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Posted: 4/21/2022 1:38:37 PM EDT
[#1]
I believe 9" or thereabouts is the optimum length for .300 BO. I suppose if one was planning on shooting super sonic exclusively, one would get a little more velocity from a longer barrel.
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Posted: 4/21/2022 1:58:43 PM EDT
[#2]
I wont be shooting supers exclusively as i plan on putting a can on it once the form 4 is processed. I got a 16 for range. I just want to get the optimum barrel length for a .300 cqb rifle I kinda like the idea of smaller barrels for doorway ease of use but just dont want to sacrifice effectiveness in any way.
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Posted: 4/21/2022 2:08:06 PM EDT
[#3]
Quote HistoryQuoted: I wont be shooting supers exclusively as i plan on putting a can on it once the form 4 is processed. I got a 16 for range. I just want to get the optimum barrel length for a .300 cqb rifle I kinda like the idea of smaller barrels for doorway ease of use but just dont want to sacrifice effectiveness in any way. I hear 'ya! Add 6" or whatever of can and a short barrel makes sense. I do believe 9" is the "optimum", but anything 6.5" or longer will work reliably. Others more knowledgeable than I will likely chime in soon. |
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Posted: 4/21/2022 2:15:26 PM EDT
[#4]
I've tested many barrels from 4.75" up to 11.5" in .300 Blk. I use a 6.5" for most things, including hunting out to 200 yards (mule deer). I'd go longer, but i always run suppressed, and I'm a dwarf so an 11" barrel and can ends up in the mud
anywhere 9-11" is great for most anything, going longer gives quickly diminishing velocity gains. to answer your question more directly, for the cqb purposes you're building the gun for, no a 12.5" won't be any more lethal than a 10.5". You're gonna be above the minimum velocity expansion threshold for supersonic rounds at that distance either way, but the shorter barrel handles faster. |
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Posted: 4/21/2022 3:00:16 PM EDT
[#5]
I don't have link for you handy, but when determining the best 300 length for my needs, I found a few charts where folks had run various lengths of barrel and measured velocity.
All of them showed velocity increases all the way to 16". I didn't see any data for barrels longer than that. What I did notice is that velocity increased rapidly, every extra inch of barrel you used, until you got to the 9" to 10" range. After that, the velocity did continue to increase with barrel length, but by diminishing amounts. I shoot suppressed and in a woodsy environment where a shorter gun is best. I chose a 10.5" barrel and its just fine for me with a can on it. Finding the charts that I looked at shouldn't be hard. I don't recall spending a whole lot of time finding them. Ballistics by the Inch is a great resource, though doesn't have 300blk in it last I checked. |
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Posted: 4/21/2022 3:35:32 PM EDT
[#6]
Quoted: So what im about to say Im quoting something ive read im not sure how 100% it is. it sounds valid to me but I dont consider myself an expert by any means. They said on 5.56 because of the supersonic rounds that 11.5" up is the best choice for both velocity and gas pressure. Now my questions. If the above is true, does this also apply to .300 blackout? I have a 16" already and im building a cqb sbr in .300. would 12.5 be more optimum than say 10.5" or even the 7, 8 that supposedly it was designed for. Thanks in advance for the info. Regarding the bolded, no. Larger bores allow more gas expansion and therefore velocity gain is shorter barrel lengths. Since 300blk doesn't have as much powder as other rifle rounds, it's gains (and losses) are less exponential, but exist none the less. 300blk is not optimized for a specific barrel length. Short barrel lengths are desirable to keep subsonic rounds' velocity under the speed of sound. This is typically associated with 9" barrels. Quick and dirty way to find the speed of sound in FPS is to take the current temp in Fahrenheit and add 1055. |
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Posted: 4/21/2022 4:17:06 PM EDT
[#7]
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Posted: 4/21/2022 4:35:55 PM EDT
[#8]
Here's a good watch
 The Best 300BLK Barrel Length & All Things 300 Blackout Answered |
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Posted: 4/21/2022 4:36:25 PM EDT
[#9]
A 9" barrel allows sub's to remain, well, subsonic. A longer barrel will allow sub's to become supersonic which defeats the purpose. If sub's are not in the mix, a longer barrel will yield more velocity. One needs to determine the overall length they want to wield along with the suppressor and go with it. If sub's are not in the mix, 300 HAM'R might be a better option to maximize velocity for the bullet.
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Posted: 4/21/2022 5:13:56 PM EDT
[#10]
thanks for the reply everyone. Im thinking 8.5 or 9" will be what im looking at since I prefer keeping it under 16" canned. Glad it wont effect
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Posted: 4/21/2022 5:19:25 PM EDT
[#11]
300 BO and 5.56 are entirely different animals. Overbore is the diameter of casing in excess of the bore. The greater the overbore the more hotel volume will be needed to burn the powder behind that projectile. The 5.56 had way more overbore than that tiny shoulder of the 300 BO.
While you are at it, look at rifling twist rates. Lots of manufacturers use the same twist rate in 5.56 and 300 BO and there is a reason for this. They did not invest in the machinery to create a faster twist rate. I like 1:5 for 300 BO and it is hard to find. |
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Posted: 4/21/2022 9:06:39 PM EDT
[#12]
With all the pistol length 5.56s out there, not sure why someone hasn’t come up with a round to match up with the shorter barrel lengths.
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Posted: 4/21/2022 9:12:10 PM EDT
[#13]
Quote HistoryQuoted: 300 BO and 5.56 are entirely different animals. Overbore is the diameter of casing in excess of the bore. The greater the overbore the more hotel volume will be needed to burn the powder behind that projectile. The 5.56 had way more overbore than that tiny shoulder of the 300 BO. While you are at it, look at rifling twist rates. Lots of manufacturers use the same twist rate in 5.56 and 300 BO and there is a reason for this. They did not invest in the machinery to create a faster twist rate. I like 1:5 for 300 BO and it is hard to find. yeah I think im gonna end up with a 1/7 most likely I havent seen anything 1/5 |
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Posted: 4/21/2022 9:17:26 PM EDT
[#14]
I went with 8" and I'm happy with it in 300blk. I know AAC said 9" was best though. Basically there's nothing to gain past 9" with subsonic rounds. Now supersonic rounds will continue to gain more velocity with the longer barrels. But it won't gain a ton compared to other rifle calibers. Of course 300blk was made with subsonic rounds in mind first. If you want supersonic rounds I'd go 6.8 SPC for more punch!!
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Posted: 4/21/2022 9:21:35 PM EDT
[#15]
yeah like i said I already have 16" 300bo this is for a canned cqb rifle. I didnt want to run a can on the 16" Im over my m16 days of long ass guns lol.
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Posted: 4/22/2022 11:06:13 AM EDT
[#16]
The most common length is between 8 and 9 inches...but you can go shorter or longer without too much issue. Just depends on what you are using the weapon for.
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Posted: 4/22/2022 2:46:45 PM EDT
[#17]
The 'optimum' barrel length for .300 BLK is 16".
My SBR is 10.5" with a 1:7 twist and it works just fine. |
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Posted: 4/22/2022 9:13:38 PM EDT
[#18]
16" is probably the ideal length from a ballistics perspective but not ideal from a "get the best out of the gun" perspective. That ideal is closer to 10" plus or minus.
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