How Much Does Barrel Length Affect .300 Blackout Bullet Velocity? 

It is very interesting but completely reasonable that during the 7 inch weasel test, you can clearly hear a crack for the shots above 1125 fps and much quieter shots for those under 1125 fps. A clear comparison of subsonic in real time.

I need a follow up video- just do 3 lengths - 7”, 10” and 16” - forget the suppressor since it makes no difference- but run a few different ammos- a subsonic round, a 150 gr fmj, then like a 110 gr match or deer hunting round- I would love to see the velocity difference of each round from different barrel lengths. Great video as always- these are some of the most helpful videos y’all put out

16" Faxon Barrel 300ACC Blackout Hornady 150 Secant Ogive 2.068 COAL CCI Small Rifle WW 296 15.8grains 1966 1940 1957 1952 1943 1940 1949 1957 1940 1935 1946 1949 1947 averge 31FPS spread 9standard deviation 1263 pounds of energy... making it a better choice out to 200 yards over 5.56. Whatever you are shooting is UNDER POWERED when it comes to 300 Blackout.

As someone who reloads subsonic 300blk, I'd like to add a few tidbits. Many powders call for about a 9mm's worth of powder to stay subsonic in a long barrel. With that little powder in a larger case, you get REALLY inconsistent results based on the orientation of the powder when shooting. I'm talking 200-300fps difference, which is INSANE, when the powder is piled towards the primer vs just lying flat in the brass. The shorter barrel length allows you to stuff more powder in the case without hitting supersonic speeds

I don't know anything about your ammo supplier but there is something off about that ammo, the velocity is way under what the 300BLK cartridge is capable of. Either that ammo was intended for shorter barrels and the powder charge was kept low to prevent unburned powder from from igniting outside of the barrel, or that is just way, Way, WAY under powered ammo, you should be seeing closer to 1900 FPS with a 147 grain pill out of a 16" barrel.

The best thing about 300BO is that you can build it however you want for whatever purpose you want. Many guys want a shorter than 8" barrel to shoot subs with a suppressor for "ear safe" home defense or truck gun. I specifically wanted a super gun and I didn't plan to fire suppressed, so I wanted the best balance between velocity with the lighter 85-125gr rounds and length to still keep it manageable and more compact, so I chose a 9" barrel with an 8" handguard so I had something to grab on to. 2200-2500fps with the light supers, and not only can I legally hunt with it, but it is still small enough to be a competent "Home defense" weapon.

Pretty sweet hearing the audible difference of the rounds with speeds below and above the speed of sound out of the sugar weasel suppressed

One of the best vids on the 300 blackout barrel lengths. Of course type of ammo does make a difference, too. Thanks, Clint.

That was insane hearing a round breaking the sound barrier, then the next one not breaking it

I built a nice 7.5” PSA 300BLK recently and I love it. Shoots smooth and cycles without issue being a pistol length gas system and having a full rifle buffer tube and stock. I love the thing and I plan on continuing to build on to it and make it a legendary SBR

Awesome vid. Thanks for taking the time to put all this together. I want .300 to be my next firearm. 🇺🇸🇺🇸

That ammo must be super mild because it was Super Slow.

Thank you for taking the time to make this video. It was extremely informative. I am a huge fan of 300 Blk. I am also a fan of it in a 16" gun and here is why. Using my Surefire SOCOM762-Mini2 and Sig Match 220gr subsonic ammo it is super quiet. However, subsonic 220gr 300 Blk drops like a stone past 25 yards and having the extra barrel length helps push it out there. On the flip side, without the suppressor and using Hornady Black 110 gr you can get some really good ballistics out to 200 yds. I know that I have mentioned both Sig and Hornady ammo, but there is one other company that I would like to give a shout out to and that is American Marksman for their Stryker 150gr 300 Blk. The ammo has performed well in all of my 300 Blk guns, especially my 10.3". American Marksman has good availability of 300 Blk and at $0.66 a round I think it is a good buy,. Their subsonic 220 gr TMJ is running at $1.02.

You need to do this same test with subsonic rounds. With and without suppressors.

That Q “pistol” functions so smoothly.. I wish I had one

In my humble opinion, I think the optimal sweet spot for 300 blackout is 12.5” Just seeing what happened between the 10” and 16” personally I want max velocity and max performance out of sonic & subsonic rounds. So 12.5” is where I’m at.

Hi Clint. I agree with you, the 8 inch keeps it compact which is what you want when moving around.

6fps is less than your max and min string velocity and possibly within your standard deviation, that is pretty consistent ammo. What is most interesting to me is that the change per inch in velocity seemed to decrease as barrel length increased, giving an idea of optimum barrel efficiency. Not exactly certain what the use case for a 145 grain FMJ at 1100fps is, but at least it keeps a few guys at the ammo factory employed.

Whats funny is i was just trying to look this up yesterday for my .300 BLK build. Thanks for bringing it to me quick.

I have a 16inch barrel 300 blk rifle and it rocks.

I've Ben waiting for Alabama Arsenal to finally do their supersonic 300 blackout video and you both drop one on same day. The odds! Great stuff as always Clint!

I am considering building an new gun in .300 blackout for home defense. Not only is the shorter barrels better for freedom of movement, but it seems to me that the slower speeds would be better to help with possible over-penetration. Seeing the differences with different barrel lengths helps to narrow down what I am willing to consider for this build. Thank you!

Thanks for an interesting video. I'd probably choose an eight-inch barrel if I were building one. I'd probably get a small linear compensator. That won't protect my hearing as much as a suppressor would, but it would help a little if I didn't have time to put in ear plugs. Knowing that the 5.5 inch barrel makes the sound uncomfortable means that I wouldn't choose that barrel length. If I win the giveaway, I will probably look for a linear compensator for mine. Seeing that .300 Blackout doesn't have a maximum at a nine or ten inch barrel was a surprise to me. I expected a small amount of increase beyond nine or ten inches, but I didn't expect the longer barrel to give that much better performance.

Great video. Thanks for taking the time and showing us!

I have been seriously considering putting a 300 Pistol together and the barrel length has been one of my recent back and forth me 😆. Great timing. And what a collection of fun there.

That Christiansen Arms bolt gun is a thing of beauty!!! I’m definitely putting that on my wish list!

Cool Test. I have a AR Upper with a 18" Wilson Combat Barrel. I have never tested the velocity but with a 120 grain load I can shoot out to 300 yards fairly easily. The problem is finding 300 blackout ammo to shoot at a affordable price.

Thanks Clint and Classic Firearms team I have been asking for thi content

I've got a 8.3" 300blk and absolutely love it. Just wish it was cheaper to shoot

Hands down THE BEST 300 blk optimal barrel length comparison. Science-y or not, the results and configurations speak for themselves. Really thank you! I have now decided on 9" barrel, appreciate your research.

This was perfect timing for me! A buddy has some .300 goodness, and now I have to get myself some to feel out, as well. Noice 😎👌🏻

Grain weights matter in these tests. I have seen testing going from 7.5 to 16 inch.... with 110gr, 125gr, and 150gr. In previous tests I saw just under 300fps difference with 110gr, 260fps with 125gr and 150fps with 150gr.

Love your channel and the effort you put into all of your content. That being said, I wish you would have tested a 12.5" and 14". I'd really like to see if there is a benefit to velocity between the 14-16" or is there a diminishing return that starts at a length you missed between the 10-16". Also, was the twist rate the same across all those ran in this video?

What is wrong with that Ammo. 1400 feet per second from 147 grain in 16” is SLOW

thanks for sharing! Working on my first AR and 300 Blackout, and was looking at a 7" barrel.

I have a 10" suppressed that I run heavy 190gr subsonic through... love it, no louder than a nail gun. Also have an 8.5" unsuppressed that I run with supersonics in 20rd mags, I keep it in a Rackbone behind the passenger seat of my car, so the shorter barrel and smaller mags make it easier to handle in a confined vehicle interior.

Thanksfor the science show. I have two 10" 300 blackout pistols, and now a 16" blackout rifle. I will use the pistols for inside deterence, and the rifle for across the yard problems. If these don't work, I'll employ the .458 Socom

Seams like the 7.5-8.5” range is the sweet spot for the 300BlK.

This is good information! I’m thinking about building one! Thanks Clint!

The proof is in the ENERGY increases as barrel length increases. It’s hard to make that big round pick up speed, but once that leaves the 16in gun it’s going to SMACK whatever it hits

I've built both a 10 inch and a 16 inch. It's interesting to see the fps difference between those 2 barrels. Thanks for the video and the great info.

I sold my 9" Virtus barrel when I finally got my 6.75", which still makes me tingle in my no-no square. Definitely the best .300blk platform on earth.

That mpp was blowin O's haha that's awesome!! You guys are great as always!

Loved this video, very informative as well as just plain cool, but I remember in the actual giveaway video for the Suger Weasel, you mentioned the rifling, so how does that change with the longer/shorter barrels, and how much does that affect velocity

mcx virtus is the best out of the box rifle around for 300blkout and 556. i love my ar15s and my cqb and battle rifle ones i would take over the sig but only because i built them for me with what i wanted. mcx is awesome and very versatile for mission specific roles.

I'd love to see the experiment on the 45 acp barrel lengths. One of my EDCs is a rock island 1911 A1 FS that I threw a 7" ported barrel on.

Love this video and Gunsngear has another video, covering barrel lengths.

300 Blackout is a brilliant round and adds a helluva lot of versatility to the AR-15 platform, essentially making the AR-15 platform chambered in 3* different cartridges: .223/5.56, .300 Blackout Subs, .300 Blackout Supers. It's basically the successor to PCCs (as it was designed to be), making them _seem_ obsolete (save for costs which, unfortunately matter more _now_ ) But just the fact that the only difference is the barrel swap, you don't need to learn a new gun, you can practice with a 5.56 equivalent or identical PCC setup, and can switch from subs to supers and get 7.62x39 performance on the fly with a magazine change?? That's some video game sh*t! I encourage everyone who can to buy an extra .300 Blackout gun or upper so we can start driving those .300 Blackout costs to be more reasonable.

I too went with the 8" barrel for mine because I plan on using my suppressor on it.

Those velocities seem really low across the board for 147 grain 300 Blk supers.

My 300 blackout has a Ballistic Advantage 6" barrel but it's for home defense and suppressed so it'll get the job done.

I think the biggest difference is in defenses ammo. Want expansion so the faster the better. Either way it’s a great round and so much fun to shoot suppressed.

Exactly the video I was looking for as a rattler owner!

Looks like the rattler is far easier to suppress across more bullet weights in .300blk, and I like that. I got a 5.5in upper on the way to me now, I’ll pair it with a 5in suppressor on a 10in handgaurd. Perfection 👌

I’ve got a 9” SBR in 300 BLK built by Advance Armament Corp. it’s an amazing rifle. Wish the company still made ARs.

Nice video. It would be great to gave such a test with suoersonic ammo too. Because I guess there is the difference with the different barrels even greater.

.22lr barrel length test would be interesting. I've tested it at my house with a Labradar. I found that it didn't slow down even in a 30" barrel. It would be neat if you got similar results.

Clint, since 300 blackout is so popular how about a video showing the difference in impact between standard velocity and subsonic ammo at distances out to 100 yards. Also a video on nods would be great.

I wanna see a part 2 with lengths between 10 and 16!

Thank you for the information Clint.

Please let the viewers know that pistol propellant is used for the 300BO instead of rifle propellant. That’s why you can have full powder burn in such short barrels, and that’s why the 300BO is a great option in short barrel pistols/rifles. Full power in short packages where 4”, or 5” is more than enough. 😉

Always interesting content, thank you.

Great video! Any chance of something similar, but with Supersonic (all un suppressed)?

My sweet 300 Blk is 7.5" with 1:5 twist. Even with the Surefire muzzle device and law tactical folder it is perfect length to fit any backpack.

Ideal 300 blackout build, side charging upper and adjustable gas block with an OFF setting, screw on suppressor set gas block off and have a straight pull bolt action, re open gas block and back to semi auto operation.

Good video, considering getting a .300 blackout and not sure the barrel length to get, your video gave me something to think about and reference, Thanks.

Great content. I love these type of videos that give you raw numbers to compare instead of just someone's opinion. Thanks Clint!

12.5 seems to be the sweet spot for velocity anything longer doesn't have a enough gain for the length

Test the newerish 8.6 blackout.. the recommended 1:3 twist is insane for a barrel

Love the video. My next gun will be in 300BO. Would be curious about the decibel difference with these guns between unsuppressed and suppressed. Something to work into the next video like this. Viewers would get a two for one.

Thanks for doing this. Always wondered if I picked the right barrel length for my "Lab Rat" (300 blk out home build(cheap)). Looks like any length will get the job done.

According to Kevin brittingham, Who was instrumental in inventing the 300 block out. A 9" barrel with a 1 in 5 twist is that is the optimum for the 300 blackout.

Did you give bullet specifics? FPS & suppressed/unsuppressed, I imagine, would be quite different when using subs vs supers

supers will tell a big difference at the barrels lengths 9-16" has a 212fps apart. I have a 10.5 and a 12.5 and l like them both

uh actually.. this is a HARD sell for the MCX rattler to me then at 5.5". it just turned a dirt cheap traditionally super sonic round into a sub sonic by virtue of it's lower velocity. thank you for doing this video!

I'm actually satisfied with this video. Great job ladies and gentlemen 👏

Really helpful! Keep it up!

Love this channel. Stay blessed

I enjoy these type videos. I have to live vicariously through them….im in NY and we cant have shoosh cans

Can the temperature of the barrel before and after and the temperature of the air change the results? Like the mpp 7.5 had same average. Just curious. Also I'd like to build a 300bo ar but is it easy to make it swappable to change caliber?

I appreciate this. Exactly what I asked for! Minus the 14.5"

How about a comparison test between .300 blackout and 8.6 blackout?

If I remember right, the significance of 9" is that it's the minumim length needed to provide enough velocity to reach sufficient frangibility. Someone correct me if that's inaccurate.

The Q suppressors are over bored to reduce back pressure so they may not be the best test for increasing velocity with a suppressor. A suppressor with a tighter bore may make a bigger difference.

One thing I'm curious about it how long it will hold that fps at distance. Where does it drop off at those different lengths. Also I like a 7-9 inch barrel for any 300blk or sub gun because I like have some rail to work with.

What was the twist rate to all of the barrels tho as you've seen that twist rate also matters, ESPECIALLY in 300bo

110grain is rated at 2400fps & with full power ammo it can make a bigger difference than the practice ammo. 12.5" is the best to not compromise EFP that is as munch as a 556 16". EFP u made turned your 300BLK into a 9 mm.

I wanna see a 20 inch 300bo suppressed. Velocity and decibels. Somethin been curious about for awhile. I just wanna see how quite you can get it.

I think the perfect is the q hb, only because its a grail for me.. but seriously the best one is the one you have when you need it. Great video

If hypersonic is not an issue, testing with 110gr projectiles may be more on point. The 147gr. is middle of the road - does not do self defence or silent well.

I was just talking about this yesterday with my coworker! Lol perfect timing

Just love a 16 inch barrel it's the look plus power

I’m very happy with 9 inches. 🤓

IMO The length issue is more of a problem when it comes to subs and twist rate that goes with the shorter barrels stabilizing the heavy rounds

Hand loads with the 110gr Barnes blacktips for my 12.5” cmmg has been a deer slayer combo for me so far…same cartridge from a 9” faxon match grade barrel left something to be desired on a big doe this last thanksgiving… even though it was an ethical harvest, it was clearly not as fast of a dispatch as the 12.5” had provided the previous three years. Going back to 12.5” this season

First time here very good job.

Never use a barrel longer than 31.5 inches on a .300 blackout because your second shot can catch up to your first one while it's still crawling down the barrel.

How come I can’t find any barrels in 14.5”? I would like to add muzzle device to bring it up to legal 16”. Any reason why? I see 16” barrels being offered then it drops down to ~10” and below with nothing in between. Can you offer who makes barrels less than 16” but greater than 12”? Thanks. BTW love your channel!

If you for some reason wanted your main rifle to be 300blk i think a full sized barrel or an SBR with a suppressor would be best, for a good side arm excellent in close quarters 9in is probably what you'd want.

@classic firearms, can you please do a video on the forced reset trigger as I would like to see your opinion on it.