308 SBR, barrel length's and ballistics

[Scott Clearman]

Long story, but I'm back on track to build a 308 AR.  I have several in .223/5.56, 300BO and I've even bought one in 6.8SPC although I cant find ammo for that one.  Which brings me back to the reality that I have been wanting an AR with more punch than the .223 or even 300BO can send, AND I'm sitting on a few thousand rounds of surplus .308 from back in the day.

My specific question is to help me decide on what barrel length I want.  Originally I was thinking 16", but lately I've been considering something like a 12.5".  This will be for a hunting (hogs, deer, coyotes) build.  Shots will be from 75-300 yards 98% of the time.  I'm leaving the other 2% open although I can't really think of a time I will shoot longer than 300.  I do plan on using a suppressor 98% of the time.

I don't currently reload, and don't have any plans to start reloading for 308.  I have enough surplus fmj for fun and don't mind buying a few boxes of hunting ammo over the counter.

I want a 'light' rifle.  That's subjective I know, but I would say definitely no bull barrels and weighted butt stocks. I'll try to build as light as practical.

So, within those parameters, (light, 308, hunting, 75-300 yards for deer size game and down)  what barrel lengths would folks recommend?  I think it goes without saying that reliability is a must.

[98Z5V]

I have a 12.5" and a 13.5" that only eat Hornady 150gr FMJ-BT handloads, and they're both accurate out to 400 yards.  Maybe more, but that's as far as I've pushed them.  Your surplus ammo should be either 147gr or 149gr, so it shouldn't be far off that, and still work.

Edited March 1, 2023 by 98Z5V

[Scott Clearman]

thank you.  Any idea about feeding factory soft point hunting ammo through those barrel lengths?

 

[dpete]

30 minutes ago, Scott Clearman said:

thank you.  Any idea about feeding factory soft point hunting ammo through those barrel lengths?

 

In my experience they will feed, but the soft points get gashed going up the feed ramps.  My handloads using them were still 1 to 1 1/2 MOA at 100 yards which was fine with me for deer in the woods up here.  YMMV

[98Z5V]

32 minutes ago, Scott Clearman said:

thank you.  Any idea about feeding factory soft point hunting ammo through those barrel lengths?

 

Never tried any, so I can't say first-hand.  Generally, on other soft point ammo through the longer guns, I have seen torn up tips.  Best bet for hunting would be loading up or finding some Barnes solid coppers, either TSX loads ot the TTSX loads (tipped solid copper).  Those things will feed in a gas gun no problem, and kill critters DRT.  Their loaded ammo line is the VOR-TX ammo. 

https://www.barnesbullets.com/product/vor-tx-rifle/

[Scott Clearman]

let me rephrase, will those lengths have enough velocity with hunting ammo for them to expand as intended?

[DNP]

Less of a rephrase and more of a different question.  I have no clue, and should sit out - but your question raises one on my end. What velocity is needed for a specific ammo to expand as intended?  Does that come up in the tables when you’re looking at load information for specific bullets?

Edited March 1, 2023 by DNP

[Scott Clearman]

6 minutes ago, DNP said:

Less of a rephrase and more of a different question.  I have no clue, and should sit out - but your question raises one on my end. What velocity is needed for a specific ammo to expand as intended?  Does that come up in the tables when you’re looking at load information for specific bullets?

I think the info on what the lower limit for expansion is available somewhere.  I say that because I have seen guys who handload reference velocities that a certain projectile they are discussing need.  Having said that, I don't know where they find the information.  I was hoping someone who had a SBR or pistol had used it hunting with factory ammo could tell me just from experience. 

[DNP]

That’s what raised the question for me. Gotta be a way to find out what velocity range you need to be in with a given bullet, then do a little rough math and know if you’ll be close. Or…build it, test it, and be the guy that can answer that question in the future. 

[98Z5V]

Best information is gonna be from Barnes, on those solid copper TSX and solid copper tipped ones, the TTSX.  See what they state for minimum velocity, or minimum ft/lbs.  What's the minimum for hogs, for ft/lbs of energy?  Depends on what kind of hogs you're talking about in your area, more than anything else.  On deer, they say it's 1000 ft/lbs of energy, but that not true.  You can kill a deer DRT with half that, because it's about shot placement more than anything else.  Coyotes, just hit em within what you feel comfortable shooting, and you'll kill 'em.  Make a good shot.

Here's an example, and how to figure it all out.

12.5" barreled 6.5 Grendel.  It runs 2271fps through the chronograph with my handload, loading the Hornady 123 ELD-Match projectile.   Hey, not a hunting projectile, but I'd sure pop a coyote with it, or a deer.  Or a javelina if it got close enough to smell me. 

Here's the chart, click it a bunch of times, and it gets bigger, blows up. 

Now, there's a section in that chart that talks about MPBR - Maximum Point Blank Range.  Hold your sights on the target, dead hold, and you can shoot something out to that distance, and get a hit inside a vital zone, PROVIDED you zero the gun for the MPBR Zero distance given.

Example on that Grendel I've got is MPBR is 290 yards.  MPBR Zero is 247 yards.  If I zero the gun for 247 yards, I can dead-hold anything out to 290 yards, and hit it in the vital zone.  Another cool thing about that, it calculates your ft/lbs of energy at MPBR.   That Grendel is still getting 927 ft/lbs of energy at 290 yards.  Would I hunt it and dead hold it, out to 300 yards?  Damn right I would.

It's math, man.  Weaponize math. 

[Scott Clearman]

9 hours ago, DNP said:

 Or…build it, test it, and be the guy that can answer that question in the future. 

I like the way you think.  

My gut said that a .308 round fired from a 12" or longer barrel would be acceptable for hunting out to 250 yard at least.  I'm in.  Looks like I'm going to build it, and I will test it and let folks know.

Looks like I'll get rid of that 6.8 and start acquiring parts.

[Scott Clearman]

Does this barrel look ok?

https://diamondbackfirearms.com/shop/db-barrel-308-winchester-mid-length-13-5-medium-4150-black-nitride/

[shooterrex]

Probably a better barrel here.

https://www.ballisticadvantage.com/12-5-308-tactical-government-carbine-length-ar-308-barrel-modern-series.html