grenadaed
Member
I have purchased a 35 whelen T/C pro hunter with a match grade barrel. I plan to reload 200 gr Barnes ttsx bt using rl15. My barrel is 26 inch all data i find is for 24 inch. what difference will i find with this difference?
barrel length vs velocity
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tyeo098
Member
Velocity!
MachIVshooter
Member
That's about right with medium sized cartridges and barrel lengths between 20" and 30"
I don't know where the 50fps/inch number came from, but after years of researching this I've never found a single documented case where anyone lost that much velocity from cutting a barrel down 1" shorter. The biggest loss of velocity I can find documented is from a guy who cut a 300 mag down to 22" from 24". He lost 70 fps. or only 35fps/inch. I doubt if there would be 50fps difference between a 22" barreled 35 Whelen and a 26" barrel.
Most cartridges have what I call a "sweet spot" somewhere between 20" and 24" where velocity gains all but stop. Going to a longer barrel will still increase velocity, but in smaller and smaller increments as you go longer. If you start cutting shorter than that sweet spot velocity losses will increase in larger and larger increments as you go shorter.
The biggest mistake shooters make is comparing the velocity on 1 gun with a 22" barrel with the velocity they get with a different gun with a 24" barrel. The 22" barrel may be 100 fps slower and they conclude that you lose 50 fps/inch. But every gun/barrel is different. You will never get the same velocity from 2 different guns even if the barrels are equal in length. Usually the difference is only a few fps, but I've seen 75-100fps difference between 2 guns with equal barrel length. I've also seen a 20" barrel shoot the same ammo 20fps faster than from a gun with a 22" barrel. The only meaningful way to determine velocity changes is to shoot the same ammo through the same barrel and shorten the barrel as you go. This has been dozens of times and the results are out there to be viewed.
In most non-magnum chamberings you will lose 15-25 fps/inch as long as the barrel is between 20-24". Going shorter and you will see bigger losses. Go longer and you will see smaller gains. I've got barrels ranging in length between 16" and 24". My chronograph confirms this as well as dozens of other shooters who have taken longer barrels and cut them shorter, chronographing ammo before and after making the cut.
The most accurate formula I've found to determine velocity gains or losses is to expect somewhere between .5%-1% velocity change. If you have a round that the book says should be 3000fps, then the velocity would change somewhere between 15-30 fps as you change barrel length.
Most cartridges have what I call a "sweet spot" somewhere between 20" and 24" where velocity gains all but stop. Going to a longer barrel will still increase velocity, but in smaller and smaller increments as you go longer. If you start cutting shorter than that sweet spot velocity losses will increase in larger and larger increments as you go shorter.
The biggest mistake shooters make is comparing the velocity on 1 gun with a 22" barrel with the velocity they get with a different gun with a 24" barrel. The 22" barrel may be 100 fps slower and they conclude that you lose 50 fps/inch. But every gun/barrel is different. You will never get the same velocity from 2 different guns even if the barrels are equal in length. Usually the difference is only a few fps, but I've seen 75-100fps difference between 2 guns with equal barrel length. I've also seen a 20" barrel shoot the same ammo 20fps faster than from a gun with a 22" barrel. The only meaningful way to determine velocity changes is to shoot the same ammo through the same barrel and shorten the barrel as you go. This has been dozens of times and the results are out there to be viewed.
In most non-magnum chamberings you will lose 15-25 fps/inch as long as the barrel is between 20-24". Going shorter and you will see bigger losses. Go longer and you will see smaller gains. I've got barrels ranging in length between 16" and 24". My chronograph confirms this as well as dozens of other shooters who have taken longer barrels and cut them shorter, chronographing ammo before and after making the cut.
The most accurate formula I've found to determine velocity gains or losses is to expect somewhere between .5%-1% velocity change. If you have a round that the book says should be 3000fps, then the velocity would change somewhere between 15-30 fps as you change barrel length.
grenadaed
Member
Thanks guys i hope this will help me. I am trying to work up load for this T/C pro hunter with a 26 inch match barrel. I am trying Hodgon BCL-2 power pushing a 200 gr Hornady spire point. Load says 62.5 grains should be 2800 fps. The other i am going to try will be Alliant reloaded 15 62 grains pushing a 200 gr Tipped triple shock Barnes load data says this should be 2891 fps.
I live in Mississippi and own land. I white tail hunt. Most shots are 100 to 150 yd but time to time i get a 300 yd shot. I purchased a 4x16x50 mm Nikon bdc scope for this rifle. I always use sand bags and very seldom have to shot off hand. Thanks for the help i think my next purchase should be a chrony. My other deer rifle is a 270 wsm shooting 110 gr Barnes group of 3 shots covered with a dime at 100 yds.
I live in Mississippi and own land. I white tail hunt. Most shots are 100 to 150 yd but time to time i get a 300 yd shot. I purchased a 4x16x50 mm Nikon bdc scope for this rifle. I always use sand bags and very seldom have to shot off hand. Thanks for the help i think my next purchase should be a chrony. My other deer rifle is a 270 wsm shooting 110 gr Barnes group of 3 shots covered with a dime at 100 yds.
MachIVshooter
Member
That's great, because we were discussing him gaining 50 FPS for 2 inches.
magnum338
Member
I'd like to make a few comments about the subject of barrel length vs velocity. Page 322 of "Hatcher's Notebook," a great old classic treatise on small arms, shows curves of velocity, pressure and time of travel of a bullet down the barrel. It shows that near the breech, where the internal pressure is very high the bullet accelerates very quickly. But as the bullet moves down the barrel the fixed amount of powder gasses must fill an increasing volume. The pressure must decrease and therefore the push on the bullet base must also decrease, decreasing the rate of increasing velocity. This is compounded by the tremendous friction between bullet and bore. This is so great that, from all I've read, it actually causes a .22rf bullet to start losing velocity past about 18" travel. Unfortunately, the question of what loss there would be cannot be answered precisely. The curves referred to are for the M1 cartridge. However, I suspect the general shape is probably the same for all. To get a general idea of velocity loss I go to that curve and look at where the velocity curve crosses the barrel length under question and just "scale" it. ("Hatcher's Notebook" might be available in the local library. I think it's extremely interesting)
The primary factor affecting velocity is "expansion ratio". This is the volume of the barrel -vs- the volume of the cartridge case behind the bullet base. For a cartridge based on the same family (e.g. 25-06 / 270 win / 30-06 / 35 Whelan), the case volume is very similar under the bullet. However, the barrel volumes are significantly different for a given length (a 35 cal barrel has much more volume than a 25 cal barrel).
So the 25-06 will be much more sensitive to barrel length than the 35 whelan. A 25-06 with a 36" barrel has about the same expansion ratio as a 35 Whelan with a 20" barrel.
What exact velocity gain/loss you'll get could be predicted by an internal ballistics program. But theory and reality don't always match up. See this link:
http://www.loadammo.com/Topics/October05.htm
So the 25-06 will be much more sensitive to barrel length than the 35 whelan. A 25-06 with a 36" barrel has about the same expansion ratio as a 35 Whelan with a 20" barrel.
What exact velocity gain/loss you'll get could be predicted by an internal ballistics program. But theory and reality don't always match up. See this link:
http://www.loadammo.com/Topics/October05.htm
TheGreatDane
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