Velocity vs. barrel length

[nyresq]

Does anyone know of a web site that list the velocities of various calibers (.308, .223,, 30-06, 7mm rem mag etc) using different barrel lengths?

I know handloading software can estimate it, but I don't handload and have no other need to buy loading software.

I need to know for a future rebarreling project coming up; was curious how much I would be loosing going to a shorter barrel.

thanks guys and gals...

 

[30-06 lover]

I had a similar question and was told that basically you loose 20-40 FPS per inch of barrel. Sorry for my lack of knowledge.

 

[rangerruck]

in the vast majority of centerfires, once you hit about 24 to 26 inches for a bbl, there is not enough velocity gain to justify adding more length to the bbl. Unless you wanna go for max velocity, then you would need about a 40 inch bbl in most cases, and even then depending on the round ,you would still only be gaining a couple 2 or 300 or so fps, from a 24 or 26 in bbl, to going all the way out to a 40 incher.

 

[USSR]

nyresq,

Need more info, such as cartridge, bullet weight to be used, rifle being used, etc.

Don

 

[dfaugh]

Need more info, such as cartridge, bullet weight to be used, rifle being used, etc.

Righto, will depend on many factors...The commonly used rule of thumb for most mid-sized centerfire cartridges, is that you will lose 40-50 fps for every inch of barrel removed. I saw a magazine article where they started with a 26" (heavy) barrel on a .308, and kept removing 2" (and recrowning) until they got to 18"...And they were losing right around 90-100 fps each time. Most interesting (to me) was that accuracy was virtually unaffected. I've always gone for the longer barrel, because they were more accurate, but this appears to be a myth, although it might be more true with sporter weight barrels.

 

[nyresq]

nyresq,

Need more info, such as cartridge, bullet weight to be used, rifle being used, etc.

Don

Don, why would the bullit weight, or rifle type matter? will a 79 gr bullit loose more velocity at the muzzle taking an inch off the barrel then say a 60 gr bullit. I understand that downrange will be a big difference, but at the muzzel shouldn't it be close to the exact same amount lost per inch? And as to the rifle are you referring toan auto loader vs a lever action or bolt action or specific brand? ie, will a winchester 70 loose more then a remington 700 or a lever action marlin? I know ARs with short barrels make a bigger difference vs long barreled ones due to the gas operation...


but for argument sake, lets say a heavy barrel remington 700 in .223. what is the velocity difference at the muzzle going from a 24" tube to an 18" in one inch incriments with a 69gr matchking?

thanks

 

[Zak Smith]

Don, why would the bullit weight, or rifle type matter?

The answer has to do with the type of powder, burn speed, amount, bore area, and pressure-- all those dynamics that occur in microseconds during ignition and combustion of the powder.

Generally more of a slower powder behind a heavier bullet in less bore area will benefit more from each additional inch of barrel length.

 

[USSR]

Thanks, Zak.

nyresq,

I don't play with anything below 6.5mm, so I'll let someone else answer your .223 question.

Don

 

[Art Eatman]

Generally: For cartridges with case proportions like the .270, .30-'06 and suchlike, you can figure on roughly 75 ft/sec per inch of barrel cut back from whatever starting point. Most advertised velocities for this general family of cartridges come from 26" barrels.

For cartridges with proportions like the .308, (.243, 7mm08, etc.) it's more like 40 to 50 ft/sec per inch. SFAIK, most available charts of velocities are based on barrel lengths around 22" to 24".

Big-case magnums run closer to 100 ft/sec/inch.

Again, this is just generalizing. About every ten years or so somebody goes to cutting and shooting, and writing about it...

, Art

 

[orangeninja]

What would a bolt action at about 16 1/2 inches in .308 look like I wonder?

 

[Art Eatman]

Poorly proportioned. Not exactly a thing of beauty and a joy forever. Loud, too!

Art

 

[TexAg]

Alduro,
Check out Ruger's website. The Frontier and Compact models both have 16.5" barrels. I was thinking of getting one, but then I figured since I am such a penny pencher I would just go for a wood stocked .308 Saiga with a 20" barrel to get more out of the .308.

 

[nyresq]

Thanks to all who posted!

Can someone with some balistics software run some numbers for a rem 700 in .223 shooting 69 gr federal match ammo with the sierra matchking bullet and tell me the difference in velocity btw a 22", 20", 18" and a 16.5" barrel in a 1-9 or a 1-7 twist.

thanks

 

[MachIVshooter]

let's first look at cartridge efficiency. Cartridges in the .223 class (short and burning around 30 grains of powder) tend to make most of their velocity in the first 18". .308 win type cartridges (~ 50 grains of powder) are best suited in 20-22" tubes. .30-06 class (55-65 grains of powder) make the most use of 24". larger magnums (burning 80-120 grains of powder) are happy in 26 or even 28" barrels. .50 BMG rifles (220-240 grain charge) need at least 28" and are most commonly found with 29-31" tubes.

So, for starters, the more powder you are burning, the longer the barrel needs to be. pretty simple. Of course, bullet weight and powder type are also major factors, but for the sake of this thread we'll stick to the simple stuff.

So, now consider that the less length a cartridge needs to develop velocity, the less it will be affected by adding or removing length. The .223 rem. does not have a tremendous change in velocity going from 16" to 24". my own tests with three rifles (one 16", one 18.5" and one 24") revealed that the spread from 16" to 24" with 55 gr. ball loads was less than 200 FPS. However, if one were to cut my .375 ultra from 26" to 18" I would expect a 400+ FPS velocity loss. I would also expect a gain of close to 200 FPS going up to 30". Why? That thing is using 103 grains of slow burning powder to push a very heavy bullet. My .308's showed an average gain of about 100 FPS from my 16" AR-10 carbine to my 18.5" G-3, which falls right in line with the common wisdom of roughly 50 FPS per inch.

In conclusion, ~50 FPS per inch is a good rule of thumb, but the only way to truly know is to test each load in rifles with different barrel lengths over a chronograph or, as a more practical approach, use a good ballistics program and enter all the variables. These programs are likely more accuracte than your loads will be consistent.

 

[Art Eatman]

Mr. Speer's #13 reloading manual sez a full-house load for a .223 with a 70-grain bullet from a 22" barrel can go 3,068 ft/sec.

So, just start subtracting the guesstimated 50 ft/sec/inch from that and you've got it!

Best we can do, this side of a chronograph. One test is worth a thousand expert opinions.

, Art

 

[Archie]

Velocity of a bullet depends on two factors...

Factor one is the ratio of powder charge to bullet weight. Obviously, all else being equal, more powder makes bullet go faster.

Factor two is the expansion ratio of the firearm. Expansion ratio is the difference between the internal capacity (volume) of the case with bullet seated versus the volume of the empty case and bore. Obviously, a longer barrel gives a greater expansion ratio.

However, a larger bore diameter gives a larger expansion ratio, all else being equal.

Cutting an inch off a .223 bore loses more velocity than cutting an inch off a .458 barrel. However, how much is lost also depends on the chamber capacity.

Do a check on line for the Powley Computer or Calculator. Just playing with numbers in the device is a shocking revelation.