J
Jerry
Guest
Is there a relationship between muzzle velocity & barrel length, all other things being equal? Will muzzle velocity for a 24 inch barrel vs. a 30 inch barrel be different or the same?
J
Jerry
Guest
Then, I wonder why I can only get to about 82% of measured velocity with my new longer custom barrel at a 15% decreased powder charge before seeing ejector marks on my brass. If you don't mind, let me include the distance of bullet to lands possibly part of the problem.... I'm at 0.069 from bullet ogive to barrel. I'm rather new to handloading so maybe I should drop the bullet back farther?
Your case capacity
Gives up. You can't get enough powder in to take advantage of the long tube perhaps. What case are you shooting?
Gives up. You can't get enough powder in to take advantage of the long tube perhaps. What case are you shooting?
J
Jerry
Guest
300 WM. I'm only at a 50 gr charge where as the book says starting charge is 66.5. I'm no where near max volume
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A very curious reply.........tell me Al, what are your listed strictures ???
I didn't list any UncleB
I think you've entered the wrong reality??My reply isn't "curious" in any way, no need for interpretation.
Said Alice
al
With that big case
That may be an issue. A case like that should be at its best with very slow burning powders.
That may be an issue. A case like that should be at its best with very slow burning powders.
You're really not giving us anything to work with here. 50 grains of what powder? Under what bullet?
Your issue has absolutely nothing to do with barrel length. 50 grains is a 33.25% reduction of 66.5 grains. There is something seriously wrong here. 99%of the time, the listed STARTING load should be perfectly safe in any modern rifle if the recipe of case, primer, bullet, and OAL is adhered to. Custom barrels may have shorter throats and a smaller diameter neck. The neck clearance is the first thing I would look at. Do you know if this is a tight neck chamber?
Andy Cross
New member
Many variables but
The relationship between barrel length and achieved velocity has many variables but the laws of physics work like this. If all the powder has been burned just before the bullet exits the muzzle you have probably achieved the maximum velocity you can obtain from that powder, charge weight, bullet, primer combination in that barrel. All bullets must begin loosing velocity after they exit the barrel. A longer barrel will not achieve much if any increase in velocity beyond the optimum length.
Andy.
The relationship between barrel length and achieved velocity has many variables but the laws of physics work like this. If all the powder has been burned just before the bullet exits the muzzle you have probably achieved the maximum velocity you can obtain from that powder, charge weight, bullet, primer combination in that barrel. All bullets must begin loosing velocity after they exit the barrel. A longer barrel will not achieve much if any increase in velocity beyond the optimum length.
Andy.
Where did you get this from?
Some thoughts;
Max pressure is in the first inch of bullet travel....
Max pressure on an airgun is before you pull the trigger.....
Are you saying you achieve a negative pressure curve once the powder's "burned?"
'M ASKIN' here....
al
Andy Cross
New member
Boyles gas law
Without writing a reply that reads like war and peace Boyles gas law states that the relationship between pressure,volume and temperature are directly proportional to one another. So once the powder has stopped burning even if the pressure is able to keep the bullet moving the drag of it in the barrel will eventually result in diminishing returns. Thus any velocity gains by increasing the barrel length will be minimal if any at all. If you have the time and money start with a barrel of 26 inches and keep re-chambering it docking off an inch each time. Plot the velocity and compare the delta curves and you will see Dr Boyle is correct.
Andy.
Without writing a reply that reads like war and peace Boyles gas law states that the relationship between pressure,volume and temperature are directly proportional to one another. So once the powder has stopped burning even if the pressure is able to keep the bullet moving the drag of it in the barrel will eventually result in diminishing returns. Thus any velocity gains by increasing the barrel length will be minimal if any at all. If you have the time and money start with a barrel of 26 inches and keep re-chambering it docking off an inch each time. Plot the velocity and compare the delta curves and you will see Dr Boyle is correct.
Andy.
I do.
I have.
As has Dan Lilja
http://www.riflebarrels.com/articles/bullets_ballastics/long_barrel_velocity.htm
And any number of others.....I'm the only one who weighs charges to the kernel of powder AFAIK. My findings were slightly different than the others', "cleaner" IMO, but no surprises.
As I suspected, you got it from your brain, and while you may well consider yourself the smartest guy in the room, it's a big room
Incidentally, deprecating phrases like "you will see Dr Boyle is correct" do little to make your case.
al
Andy Cross
New member
I rest my case
If you have already done a test like this then there isn't any more to say. I rest my case. I would like to see the plots if you still have them. As far as Dr Boyle is concerned he was the one who proved this relationship to be correct and as a result became a law. I have a great respect for pioneers like him.
Andy.
I do.
I have.
As has Dan Lilja
http://www.riflebarrels.com/articles/bullets_ballastics/long_barrel_velocity.htm
And any number of others.....I'm the only one who weighs charges to the kernel of powder AFAIK. My findings were slightly different than the others', "cleaner" IMO, but no surprises.
As I suspected, you got it from your brain, and while you may well consider yourself the smartest guy in the room, it's a big room
Incidentally, deprecating phrases like "you will see Dr Boyle is correct" do little to make your case.
al
If you have already done a test like this then there isn't any more to say. I rest my case. I would like to see the plots if you still have them. As far as Dr Boyle is concerned he was the one who proved this relationship to be correct and as a result became a law. I have a great respect for pioneers like him.
Andy.
This is all fine and good Andy but you're begging the question..... WE ALL KNOW that at some point the bullet will begin to slow down, and WE ALL KNOW if we've graduated HS that Boyle's Law is part of the reason but it's irreverent to the op's question.
NOT in the freakin' BARREL! Especially not a 26" barrel!
Why postulate some event that "would happen were the barrel long enough?"
It's confusing, non-useful information IMO.
He asked about real-world barrels with real-world chamberings and you come back with Boyle's Law????
C'mon
People come here with real questions looking for real answers....
If the dude had asked "If I jump off the front porch will I hit as hard as if I jumped off the water tower?" your answer would have been "Well, The Law Of Universal Gravitation States that you will accelerate at the rate of prox 9.8M/s BUT, the same law ensures that our planet is enveloped in a blanket of gas which inhibits this acceleration so at one point you'll achieve a stability which turns into a negative acceleration........we call this "Terminal Velocity" and blah and blah and blahhh"
Really? And this helps me HOW?
I would have answered "no."
It is my considered opinion that my first answer completely and succinctly answered the op.......no?
If not, please explain.
al
Andy Cross
New member
Yes or No
Original question
Is there a relationship between muzzle velocity & barrel length,
Yes
all other things being equal? Will muzzle velocity for a 24 inch barrel vs. a 30 inch barrel be different or the same?
Different
Any one reading you last post could be excused in thinking you were upset. I didn't mean to do that.
Andy
This is all fine and good Andy but you're begging the question..... WE ALL KNOW that at some point the bullet will begin to slow down, and WE ALL KNOW if we've graduated HS that Boyle's Law is part of the reason but it's irreverent to the op's question.
NOT in the freakin' BARREL! Especially not a 26" barrel!
Why postulate some event that "would happen were the barrel long enough?"
It's confusing, non-useful information IMO.
He asked about real-world barrels with real-world chamberings and you come back with Boyle's Law????
C'mon
People come here with real questions looking for real answers....
If the dude had asked "If I jump off the front porch will I hit as hard as if I jumped off the water tower?" your answer would have been "Well, The Law Of Universal Gravitation States that you will accelerate at the rate of prox 9.8M/s BUT, the same law ensures that our planet is enveloped in a blanket of gas which inhibits this acceleration so at one point you'll achieve a stability which turns into a negative acceleration........we call this "Terminal Velocity" and blah and blah and blahhh"
Really? And this helps me HOW?
I would have answered "no."
It is my considered opinion that my first answer completely and succinctly answered the op.......no?
If not, please explain.
al
Original question
Is there a relationship between muzzle velocity & barrel length,
Yes
all other things being equal? Will muzzle velocity for a 24 inch barrel vs. a 30 inch barrel be different or the same?
Different
Any one reading you last post could be excused in thinking you were upset. I didn't mean to do that.
Andy
The original poster stated in his second and third posts that he had pressure signs using 50 grains of powder where the suggested starting load was 66. Did not say what powder, what bullet, etc. His original question not withstanding, he has bigger problems than wondering if his barrel is too long. It appears that he has left the building.
XBBR Shooter
New member
Sorry Andy, but you are wrong. Boyle's law does not apply here at all. It is not that complicated.
In a "normal" cartridge/powder combination (not 5gr of BullsEye in a 300WM)... the pressure peaks at about 6 to 8 inches, and that is the place of maximum acceleration rate... but past the peak, the pressure continues to exert more force on the back of the bullet, than the friction on the bullet, so it continues to accelerate until it leaves the barrel.
A 308 will have ~12,000 to 14,000 psi of barrel pressure when the bullet exits the barrel - that is more than enough to keep the bullet gaining velocity, even though the powder has completely burned - it is raw gas pressure at work. Maybe if the barrel was 15 feet long, you might reach the point when the pressure was equal or less than friction, and the bullet would no longer gain velocity... but that is not in the framework of this discussion.
SGJennings
New member
I've never had the situation in a CF, but in a RF, it is well-established that max velocity is with a 16-18" barrel.
Edit: I remembered a practical test about the question. Looked it up: http://www.6mmbr.com/blogjan2006.html .
Edit: I remembered a practical test about the question. Looked it up: http://www.6mmbr.com/blogjan2006.html .
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