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Has anybody taken the shortened 308 case similar to the 270AR, 7mm Valkerie, and the 358 Yeti and made other cartridges? I have three in mind, a 5.56, 6mm, and a .338.

The .338 is the one I'm most interested in. I'd like to do a 12.5" barrel similar to what LivnOutdoors68 and BiggDawg did with the 358 Yeti. I think in a short version, it'd be right on the heels of an SBR .338 Federal, except in an even lighter and shorter package.

One nice thing about the 338 caliber is the large choice of bullets. Some of the bullets I'd try would be the light barnes bullets, 180gr Accubond, 200gr BT, and some of the sub 200 grain cup and core bullets.
 

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Has anybody taken the shortened 308 case similar to the 270AR, 7mm Valkerie, and the 358 Yeti and made other cartridges? I have three in mind, a 5.56, 6mm, and a .338.

The .338 is the one I'm most interested in. I'd like to do a 12.5" barrel similar to what LivnOutdoors68 and BiggDawg did with the 358 Yeti. I think in a short version, it'd be right on the heels of an SBR .338 Federal, except in an even lighter and shorter package.

One nice thing about the 338 caliber is the large choice of bullets. Some of the bullets I'd try would be the light barnes bullets, 180gr Accubond, 200gr BT, and some of the sub 200 grain cup and core bullets.
I had a 338wssm at one time 18". It would only push a 215 Sierra to 2550fps. Almost double the weight of a 6.8 at the same velocity but still slow enough that the bullets may not expand at distance.
 

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there is the 6mm br, 6brx

i made the 6mm lynx which is a stretched 6 brx using lapua case, same length case as the 270ar, and my 257 bobcat. we push 105's at 3050 and 95's at 3250 with it.

i also have the 22 hellcat on the x 47 case that has 22-250 or a little better performance it is for the 65 grain and under 223 bullets. it is a straight neck down of the lapua 6.x47 brass then trim to 1.8.

i have ran numbers and played with 338 version in ql and quickdesign i just didn't like the numbers well enough. same with 8mm but i am leaning towards doing the 8mm just for fun but i may base it off the br case or the new dasher case from norma which would make it a touch shorter than the valkyrie and let a few more bullets fit.

after running them all the 270ar and 7mm Valkyrie i think are the 2 best/ versitile powerful rounds for the ar15.
 

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I've always thought a good wildcat for the AR would be a 308 cut at the shoulder with a .429 bullet, similar to a lengthened 44AMP. A 300gr bullet would have an OAL around 2.0"
 

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Has anybody taken the shortened 308 case similar to the 270AR, 7mm Valkerie, and the 358 Yeti and made other cartridges? I have three in mind, a 5.56, 6mm, and a .338.

The .338 is the one I'm most interested in. I'd like to do a 12.5" barrel similar to what LivnOutdoors68 and BiggDawg did with the 358 Yeti. I think in a short version, it'd be right on the heels of an SBR .338 Federal, except in an even lighter and shorter package.

One nice thing about the 338 caliber is the large choice of bullets. Some of the bullets I'd try would be the light barnes bullets, 180gr Accubond, 200gr BT, and some of the sub 200 grain cup and core bullets.
270 AR and 7mm Valkerie need a longer barrel for the performance which results in a heavy rig for an ar15, a 308 family cartridge in a G2 variant would be better for ammo availability and be about the same package weight/size

the 358 yeti has the advantage for a short light rig (12"-16" barrel) and still have some performance, as long as you dont plan on poking at distance

I would guess 338 would be closer to 358 yeti???

all depends on what a guy needs and wants
 

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Why not 338 Spectre? uses available 6.8 bolts and mags. Also look at the price of 338 bullets before you go through the trouble of building one.
 

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Why not 338 Spectre? uses available 6.8 bolts and mags. Also look at the price of 338 bullets before you go through the trouble of building one.
Where would one find a barrel? about 4-5 years ago I looked and wanted a 338 Spectre but never could find a barrel. I look every now and then and still no luck.
 

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270 AR and 7mm Valkerie need a longer barrel for the performance which results in a heavy rig for an ar15, a 308 family cartridge in a G2 variant would be better for ammo availability and be about the same package weight/size

the 358 yeti has the advantage for a short light rig (12"-16" barrel) and still have some performance, as long as you dont plan on poking at distance

I would guess 338 would be closer to 358 yeti???

all depends on what a guy needs and wants
I don't agree on barrel length. An 18" bbl on the Valkyrie run right at the edge of 7mm-08 performance. I can easily get 2500 with 160 gr. in that bbl if I need a heavy bullet. My rig uses a standard A2 stock, and even with a scope the weight isn't excessive. It balances very nicely and has excellent accuracy, especially with the 139/140 gr. bullets.

The .358 Yeti is running between the best .35 Remington and the .358 Win, neither of which was designed or intended for long range shooting. Any bullet suitable for either of those will work just fine in the Yeti.

The key to these rounds is the bullets available for them. Any of the .223, 6mm, .277, and 7mm are moving fast enough that expansion isn't an issue. Neither is the selection for the .358 an issue, except for maybe the 250 gr. spitzers. Any of the 225 and under will work dandy at Yeti/Rem/Win velocity.

For the .308, 8mm, .338 diameters most of the bullets are designed for full sized standard or magnum length rounds. You can't push them fast enough in an AR format to make them work properly. Also, once you get above 7mm, if you keep the weight down so you can generate enough velocity, the fatter the diameter, the lower the BC and the short the range overall. I think that's one reason the .338 Federal has never been much of a noise. If you can live with the shorter range potential, and the limited selection of suitable bullets it would probably work fine. To me, the 7mm Valkyrie is the top of heap in terms of power in the AR-15 format for normal range use. For a short range thumper (200 yds or less), the .358 Yeti or the .45 Vrap is more than enough.
 

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Why not 338 Spectre? uses available 6.8 bolts and mags. Also look at the price of 338 bullets before you go through the trouble of building one.
I'm currently working on a spectre now. Doing research on powders and bullets using quickload.
 

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I'm currently working on a spectre now. Doing research on powders and bullets using quickload.
Let me know how it goes with the 338 Spectre loads.

I've got a 10.5 barrel and brass from SBR. Dies case holder and case gauge from CH4 dies.

The voices in my head said why do 9mm AR when you can do a subsonic rifle.

So far so good, Just waiting on bullets. Some 338 hunting bullets are $1 each or more, crazy.

Hawk bullets put in a custom order for me for a 300 grain bullet that will expand at slower velocity.
 

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Barrels and brass have been up on SBR since at least Jan or Feb 2016. I got the 10.5"
Had it cerakoted and just put it in a products side charging upper last night.
 

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The Spectre was designed as a low pressure SBR cartridge that used 10mm brass? With 6.8 brass you can load it up, interested to see how it turns out for you? I would think basing it on the grendel case might work better though?
 

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The Spectre was designed as a low pressure SBR cartridge that used 10mm Magnum brass? With 6.8 brass you can load it up, interested to see how it turns out for you? I would think basing it on the grendel case might work better though?
Fixed it for you
 
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