M1A SOCOM how much velocity lost with the short barrel?

[SIGarmed]

Does the 16' barrel cause a significant loss in velocity? How much velocity are we talking here?

I just sold my M1A scout squad rifle that I never used to finance other things. I want to buy a SOCOM sometime next year to make up for it. I already have a National Match that I won't sell for anything so I know how good these rifles are.

 

[Gewehr98]

Most gunrags attribute losses up to 50fps per missing inch of barrel.

The M14's original barrel length was 22 inches, (25 1/16" w/flash hider) so you've removed 6 inches of powder combustion length from the tube with the 16" M1A SOCOM variant. That means up to 300fps velocity loss. You'll have to weigh the benefits of a short, handy M1A modification compared to the decrease in performance with respect to exterior ballistics. There's a certain amount of "kewl" factor that needs to be addressed with the SOCOM mod, too. Regardless, your range table card or chart should reflect that change before you start dialing in long-range zero with that stubby SOCOM model.

My personal opinion is that it brings the terminal performance of the M14 family down closer to that of the 20" M16/AR15 variants, especially at longer ranges.

 

[geekWithA.45]

At the Muzzle:

150 grain .308: 2820 mv = power factor 423

let's lop 300 fps off, and we have power factor 378


62 grain .223: 3020 mv = power factor 187

At 500 yards:

62 grain .223: 1460 = pf 90

150 grain .308: 1205 = pf 180

less 300 fps (I know, there's a curve here, but this is back of the envelop, mmmkay?) still = 135, which is still quit a bit ooomphier.


Incidentally, when I chronoed my 18 inch scout squad, I was getting around 2700+/- 20 out of the 144 grain milsurps, so the 50 fps/inch figure seems reasonable.

Personally, I think the SS is a better compromise than the socom.

 

[Blueduck]

Is the SOCOM's Barrel *really* 16" or is it shorter with a permanantly attached brake making up the 16" limit ???

 

[Art Eatman]

A reasonable rule of thumb for velocity losses:

For the hotshot magnums, around 100 ft/sec per inch.

For slightly overbore stuff like the '06, around 70 ft/sec per inch.

For the .308-style stuff, probably around 50 ft/sec per inch.

Nothing hard and fast, here, but reasonable, based on the various tests where somebody cut off one inch at a time and chronographed the changes in velocity.

Art

 

[OtG]

Does the 16' barrel cause a significant loss in velocity? How much velocity are we talking here?

I just sold my M1A scout squad rifle that I never used to finance other things. I want to buy a SOCOM sometime next year to make up for it. I already have a National Match that I won't sell for anything so I know how good these rifles are.

Well lessee here...
According to my August American Rifleman, they tested 3 different cartridges for accuracy and velocity (measure 12 ft. from muzzle):
Black Hills 150 gr. Nosler BT 2685 fps 2419 ft.-lbs.
Hornady 168 gr. A-Max Match 2523 fps 2375 ft.-lbs.
Black Hills 168 gr. BTHP 2467 fps 2371 ft.-lbs.
all with a 16.25 in. barrel.


From manufacturers sites:
Black Hills 150 gr. Nosler BT 2950 fps 2512 Ft. Lbs.
Hornady 168 gr. A-Max 2700 fps. 2719 ft.-lbs.
Black Hills 168 gr. BTHP 2650 fps 2620 Ft. Lbs.

Unfortunately, they don't mention the barrel length they're using. I have no clear idea, so I'll not speculate.