Home Forums Reloading Big Game Rifles .375 SOCOM load development

For folks in the .375 SOCOM game with me... consolidated data.

With the Sierra 200s back in Stock FINALLY... time to work on some loads further. Asked a friend to run me some QL data based on what we had GUESSED would be good powders... His typing is in blue.

Preamble:

Do NOT use this data under any circumstance. It is totally safe in my gun, but NOT IN YOURS. If you choose to use... you are using at your own risk and ALWAYS start with reduced loads)... so endeth my CYA. Thank You for your attention.

Three guns used:

Remington 700 (22" GM barrel 1:12)
18" AR-15 (AA piston)
10" SBR

Test scopes were 1.2-6 Minox ZA-5 HD (those scopes have since been changed to 2-10 Minox ZA-5 HD... the SBR kept her 1.2-6x). Can is a custom Lane .375 Cory made for me.



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Tested Pills: 200 Sierra (2900s)



0.840" Long

2.126" Loaded COAL (box says 2.130")



Target @ 100 yards (right most group) Max load of A2520 which was 49.7gr 100% fill. Vel: 2385 (ACTUAL was 2575 Average)



Dots are 5/8" or 3/4" (I forget)... see barrel muzzle at bottom of pic for further scale.

Looks like A2520 was a pretty good guess. A couple alternates you may want to try with their max loads (based on 35000psi) are:

A2495 max 47.9gr which is 103% fill vel: 2441
A4064 50.6gr which is 110% fill vel: 2424
AR Comp 45.1gr which is 99% fill vel: 2411
IMR 3031 48.8gr which is 104% fill vel:2405

The above powders listed a higher predicted velocity than a max load of A2520 which was 49.7gr 100% fill. Vel: 2385

Based on the barrel time of the accurate 200gr loads with 49.5gr of A2520, 2.126" oal, 2373 fps, the following loads will produce a similar barrel time (1.254 millisconds):

A2495 48.0gr, however this is a max load at 35477psi.

A4064 50.7, however this is a max load at 35289psi

AR Comp 44.5 gr @ 33614psi

IMR 3031 45.3gr @ 33861 psi


He and I are working on a "Barrel Time Theory" to predict load accuracy across a variety of powders.

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As for the 270... why bother?

I bought these pills (LOTS OF THEM) as Factory Seconds from Midway at $0.18 each... I am really trying to get them to work as cheap plinkers for the AR and SBR...



FYI... I also own a .375 RUM, but whoever wants to shoot a .375 RUM several hundred/thousand times please raise their hand.

SO...

270s are:



1.127" Long

2.213" Loaded COAL (box says 2.215")

[img]http://pic20.picturetrail.com/VOL1325/13762207/24785736/413594132.jpg[/img]

Target @ 100 yards (top most group) THIS LOAD IS BEYOND MAX!!!

39gr of AR Comp at 2.213" says 2074fps(ACTUAL was 1920 AVERAGE), and 37151psi. The barrel time is 1.401 ms. This is definitely a max load based on the program.

The best estimated powders based on 35000psi max pressure are:

A2495 40.2gr 98%fill 2051fps
A4054 42.6gr 104%fill 2046fps
IMR 3031 38.8gr 99%fill 2039fps
AR Comp 38.2gr 94% fill 2035fps

Based on barrel time of 1.401ms,

IMR 3031 39.6gr, 101% fill, 2082fps, 37236psi

I'll report back as we continue our tests

P.S. My water measurements were:

Fired brass with spent primer

183.2 grain empty

242.4 grain full

End of this video is good recap on the Sierra 2900s

https://www.youtube.com/watch?v=lCtvdRHVeaE

Not quite the math of a 35 Whelen, but very much the math of a .375 Whelen.

https://en.wikipedia.org/wiki/.375_SOCOM

https://en.wikipedia.org/wiki/.35_Whelen

https://en.wikipedia.org/wiki/.375_Whelen

Probably the most formidable AR-15 round ever devised out to 250-300 yards.

Neck and neck with the .358 Winchester

https://en.wikipedia.org/wiki/.358_Winchester

Was doing some .358W loads a while back... Using A2520 and 200 gr pills.

SO WHAT???

The charge turned out to be the exact same charge under a 200 gr. pill (just like the .375S) and the FPS was the same (+/-10 FPS)

So yeah... pretty much EXACTLY .358W... just a bigger bullet... and an AR-15 platform