barrel length vs fps

[charger 1]

I'm sure we've all heard the thought of additional length creating additional FPS, but when does that theory become void. I mean a barrel a mile long would not shoot faster with the same round as a 24" barrel. Ya that example is extreme, but it must come into play somewhere. I have a chance to buy a 1/18 twist 50 cal barrel for that new lever I got and chamber 50 ak. It sits as blank 36" now. Weight and length in the field matter not to me, so I'm thinking 30 as opposed to the 26 0n it. Will that big cal notice much diff?

[joeb33050]

The tests I've read leave me with the sense that changes in barrel length do not result in substantial changes in MV. I have, somewhere, a test of a barrel being shortened and MV tested at the different lengths. The result, as I remember, is that the "rule-of-thumb" about 25(or some other number) fps per inch of barrel isn't a good one.
If you ask a person with QUICKLOAD to run the numbers, you can see the estimated MV change for any barrel lengths.
A 30" barrel is a LONG barrel on a lever gun.
joe brennan

[Bass Ackward]

Ever use a hand pump to pump up a bicycle tire? How about using that same pump to pump up a car or tractor tire. That's bore diameter. If you keep case capacity constant, you eventually are forced to use powder speeds faster to get good ignition and as a result pressure spikes are much shorter and much closer to the case.

Regardless of velocity gain though, the best advice is to be rational based upon the action type you are going to use. But the extra weight can take the jab out of recoil too.

[danski26]

I did a paper on this in a college physics class. You are correct in the thought that at some point velocity will decrease at long barrel lengths because friction overcomes propulsion. There are several factors in play here.

Including but not limited to:

Barrel material
Barrel interior finish
Projectile make up
Projectile bearing surface
Projectile diameter
Twist rate
Depth of grooves or height of lands :-)
Type of rifling
Max pressure
Pressure curve
Lube if any
Ambient conditions (bara pressure, temp,humidity....ect)

I used a formula from the Army that they used to predict max powder charges in there artillery pieces however it does not have a direct translation to firearms.

There are two ways to predict at what length the velocity loss will start. First is to make a formula useing all of the variables i pointed out (and a few i forgot i'm sure) or by trial and error.

I have a 30" tube on my 308win match rifle and velocity still increases at this length with my set of variables. I "believe" it's safe to say a 22LR will lose velocity in a 30" barrel. Anyone tested it and dissagree?

Between that, either test it yourself or use the S.W.A.G. method.

[Glen]

As I recall, someone has tested this in the dim and distant past, and with a .22 LR the break point was about 16". I do know that years ago a friend and I were chronographing a bunch of stuff and my 14" Contender was consistently faster than his 24" .22 rifle. For something with the case capacity of the .50 Alaskan, I would expect the break point to be well in excess of 30".

[Pepe Ray]

The 22LR/RF has been tested by Many. Prior to the Stinger and the current crop of "supers", The consensus was that 16" was all you needed to wring out the best that a .22RF had in it. Today all bets are off.
A number of years ago one of our gun rag columnists did a feature to address your question. Now remember, this is from an old mans' memory, The tester used an extremely long blank 4ft or more, chambered in a pistol ctg. .32 SWlong AIR.
I'm tempted to dredge up more "facts" but to preserve my credibility I must apologize and go to my files to find the article.
Forgive me if I don't get right back to you. I'm getting married on Sat. and have a lot on my mind.
Pepe Ray

[45 2.1]

Forgive me if I don't get right back to you. I'm getting married on Sat. and have a lot on my mind.
Pepe Ray

Congradulations on your impending nuptuals Ray

[mike in co]

a tool like quickload is very valuable in questions like this. you can go load your data and see what comes out.
remember it is only a tool "not fact"....just something to gauge by.


mike

[Blammer]

I'd probably go with a 24" tube.

[felix]

Go for gun balance, and feel. Nothing else matters in the end because if the gun feels good and is accurate enough, that gun will be used more than any other. Just make sure of the sport first. A BR gun will feel much different than a bi-podded varmit gun or a carry quarry gun. ... felix

[1Shirt]

Gotta go with Felix and his comments. If I have to carry it in the mts. or walk a long distance, would prefer a short, stout bb on a rifle that balances. If the bbl was 18" was stiff, and the rifle weighed (w/scope) under 8lb. I would probably be content with a vol. reduction compaired to carrying that same rifle w/a 24" bbl that was heavier and did not have a good carry balance.
1Shirt!:coffee:

[BOOM BOOM]

HI,
I w/ Felix, the only time that would be modified would be in a ML or a real hard recoiling cartrage. For a ML the old time tests for blk powder was 34" IIRC.

[leftiye]

Charger, I'm not familiar with the .50 AK but unless that case is monstrous big I'd not expect it to use much barrel length. They used to talk about something called overbore cartridges. What they meant was ctgs. that had more powder that was efficient in a given barrel length. IIRC they thought that ctgs with a 7.5 to 1 bore to case expansion ratio was about all the bigger a case should be in relation to bore volume. Nowadays, all of the big cased new ctgs are way more overbore than that, so it is a matter of opinion.

You could finger out how much water your case will hold to the base of the boolit, and see how many times larger your bore volume was than that in your desired length. More than about 20 to 1 is getting to be superfluous length, probably. The powley computer had a sliding scale that gave expansion ratios and allowed one to calculate the concept you are considering for various barrel lengths. You could see when expected velocities would drop off as the barrel got longer.

The 45-70 never needs a tube longer than about 22 -24 inches long (though there are 45/70s that people like to have longer barrels on). Huge expansion ratio. That being said- in your .50 another consideration may be more important. That being that you have to stand behind it; and more length =more weight. This has to be balanced by such thangs as whether or not you might have to get on target muy rapidamente to keep from getting dead! I think Felix was right- make the gun to fit the use that you have for it, there WILL still be sufficient expansion ratio!

[charger 1]

Interesting to note how some of the old guns had barrels up to and including 36". musta been for sight radius

[kodiak1]

Go back 3 or 4 issues of rifle or handloader and read the results of the test preformed on a 30-06. I believe it started at 30" and had group of shells shot through it diff weights and makes. Then 1" was cut off and same bullets shot over chrony same order. This was repeated till the barrell was 12" long I believe and the change down to 20" was minimal then 18 to 16 there was a little more variation in velocity. The on thing that did stay constant was the amount of noise got louder and louder and louder.
Ken.

[charger 1]

Go back 3 or 4 issues of rifle or handloader and read the results of the test preformed on a 30-06. I believe it started at 30" and had group of shells shot through it diff weights and makes. Then 1" was cut off and same bullets shot over chrony same order. This was repeated till the barrell was 12" long I believe and the change down to 20" was minimal then 18 to 16 there was a little more variation in velocity. The on thing that did stay constant was the amount of noise got louder and louder and louder.
Ken.

Not saying your wrong but I struggle to see no diff in a bottle neck from 30-20. I know theres been lots of times that a load has been given to me and for love or money I cant get the FPS the guys sayin he gets. Sooner or later I see him at the range and it comes to realization he's got 2,4,or 6" more barrel

[leftiye]

Charger, You've got it. Those old (note the operant factor here is old!) guns had longer barrels for sight radius. Plus back then it was more the style, just after the inception of smokeless powder. The old timers used to think that longer barrels were more accurate. Back in the 60's it wasn't uncommon for someone to ask you if you thought that longer barrels were more accurate- just to see if you knew anything. The expansion factor is as previously explained, and it has about the effect that the Handloader article outlines- for the 30-06. Straight(er) walled bigger bore cartridges with higher expansion ratios show the same effects with even shorter barrels.

[waksupi]

Forgive me if I don't get right back to you. I'm getting married on Sat. and have a lot on my mind.
Pepe Ray

A master of understatement!

[piwo]

Interesting to note how some of the old guns had barrels up to and including 36". musta been for sight radius

many "longrifles" were just that.. 55-61 inches long and barrles in excess of 44+ inches. The site radius on my rifle is 37 inches and it is a lose recreation of a surviving original. I have "Rifles of Colonial America" volumes l and ll: looking at the detailed photo's of the hundred of surviving originals never ceases to amaze.8-)

[Bass Ackward]

One thing I forgot to add, common sense really, is that if you aren't sure, err to the long side. You can always shorten up later and re-crown.

[charger 1]

One thing I forgot to add, common sense really, is that if you aren't sure, err to the long side. You can always shorten up later and re-crown.

Now your speakin my lingo. I'm thinkin 30"

[Larry Gibson]

Bass nailed it as usual...err to the long side. While I have numerous short barreled rifles (and shotguns) I prefer the longer barrels. I've had a love affair with the M1 Carbine for 40+ years and still have my first "real" rifle, a M94 Carbine. However, I've found that a well balanced rifle with a 24-26" barel is no more cumbersome than a shorter barreled rifle. I've hunted (both four legged and two legged critter - the two legged being the most dangerous as they had AK/SKS/RPD claws and teeth) in some of the thickest jungles in the world, both CA and SEA. Then anyone who's hunted the Coastal Mountains of the Pacific NW knows what "thick" is. I've not found a shorter barrel to be any handier in those conditions. I've also done a lot of CQB with numerous types of weapons and again never found a M14 to take back seat to anything shorter other than a M1911 ins some reall smally rooms.

Many who cut back barrels say (said it myself) you don't really give up that much. Fact is; you do "give up". You give up velocity and sight radius. Sometimes you also give up balnce which can make the rifle unwieldy enen if it is short. I've a 30-06 rifle I cut back from 24" to 20". I cut it 1" at a time a chronographed several loads. With medium burning powders I lost 25-23 fps but with 180 gr bullets and 4350 or 4831 I lost 45-50 fps. That rifle is 200+ fps slower than the same 180 gr load out of a 26" barrel. Is the shorter barreled rifle any "handier" than my rifle with a 26" barrel, no it's not. Did I really "not lose very much"? Well how much do you get when you go from an '06 to a 300 Win mag, abouut 200+ fps isn't it? Does it matter? Probably not if your ranges are short but since I shoot a lot of longer ranges I've learned that giving up 200+ fps is in fact a lot.

Then as mentioned thier is sight radius, if your eyes are going south but you still like to use iron sights then the longer barrels enable you to do just that, the short ones don't.

Larry Gibson

[joeb33050]

Many who cut back barrels say (said it myself) you don't really give up that much. Fact is; you do "give up". You give up velocity and sight radius. .

Then as mentioned thier is sight radius, if your eyes are going south but you still like to use iron sights then the longer barrels enable you to do just that, the short ones don't.

Larry Gibson

The book has an interpretation of a Rifleman article that deals with, among other things, sight radius. See http://sports.groups.yahoo.com/group/CB-BOOK/, Chapter 7.3 SIGHTS, the heasing "Factors of sighting error", and test 6. You will see that after 20 or 25 inches between the front sight and the eye, not much is gained by longer barrels. I'd guess that in a lever gun the peep to barrel is 4-5 inches, so we're talking about after 24 inches longer barrels don't make sighting more precise. Somewhere in there.
joe brennan

[joeb33050]

Handloader, October 2006, page 48, "Much Ado About Nothing...or Almost Nothing" is about barrel length and velocity. John Barsness quotes some Phil Sharpe testing from 1949 and his own testing.
The sense of the article is that within reasonable bounds of barrel length, MV doesn't vary enough to be worth worrying about.
joe brennan

[44man]

Take a muzzle loader or for that matter the 45-70 with black powder. Just use a nominal barrel length, nothing ridiculous. Keep adding powder, in the case of the cartridge, you have to compress more. Soon recoil goes way up, noise goes up and velocity will DECREASE for each addition of powder. All of the powder will not burn in the bore and the additional powder weight being pushed out adds to the boolit weight.
Now take a .300 Weatherby with a 26" barrel. That length is actually still too short for maximum efficiency. Cut to 24" and the loss is not that bad but if you keep cutting, all of the powder will not burn and you get close to a 30-06. So you start using faster powders! Now of what use is the huge case that is half empty?
Pistols with short barrels suffer greatly with large cases and faster powder has to be used because the slow rifle powders will not all burn. All you do is add to the weight being shot. The huge powder space that is not used with the faster powders helps to reduce chamber pressures, but you have a hard time getting rifle velocities.
My take on it is if you want a short barrel rifle, match the caliber to it. There is no sense putting a .300 mag on a 20" barrel when a lesser caliber will give the same results.
It is a balancing act for sure.
Some guys want a .500 S&W or a .475 with a 2" barrel----MY, MY! :roll: