Help Develop a New Cartridge: The .358 Ocelot

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CmdrSlander

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Highroaders,

I call upon you to help me develop a new wildcat cartridge, henceforth known as the .358 Ocelot. The .358 Ocelot is intended to fall between the heavyweight .458 SOCOM and the much-discussed .300 AAC BLK in terms of ballistics and terminal performance.

The Goals for this Project:

-Bridge the gap between the smaller alternative AR15 cartridges (6.5 Grendel, 7.62x35mm AAC BLK, 6.8 SPC etc.) and the heavyweight calibers (.458 SOCOM, .50 Beowulf).

-Create a relatively (compared to .458 SOCOM, which is like shooting a 12 Gauge when run through an average carbine profile AR) soft shooting cartridge with a large bullet (.358 Diameter) that is suitable for defense, assault (LE/Military), and the elimination of medium game, which is to specifically include reliable one shot stopping of the hogs that plague Texas and the American South.

-Attain ballistic (bullet drop, effective range etc.) performance superior to the .458 SOCOM and .50 Beowulf

-Utilize standard AR15 Magazines

-Utilize a widely available parent case to speed adoption.

-Utilize .358 Caliber Bullets

-Utilize a fairly common rifle powder to speed adoption

I need recommendations on what parent case and powder would be suitable for this new caliber. I hope that this thread is long lived, and though my financial situation prohibits me from investing in the development of this I dream of seeing my concept realized even on a small scale by a better equipped handloader. Note that though the requirements are rather AR-Centric, I would love to see/create bolt guns chambered in .358 Ocelot and could see a definite market for it in shorter barreled "brush guns" especially since the case size limitation imposed by the AR platform means that the .358 Ocelot will likely work in micro-length actions, allowing for very quick bolt operation.

General thoughts on my ideas are welcome.

Consider this cartridge and its development to be fully open source, I do not plan to make money off this and am not in the firearms/ammo industry.

Timeline (will be updated as progress is made):

-Within 6 months I'd like to see standard case dimensions and pressures drafted for the .358 Ocelot.

-Within 2 years I'd like to see factory barrels, bolts and upper receivers for the .358 Ocelot.
 
I'm not really an expert at this, but there isn't much between, in terms of base size between the 6.8 SPC (.42) and 50 Beowulf (.51). Seems like the best parent case would be something like a .308 Winchester (.47). 450 Bushmaster is .50.

A shortened, necked up .308 has the right sound to it.
 
The AR10 is a heavier and less common platform with varying standards, a such I do not consider it to be suitable for the .358 Ocelot. AR15 alternative calibers see much faster adoption because of how common the platform is becoming.
 
The 6.8 SPC cartridge already has good bolts and mags available, and will give you decent powder capacity. However, the already developed .338 Spectre doesn't have much shoulder left and I am not sure there would be enough left for the .358.
338spectre_brass.jpg
 
Since the 9x39mm is based on the 7.62x39mm round, would it have the same feeding problems in AR's?
Click to expand...

Looking at the Wikipedia link, it seems to have a much straighter wall than the 7.62x39.
 
The more I think about using a 308 Win as a parent cartridge, the more it makes sense for a bunch of internet commandos embarking on a new cartridge: lots of available parts due to the AR10 style platform. There will be much less need to make custom parts. Make a reamer and dies and turn the BCG to fit a 308 AR bolt.
 
When taking about engines there’s a saying, “there’s not substitute for displacement.” The same is true for firearm cartridges; when it comes to performance -- case capacity is everything. It’s really as simple as that. Performance potential equals how much powder you put behind the bullet.

Consider the overflow capacity of the following existing cartridges:

.458 SOCOM -- 61 grains H20
.25 WSSM -- 52 gr
.30 Rem AR -- 45 gr
6.8 SPC -- 36 gr
7.62x39 -- 36 gr
6.5 Grendel -- 35 gr
6x45 -- 32 gr
.223 Rem -- 31 gr
.300 BLK - 26 gr

Effective case capacity would be something less once you get a bullet seated, but in general, that’s what we have as a starting point.

Midway between the .458 SOCOM and the .300 BLK (61 + 26 / 2 = 43.5) is the .30 Rem AR. Neck that up to .358”. If you seat a 180 gr Hornady spire point, keeping the COAL at 2.260“, then there’s now about 37.5 grains of empty space behind the bullet.

Keeping with the .30 RAR’s 55 kpsi SAAMI pressure spec, work up a load with some Varget or 4064, two powders that would be ideal for this cartridge’s expansion ratio. You should be able to safely get to about 2250 fps from a 20” barrel, giving 1960 ft-lbs of energy at the muzzle.

Recoil energy would be about 11.2 ft-lbs. Compare that the .458 SOCOM firing a 300 gr bullet at 1900 fps -- it has the recoil energy of 19.5 ft-lbs. So, we're not quite half that.

According to the Matunas Optimum Game Weight Formula this combination (180 gr, .358" bullet, at 2250 fps) would be adequate for animals up to 530 lbs. That encompasses everything up to and including Caribou and all but the very largest Black Bears. Hogs? Not a problem.

Is this superior performance to the .458 SOCOM? Strictly speaking, it can’t be since it’s case has less powder capacity, but it really depends on how superior is defined.

Personally, I’d like to see Remington take the .30 RAR and neck it DOWN to 7mm. Offer up cases, uppers, and all the goodies. Now, that would be something useful and something I’d lay some cash out for. But, you know, we Americans be lovin’ us some thirty cal, so I doubt it ever happens.
 
CmdrSlander,

I guess I'm thinking along the same lines as Zane. The .358 Win is a necked up .308 Win. They just didn't have a need to shorten the case for their application. You could however use that as a model. There are known loads and ballistics data for that cartridge.

If you really want it to be an AR15 cartridge you could shorten the case down to the length of a .233 Rem and then reform the neck and mouth to maintain the 20 degree shoulder and neck length of the .358 Win. From a design perspective you'd be removing length from center of the body. Now determine your case capacity and look for a starting load from the .358 Win load data using a powder charge that will fit within that capacity limit.

I hope to hear more about how this works out for you.

Best of Luck.
 
Since the 9x39mm is based on the 7.62x39mm round, would it have the same feeding problems in AR's?
Click to expand...
7.62x39 has feed problems in AR magazines and magwells. That is due to the 7.62x39 case taper causing the round stack to want to curve, and the AR magwell being, well, non-curved.

Blowing out the 7.62x39 case walls to a straighter design will alleviate that issue.

I'd base it on the 9x39mm.
Click to expand...
Looks like we're done here; the desired round already exists.

:)
 
I would be concerned that .358 pistol bullets might not hold up to the velocities the round could generate. I would also be concerned about feed issues in that platform
 
I don't know that common .358" pistol bullets are the intended projectile.

The original 9x39mm load used a 250gr. bullet.
 
There really isn't much new under the sun.

Lets call it the .35Remington, and be said and done.

Accomplishes what you want, and was originally offered in a semi-automatic. And 100yrs ago, at that.
 
Many years ago Guns and Ammo created a wildcat cartridge the 357x39,a 7.62x39 opemed up to take .357 pistol and .358 rifle bullets. Chambered in a Mini 30 it equaled or slight beat 35 Remington ballistics. Sounds like that's the cartridge you may be looking for.
 
Many years ago Guns and Ammo created a wildcat cartridge the 357x39,a 7.62x39 opemed up to take .357 pistol and .358 rifle bullets.
Click to expand...
Wait! G&A was in cahoots with the Soviets? :what:

Oh...no no, the 9x39mm was totally different. Never mind! <Whew!>

;)
 
Actually, I am curious about the 9x39mm. In looking around the 'web I've not been able to find out whether the Soviets blew the case out to .356" like the western style of 9mm, or up to the .365" diameter of the 9x18 makarov round.

One is technically smaller than a .358, and one is slightly larger, obviously.
 
Is anyone acquainted with the .30x47mm cartridge? It appears to be a shortened .308, used in hunter-benchrest competitions? Would necking THAT up to .358 leave sufficient case capacity to develop desired velocities within acceptable pressure envelopes? And MUST it be put in an AR or AK platform? Would it not work well in a FAL (which is slightly overstretched with the 7.62x51, a detriment to its accuracy), with the reduced case dimensions perhaps allowing the rifle to become a better-than 2 M.O.A. implement?
 
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