338 subsonic round

[Ron458]

Any intrest in a 338 subsonic round for the AR15? The 338 spectre & Whisper brls are very expensive. Just wondering if there would be any interest. IM if interested.

[redtazdog]

Any intrest in a 338 subsonic round for the AR15? The 338 spectre & Whisper brls are very expensive. Just wondering if there would be any interest. IM if interested.
I have a 300 and want a bigger cal like maybe a 458 socom :grin:

[Ron458]

Dont forget the 50AE! The 500g XTPs are easy to run at subsonic speeds. I am also working on a subsonic 458 based off the 50AE & designed around a 9-10" brl. I was just looking at any intrest in a 338 based round that dies & brass are inexpensive & my brls would run the same as the 300W:smile:

[Spook]

I've got 458 socom , 50 EBG and 510 Whisper that I shoot subsonic...lots of fun.

What kind of twist are you thinking for the 338?

[Ron458]

Ive picked up a 8twist Shilen. I want to be able to shoot a variety of bullets & velocitys like the 300whisper. I heard SSK uses an 8twist for their 338Whisper on the BR case. Im using the AR15 308 dia bolt from MGI(for the socom) Bolt should yield 35K psi. More then enough to give me what I want out of the 44AMP brass I am using. Dies can be had for $30. Seems like a way to get into the 338 game without spending a fortune. Here is a pic of my idea(left) next to the 338Spectre(right).
http://i53.photobucket.com/albums/g61/ron458/338.jpg

[LouBoyd]

Here's another option for a subsonic AR-15. This 600 grain bullet will shoot subsonic from a 16" Alexander Arms Beowulf rilfe with the standard 16" twist. The bullet is available from
http://www.alliancearmament.com/thebeast.aspx

http://www.alliancearmament.com/images/products/detail/600gr.jpg

If I was going to bulld a subsonic 338 AR it would be a 338/7mmBR in a DPMS LR-308. 300 grain 338 SMKs could shoot from the magazine.. Will the 338 Specter shoot heavy low drag bullets from a AR-15's magazine? If not why not just use the 300 Whisper?

[Ron458]

A shorter case on any subsonic round would be best to keep load density up. The 50AE would fill this better than the 50b for that reason. As for the 458, shorter is better again. Here is the 458 Short with 350, 405, & 600g projectiles. I designed this around 9-10" brls. She will get a workout thursday time permiting:uzi2:
http://i53.photobucket.com/albums/g61/ron458/458short005.jpg

As for the 338, with the MGI bolt being released soon I am planing on running the 338BR case & just down load for the subsonic 338.

[LouBoyd]

Ron458 - What are the brands/models of each of the bullets shown in the picture you just posted? Are those standard 458 Socom cases?

For spitzer bullets I'd agree on the 50 AE giiving better load densities than the 50 Beowulf, but using the 600 grain RBT shown above seated to standard 50 Beowulf OAL the load density just right for subsoinic use. The long shank and short ogvie engages the rifling with little jump. The rebated boattail is mostly to use up case capacity and add weight rather than giving higher BCs. It's not a partularly low drag desing though it's mass makes the BC higher than other bullets which will feed though an AR-15 magazine. Yes, it could be used with a 50 AE case in a custom chamber but not in a SAAMI spec 50AE chamber. It was designed specifically for the 50 Beowulf standard chamber and 16" (length and twist) barrel for use in magazine fed AR-15s. I wouln't consider it for a subsonic bolt action. For that i'd use the cartridge next to the far right below. It's 582 gn with a subsonic G1 BC greater tnan 1.0 and will feed nicely from a Rem 700 LA magazine. Its case capacity is close to the larger diameter but shorter 458 Socom next to it. For that you could probably rebarrel a Browning or a Cobb MCR to shoot it if a semi-auto is more desirable. Perhaps even an M1 Garand.

The cartridges left to right are 223 rem, 458 Socom with 280 gn Lehigh flat base, 338/7mmBR with 245 gn Lehigh boattail, 308 Win, 458 Socom with 582 gn Lehigh boattail, 458x2 American with 582 gn Lehigh boattial, and a 7mmStW. The end and middle cartridges are just for size comparison..


http://i174.photobucket.com/albums/w108/ubvri/Ballistics/lehigh.jpg

[Ron458]

350g Hornady SP, 405 Rem SP & I belive the last 2 are 600g Hornady FMJ. I have had these sitting around for some time now. You can still get the 550g FMJs. The cases are 50AE & the rebated rim is the 50B shortened to 50AE length.

[sigmatero]

Why the 44 AMP as compared to either the 10mm Magnum or the 7mm BR? Can you give specifics on the economies (brass price, die price, etc)? I'm thinking of building a .338 Spectre. Thanks.

Ive picked up a 8twist Shilen. I want to be able to shoot a variety of bullets & velocitys like the 300whisper. I heard SSK uses an 8twist for their 338Whisper on the BR case. Im using the AR15 308 dia bolt from MGI(for the socom) Bolt should yield 35K psi. More then enough to give me what I want out of the 44AMP brass I am using. Dies can be had for $30. Seems like a way to get into the 338 game without spending a fortune. Here is a pic of my idea(left) next to the 338Spectre(right).
http://i53.photobucket.com/albums/g61/ron458/338.jpg

[Ron458]

I have the 338BR reamer on the way. The AMP is less expensive but after some consideration the BR case is the way I am going to go.

[LouBoyd]

My gunsmith has suggested that he can make a 338/7mmBR chamber by first running a 7mm BR reamer with a 338 pilot, then run in a reamer for a 338-06 to cut the neck them a 338 throat reamer if the throat needs to be deeper (it will for 300 SMKs) Personally don't want a 338/7BR in an AR-15 becasue the magazine won't handle the long bullets and if it won't magazine feed why bother with an AR? It would work in an AR-10 or DPMS LR-308 which already has the right bolt face. If the magzine is too short to load over 240 grain 338 bullets you might as well use the 300-221. With subsonics about all you get with larger diameter bullets of equal weight is lower BC and less range,

Max weitght for available bullets
224 - 90 gn Matchking
264 - 142 gn Matchking
284 - 180 gn Berger VLD
308 - 240 gn Matchking
338 - 300 gn Matchking
375 - 330 gn Lehigh (solid VLD) 350 Wooleigh not VLD
408 - 375 gn Lehigh (solid VLD)
416 - 582 gn Lehigh (solid VLD) 700 gn cast bullets not VLD
500 - 600 gn SPRBT (for 50 Beowulf or 500 S&W stanadard chambers) Not low drag.
510 - 800 gn Barnes solids

If you know of heavier commercially avaialable low drag bullets in each caliber I'd be interested.

[Ron458]

Dont forget the MGI lowers that except 308 mags. This along with their 308(high pressure) bolt to be released soon you will have an AR10 in the AR15 package.

[LouBoyd]

Hi Ron,
I only see a interchangable 223 - AK47 magazine on the MGI site. Do you have a link about a stretched AR-15 which can take 308 sized cartridges. That would be great for a 338/7mmBR. There are (were) the Cobb MCRs whcih could do up to 300 Win Mag length

[Ron458]

My understanding is they are working out mag issues. Variations in mags & such. Looks like it might be a little longer:mad:

[LouBoyd]

Seems a lot simpler to just go with an LR-308 or AR-10. Both work fine with 308 cartridge length and pressure. It will even handle the 300 Saum 300 WSIM sized cartriges.
For one thing the AR-15 bolt and carrier are too short to cycle a 308 besides being too weak. What's left of an AR-15 modified to 308 which differs from the LR-308? Lots of LR-308 parts interchange with AR-15's. (stocks, grips, triggers,l etc. With decent bc bullets the 338/7BR is a 2.8" (308) length cartridge. With a decent BC bullet the 458 Socom is a 458 Win Mag length cartridge! It jsut wastes their performace capability to use them in short actions.

[Ron458]

Seems a lot simpler to just go with an LR-308 or AR-10. Both work fine with 308 cartridge length and pressure. It will even handle the 300 Saum 300 WSIM sized cartriges.
For one thing the AR-15 bolt and carrier are too short to cycle a 308 besides being too weak. What's left of an AR-15 modified to 308 which differs from the LR-308? Lots of LR-308 parts interchange with AR-15's. (stocks, grips, triggers,l etc. With decent bc bullets the 338/7BR is a 2.8" (308) length cartridge. With a decent BC bullet the 458 Socom is a 458 Win Mag length cartridge! It jsut wastes their performace capability to use them in short actions.
Louboyd, I have to agree with you. I realy do but the only problem is I dont want or need another AR platform. If I were "mainstream" or "conventional thinking" the ony thing in my safe would be my G30 & my Marlin guide gun in 45-70!

[Ron458]

I just finished my 11'brl. Using an 8twist shilen. Just calculating gas port. Running a pistol lenght system. I trim BR the case to an oal of 1.4 & the Hornady 225g Spire point when seated to the grove, 2.255oal drops right into the 6.5Grendel mag. I need to get some 300g 338SMKs & see how they seat in the case. Everything seems to point to this working:smile:

[hatchet]

Can anyone help me with pressures for a 338 whisper?? I have a old 95 C:smile::confused:hilean action and would want to run this baby with 300 grn matchkings for a woods rifle here in pa. These would be set for the subsonic version based on the 7 br. The action is for only 46,000 cup and below.

Thanks for your assistance,

Hatchet

[Ron458]

I see no reason it wont work. My load program shows 300g SMK at 1200fps with H110 running 40k cup.

[hatchet]

Ron,

Thanks for the response. Gunsmith was curious on pressures. Have a great holiday!!

Hatchet

[hatchet]

Ron,

Do you have any load data for the 338/br?? I will be gathering up materials and supplies for this project as soon as i get back to work.

thanks,

Hatchet

[Ron458]

I have QL data & a 300g SMK load data I can send you. Shoot me an email & I will send you what I have. ron458will@verizon.net

[Ron458]

Short video of the 200g Speer hot core around 1700fps.
http://www.youtube.com/watch?v=q7p4zPgAOFo

[Ron458]

I picked up a LMT high strength(super bolt) & opened it for this conversion. Also turned a 16.5" Shilen brl. Mid length gas setup. Breakin rounds(all 20) went into one hole @ 50yds. I was running the 225g Hor. SSP to 1700fps avg. This bolt should give me 45K psi to work with. I am working on the upper limits of the 338BR. 338Whisper was a no brainer.