Texas Hunting Forum

Suppressed SBR 308 VS 300BLK

Posted By: KRoyal

Suppressed SBR 308 VS 300BLK - 10/06/15 07:22 PM

Looking for something a bit shorter than my current hog setup.

I have a CMMG MK3 CBR 16" with YHM Phantom 30 QD, it wears a SWFA 1-4x scope in LaRue mount. I run the ERGO F93 stock completely collapsed. I have a pretty short length of pull. So with the 8.5" can hanging off the end of a 16" barrel the rifle is pretty unbalanced. Very front heavy.

Currently with stock fully collapsed and suppressor attached the gun is 39" over all length.

Pros for the 308:
I already own the platform so I could pay $200 for stamp and buy the 12.5" CMMG Barrel, 11 MK3 CMMG Keymod Rail, Adjustable gas block, and mid length gas tube all for around $550.
308 hits harder than the 300BLK even in the 12.5" config it will still push the 168's at around 2350FPS
I'm already setup to reload this caliber

Cons for the 308:
Muzzle blast, don't know how that will equate to sound suppression. Yes my suppressor is rated for it all the way down to 10.5" barrels
12.5" barrel would only save me 3.5" of barrel over the current 16" I don't know if that is worth $550 to me
Weight at around 12 pounds with suppressor

Other option was thinking of selling the CMMG since I wouldn't really have a use for it anymore and build a new 300BLK SBR. Would change the SWFA scope over and would still have my bolt 308 for longer ranges if need be. Priced it all out and looks to be around $1300 with stamp to get it built.

Pros for the 300BLK:
Round was meant to be shot suppressed out of a short barrel
With the 8" barrel and suppressor attached I'm looking at 29" over all length, which is pretty dang short
Cycles subsonic rounds, with the new bullets made to expand at subsonic speeds this makes it enticing

Cons for the 300BLK:
Round isn't a show stopper
Not setup to reload the round so will add even more costs to the build
Not sure the effective distance of a 8" barrel with this caliber


What would you guys do?

308?


300BLK?
Posted By: KRoyal

Re: Suppressed SBR 308 VS 300BLK - 10/06/15 07:26 PM

This is actually a closer representation of what the difference in lengths would be.

The top gun is my CMMG MK3 with suppressor attached and the middle is my 10.5" 556 SBR. The SBR is 27" over all length so the 300BLK would only be 2 more inches than the SBR with suppressor attached. That is a really small package!!!

Posted By: DocHorton

Re: Suppressed SBR 308 VS 300BLK - 10/08/15 03:25 AM

In my opinion its not worth $550 in barrel and parts just to save 3.5" on your .308 gun. If it were me and you wanted to keep your .308 I would spend a little more and get a 6" suppressor instead and that will save you 2.5" plus weight and give you two suppressors.

I had considered the same thing as you, but I decided to go as short as possible so I sold my AR 10 and went with the 300 BO with 8.5" barrel. I figure it's good out to about 200 yards and that's as far as I will shoot anyway.

Like you, I still have the .308 bolt gun if I need to shoot farther. I wouldn't even worry about reloading because you can get Chad's reloads for a pretty good price.

Here's my 8.5" 300 BO with thermal..






Posted By: Tactical Cowboy

Re: Suppressed SBR 308 VS 300BLK - 10/08/15 03:59 AM

Subsonic only, 300. For a real gun, .308.
Posted By: J.G.

Re: Suppressed SBR 308 VS 300BLK - 10/08/15 10:46 AM

Is it going to be a walking hog hunting rifle?
Posted By: boonee

Re: Suppressed SBR 308 VS 300BLK - 10/08/15 11:20 AM

I have both, but I really like my 300 Blk. SBR. The whole package just has a great balance. I'm hunting in a river bottom, at a MAX. range of 150 yards. 75-100 yards in the norm. I don't use "expandable" sub bullets, I shoot lead out of mine. 240 grain HARD lead.
Posted By: KRoyal

Re: Suppressed SBR 308 VS 300BLK - 10/08/15 12:58 PM

Originally Posted By: FiremanJG
Is it going to be a walking hog hunting rifle?


Yes sir, we do a lot of hunting on corp land up near Lake Texoma and they don't allow for any off road vehicles so you have to walk it all. We sometimes walk 6-7 miles up and down hilly terrain and through thick brush. The weight really isn't a factor, its really the length I'm worried about.

Thanks for the replies guys.

Doc I already have a titanium 30 cal suppressor coming for a website I did. Just have to wait until they're done.
Posted By: BCJ

Re: Suppressed SBR 308 VS 300BLK - 10/08/15 01:13 PM

For a short hunting caliber you might look at the 6.8spc instead of the 300 blk out. It was meant to be a full power caliber out of a short barrel and works with a 308 suppressor
Posted By: Mike Honcho

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 06:27 AM

I have 300bo sbr and 20" bolt 308 and i think for a dedicated sbr suppressed the 300 blk cant be beat. A reason is load density, the 300 blk really shines compared to others and can make for a very accurate platform in an sbr. Plus you wanna run supers it is a very good cal like 30/30 good out of a 9" bbl with 110 supers. The bees knees would be sbr in 358 mgp aka 35x6.8 spc ii. Supers can even take out elk inside 200yds or 338 thumper sbr or 9mm sbr with 5" bbl shooting 147gr hps this is a sweet carry rig and solid inside 100 yds on pigs. I love a 308 bolt suppressed with 20" bbl, but gas gun 300 bo all the way for factory.
Posted By: KRoyal

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 12:40 PM

That is what I run for longer ranges is a Savage FCP10-SR 20" suppressed. I got my CMMG MK3 up for sale if I can get what I'm wanting for it, I'll be building the 300BLK for sure. Just have to see if anyone bites on my MK3.

Brian thanks for the input about the 6.8SPC I've had one before that Tanner built and it was a very nice gun, but really liking the fact I can use same mags and bolt as the 556 for interchangeability.
Posted By: J.G.

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 01:26 PM

Run the ballistics on a .308 shooting 150 grain bullets, I picked 150's to regain some velocity that was lost in a short barrel and a gas gun. You know about the MV they will be leaving for a given barrel length.

Compare those ballistics, specifically ft/lbs of energy to the .300 B.O.

Which ever hits the hardest is the one I would pick, because I hate hogs and they should be killed with extreme prejudice.
Posted By: KRoyal

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 02:06 PM

Originally Posted By: FiremanJG
Run the ballistics on a .308 shooting 150 grain bullets, I picked 150's to regain some velocity that was lost in a short barrel and a gas gun. You know about the MV they will be leaving for a given barrel length.

Compare those ballistics, specifically ft/lbs of energy to the .300 B.O.

Which ever hits the hardest is the one I would pick, because I hate hogs and they should be killed with extreme prejudice.


Here are 2 calculations. The 308 has a substantial amount more energy than the 300BLK, but with the 12.5" barrel and 8" suppressor I'm still looking at lugging around a AR10 with 20.5" barrel. Not to mention the length added to the gun with the difference in AR10 and AR15 receiver lengths.

Something doesn't seem right though. I calculated my 10.5" 556 shooting Hornady 75gr BTHP and it shows to have more energy on target than the 300BLK.

125 Hornady SST running at 1850FPS out of a 8" barrel.

168 Hornady AMax running at 2340FPS out of a 12.5" barrel

75 Hornady BTHP running at 2500FPS out of a 10.5" barrel
Posted By: KRoyal

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 02:11 PM

Chad is showing he gets 2230FPS out of his 125SST's out of a 16" barrel, even if I could get 2000FPS out of a 8" the energy increase on target compared to the 556 doesn't really justify a new $1200 SBR LOL.

125 Hornady SST running at 2000FPS out of a 8" barrel
Posted By: J.G.

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 03:16 PM

"Something doesn't seem right though. I calculated my 10.5" 556 shooting Hornady 75gr BTHP and it shows to have more energy on target than the 300BLK."

That does not surprise me in the least. That is why I wanted you to run the numbers.

In order to gain ft/lbs, of course you need first bullet weight (and BC for down range), but it also has to have velocity to deliver any energy. What if you stood 50 yards from me and I just threw a bullet at you? It wouldn't hurt you and you would throw it back while calling me a bad word. But if I sent it out of a rifle then it's a different story, same projectile, but it now has velocity which equals energy delivery.

I suspected a short .223 with a sizable bullet would hit harder than a .300 B.O., but I wanted to see what the calculator told us. Looks like you either stick with your short .223, or build a short .308 IF you are concerned with energy delivery from a short barreled rifle.
Posted By: Brother in-law

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 03:24 PM

Where does quietness of the rounds weigh in?
Posted By: KRoyal

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 03:48 PM

Yea Jason, that's what I am thinking. May just stick with the 556 with a the 75gr BTHP which stabilizes fine out of my 10.5" 1:7 twist barrel. Save my money and just buy a ton of the 75gr ammo.

Patrick, I don't really care about the quietness as long as it is hearing safe. Yes, of course quieter the better, but its not a huge deal. I love shooting subs out of my 308 but subs are really just a novelty to me. I'll be hunting with supers, I know the 300BLK supers will be quieter than the 308 supers but not a real discernible difference from a hear stand point. You'd probably need a dB reader to really tell the difference. I have a stubby 5" suppressor on my 556 right now and it is hearing safe, but not as quiet as the 556 shot with the my Phantom 30 attached. Might just get another 556 YHM adapter and put it on my 556 and put the stubby on my 22LR upper.
Posted By: TexFlip

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 04:00 PM

Why not just build a 300blk SBR upper for around $300 and use it on the SBR lower?
Posted By: KRoyal

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 04:34 PM

Because that makes too much sense, like full guns not uppers and lowers. Thinking of building a sbr lower because I don't like just having an upper.
Posted By: TexFlip

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 04:44 PM

I get it. I buy optics for guns I don't own so I have an excuse to buy the gun.
Posted By: KRoyal

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 04:45 PM

Lol yup
Posted By: shumpertdavid

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 05:03 PM

Since you already have the SBR lower with a stamp, you could build an upper, see if you like it, and if you do then file for the stamp and finish out the SBR lower for the 300. I built a 7.5" 300 pistol the first part of this year. My first suppressor approval just came back and I'm currently awaiting the suppressor arrival. Then I'll SBR the 300. My buddy has the same basic setup I do currently. With the pistol buffer, sig brace, 7.5" barrel, running through his magnum can it's the length of a standard 16" ar. Shooting his subsonic loads it has the same point of impact at 50 & 100 yards. So far we've seen no signs that the bullets are not stabilized in the shorter barrel shooting subs. It is quiet and puts a smile on your face with each pull of the trigger.
Posted By: lglidewell

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 09:20 PM

I've got both as well and also a 308 bolt gun. The 8.5" Noveske barrel on my 300blk out is the cats meow! Sucker is small, light and still easily maneuverable with my 308 cal can. My DD MK18 556 10.3" barrel shows 26" on the paperwork so my overall length of the 300blk out is almost 2" shorter.

Under 200 yds, that 300bo will do what you need. Ammo is readily available until you get your reloading stuff ready. Right now I'm shooting the cheap Remington UMC 120gr (supersonic) you get from Academy for like $13-$14 a box. I haven't tried them, but they also make 220gr subsonic as well for $17.50 a box.

I was on the fence a long time about the 300. But finally a buddy talked me into it and now I bring the 300 SBR EVERYWHERE with me. I still need to upgrade the handguard.




110yds DRT. The exit hole was the size of a 50 cent piece with the cheap Rem UMC 120gr.
Posted By: KRoyal

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 09:57 PM

Dang that gun looks tiny LOL. Still on the fence bang
Posted By: KRoyal

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 09:58 PM

But the 12" 308's are sexy and pack a hell of a punch.

Posted By: J.G.

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 10:12 PM

^^That^^ Do that!
Posted By: KRoyal

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 10:48 PM

wouldn't be too bad I'm thinking. Would be a freaking hammer!!
Posted By: KRoyal

Re: Suppressed SBR 308 VS 300BLK - 10/09/15 10:50 PM

12.5" 308 next to a 7.5" 556

Posted By: J.G.

Re: Suppressed SBR 308 VS 300BLK - 10/10/15 12:49 AM

Stop it!!!

Now you have me wanting a short AR-10 to go on the lower I have.

nidea Short 6 Creedmoor
Posted By: J.G.

Re: Suppressed SBR 308 VS 300BLK - 10/10/15 01:10 AM

Scratch that. 12" 6.5 Creedmoor. Split the difference between a .223 (5.56mm) and a .308 (7.62mm) Load it with 123's or 130's thick fluted barrel and hang a 10" Tiger Shark on the end.

Straight up gangster!
Posted By: KRoyal

Re: Suppressed SBR 308 VS 300BLK - 10/10/15 01:46 AM

Haha that's what I'm talking about up up
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