Understanding barrel length in relation to accuracy

[thefitter]

Obviously speed is important to accuracy, you want to remain stable to the target. But how does barrel length affect accuracy?

One barrel 20" and one barrel 28". First barrels round is supersonic at the target, second barrels round is supersonic + at the target. Is the faster bullet always better at long range?

If you can find a accuracy node at the lower speed and still be supersonic/stable whats the point of going faster? Wind?

Sorry if this is not clear... it makes perfect sense in my mind.

Thanks

 

[wapiti25]

Yes, slower would give you more wind drift and drop.

 

[Steve Blair]

The highest B.C. bullet you can shoot will do more for you in the wind than velocity. That said, velocity helps, too. If you are shooting long range BR, it may not be as relevant and there is a weight issue. Shooting F-Class, there are two major attractions to long barrels; mass and velocity. Most F-Open shooters use Ø1.25" straight barrels to maximize stiffness and add some weight. My .300 WSM weighs ~21.75 lbs., 1/4 pound under the limit and has a 34" straight Krieger. It helps when you fire 75 rounds in a day. [br]
Stability is only an issue near the muzzle. Provided the initial spin is sufficient, bullets become more stable the farther they travel. As bullet velocity slows, spin does not slow as much. I look for a wide, forgiving node that will tolerate some temperature change, barrel heating, etc. If that means giving up 100 fps, I would.

 

[Nvreloader]

To go along with, The Fitter's OP,

Does the Highest BC count for ALL these high BC bullets in these calibers, 224, 264, 284 and 308, or just certain calibers?

What about at the different elevations of MSL to 10,000' using the same load/caliber for all elevations, using short or long bbls, that have the same MOA accuracy from either barrel lenghts?

When shooting at different eleavation, from Sea Level to say 10,000', how much cushion is required to stay in this subsonic area?

IIRR, subsonic is about 1200fps (give or take) at SL? Correct.

Is one caliber better than the other?
I have read so much about which caliber is better than the other, it is confusing, to say the least,being new to this game.

If I can use the highest BC 224 cal bullet at 3600 fps -vs- the highest BC 308 cal bullet at 2600 fps and have the same MOA at that range and elevation, from the same bbl length etc.

Why should I subject myself to more recoil, higher componet costs etc, with the larger/heavier calibers??

Tia,
Don

The highest B.C. bullet you can shoot will do more for you in the wind than velocity. That said, velocity helps, too.
Stability is only an issue near the muzzle. Provided the initial spin is sufficient, bullets become more stable the farther they travel. As bullet velocity slows, spin does not slow as much. I look for a wide, forgiving node that will tolerate some temperature change, barrel heating, etc. If that means giving up 100 fps, I would.

 

[Steve Blair]

Highest B.C. bullet producing the least wind drift is true in any caliber. [br]
Sea level is worst case. If your bullet is stable at sea level, it will be at any higher elevation. The higher velocity load will have less wind effect, bullets being the same. [br]
Speed of sound varies with atmospheric density but is ~1126 fps at sea level in dry air and 68°F. The best approach is to stay above 1.2 mach, ~1350, at the target. [br]
The larger the caliber, the higher the bullet B.C., all other things being equal. There is a point of diminishing return regarding recoil. You will not see many people shooting .338 Lapua rifles in F-Open. Although the rifles can weigh up to 22 pounds, they cannot have a muzzle brake and that is a lot of recoil to absorb over ~75 rounds. Also, rest and bag handling becomes an issue. The sweet spot in F-Class seems to be 7mm but new caliber .30 bullets may change the equation. The reason to use a larger caliber and higher B.C. bullet is simple. As German Salazar once said, "B.C. is the gift that keeps on giving." Velocity is lost pretty quickly but B.C is all the way to the target. As an example: My 6BR shoots bullets with a G7 B.C. ~.30 at 2940 and one of my F-T/R rifles shoots bullets with a G7 B.C. ~.41 at 2470. Guess which one has less wind drift. Hint: it's not the 6BR. [br]

 

[thefitter]

Highest B.C. bullet producing the least wind drift is true in any caliber. [br]
Sea level is worst case. If your bullet is stable at sea level, it will be at any higher elevation. The higher velocity load will have less wind effect, bullets being the same. [br]
Speed of sound varies with atmospheric density but is ~1126 fps at sea level in dry air and 68°F. The best approach is to stay above 1.2 mach, ~1350, at the target. [br]
The larger the caliber, the higher the bullet B.C., all other things being equal. There is a point of diminishing return regarding recoil. You will not see many people shooting .338 Lapua rifles in F-Open. Although the rifles can weigh up to 22 pounds, they cannot have a muzzle brake and that is a lot of recoil to absorb over ~75 rounds. Also, rest and bag handling becomes an issue. The sweet spot in F-Class seems to be 7mm but new caliber .30 bullets may change the equation. The reason to use a larger caliber and higher B.C. bullet is simple. As German Salazar once said, "B.C. is the gift that keeps on giving." Velocity is lost pretty quickly but B.C is all the way to the target. As an example: My 6BR shoots bullets with a G7 B.C. ~.30 at 2940 and one of my F-T/R rifles shoots bullets with a G7 B.C. ~.41 at 2470. Guess which one has less wind drift. Hint: it's not the 6BR. [br]

Thanks. I do all my calculations at sea level.

As I said in a previous thread I want to build a "stubby" long range bolt action rifle. I have the bullet and caliber figured out (7mm 180gr / 7mm SAUM) and I have loads that will keep me super sonic at 1000 yards. I'm just trying to understand if the accuracy will be effected by the BARREL LENGTH ALONE as long as I'm supersonic all the way to 1000.

 

[Steve Blair]

Thanks. I do all my calculations at sea level.

As I said in a previous thread I want to build a "stubby" long range bolt action rifle. I have the bullet and caliber figured out (7mm 180gr / 7mm SAUM) and I have loads that will keep me super sonic at 1000 yards. I'm just trying to understand if the accuracy will be effected by the BARREL LENGTH ALONE as long as I'm supersonic all the way to 1000.

[br]
No, BR guys shoot 20-22" barrels and you cannot poke too much at their accuracy. There will be more muzzle blast and recoil but no reason why it cannot be accurate.

 

[thefitter]

Thanks. I do all my calculations at sea level.

As I said in a previous thread I want to build a "stubby" long range bolt action rifle. I have the bullet and caliber figured out (7mm 180gr / 7mm SAUM) and I have loads that will keep me super sonic at 1000 yards. I'm just trying to understand if the accuracy will be effected by the BARREL LENGTH ALONE as long as I'm supersonic all the way to 1000.

[br]
No, BR guys shoot 20-22" barrels and you cannot poke too much at their accuracy. There will be more muzzle blast and recoil but no reason why it cannot be accurate.

So a 16"-18" barrel would still be accurate at speed? Remember I said "stubby"! 8)

 

[Steve Blair]

So a 16"-18" barrel would still be accurate at speed? Remember I said "stubby"! 8)

[br]
That is a lot of powder for a short barrel. The blast could be fierce. Best results will probably come from the fastest powder that will deliver the velocity you need. If you find an accurate load, there is no reason why it would not work at 1000. A pointed 180 Hybrid only has to start around 2400 to be 1400 at 1000.

 

[thefitter]

So a 16"-18" barrel would still be accurate at speed? Remember I said "stubby"! 8)

[br]
That is a lot of powder for a short barrel. The blast could be fierce. Best results will probably come from the fastest powder that will deliver the velocity you need. If you find an accurate load, there is no reason why it would not work at 1000. A pointed 180 Hybrid only has to start around 2400 to be 1400 at 1000.

That's what I'm thinking. I'm going with a long action so I can seat long, get more speed and keep the pressures down. Quickload is giving me almost a dozen powders to choose from that will give me 2500fps from a 16" barrel, but I might go with a 18". Example: 63gr of RL25 is 100% fill and 99.68% burnt @ 2500fps in a 16".

Obviously I will run a big brake but this will be a fun experiment. ;D

 

[Darrel Martin]

I think the the guys from the Houston warehouse declared that 213/4 inch is the most accurate barrel length.To go shorter gives more loss of speed and no gains except in maneuverability and less weight.


"But no bit of information was, Virgil believes, more valuable than a little advice Jim Gilmore passed along. Jim said a barrel MUST be 21 3/4” long for optimum accuracy. That precise length, he stated, sets up a vibration pattern that duplicates well from shot to shot. Virgil faithfully followed that advice on his guns."


http://www.angelfire.com/ma3/max357/houston.html

 

[NateHaler]

So a 16"-18" barrel would still be accurate at speed? Remember I said "stubby"! 8)

Friend, there are guys shooting XP 100s with very good accuracy at long range, i.e to 1,000y. Will it be more of a challenge in the wind? Probably. So what...

Would I rather shoot a .50 BMG with a BC of about 1.00 or a 6BR? For me, it's the latter. There's always a tradeoff. Make your best deal and let us know how it works out!

 

[thefitter]

I think the the guys from the Houston warehouse declared that 213/4 inch is the most accurate barrel length.To go shorter gives more loss of speed and no gains except in maneuverability and less weight.

"But no bit of information was, Virgil believes, more valuable than a little advice Jim Gilmore passed along. Jim said a barrel MUST be 21 3/4” long for optimum accuracy. That precise length, he stated, sets up a vibration pattern that duplicates well from shot to shot. Virgil faithfully followed that advice on his guns."

From light bullets and fast burning powder, the "Houston Warehouse" is good info - IME.
What say for heavy bullets and slower burning powder?
Short range verses long range, two different games.
For long bullets and slow burning powder, my advise is to get all the powder burned before the bullet leaves the barrel.

My 2-cents
Donovan Moran

That's why I'm going to start with the 63gr of RL25 @ 100% fill and 99.68% burnt. I will also try 67.6gr of Hodgdon Retumbo @ 107% fill and 98.7% burnt.

 

[Steve Blair]

That's why I'm going to start with the 63gr of RL25 @ 100% fill and 99.68% burnt. I will also try 67.6gr of Hodgdon Retumbo @ 107% fill and 98.7% burnt.

[br]
I would try toward the other end of the suitable burn rates, H4350 and H4831. The muzzle blast from RL25 and Retumbo would be pretty entertaining.

 

[pmarauder]

That's why I'm going to start with the 63gr of RL25 @ 100% fill and 99.68% burnt. I will also try 67.6gr of Hodgdon Retumbo @ 107% fill and 98.7% burnt.

With the 7 SAUM? I dont know. I was crunching powder at 64 w/ H1000 and the 180 hybrid. FB is .166 or so. I think your optimistic to try and get 67.6 grains of retumbo in there.
I burned up alot of powder before i settled on H4831. Running the 180 Hybrids at 3k. ES of 4 to 5 fps.
I have a few targets at 1k that I saved for load development using a Mcmillian A-5 with a track plate. (not a bench gun) one group was 3.3x1" the next was 2.5 x 2"

That powder should also work in a short barrel.

 

[Ing. Michael W. Mayerl]

Obviously speed is important to accuracy, you want to remain stable to the target. But how does barrel length affect accuracy?

One barrel 20" and one barrel 28". First barrels round is supersonic at the target, second barrels round is supersonic + at the target. Is the faster bullet always better at long range?

If you can find a accuracy node at the lower speed and still be supersonic/stable whats the point of going faster? Wind?

Sorry if this is not clear... it makes perfect sense in my mind.

Thanks

For every caliber and every load (slower faster powder) there is a different perfect barrel length.
Most barrels are too long. There is one point where the bullet gets a high velocity and low muzzle velocity spread. Is the barrel longer, the muzzle velocity rise a little bit but also the spread rise because the friction between the barrel and the bullet has a higher effect on the bullet.

For excample:

In 308 Win I prever 18-20" barrels.
In 17 HMR a 17" barrel is best.
And in the 300 RemUltraMag a 22" barrel with Norma MPR powder bring the best result with no lost of speed.

 

[Steve Blair]

For every caliber and every load (slower faster powder) there is a different perfect barrel length.
Most barrels are too long. There is one point where the bullet gets a high velocity and low muzzle velocity spread. Is the barrel longer, the muzzle velocity rise a little bit but also the spread rise because the friction between the barrel and the bullet has a higher effect on the bullet.

For excample:

In 308 Win I prever 18-20" barrels.
In 17 HMR a 17" barrel is best.
And in the 300 RemUltraMag a 22" barrel with Norma MPR powder bring the best result with no lost of speed.

[br]
There is no such thing as a "perfect" barrel length. There may be a length that meets specific criteria best but will not work well for other criteria. Your stipulation of 18-20" for .308 may be fine for you. But, a Palma shooter needs a very long barrel, typically 30-32", to reach acceptable velocity and provide a long sight radius. [br]
As an engineer, you should know better than to make flat, unqualified statements.

 

[thefitter]

That's why I'm going to start with the 63gr of RL25 @ 100% fill and 99.68% burnt. I will also try 67.6gr of Hodgdon Retumbo @ 107% fill and 98.7% burnt.

[br]
I would try toward the other end of the suitable burn rates, H4350 and H4831. The muzzle blast from RL25 and Retumbo would be pretty entertaining.

I'll run those two tonight. The RL25 and Retumbo have the highest % powder burnt. So I thought they would be the most efficient.

 

[Lazydays]

Obviously speed is important to accuracy, you want to remain stable to the target. But how does barrel length affect accuracy?

One barrel 20" and one barrel 28". First barrels round is supersonic at the target, second barrels round is supersonic + at the target. Is the faster bullet always better at long range?

If you can find a accuracy node at the lower speed and still be supersonic/stable whats the point of going faster? Wind?

Sorry if this is not clear... it makes perfect sense in my mind.

Thanks

a lot more to the equation than bullet speed. The shorter barrel (assuming they are of the same contour) will be several times more rigid than the longer one in this case (Lilja said a 21" seven contour is 2.75 times stiffer than the samething in 26"). If the case your using is one of the smaller capacity cases your simply wasting steel and time with the longer barrel. Then there is the stabalization factors to be injected. Spin the bullet too fast and you create a problem with the error in the C/G, and of course we already know what happens when it's too slow.

I proved some of Lilja's thoughts a few years back with a .223 Remington barrel. It started life as a 26" barrel, and was good for about 3350 fps with a fairly good load. Didn't group all that well (actually rather dismall). I cut metal off the big and the small end of the barrel to end up with a 20" barrel. The chamber was the same cut from a .223 N.M. reamer. Otherwise everything was the same barrel wise. Lost about 75fps in velocity, but groups shrank dramaticly. Barrel was still junk, and not all the shrinkage of course was from the barrel, but am certain that at least 60% was. Had I chose to use a .222 Remington reamer (wish I had), I think I'd been even better off. Or had I gone with a 6x47 Lapua, I'd have lost more velocity. Perhaps 200fps.
gary

 

[Nvreloader]

Question,

When the barrel lengths are being quoted, ie: 21-3/4" etc,

is this from the bolt face to muzzle end,

or the useable length of the barrel rifling etc ??

Tia,
Don