.358 Yeti -My first Wildcat Adventure!

[Scrumbag]

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.

Would a modern AR-10 not be close to that weight?

 

[Livnoutdoorsxd9]

Maybe you'd get close with ones like the DPMS G2, but there are a lot more AR15s in the hands of shooters than AR10s which makes for an easier barrel/ bolt/ mag swap than in the larger frame AR while being able to still achieve a similar level of performance.

 

[eldon519]

Have you figured out what kind of magazine you would need?

 

[AKMtnRunner]

I love the ingenuity and hope you find a solution to work in an AR15 variant. I have to wonder though . . . if you're seeking 308 win performance (180 gr @ 2600 fps) from a 308 case, what angle are you coming from that hasn't already been tried by AR10 variant designers to strengthen the existing AR15 platforms?

 

[Jim Watson]

Ken Waters got a 200 gr to 2400 fps from a 20" bolt action .358 WIn.
Seem like you would be pushing that smaller case gas gun awful hard.

I think Quickload would be a worthwhile investment.

 

[Ohen Cepel]

Good on you for giving this a shot (pun not intended).

I really like the .308 brass start point and the AR15 platform.
Much easier to get punch out of the AR10 but I'm with you, it's big and clunky in my mind.

Good on you for also taking advice and well intended criticism correctly.

I'll be watching this as it goes along.

 

[redneck2]

I have an AR in .358 WSSM. IIRC velocity is about 2,700 with the 180's/200's. I gotta think the WSSM case is gonna wring all you will get out of a .358 in a standard length cartridge.

Mine has a Shilen Ultra Match barrel. Shoots .4's.

Cases are kinda expensive and have to be fire formed

 

[Livnoutdoorsxd9]

Something similar to the 800 Series bolt from AR Performance is what I'm looking for. That bolt is rated above 62k PSI. Running the short, fatter case at a higher pressure allows for fast burning powders in the magnum pistol range to be used. (i.e. AA1680, AA5744, W296, IMR 4227, and Lil Gun)

Prior to this endeavor I was working with the 358MGP, a wildcat for the AR15 based off a 6.8spc case opened to .358 diameter. With 34g of AA1680, a 180g hotcor was chronographed at 2510fps with the beginning of pressure signs. That case holds approximately 37g of H2O. The Yeti before firing holds 46g of H2O. With a reinforced bolt and ~9 more grains of capacity, I don't see why an additional 90fps could not be gained.

@Eldon519 Mags are up in the air until I have an AR chambered in the caliber, but PRI 6.8 mags have been working well for me with my other wildcats with similar case body dimensions.

 

[jerkface11]

.450 bushmaster mags may work with it too.

 

[arizona_cards_11]

Definitely a beautiful looking cartridge, very balanced. I hope you achieve your goals!

 

[Panzerschwein]

This begs for a supressed tac platform, maybe also SBRd, with ultra heavy weight bullets driven just to the edge of supersonic.

It would be like an American AS-Val, a niche the .300 BLK doesn't really fit as well.

 

[Livnoutdoorsxd9]

Well a lot of time has passed, and a LOT of progress has been made. I have real world velocity and pressure data, and we are right on par with my predictions!

We have successfully pushed a 180g 2600fps from a 16" barrel, and 200g@ 2500fps. I have also been able to chronograph my 12" AR which produced 2435fps with a 180g bullet. All velocities have been achieved in the 55-58k PSI range. Well below the 65K psi threshold of the bolt we are using.

I have gotten the gas port dialed in and it is cycling perfectly. Here's a short clip of 5rds rapid fire:
https://youtu.be/FbJur5nSjlM

 

[Gtscotty]

Very cool! How did you obtain your pressure data? Have you developed any heavy subsonic loads?

 

[Livnoutdoorsxd9]

Pressure data was collected with the Pressure Trace equipment. I have some 310g cast, coated bullets coming for testing with subs.

 

[MachIVshooter]

We have successfully pushed a 180g 2600fps from a 16" barrel, and 200g@ 2500fps. I have also been able to chronograph my 12" AR which produced 2435fps with a 180g bullet. All velocities have been achieved in the 55-58k PSI range. Well below the 65K psi threshold of the bolt we are using.

Well, congrats, and I stand corrected. What powders are you using to hit those numbers at those pressures using a small-ish case and firing out of short barrels?

Also curious how the Pressure Trace is calibrated, and if you had a control to ensure accurate readings. Without calibration, you'd get wildly different numbers from the same load if, for instance, one chamber was 416 stainless with .220" chamber walls and the other normalized 4140 Chromoly with .300" chamber walls.

 

[358Hoosier]

OMG, I totally want one of these. I'm a huge 358 win buff and would love to have a 35 caliber AR.

 

[eldon519]

I'll admit I'm skeptical. Those are 22" .358 Win ballistics from a barrel length 6" shorter with a smaller case size and supposedly less pressure. I'm open minded, but I'm struggling to compute.

 

[Livnoutdoorsxd9]

Well, congrats, and I stand corrected. What powders are you using to hit those numbers at those pressures using a small-ish case and firing out of short barrels?

Also curious how the Pressure Trace is calibrated, and if you had a control to ensure accurate readings. Without calibration, you'd get wildly different numbers from the same load if, for instance, one chamber was 416 stainless with .220" chamber walls and the other normalized 4140 Chromoly with .300" chamber walls.

The powders tested at this point are AA1680, AA5744, IMR 4227, and WW296.

As far as pressure trace, I was not the man operating it. My good friend Bruce, who is now onto developing his 5th wildcat is the whiz with that system. I know he did have to adjust the calibration based on the barrel being stainless versus cmv, but beyond that- it's Greek to me.

I have my share of knowledge on the topic, but with this project, I have not been afraid to ask for help from those that know much more than me. Without the help of those people, I'd still be in the concept phase.

 

[CarJunkieLS1]

When this .358 yeti is available ill be getting one for sure. Bruce is a genius when it comes to wildcat AR catridges. I know him through FB groups and have had a few phone conversations with him. I'm in love with his 7VAR and I own one. It's my favorite rifle. This 358 has got my attention for sure

 

[Livnoutdoorsxd9]

When this .358 yeti is available ill be getting one for sure. Bruce is a genius when it comes to wildcat AR catridges. I know him through FB groups and have had a few phone conversations with him. I'm in love with his 7VAR and I own one. It's my favorite rifle. This 358 has got my attention for sure

You got that right about Bruce! I've got a 7var and 22hellcat of his. You'll be pleased to know that he's been huge in the development of the 358 Yeti, so you know it's been done right! He currently has a 16" AR test barrel for the 358 Yeti to continue pressure testing.

 

[TRX]

You might be able to use .357 Auto Mag dies for that, depending on compatibility of case tapers. Your cartridge is basically a stretched .357 AMP.

 

[Livnoutdoorsxd9]

You might be able to use .357 Auto Mag dies for that, depending on compatibility of case tapers. Your cartridge is basically a stretched .357 AMP.

The 357 amp has a different shoulder angle and the body taper is different from what I gleaned just now. I am having custom dies made for proper sizing of the cases. Up to this point, I have used a 6.5x47 die that I have modified to suit my needs.

 

[Elkins45]

I'll admit I'm skeptical. Those are 22" .358 Win ballistics from a barrel length 6" shorter with a smaller case size and supposedly less pressure. I'm open minded, but I'm struggling to compute.

Yeah. I would be a little afraid of that bolt blowing through my face at those velocities, no matter what sort of enhanced steel it were made from. No offense to your gunsmith and engineer but a 308 boltface on a 223 bolt just scares me at those sorts of pressure. Those lugs have to be quite thin unless you redesigned the extension too.

A 200 grainer at 2000 fps is something I would be more comfortable shooting in volume.

I wish you much luck. I think I would just have built an AR10 in 358 Win and called the extra weight/bulk the cost of safety. It would undoubtedly have been cheaper too.

 

[Livnoutdoorsxd9]

Yeah. I would be a little afraid of that bolt blowing through my face at those velocities, no matter what sort of enhanced steel it were made from. No offense to your gunsmith and engineer but a 308 boltface on a 223 bolt just scares me at those sorts of pressure. Those lugs have to be quite thin unless you redesigned the extension too.



A 200 grainer at 2000 fps is something I would be more comfortable shooting in volume.



I wish you much luck. I think I would just have built an AR10 in 358 Win and called the extra weight/bulk the cost of safety. It would undoubtedly have been cheaper too.

I suppose I didn't articulate the current status of the bolt situation. I am using a bolt and extension specifically designed for the .473 bolt face by a well known manufacturer that has been running this setup with rounds that regularly operate at 65k psi for the past 8 years. I am not using a standard extension, nor am I using a 5.56 bolt that has been machined to accept a .473 case head.

I appreciate the well wishes and concern.

 

[Elkins45]

I suppose I didn't articulate the current status of the bolt situation. I am using a bolt and extension specifically designed for the .473 bolt face by a well known manufacturer that has been running this setup with rounds that regularly operate at 65k psi for the past 8 years. I am not using a standard extension, nor am I using a 5.56 bolt that has been machined to accept a .473 case head.

I appreciate the well wishes and concern.

OK then I feel much better about it.

Drop me back into the "I would love to have one of those" category.