338 subsonic round

[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

[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]

Originally Posted by 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.

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

[hatchet]

Can anyone help me with pressures for a 338 whisper?? I have a old 95 Chilean 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.