My wife was cleaning out my 4Runner the other day, I hate it when she does that, and came across an old copy of Rifleshooter magazine. On the cover it anounced an article on barrel length vs velocity. Unfortunately they do not give all the information that I know that most of us would like to see in the article but what they do give I will post for you all.
 
  22-250
  H-380 powder
  55gr bullet
 
  27" 3469fps
  26" 3451fps
  25" 3425fps
  24" 3407fps
 
  270 Winchester
  H4350 powder
  130gr bullet
 
  27" 3115fps
  26" 3093fps
  25" 3071fps
  24" 3054fps
  23" 3035fps
  22" 3027fps
  21" 3001fps
 
  300 Win Mag
  RL-22 powder
  180gr bullet
 
  27" 3055fps
  26" 3031fps
  25" 3024fps
  24" 3003fps
  23" 2984fps
  22" 2960fps
 
  300 RUM
  H4895 powder
  220gr bullet
 
  27" 2740fps
  26" 2709fps
  25" 2685fps
  24" 2663fps
  23" 2636fps
  22" 2612fps
 
  340 Wby Mag
  RL-22 powder
  250gr bullet
 
  27" 2837fps
  26" 2817fps
  25" 2809fps
  24" 2791fps
  23" 2777fps
  22" 2755fps
  21" 2731fps
 
 These are the results that they listed. Would I trust Gitanos results more? Yes but then he's smarter than most gun writers and pays significantly more attention to detail. It will be interesting to see how his results compare to these.

Thanks for the vote of confidence HB, but to tell the truth, this is interesting information. What was the publication date of this volume if you please?
 
Holy smokes!:eek: This data strongly suggests that in cases from 22-250 to .340 Weatherby, the change in muzzle velocity per inch of bbl is on the order of 20 f/s!
 
Here below are the numbers rounded to whole numbers:
 
22-250
H-380 powder
55gr bullet
 
27" 3469fps
26" 3451fps 18
25" 3425fps 26
24" 3407fps 18 Average 21 f/s
 
270 Winchester
H4350 powder
130gr bullet
 
27" 3115fps
26" 3093fps 22
25" 3071fps 22
24" 3054fps 17
23" 3035fps 19
22" 3027fps 8!
21" 3001fps 26 Average 19 f/s
 
300 Win Mag
RL-22 powder
180gr bullet
 
27" 3055fps
26" 3031fps 24
25" 3024fps 7!
24" 3003fps 21
23" 2984fps 19
22" 2960fps 24 Average 19 f/s
 
300 RUM
H4895 powder
220gr bullet
 
27" 2740fps
26" 2709fps 31
25" 2685fps 24
24" 2663fps 22
23" 2636fps 27
22" 2612fps 24 Average 26 f/s
 
340 Wby Mag
RL-22 powder
250gr bullet
 
27" 2837fps
26" 2817fps 20
25" 2809fps 8!
24" 2791fps 18
23" 2777fps 14
22" 2755fps 22
21" 2731fps 24 Average 18 f/s
 
I'm genuinely surprised. If this is indeed accurate, then it is really difficult to argue against a 20" bbl vs a 24" bbl for most rifles. There's not even a trend within a cartridge.
 
So... For a 300 Win starting at 24" and going to 20", (a big difference really when you consider weight and "portability"), you'd go from 3003 f/s at 24" to 2927 f/s; a loss of 76 f/s. Boy! I might go for that, and work on tuning the charge to the shorter bbl.
 
Which has me thinking a bit more. I already have three different models of milsurp rifles chambered in 7.62x54R with 3 different bbl lengths: the 91/30 at 28-ish", the m39 at 26-ish", and the m38 or m44 at 20-ish". I do believe I have MV data with milsurp ammo for each of these rifles. I'll check to see what the change is. Of course this is not the same as checking the same rifle with different lengths of the same bbl, but it will give us a ball park idea about the validity of the above numbers.
 
Back when I have those numbers.
 
Paul
 
OK, here are the numbers, and aren't they interesting.
 
Model . ..bbl length . Average MV
M91/30 - 28.5625" -- 2779
m-39 - -- 26.875" - - 2762
m-38 - -- 20.375" - - 2679
 
So, 28.5625 minus 26.875 equals 1.6875". 2779 minus 2762 equals 17. 17 divided by 1.6875 equals 10 f/s per inch.
 
26.875 - 20.375 = 6.5
2762 - 2679 = 83
83/6.5 = 13 f/s per inch
 
28.5625 - 20.375 = 8.1875
2779 - 2679 = 100
100/8.1875 = 12 f/s per inch.

Holy Cow! Now it is true, that these are three separate rifles. However, these MVs were collected on the same day, and were using exactly the same lot of milsurp ammo. I'm not so sure a 91/30 bbl needs to shortened here folks.

Paul

Gitano / HB,
 
That sure is interesting information!!!!!
 
There goes all my theories for long bbl rifles.
 
I agree, no need to mess up a nice rifle which will just confirm what we now already know.  I mean how accurate do we really want to be with this?
 
I must confess that I am also very surprised that the velocity change seems to effected almost nothing by the calibre.  I would really have expected more of a calibre specific difference.
 
Regards.
 
C

This is from the Sept/Oct 2003 issue of Peterson's Rifleshooter. It gets a bit different when you use different rifles. He does post a comparison between two 7mm Rem Mags. One with a 24" barrel and one with a 26" barrel and our results are quite different there.
 
 66gr H-4831
 154gr Jensen
 24" 2907fps
 26" 3030fps
 
 65gr H-4831
 160gr Partition
 24" 2826fps
 26" 2900fps
 
 Fed. Fact load
 160gr Partition
 24" 2772fps
 26" 2844fps
 
 Rem Fact load
 150gr BTip
 24" 2842fps
 26" 2961fps
 
 Win Fact load
 160gr Silvertip
 24" 2709fps
 26" 2873fps
 
 Rem. Fact load
 160gr Swift A-frame
 24" 2767fps
 26" 2872fps
 
 Win. Fact load
 150gr PP
 24" 3024fps
 26" 3100fps
 
 I do wish that they would have listed things like their sample size. Were these numbers from 3 shots or 10? In the interest of accuracy I belive that a minimum of 10 shot would be in order. Even given the velocity data I would not want every rifle to come with a 22" barrel. There are some calibers where I would like the muzzle blast as far away from my face as possible and so I would chose the longer tube but I think that in most nonmagnum calibers that a 22" barrel is just fine. It does appear from comments made in the article that he feels that there is a significant difference between the feel of a 22inch barrel and a 24inch barrel. I personally disagree but in this case it's up to the individual I suppose.

Let me offer my 'take' on this additional information.
 
66gr H-4831
154gr Jensen
24" 2907fps
26" 3030fps 123 f/s or 61.5 f/s/in
 
65gr H-4831
160gr Partition
24" 2826fps
26" 2900fps 74 f/s or 37 f/s/in
 
Fed. Fact load
160gr Partition
24" 2772fps
26" 2844fps 72 f/s or 36 f/s/in
 
Rem Fact load
150gr BTip
24" 2842fps
26" 2961fps 119 f/s or 59.5 f/s/in
 
Win Fact load
160gr Silvertip
24" 2709fps
26" 2873fps 164 f/s or 82 f/s/in
 
Rem. Fact load
160gr Swift A-frame
24" 2767fps
26" 2872fps 105 f/s or 52.5 f/s/in
 
Win. Fact load
150gr PP
24" 3024fps
26" 3100fps 76 f/s or 38 f/s/in
 
 
These values range from 36 to 82 f/s/in within a pair of rifles. Looking at this data objectively, I draw four conclusions:
1) Muzzle velocity is proportional to barrel length. (Wow.)
2) The muzzle velocity-barrel length relationship is primarily a function of bullet type - probably due to the differences in bearing surfaces. (This is news.)
3) Each rifle behaves sufficiently independent of barrel length that no generalized predictive model based on barrel length can be derived.
4) Because of (3), any attempt to build a generalized bbl length vs MV predictive model is basically an exercise in futility. Building models has a single, well-defined purpose - prediction. If you cannot predict from the model, or if the model requires too much a priori knowledge to build, then it has no value.
 
A very key piece of information is missing from this last data set - pressure. As the cartridge "model" (66gr H-4831 -154gr Jensen, for example), changes, so will the pressure. MV is highly dependent on pressure. Without pressure data for each muzzle velocity group, there's no way to know how much affect pressure may have had on the change in velocity relative to the affect of changing bearing surfaces. It is true that the rate of change (f/s/in), should be independent of presssure, but without the pressure data, that is an unsubstantiated assumption.
 
I would have hoped to be able to take the bbl length vs muzzle velocity data and make estimates of performance for a rifle yet to be built. (This is essential engineering.) That is not likely possible. Or, if it is possible, the initial constraints will be so specific that the model won't provide any "new" information. (The outcome will already be known before you "turn the crank" on the model.)
 
I have to say I find this disappointing.
 
Paul
 
HB, what do you think about making this thread "sticky"?
 
Paul

It's stuck.

This is very interesting material and I apprecaite all of you taking the time to share the information.  It supports something I have suspected for years but that was contrary to published wisdom...

 
Thanks

Great thread....very interesting....I think I'll leave my Sako's the way they are but the 03a3 may get trimmed. Regards, Rick.

So in the long run barrel length, on average, doesnt mean a whole lot?  I mean if I want a short say 18 inch barreled jungle gun I wouldnt be losing much velocity in most cases or would I?  There must be some reason they make certain lengths to barrels.  Isnt there usually a minimum length needed to stabalize a bullet?  I mean I couldnt very well shoot a 7mm Rem Mag out of a 10 inch barrel and expect much, could I?  There does have to be some medium to work around.  Seems like 22 inches would be the medium in most cases, with 24-28 being long and 16-20 being short.  I personally feel that for general hunting anything between 20-24 is more than great.  Anything longer than that is a bit rediculous.  Except for special shooting needs, ie target/competition shooting.

Quote from: KanibalSo in the long run barrel length, on average, doesnt mean a whole lot? Depends on what "a whole lot" means to you. I mean if I want a short say 18 inch barreled jungle gun I wouldnt be losing much velocity in most cases or would I? Down from what length in what cartridge? As you can see, in a large number of common cartridges the loss per inch of bbl is about 20 or so f/s. If you started with a 28" bbl, you'd be losing something like 200 f/s. To some, me included, 200 fps is significant. Change the starting length to 22" and you've only likely lost 80 f/s. "Significance" is considerably more subjective at that point. There must be some reason they make certain lengths to barrels. In large part, it's marketing. However, in the case of the really large-cased newer "magnums", the performance gain isn't noteworthy enough to support all the associated hype. For example, the difference between the 7mm Rem Mag and the 7mm STW is "insignificant" if both rifles have 24" bbls. That is of course by my definition of "insignificant". However, the manufacturers agree with me enough to only make those rifles in 26 and 28" nowadays. :) Isnt there usually a minimum length needed to stabalize a bullet? Length of bbl is irrelevant (to a point) to gyroscopic stabilization. Muzzle velocity, bullet length and twist rate are the relevant variables. I mean I couldnt very well shoot a 7mm Rem Mag out of a 10 inch barrel and expect much, could I? Not in velocity perhaps, but it wouldn't have anything to do with gyroscopic stability. Now, if you'll give this idea some more thought, (and I do mean think about it) you'll start to see why some old codgers, like me, are so unimpressed with the "new" super-magnums. There does have to be some medium to work around. Seems like 22 inches would be the medium in most cases, with 24-28 being long and 16-20 being short. I personally feel that for general hunting anything between 20-24 is more than great. Anything longer than that is a bit rediculous. Some might disagree. Except for special shooting needs, ie target/competition shooting. Don't forget the BATF... they have both barrel length restrictions (18" in a "long gun") as well as over-all rifle length restrictions - (I don't recall what OAL value is.)

Paul plus 5

I realise this is not velocity related but there is an advantage to a longer barrel- less noise.  The disadvantage it trying to maneuver the thing in the underbrush.   Another issue is weight. This can be either an advantage or not.  On one hand a heavier rifle will recoil less. on the other it will be harder to tote.:D Just some food for thought.  Velocity is nice but accuracy is everything.

The best way to test this would to be use 1 barrel of each caliber starting at 28" after every set cut one inch off of the barrel recrown and go again,  cut shoot, cut shoot.  this is the only way to get positive results.
 
 Some barrels have tighter/looser bores than others no two are the same.  
 IE
 243 #1 has a 22" shilen barrel
 243 #2 has a 27" shaw barrel
 
 if this theory is correct 243 #2 would shoot faster than 243 #1,  when in reality 243 #1 could shoot faster velocity's than 243 #2 depends on throats, freebore, etc.  if you compare an 8 groove barrel to a 6 groove barrel that will net a big diff.
 
 but the point is and someone has done it,  for the test to be true you must shoot your aggregate,  cut an inch,  shoot your aggregate and cut.  using the same barrel,  thats the only way to get the right answer.

Quote from: Kells81The best way to test this would to be use 1 barrel of each caliber starting at 28" after every set cut one inch off of the barrel recrown and go again, cut shoot, cut shoot. (It is true that this would be the method to use for "best" results for a single barrel, but there's more to this subject than that.) this is the only way to get positive results. (Actually, doing things this way, and using your later logic, this is not correct.)
 
Some barrels have tighter/looser bores than others no two are the same.
IE
243 #1 has a 22" shilen barrel
243 #2 has a 27" shaw barrel
 
if this theory is correct 243 #2 would shoot faster than 243 #1, when in reality 243 #1 could shoot faster velocity's than 243 #2 depends on throats, freebore, etc. (Actually, the second barrel shooting slower than the first is more "a theoretically possibility" that the likelihood of the first barrel shooting slower.) if you compare an 8 groove barrel to a 6 groove barrel that will net a big diff. (Actually, the rifling, "throats, free-bores, etc." have almost nothing to do with muzzle velocity as long as: 1) the cases are of the same design (say .243 Win. for example), 2) the max pressures are equal, and 3) the area under the pressure-time curves are equal. These are all conditions that can be accomplished fairly easily between different rifles. But more importantly here, the issue isn't one for comparison between rifles. It is an issue of what might happen to the muzzle velocity of a specific barrel if it is shortened. In such case, the rifling, "throats, freebores, etc." remain identical. A shorter barrel provides a shorter time interval for the expanding gasses to work on the bullet. The shorter "work time" means lower velocity. Remember, a general PREDICTION model was the primary thrust of this thread, not the exact value for a specific barrel.)
 
 
but the point is and someone has done it, for the test to be true you must shoot your aggregate, cut an inch, shoot your aggregate and cut. using the same barrel, thats the only way to get the right answer. (Here your choice of the word "right" is probably mis-applied. "Right" can only be used in a specific context, and the context of this thread is trend and scale, not absolute value. Specifically: "Trend" - "Does the velocity go up or down when a barrel is shortened?", and "Scale" - "On average, does it go up or down by 25'/sec/in or 50'/sec/in or 100'/sec/in...?" The precise value for a specific barrel isn't, as you point out, possible to determine without cutting off the barrel and testing. However, using this logic, combined with your assertion of "The best way to test this would to be use 1 barrel of each caliber starting at 28" after every set cut one inch off of the barrel recrown and go again, cut shoot, cut shoot" renders ANY experiment to detemine the effect of shortening a barrel either moot or useless. Once you've determined the effect for the specific barrel, you've ruined the barrel. When you put on another barrel, according to your assertions of the effects of "throat, freebore, etc.", you'd have to start all over again to detemine the "right" values. Once you determined those "right" values, the new barrel would also be ruined so you'd have to start with a new barrel, and so on.)

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What the data presented in this thread appear to show is that about all that can be said about shortening a barrel is that the muzzle velocity will go down - in other words, the trend. Since this information is available from the pressure-time curve, it is unnecessary to physically shorten the barrel to predict this trend. Unfortunately, bullet design, case design and the powder used, tend to confound determining a precise change-per-unit-length, of that trend. Therefore, a generalized predictive model - for purpose of determining the effect of shortening a specific barrrel - is almost impossible to create. What we get from the data presented here is that shortening the barrel will lower the velocity by something between about 15'/sec/in to something like 50'/sec/in... with the most important phrases being "something between and something like".
 
Paul