After truing ID on the .224" mandrel, I checked neck thickness & concentricity. Concentricity was not bad, given all that squeezin', but they did measure .018-9" That's a bit thicker than I'd care to run, so...time for the K&M turner! But first, have to address case length, as all that necked down brass has to go somewhere. Case length increased over .010" from virgin 7SAUM (~2.023--->~2.034") So, a quick trim got them all uniform @ 2.025", and now the shoulder will index true on the neck turner...
Set the K&M up and got to shavin'!
I did feel the cutting mandral take a bit of material from inside the neck, and I turned juuuust slightly into the shoulder to keep any potential issue of 'donuts' at bay. Viola, a nice, true .015" neck thickness...
Final thing, pick a bullet & find a seating depth! Seeing as how those finished cases ended up with nice, long necks, and this is gonna be a fire breathin' dragon, I didn't want to start too long on OAL. Basically, I eyeballed an 80Amax up & went from there. Here's an 80Amax @ 2.770", base of bullet is just above the shoulder, and there's plenty of bearing surface to chase lands. this length isn't set in stone, just wanted to get a baseline 'dummy' round sent out to JGS to get a reamer print worked up...
Here's what a loaded .220 REDLINE looks like!
Since this sucker is gonna run right at/beyond the redline of any .224 caliber I'm aware of, the name seemed appropriate
Loaded round measurement of .254, (.224 + .015 + .015)
That .252 bushing in the pic above will allow .002 tension upon re-sizing, should work OK for the time being. If this monster shoots & yields intended performance, I can see a set of custom dies in the future...
So, there ya have it! A .22-7SAUM...aka the .220 REDLINE. For reference, heres the REDLINE next to a 6.5SAUM4s /140JLK...
That about does it, for now!
Dummy is off to JGS, I'll await a print to confirm specs, then get a reamer ground! In the meantime, will be impatiently waiting to get this monster throttled up. ~71grains of capacity under a .224 caliber boolit is gonna make some heads spin, I hope!!! Quickload predicts both H1000 & Retumbo to have great potential at modest case pressure...
Until then, thanks for coming along on this wildcat ride!!! Will keep y'all updated...
