.358 Yeti -My first Wildcat Adventure!

[Livnoutdoorsxd9]

.358 Yeti

The .358 Yeti is a mid-bore wildcat being developed for the AR-15 platform with the balance of speed and power in mind. It is based off plentiful 7.62x51 nato brass shortened to 1.646" and necked to .358 diameter. I chose to base it off of nato brass for the fact that it is the thickest, meaning that any other brass with the .473" head will be useable. The chamber has been designed with brass making in mind meaning there is no neck turning necessary. Simply chop the brass at the neck/ shoulder junction, run through a sizing die, final trim, and chamfer/ debur (Sound familiar?) A slight increase of capacity will be gained once fired, but I do not classify this round as one requiring fire forming.



My performance goals for this cartridge are to get a 180g projectile up to 2600fps from a 16"-18" barrel and a 200g to 2500fps. Testing will determine how close we can get to that goal.



Useable projectiles are in the 180g-225g range with the option of lighter projectiles such as those for 38/357 and 9mm as well. The cartridge is designed around the primary use of 180-200g projectiles such as the Speer Hotcor, Hornady interlock, and Hornady FTX. Some Barnes and Nosler offerings are also possible with the removal of the ballistic tips.



A strengthened 458 SOCOM bolt will be used to accommodate the .473 case head of the parent brass. Additionally, I have spoken with a well known barrel extension manufacturer and I are discussing a newly designed extension to allow for better feeding of the .358 diameter bullet. This should handle up to 55,000psi , and pressure testing will be performed in a Savage model 10 to ensure loads stay within those levels.



Latest progress:

Earlier this week I received the die that I had modified for forming 358 Yeti brass from my gunsmith. Now that I am able to form brass to the proper dimensions, I am able to get the last few measurements needed to complete the reamer print. Once those measurements are determined, I will send out for the reamer and gauges. When the reamers are delivered, I will then have the first 358 Yeti barrel chambered for my Savage. That's when the real fun begins!







Welcome to the beginning, fellas! Feel free to share ideas, ask questions, or just tag along for the ride. This is going to be fun!



Here is a video of the brass forming process:

[video]https://www.youtube.com/watch?v=sii2wC9RnAk[/video]



These are the first makeshift cases made in a 257 Bobcat die, then expanded.





These are the cases made with the newly modified die. (Much Better) along with one next to a 277wlv





5.56-.358 Yeti-7.62x39





277WLV-.358 Yeti









Formed Brass





Example of Extension (Not actual piece)





Bolt

 

[Panzerschwein]

Very cool! It reminds me of the Russian 9x39mm cartridge.

http://en.wikipedia.org/wiki/9×39mm

I think .358 Yeti would be perfect for an SBR with suppressor, kind of like an American AS Val.

 

[MachIVshooter]

Neat idea, and I like .358 bore!

Having said that.............

My performance goals for this cartridge are to get a 180g projectile up to 2600fps from a 16"-18" barrel and a 200g to 2500fps. Testing will determine how close we can get to that goal.

Ain't gonna happen at safe pressures. The much larger .35 Whelen will barely hit those numbers from an 18" barrel, and the full size .308 cannot manage to spit out a 180 from a 16" AR any faster than 2,500 FPS, with most of the loads I developed running closer to 2,350.

I think you'll be looking at 2,100-2,200 FPS max with 180s. To hit you goal, you'd need the .308 AR platform and the already extant .358 Win. loaded hot.

 

[Livnoutdoorsxd9]

Neat idea, and I like .358 bore!



Having said that.............







Ain't gonna happen at safe pressures. The much larger .35 Whelen will barely hit those numbers from an 18" barrel, and the full size .308 cannot manage to spit out a 180 from a 16" AR any faster than 2,500 FPS, with most of the loads I developed running closer to 2,350.



I think you'll be looking at 2,100-2,200 FPS max with 180s. To hit you goal, you'd need the .308 AR platform and the already extant .358 Win. loaded hot.

I appreciate your interest, and constructive criticism, genuinely. However, I have already come within 100fps of those numbers in a different 35cal wildcat based off a 6.8spc case. The 358 Yeti has 9 more grains of capacity than the one based off the 6.8 case.



Looking at Hodgdon reloading data, the Whelen operates at a max of 50,000 psi. The velocities shown for various loads are in the 2750-2890fps range from a 24" barrel. Approximating a 20fps loss per inch all the way down to 16" puts velocity in my projected range of 2600fps for a 180g. Now I know that its not a complete apples to apples comparison since the Whelen is using much slower powders than the Yeti will use, but it is an indication that I'm not too far off in my estimation.



All load development will be done in a Savage model 10 chambered in the round so that pressure testing will be able to be done. By the time I'm ready to move to the AR15 platform, we should have a more robust bolt and extension available to handle the 50-60k psi operating pressure. Testing may also show that I do not need to run pressure that high to achieve the velocity I'm looking for.

 

[Robert]

This looks like a very interesting project. Please keep us informed on your progress.

 

[taliv]

cool

are you going to get that revolver chambered in it too? that would be kind of a fun pair

 

[jerkface11]

What about bolt strength with the larger case head?

 

[bannockburn]

Neat wildcat concept. Look forward to seeing your results with both cartridge and gun.

 

[Livnoutdoorsxd9]

What about bolt strength with the larger case head?

I am currently working with a bolt manufacturer than specializes in high strength bolts for larger than standard case heads. Material will be added, possibly to the point of redesigning the barrel extension, in critical areas in order to handle the increased pressure and bolt thrust. I realize this all sounds pretty vague, but we're at the drawing board with the bolt at this point, so as I know more- I'll share more.



The Young Mfg bolt is sort of a jumping-off point for putting the cartridge in the AR, but there is a good chance that I won't even use it.

 

[eldon519]

Is there any particular purpose or design goal you have in mind beyond just velocity? Like hunting, filling a niche or performance gap, etc?

Could be interesting to get a fast twist barrel and try some heavy subsonics in the 300gr range.

 

[Livnoutdoorsxd9]

Is there any particular purpose or design goal you have in mind beyond just velocity? Like hunting, filling a niche or performance gap, etc?



Could be interesting to get a fast twist barrel and try some heavy subsonics in the 300gr range.

The main purpose of the round is to be a hard hitting hunting round in the lightweight AR15 platform at an affordable cost. Looking at the other 'thumpers' available for the platform, even with reloading, they are still pretty costly to feed. If I am able to achieve my anticipated velocities, the 358 Yeti will provide more energy than the 6.8, 300blk, 450 Bushmaster, 458 Socom, and 50 Beowulf.







Subs will be something that I'll play with down the road. I'm planning on building a Form 1 suppressor for the 35 cal projectile, if nothing else, for shooting supers while hunting. Lots of possibilities with this one!

 

[Walkalong]

Very interesting for sure.

 

[jerkface11]

Wouldn't it be easier to base the round on a cartridge already established in the ar15? 458 socom comes to mind.

 

[Livnoutdoorsxd9]

Possibly, but the price and availability of 458 brass versus the price of milsurp 7.62x51 brass is night and day. Also, the operating pressure of 458socom is 35k psi. As you choke that case down, the same powder charge increases pressure, forcing you to down load the cartridge. That would hurt the performance.

 

[jerkface11]

I'll be keeping an eye on this.

 

[Elkins45]

I can see myself enjoying one of these with cast bullets for some (relatively) cheap big bore auto fun.

 

[Clint M]

Interesting, looks like a fun project. I have seen wssm uppers have you looked at going that route ? If you have to go to a tungsten bolt be careful as the material is brittle, not to mention expensive. I'm not an AR builder so I'm not up to date on what's available.

 

[Livnoutdoorsxd9]

I have seen the WSSM uppers, but going that route leads to brass scarcity and increased cost. The bolt being developed will still be steel; 9310 with a proper heat treat will be used. The differences will be in where material is added to prevent breakage.

 

[jerkface11]

450 bushmaster brass might be a good parent case too.

 

[Livnoutdoorsxd9]

Yes it may, but again you run into the big difference in brass availability and price. $25/100 for once fired 308 versus $46/50 new Hornady

 

[MachIVshooter]

I am currently working with a bolt manufacturer than specializes in high strength bolts for larger than standard case heads.

The bolt being developed will still be steel; 9310 with a proper heat treat will be used.

9310, being the second most common bolt material after Carpenter Steel's C158 alloy, is only about 7% stronger than the "standard" C158. It's a very good steel (when properly treated and tempered), but a far cry from a super alloy.

The amount of bolt thrust you're going to see, even at moderate loadings, will likely be too much for the AR-15 sized bolt lugs. Remember, too, that even if you get the bolt to hold, the reciprocating lugs in the barrel extension are the other half of the equation.

I think I'd be looking at an entirely different bolt design, as in machining a .308 AR bolt to fit the 5.56 carrier, and reducing the lug OD slightly to compensate for the smaller RE OD that will fit the 1" bore of the 5.56 upper. Something along the lines of taking the standard .880 down to .800". You'd still have a whole lot more engagement and beefier lugs than a 5.56 bolt.

 

[Scrumbag]

Interesting idea.

My question is why not start with an AR-10 and use 358W?

 

[Livnoutdoorsxd9]

I don't have a clear cut answer on the bolt and extension at this time, but it is more than likely that a completely redesigned bolt and extension will be developed for this cartridge. What exactly will be needed as far as strength will be determined by the pressure readings I get from the savage bolt gun.



The AR10/ LR308 platform doesn't interest me. I had one for a brief while and didn't care for the associated weight. A 7-8# AR15 in a potent round like this is much easier to handle in the field to me, and I believe most hunters that would utilize the round would agree.

 

[MachIVshooter]

What exactly will be needed as far as strength will be determined by the pressure readings I get from the savage bolt gun.

Do not conflate chamber pressure with bolt thrust. Totally different animals. Two cartridges with identical bore size and case capacities can have very different bolt thrust. You are going with a short and (relatively) fat design; it'll have about 25% less lateral surface area than a straight walled case of the same internal capacity. Less surface area in contact with the chamber=less friction=more bolt thrust. You also have a shoulder, which further increases bolt thrust vs. a straight case. Case taper matters too, although the .308 case has very minimal taper.


Not trying to discourage at all, just offering my input as someone pretty familiar with wildcatting and hot rodding cartridges, as well as metallurgy and machining.

 

[Livnoutdoorsxd9]

I know they're not the same, but the chamber pressure plays a role in the bolt thrust.

I appreciate the input! I'm by no means an expert, and appreciate any and all info I can get to help make this project a success.