13.5" 308 vs 9" 300 AAC

AR/M4 Beyond 5.56/.223
1

Is there too much lost in the 308 round to cut a barrel to 13.5" vs staying with a 9" 300 AAC AR 15 using the new barnes bullets that expand out to 300 yards?

From what I have read a 150ish grain 308 bullet will be about 2400 fps from a 13.5 barrel. Compare that to a 9" AAC using the new barnes bullet at aprox (if memory serves) 2100 fps, is anything gained using the much larger 308 platform other than bullet weight?

Example:
LMT MWS with 13.5" barrel, weight with optics/ammo around 10lbs, oal aprox 34"

AR15 300 AAC 9" barrel, weight with optics/ammo 7-8lbs (guess), oal aprox 28"

What would the energy at 300 yards be with both guns? Pick the best ammo you can use. Does the 308 out perform the 300 by a large enough margin to justify the extra weight/expense? Think pig hunting here. MWS is going to be about twice the cost of a dedicated 300 upper to add to existing lower (food for thought).

Maybe rsilvers can put it into his software and run a test.

2

The 308 will be a 150 grain and the 300 BLK will be a 110 grain - so the 308 is still much more powerful.

But short barrel 308s are brutal for noise and blast.

You just need to decide if 300 BLK is “powerful enough.”

3

I think your weight estimate on the MWS is a little optimistic depending on your optics choice. I would expect it to come in around 11-11.5lbs with an Aimpoint and full mag. If you went for the 14.5" PredatOBR from Larue you could shave 1.5lbs from that—still heavy and expensive.

My GAP-10 showed up yesterday (weighs the same as a MWS), and while I think it is an awesome rifle it is heavy and expensive.

AR-15 variants help provide a way around these two variables at the cost of energy, ballistics, and terminal performance—you just have to figure out what is more important to you.

4

I bet that the OP’s weight estimate is correct with a T-1…especially with the new LM8 MWS chassis.

A 13.5" MWS with the right optic can effectively reach out well past 600yds.

The only thing more badass then a KAC PDW is a MWS 13.5" imho:cool:

5

I kinda swore off 308s with barrels under 16 inches. KAC realized this also - they had a 14.5 inch SR25 and changed it to 16.

If I got a 16 inch 308 and was on a smaller budget, I would get the LaRue PredatAR or a SCAR17. With a larger budget I would get the SR25.

I would consider the LMT but I would have to plan to reprofile the barrel to make it lighter.

6

Its really a matter of need.

What is the maximum range you realistically expect to shoot?

Most likely <200 yards for hogs?

The 308 is clearly more powerful with more range.

It is also heavier, more costly and more recoil and more blast.

Any of the AR15 variants will be lighter, more cost effective, have less recoil and less blast.

300 BLK should be quite effective out to around 200-300 yards.

6.8 SPC should be quite effective out to around 275-400 yards, with an increase in magazine cost.

The cost of premium hunting ammo will be very similar between the two.

7

I love the new breed of 16" .308 semi-auto’s.

If I need to go to a shorter barrel, then I would go with a 6.8 mm or a .300 BLK.

8

Whole lotta good advice here.

9

Indeed! Thanks for the replies.

10

I was getting just over 2400 FPS with 147 grain Radway Green through my 16 inch FAL Congo. I would never consider anything under 16 inches for a 7.62x51. It’s just impractical.