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Old August 07, 2018, 14:41   #1
jhend170
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Wondering about wildcat development

So I'm looking at the popularity of the 6.5 projo recently, and wonder what more could be done with it or a 6.8 (.270). I got to thinking... what would happen if we plugged one of those into a .458 Socom case? I realize that's some serious necking down of the case, but it would seem to be pretty similar to the WSM cartridges that I already have a love for. With a case capacity of over 61gr as a .458 socom it's actually greater than a 6.5 Swede and Creedmore, within 1gr of the 8mm Mauser, and double that of the Grendel. I see the potential for a very fast, flat shooting cartridge that could outperform the Creedmore and a lot of others from an AR-15 platform. Has anyone done it? I'd be very interested, as short fat cartridges have greater potential for accuracy. I'd say ideally it would have an Ackley-style shoulder, but I'm thinking the feeding issues would render that a no-go in the AR, but the standard neck would likely be ok without much of an accuracy price. What do you all think?
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Old August 07, 2018, 17:11   #2
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I think I'd buy/build an AR 10 in 6.5 Creedmoor and call it good.

Forming dies, custom reamers et all gets expensive, rather spend the money on brass, bullets and trigger time.

The 6.5X40 is about the most 6.5 badass bang you can get out of the AR 15 that I'm aware of. When I am aware that is, ya know.
You could go Ackley and do a 30deg. shoulder and add two more powder grains if you like. Using Rem 6.8 SPC brass should uncomplicate things a bit knowing that round will work in an AR 15 PLATFORM.

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Old August 07, 2018, 18:28   #3
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"If you build it, they will come". I love wildcats, in fact some poor heir of mine is going to have a stroke when they go to the store to by ammo for Uncle Huey's cool looking rifle they choose out of the pile to discover nobody makes ammo for it or if it's one they do will be five dollars per trigger pull. Tore down both my AR's in 20 Tactical and said no more AR cats then promptly fell in a TAC 6 and a 270 AR barrel. What you have is a fine idea and might require alteration of feed ramps (an upper is only $50 on sale) and your kitty barrel is always going to be a kitty so no loss if decide you don't want to clean it's litter box anymore, so chump like me will buy it.

458 SOCOM Political digression alert:
Remember when go to the 458 case you drop to ten round capacity. If your making magic like swinging a 458 SOCOM hammer it's worth the loss in capacity as zombies lay down when hit with a 458 SOCOM. Darn shame Clinton wussed out after the Blackhawk incident and pulled us out of Somolia. We could have stayed in that, done our job saving lives and showing Bin Laden who was Adid's puppet master Americans don't back down. But after Mogadishu and withdrawal from Somalia Osama bin Laden even denigrated the administration's decision to prematurely depart the region stating that it displayed "the weakness, feebleness and cowardliness of the US soldier".

Had Bill Clinton's Secretary of Defense not refused to release our M1 Abrams tanks sitting on ready the battle may have played much differently. Why fly the M1's over if going to leave them in the parking lot? Reminds me of Hitlary's decisions in Benghazi. Like her husband's refusal to send troops into Rwanda believe had she been elected we would be having troop cuts, military budget cuts to go with raising taxes to fund bringing all them terrorists to U.S.

Since the 458 SOCOM was developed as a response to the amphetamine jacked up skinnies, had we stayed in that game and pushed the 458 SOCOM through the pipeline faster the 75th Rangers and Delta force may have had a much better advantage in their quick and quiet raids as could have dropped their hostiles first shot using subsonic ammo so not to draw hundreds of skinnies into each A.O. in first minutes of a snatch & grab. Would like to get some real first count reports of it vs 5.56 in putting down the Al Queda trained skinnies.

Back on topic
Decreasing body taper and lessening the shoulder angle to get more case capacity which was Ackley's standard M.O. might be a problem to do with the 458 as need some body taper to help case release from chamber wall and say a 30 to 60 shoulder angle to aid in feeding. Next would be modeling the resulting case in ballistics software to try and determine where your bullet diameter is going to fall in the range from optimum to overbore. Have my fair share of overbore cartridges that throat life is measured in hundreds of rounds for more overbore to 2,000 for some of the lesser overbore rifles. Have done cryo freezing, melonite, moly coated bullets and all sorts of tricks to extend bore life of overbore cartridges but if truly overbore no trick will make a throat last long so would try to solve that with research and computer modeling before having a reamer made.

I found this thread over at barfcom about issues with the immense pressure on a case only designed to handle lower pressures and a bolt with a 35,000 psi maximum operating pressure due to how much metal has to be hogged out to fit the rim of the case is going to present some potential issues.

https://www.ar15.com/forums/ar-15/_3...g_/121-623076/

With people pushing pressures of smaller diameter cases upwards of 70,000 psi don't think the chamber pressure will be a deal but how much pressure the brass, primer and bolt can take. Remember the 458 SOCOM uses a large pistol primer which is made of a softer and thinner metal than rifle primers but if look at 454 Casull and 500 Smith. The pressure impulse of a straight wall pistol case where a big bullet is being fired from a relatively short barrel using fast powder (also some pressure bleed off after bullet jumps from the cylinder to forcing cone of barrel) is going to be much different than an overbore bottle neck rifle cartridge. Of course you could use rifle primers in the 458 cases as the difference in pistol primer and rifle primer size is length and it's only about the thickness of a sheet of paper but high primers are a horrible way to cause a rifle to fire when bolt closes so you would need to use a rifle primer pocket reamer to cut your primer holes to proper depth and then I would uniform and debur flash holes as its something I do to all of my cases, even pistol.

But we can look at cartridges like 460 Smith & Wesson which uses large pistol primers operates at 60,000 psi but the 500 I believe uses rifle primers. I would buy good quality 375 SOCOM brass rather than 458 as a lot of your sizing issues have been already handled. I would start with the 375 SOCOM case then first reaming the primer pockets out to rifle primer depth and using rifle primers. After that would then do best possible modelling and computer simulation to determine final bore size. I would lean toward 0.277"/6.8 being absolute smallest size and then looking at 0.284"/7mm (I am a huge 7mm fan and own them from 7mm-08 through 7mm Rem Mag along with 7mm Practical and 7mm RUM) believe the 7mm/375 SOCOM would work similarly though not as stout as the 7mm SAUM with its short fat case. Could use the same 60 shoulder angle as the 7mm SAUM and bet would be able to easily work through any feeding issues.

Would also look at 30 caliber and 338 as each have a wide variety of very aerodynamic projectiles and your probably extending throat life with every increase in bore size but the lower B.C. using same weight projectiles in the 2834"/308"/338" range as bore size increases steals from your objective of turning the 458 into a flat shooting "short magnum". If this was my project odds are due to my love of 7mm would order up a 7mm with 60 shoulder angle varient on the 458/375 SOCOM case and barrel along with dies and start working loads.
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Old August 08, 2018, 09:52   #4
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Thanks for the input. Looks to be worth looking into further. Like you, Huey, I figured the .277 to likely be a bit easier to work cases down to, but the 7mm idea certainly has merit as well, and there has never been anything wrong with a .30 of course. My primary thinking though was short-fat case with a high-BC projo in the 130 to 150gr range, and that falls right into 6.5 to 6.8 territory, but a 7mm should certainly work as well.

So where would you start for chamber reamers? What I foresee as a significant obstacle is a barrel in one of the chosen calibers that can be cut to the 458/375 case size. Much like the excessive metal removed from the bolt face, can't remove too much from a chamber either and remain structurally sound. Also, who can make custom dies?
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Old August 08, 2018, 15:58   #5
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The barrel is the easy part once you have a reamer. Would check with Dave Manson, GA Precision, Pacific Tool, Clymer and the usual suspects. Would ask them if already done anything similar to your project before go too far as might be somebody out in Montana killing coyotes with exactly what you are thinking of already. Once you have your reamer Whidden, Warner, Hornady, Redding, Lee and others will spin you up a set of dies using your reamer.

For a barrel would buy a full 1" barrel blank in caliber chosen and send to whoever you might want to use to chamber and profile it for you. White Oak Armament, Deadshot Barrels, X-Caliber and many more will chamber your blank, turn it down to desired profile and install barrel extension. Considering you are building a single stack rifle might want to discuss a custom barrel extension that has a fat centered feed ramp and then modify upper to mesh. Would also have them heads pace your bolt as one less issue to bite you on the @$$.

Without Google searching believe reading where 458/375 SOCOM has already been necked down to 0.357". A 35 caliber version doesn't make a huge change and would be a single step forming 375 brass down then trimming. As much as I like 7mm seems like 308 caliber would give you least amount of trouble and widest variety of projectiles but smaller bore you go flatter it will shoot. My favorite bolt rifle calibers for building flat shooting rifles in past have been 224, 257 and 284. Bigger and then have always stayed with already developed cartidges like 300 Win Mag and 338 Lapua. Have done more oddball 224 and 284's of all others combined. 22-250 Ackley Improved and 7mm Practical are my two favorite cats followed by 22 Hornet Improved.

If had unlimited funds and better manual machining skills would be turning out a couple of wildcats per year. Right now am interested in Nosler cartridges/cases and could spend a couple years just working with the 22, 26 and 28 Nosler. Have three 22 Nosler AR's as can screw them up myself and with bolt rifles don't see the need as my Ackley Improveds and new 22 CHeetah will outrun the Nosler round all day long. Believe it won't be long before I have a 28 Nosler even though already have too many 7mm's. 6.5 is relatively new caliber for me as did build an AR 15 in 6.5 Grendel didn't shoot 200 rounds through it before selling the barrel and bolt.

Am liking my 6.5 Creedmores as started with a Tikka T3 for 500 to 850 yard coyote field have access to. It's a commercial poultry farm 20 minutes from my house and every evening there are yotes lurking about trying to slip into the houses with hundreds of thousands chickens. When Springfield released their 6.5 Loaded M1a have to have one and liking it so can't say anything bad about the flat shooting 6.5 but wonder how taking the 458/375 SOCOM all the way down to 6.5 and it's odd how an increase in 0.007" from 257 calibers has overtaken them so quickly. It does give you basically a 40 grain increase in bullet weight and better ballistic coefficient so it may be a big ding in quarter bore offerings in coming years for us quarter bore fan boys.

If your inclined to do a 6.5 wildcat on the 458/375 SOCOM case don't let me talk you out of it as might likely be the best bore/bullet for the job. If have a selection of dies and especially bushing dies playing with a few cases just to see how the brass reacts to being manipulated down to different diameters might be a inexpensive way to start the process. I have all sorts of case forming dies for the intermediate steps of mashing parent cases to smaller versions or wildcats as well as bushing dies. I did search for 375 SOCOM bushing dies which would ease your task but don't exist in my searches.

I did find this cartridge design drawing on a varmint website asking for comments but OP never mentions if went beyond a drawing.



If this has been done then basically your good to go on what the cases will take in being worked. I don't see any sense in it with so many hotrod 224's already but whatever floats someone's boat. Experimentation is the mother of invention. Hope you take this venture past discussion as am interested in its results and if works will be happy to rent your reamer and help offset your development costs. Remember if you do come up with a successful cat can recoup fair amount of your cost renting out reamer to others who like your idea and results. If it's a 7mm will probably rent the reamer as can't stand not owning a new 7mm wildcat. 7mm bullets like 6mm just seem to love floating for obscene distances and flying true as does 6.5. I don't want to like 6.5 but can't argue with it as found it works too.
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