How Does Barrel Length Change Velocity 

I'm more than a little jealous of that pistol pack. Still, it is further proof that Paul does indeed "like the classics".

I’m a new shooter and finding your channel has been one of the best sources for finding a1 content. I’ve learned so much in very little time. Very much appreciate you!

Unless I’m working I automatically stop whatever I’m doing. And turn on the video as soon as I see that PAUL HARRELL notification. Mr. Harrell is the man!!!

This isn’t a gun channel, it’s a science channel featuring guns

I think it's fascinating to hear the subtle changes in sound with the different barrel lengths during the shooting portion.

The most educational firearms videos on RU-vid.

One of those differences in velocity might be due to the ammo companies selecting a powder that has its best burn in a 4 inch barrel.

Nothing like watching Paul Harrell while maintaining your guns

I was thinking “Pistol Pac” almost as soon as you started talking. And you found one! 👍This is a great comparison. Too bad Ballistics By The Inch isn’t still collecting data; they could certainly use this. Thanks!

Yup, I am a fan of the 4" barrel. That Dan Wesson set is beautiful.

Hi Paul A resource that may be relevant to this topic is a website called "ballistics by the inch". They have tested multiple calibers by cutting down a long barrel 1 inch at a time. They also have a section on the effect of various cylinder gap distances. Very interesting stuff. Not trying to take anything away from your presentation, just thought it may be of interest.

Sad to say, I know exactly what Mr. Harrell was referring to when he mentioned trying to find the right part of the trifocals to aim through. As my octogenarian father says, “getting old is not fun, but it sure beats the alternative... “

4” barrel is optimal balance for carrying and velocity for 38 spl/.357. That’s why most revolvers are offered in ~4”. The adage is for every additional 1” of barrel, there is a gain of 100 FPS. But as Paul stated, it depends on gun and ammo and there are diminishing returns. I think it was Shooting Times that used a Ruger Blackhawk and cut the barrel down 1” at a time and measured the velocity. Article was probably 25 years ago.

I love Paul's pedantic obsession with good testing. Most RU-vidrs would have gotten different models of revolvers at different barrel lengths and called it a day.

What I've learned from this is what I always suspected- Fiocchi is light on powder, heavy on the box's suggested FPS number.

And what is the only logical answer to this predicament?: The Dan Wesson Pistol Pack. Of course! I still remember when these revolvers came on the market, they seemed like the coolest thing since the invention of coca cola

It doesn't matter! 2 inches is large enough!!!!! *starts crying*

The one point I would like to make is that the point of Complete Combustion is not necessarily the velocity vs barrel length inflection point - it is often after, and very rarely before then, instead being the point at which the force on the bullet resulting from pressure differential inside the barrel drops below the force of frictional drag on the bullet. As propellant burns, it indeed builds pressure, and the bullet begins moving before that propellant has fully burned (ideally - see various overpressure failure scenarios). Pressure will only increase for as long as the propellant burns, but that pressure increase will only continue as long as the increase in gas volume outpaces the dynamic increase in volume behind the bullet. Most powders burn fast enough with enough volatility (the amount of gas created per mass of powder) that this isn't an issue, but it can happen on rare occasion. Even when combustion completes (in situations where the bullet hasn't yet cleared the barrel), there will very likely still be a large pressure differential acting on the bullet in the barrel. As the bullet accelerates, the frictional drag on that bullet will increase, being proportional with the bullet's velocity. As long as this frictional drag is less than the force created by the pressure differential, the bullet will continue to accelerate. As the bullet travels down the barrel, the internal volume behind it will continue to increase, which will lower the pressure differential and resulting force, lowering the bullet's acceleration until a point where the frictional drag overcomes the force of the pressure differential, slowing the bullet back down. Air pressure will also build up in front of the bullet as it is being accelerated, as the air in the barrel has to go somewhere, and this will contribute in various measures to reducing the efficacy of progressively-longer barrels. In short, in the overwhelming majority of cases, a longer barrel will yield higher velocities, but it will do so with diminishing returns (requiring a linear increase in mass and length for a diminishing increase in velocity), and even then only to a point where an even longer barrel will actually hurt your velocities. A 16-inch barrel will do quite well with standard-pressure 9mm, for instance, getting pretty much everything it can out of it. Velocities just barely start to fall off from their peak at around 18 inches, so something like a 24-inch barrel would have quite poor performance. Most sources I can find claim that 9mm pistol powders undergo complete burn inside 6 inches of barrel length, but there is still a marginal increase (+10%-15% depending on load) in muzzle velocity up to 16-17 inches of barrel length.

I see Papa Paul drop a video. I click.

Came to learn about muzzle velocity in relation to barrel length, left Googleing around to buy a Dan Wesson Pistol Pack...

Great topic and nifty test equipment. I liked how you tried to mitigate the other factors by using the same frame but different barrel lengths.

The most impressive part of this video is avoiding all the jokes, aside a small one.

Paul, I appreciate you for your service, skills and experience in this field of study and practice. I find that you always do a great job collecting and showing your topic data with a variety of weapons, ammunition and testing mediums. Your analysis of each topic, the data and the results are interesting, insightful and often helpful in my own journey with weapons, ammunition and accuracy on the range and in the field. Thank you and keep up the great work on your channel. I wish you great future success in all your personal life goals. Thanks again, sir. Thomas

Paul you are the best! You have set the standard on all gun related reviews!

Great job Paul (and team). From the thousands of videos I’ve seen, I’m pretty sure you’re the first to actually mention there are other factors in velocity, and definitely the first to actually overcome that obstacle in demonstrating it. It did seem to show the heavier bullets did take a little longer to get up to speed, but I was surprised that 8” made little difference. My gf insists that it does.

Very interested in this topic. Thanks to those who annoyed Paul enough to make him do it.

Good topic. I remember reading Elmer Keith's book where this was discussed.

Count on Paul to find something like "the Dan Wesson Pistol Pack". I love it, thanks for being awesome , Paul.

What a great topic! Velocity has always been a major contributing factor when it comes to the handguns I choose and the specific round round that's best for said platform. Tons of people don't even consider this, and when they do it seems like the choice is based on the fastest round possible. I've always wondered if there was some kind of equation to go by when it came to estimating velocity from one barrel to another. It took me a long time to find the best round for the 4.5" pistol I use for the home. So many resources out there seem to test in barrel lengths of 3-4". I've also heard a steeped chamber can greatly effect velocity too.

I concur with virtually everything in your explanation about how barrel length affects muzzle velocity. The quibble is with the relationship between pressure build up and bullet pre-muzzle movement. Some years ago I had two clients. One was a handgun manufacturer, who, as a result of more modern piezo pressure sensors, was interested in the same question but uncertain as to how to develop data to answer it. The other was a scientific outfit whose capabilities seemed to be exactly what was needed. I put both clients together and was rewarded with the opportunity to go along for the ride and see what was learned. And, for the record, putting these two groups together was my sole contribution; I claim no personal expertise on the subject. It turned out that for loads like mid-range to factory normal using propellants like Bullseye or Unique, peak combustion chamber pressure occurred before the bullet began to move out of the case. For higher pressure rounds using typically “slower” propellants, such as Win 296/Hodgdon H110, the bullet began to move before peak combustion chamber pressure was achieved, but only by a very small amount (less than about ¼ to ½ of an inch, from memory). A couple of other things of possible interest that I learned. No. 1 is that the point of peak chamber pressure signals the completion of whatever degree of propellant combustion is going to happen. No. 2 is that as the bullet begins move down the bore, the effect of the Ideal Gas Law and the resultant increase in combustion chamber volume causes post-combustion combustion chamber pressure to decrease. However and No. 3, so long as combustion chamber pressure during down-the-bore bullet travel exceeds a given value (dominated by friction of the bullet within the bore), bullet velocity would continue to increase (up to the point of bullet exiting the muzzle and combustion pressure venting to the atmosphere).

Since I only see pistols there, I’m going to ask this question ahead of time, as I begin watching. What is the effect of a 16 inch barrel on a 9mm PCC? I ask because I have been told that 147 grain for instance, is ideal for this length. I’m assuming because the barrel speeds this heavier but usually slower round up. I want to confirm the validity of this. Edit: loved the attention to detail and dedication to giving us the “boring” stuff (that isn’t boring). I see a Paul Harrell video and am watching within minutes.

There's a group called ballisticsbytheinch that did some pretty extensive testing back in the day with barrel blanks for several dozen calibers and cut them down inch by inch while recording the results. Their data is still published online for anyone interested.

Dan Wesson is so choice -- just an amazing interchangeable kit. I love my CZ's! +1 Like

14:23 Man I was not expecting that lol. Excellent demonstration, as usual.

I tried the trifocals and it was too much for my brain to handle. Every time I would approach an on coming car, it looked like starlight in about 5 different directions.I stuck with the bifocals. Great video as always!

WOW! I stopped the video just to say THANK YOU! and "Three Cheers for the Dan Wesson Pistol Pack!" SOOOO COOOOOL. Now I will watch the rest for the rational data with an attempt at emotional detachment. But if I had a tail, it would be wagging.

Good test. I’m a bit surprised there was not more difference from 4”-6” and 6”-8”. I suspect most factory loads are optimized for the more common barrel lengths so 6” is probably about the longest that would give you any significant gains. If you roll your own and use slower burning powders you could probably see a more significant difference in the longer barrels. I use 7.5” and 6” revolvers for hunting on occasion and also reload, but I don’t own a chronograph unfortunately so I don’t know if any of my loads are really getting the most out of my pistols. Maybe it’s time to invest in a chrono.

I was curious why I hadn't seen a new Paul Harrell video in a while... Found out I was magically unsubscribed by RU-vid again. Don't be an idiot like me and make sure you're still following Mr Harrell for his great videos!! Keep up the great work Sir!

One thing to consider is that it takes more energy to accelerate the faster you go, so an increase from 1200fps to 1300fps is not the same additional energy on target as an increase from 1300fps to 1400fps. The returns might not be quite as diminishing as they seem simply by looking at chronograph velocities.

Thanks for the video, Paul. That pistol set sure is nice!

That Dan Wesson is a sweet gun. I have one with a 6in and i love it. Also I called "The Dan wesson pistol pack" right before he said it. I was very proud of myself XD

That suitcase looks great - reminds me of the one I saw in the "Taxi driver" when Travis was buying guns

Very informational as usual. Thank you team PH

The greater velocity is probably due ALSO to the greater amount of time that the pressure is acting on the bullet. Pressure exerts a force. A force over a time frame generates an impulse which generates momentum. Momentum is equal to force times time (longer barrel equaled greater distance and therefore greater time and greater momentum).

Someone must have blown all that orange lung tissue onto the ground with a 9mm

Beautiful Dam Wesson pistol set sir. Thank you for doing this demonstration. My take away from this is that after you hit 6" in barrel length you are quickly approaching the point of full combustion for the powder charge. It would be interesting to see if different calibers would have different barrel lengths where this effect begins.

I recently streamed the TJ Hooker pilot episode. Hooker has a Dan Wesson pack in his trunk and pulls it out and used them six inch to save the day. I like the efforts you make to level the field.

In fifteen minutes, I went from complete ignorance of the existence of that pistol pack to wanting one.

Paul, in light of your last vid, I wish there were a way for you to test a selection of what the anti-gunners used to call "Saturday Night Specials", a media buzz term much like Assault Rifle and Mass Shootings. They weren't great, or even good for that matter, but they sure were "the gun you have" for a LOT of people who couldn't afford anything else for self defense.

Colonel Hatcher (?) did many tests on popular gun-myths of the day. When he was cutting down rifle barrels, he found that under a certain length that the spread in muzzle velocity became unpredictable. Shorter barrels in general do give lower muzzle velocity, but also can lead to greater velocity spreading. A 8" barrel may have diminishing returns, but I would warrant that it would have less velocity spread overall.

can you do more .40 s&w, but not 180gr, between 135gr and 165gr. also can you use federal hst & punch, winchester ranger t-series & supreme elite pdx1 & silvertip & defender, hornady critical duty & defense, underwood, buffalo bore, sellier & bellot(jhp & fmj), doubletap, corbon, black hills ammo, remington golden saber & ultimate defense, prvi partizan(jhp & fmj), fiocchi(jhp & fmj), speer gold dot, sig sauer v-crown, blazer, pmc, magtech and grizzly ammo. through your meat simulation target and ballistics gel & through barriers like glass, sheet metal, drywall and plywood in front of the ballistics gel and meat simulation targets? and also the meat simulation and barriers like glass, sheet metal, drywall and plywood targets from different distances for performance at different distances? and vs 9mm, 9mm +p & 9mm +p+ and .45 acp & .45 acp +p+ through all the same for the 9mm, 9mm +p & 9mm +p+ and .45 acp & .45 acp +p thx!

good video Paul. I would like to add that, there is a fantastic data table of barrel length vs velocity available online. Ballistics by the inch, is the name I believe, although the project is no longer active, the data is still available.

Just found your channel. Might be my new favorite

14:24 "As barrel gets longer we see diminishing returns... Yes I know." 😂😂😂

The information Paul provides is priceless. Thank you again, sir, for the great informative content.

Paul Harrell: The "Alton Brown" of firearms.

2:15 - Paul's words: discussing typical handgun length barrels Paul's hands: describing a fish that broke his line.

depends on the powder slow powder will likely get more vel from a longer barrel

Goodbye Paul, we miss you dearly

Great to hear the Pileated Woodpecker in the background. @ 8:20

Thanks for the presentation Paul. Accurate, to the point and excellent gun safety.

Love the content. One small complaint though, I always find that your mic is super quiet. Do you just use the mic on the camera to record audio or is there a mic on person? Would you possibly be open to donations of a mic? I find your videos extremely informative and entertaining, but just a little hard to hear sometimes. Ive been wanint to make this comment for a long time, but always catch your vids when they have 5000 comments and i get lost in the sea of them. Hopefully this one gets through

Thanks! I was a bit surprised at how little the velocity changed with barrel length.

Thanks Paul. Never seen that Dan Wesson package before, what a cool setup.

May you please do a video on .22lr, and simply test hand guns and rifles with different barrel length. I wonder where the diminishing returns start with a small caliber like the .22lr. I've always used a 22" barrel on my rifles, but I wonder what the most ideal barrel length would be. If there's already a video on this, please share.

13:08 I'm seriously impressed by Paul's ability to point to the bullet velocities on the graph without looking at them

Looking forward to doing this again with regular .38 cartridges. Not a fan of magnums and super 38s. It is because of people bringing these to our local shoots I wear both ear plugs and ear muffs. The idea of shooting a magnum or super 38 in my home without ear protection makes my ears ache. Tinnitus is a real thing. Thank you to Paul Harrell, the behind the camera support team and subscribers for keeping up production of new videos.

Great stuff Paul. I had never seen that Pistol Pack before.

As usual, another excellent video. Thank you sir. Keep up the good work.

This is a great test with the same gun but different barrels. I remember a test where they cut down a barrel more and more of by 'ballisticsbytheinch' for various calibers. So some who want additional barrel lengths, can get an idea from there.

Any video that gives you an excuse to buy a Dan Wesson pistol pack is a good video 👍

The obvious follow up is a video titled, "How barrel length effects acuracy" showing it with the different ar-15 platform lengths.

Paul your ballistic studies are the best man

I knew Paul was frozen in time in the 1980s….but brown plastic with smoker yellow briefcase is too much

That pistol pack is so interesting.

Excellent presentation. Shocked at how little difference going from 4" barrel to 8" makes.

Really love your videos Paul, keep them coming, and while some may find longer video formats boring I really love sitting down and listening to an hour and a half of what you have to say in its entirety. Keep on ignoring those who've only shot a gun through their computer screens, because to me your one of most in depth firearms expert that really has impacted the way I see things.

I'm genuinely surprised the numbers stayed so low.

Thanks, Paul, for your videos, especially the commentary. I appreciate your simple, but informative explanations.

Several years ago, like about 1982 or 83, I did a similar test with a couple of friends of mine. We used .38 Special, 158 grain SWC ammo, and the guns we used were a Smith & Wesson 2" J frame, a Ruger Security Six with 4" barrel, a Ruger Blackhawk with 6 1/2" barrel, and a Savage Mdl. 24 .357 Magnum/20 gauge. The results were kind of fascinating. I don't remember the exact bullet speeds now (1982 WAS 40 years ago), but they varied from about 850 fps in the J frame to roughly about 2100 fps out of the Savage 24. With the pistols, each two inches added a couple hundred fps to the bullet speed. The Savage really blew us away. We really weren't expecting that much of an increase in bullet speed. Barrel length really does make a significant difference with any given caliber about how fast the bullet travels. The ammo we used all came out of the same box, so the only difference in our equation was the barrel length.

What I find very refreshing in Harrell's videos is the lack of "please press the subscribe button below" requests.

Good to see you, sir. Hope all is well.

This is the big flex version of this question. Ammo and a Dan Wesson with all the barrels and the case. 😁

I have absolutely no use for a pistol pack like that, but damn I want one now.

I think some people disagree with this guy just so they can disagree 😂 great video as usual.

I wish Paul was a recruitable merc in all of my tactical computer games.

great to see you looking well sir and that is a Very nice addition to your collection best wishes stay blessed

Did anyone else notice the pile of “lung tissue” in the bottom right corner at the beginning? I love this guys videos.

Also Paul, the case for a longer barrel for hunting when using say a Buffalo Bore round that has a slower burning powder, that is really optimized in my lever gun by the way with a 16" barrel, but would get increased velocity out of an 8 or 10" barrel as opposed to ammunition designed for shorter barreled pistols.

Loved the pileated woodpecker going off at 8:20 mark LOL Type (ie; fast, slow, burn rates etc) of powder affects velocity about as much as barrel length

Awesome video Paul. That’s a nice revolver by the way. I really like how that set has the extra barrels. Thanks for another great video.

When he said, "Yes I know," my brain lagged for a second, and then I smiled. The one time my mind wasn't in the gutter, lol.

I love the fit and finish and quality of the Dan Wesson handguns.

Thanks for sharing your videos and keep them coming please.

thank you Paul, I needed to see this

Thanks for this, Mr. Harrell. I have been quite curious about this subject.

Boy ..... that brings back memories. I used to own and compete with a Dan Wesson .44 magnum pistol. You could even change the barrel shroud.

Here's another vote for a comparison between 4" to 6" revolvers and same-caliber lever-guns. For instance, I have pairs or sets in: .32-20, .357 Mag, .44 Mag and .45 Colt. I'd be happy to ship a pair or two up to you for testing. Or maybe I should throw my hat in the video-producing ring... It'd be too cluttered to include autos, as Alton Brown says, that'd be another show. There are plenty of pairs of 9mm, 40, 45, even a mixed revolver/semiauto rifle with the .30 Blackhawk and M1 Carbine.

Dan Wesson makes some beautiful stuff. Great video 👍

Pretty disappointed that the solution wasn't "You guessed it, Frank Stallone."