Muzzle Velocity Question

[Missed_dinner]

To my understanding, the longer a barrel is, the higher the muzzle velocity, right?

So am I correct in saying that just like different calibres, the action is set differently in order to change the fps to keep them sub 12ft/lb. The same applies to barrel lengths to match the muzzle velocities???

and if the the two barrel lengths have exactly the same set up then the longer one must have a higher muzzle velocity even if it is only fractional?

[CuppaT]

Everything has it's optimum.... longer barrels are generally more efficient, but there is a limit which if crossed the barrel would be less efficient.
So yes, different barrels lengths will need different amounts of air. But barrel length is more than this, it is about being short enough to use in a hide, or long enough to give a better hold. It's different strokes for different folks. Just buy and use what you're comfortable with.

Example: a .22LR is generally most efficient with a 16" barrel, however a .17HMR is generally most efficient with a 20" barrel. Not an example of air rifles but it does go to show that there is more to this than worth worrying about.

[bighit]

some info here
http://www.pyramydair.com/blog/2005/...irgun-barrels/

[philipk5]

That assumption is as accurate as saying red cars are faster than blue cars!

It is a very complicated subject that I know enough about it to say I know nothing about it.

Looking forward to others comments.

[Turnup]

To my understanding, the longer a barrel is, the higher the muzzle velocity, right?

So am I correct in saying that just like different calibres, the action is set differently in order to change the fps to keep them sub 12ft/lb. The same applies to barrel lengths to match the muzzle velocities???

and if the the two barrel lengths have exactly the same set up then the longer one must have a higher muzzle velocity even if it is only fractional?

There is an optimum barrel length. Take an extreme (I often find that extreme examples aid the understanding) Really really short barrel, say 5mm, then the great majority of the air will be vented after the pellet has left the barrel, so low efficiency, low MV. A really really long barrel, say 5 meters, and the pellet will have a significant mass or air in front of it, reducing acceleration, and after some maximum velocity is reached, friction against the barrel will make it slow down.

For a given action and barrel, then there will be a length which delivers the maximum MV, shorter or longer will result in lower MV. I think that similar reasoning would apply to BP and nitro powered firearms, but the actual lengths are probably longer, and of course the burn rate of the propellant is also a factor (slower burn rate needs a longer barrel for best efficiency)

[robinghewitt]

There used to be a thing on long barrelled springers that you could increase the power by sawing the end off a bit.

The only possible explanation is that the pellet was actually slowing down towards the end rather than speeding up.

In old fashioned cannon the optimum barrel length was 25 calibres, (probably need a bit more in an airgun, I just put that in for fun)

[rhyslightnin]

There used to be a thing on long barrelled springers that you could increase the power by sawing the end off a bit.

The only possible explanation is that the pellet was actually slowing down towards the end rather than speeding up.

In old fashioned cannon the optimum barrel length was 25 calibres, (probably need a bit more in an airgun, I just put that in for fun)

This extra mv through shortening a barrel could be due to the choke being removed preventing the pellet from being decelerated by the narrowing of the barrel more so than the effect of the barrel being shorter.
I could be wrong but i think its more likely than the barrel being more efficient shortened.
Rhys

[angrybear]

There needs to be enough length for the available blast of air to accelerate the pellet up to the required velocity, once it's reached that velocity job done, so a pellet with more mass/area ratio requires a longer barrel because it will accelerate slower, and if FAC going for max power then a longer barrel allows for longer acceleration.

Equally once at max velocity, for the available air blast, any further barrel length is detrimental as it will only cause friction & slow the pellet.

So I think the answer to all 3 questions is;

yes, up to a point, but not necessarily so.

[Benelli B76]

Longer barrels definitely make a difference on PCP and C02 performance, but springers are different and barrels that are too long can tend to slow down the pellet. John Bowkett did some tests with a spring rifle and published his findings in one of the magazines.

Baz

[Mr. Gen]

There is a lot of useful information and even more useless speculation on this subject.

If anyone is interested I cut a 14.5 inch HW80 barrel down to 8.5 inches and had to increase power by around 40% to attain 12 ft lbs.

The increased recoil was offset by the quick lock time and the gun remained accurate and less hold sensitive.

My own preference is to run a springer at it's intended optimal power setting with a shorter barrel than strangle the action down with sleeves, piston heads and reduced swept volume. But then again I use my guns mainly for hunting and am not afraid of recoil.

I have some data (and more importantly some superbly accurate home carbined rifles) if anyone is interested.

Pat

[short-carabine]

Longer barrels definitely make a difference on PCP and C02 performance, but springers are different and barrels that are too long can tend to slow down the pellet. John Bowkett did some tests with a spring rifle and published his findings in one of the magazines.

Baz

Up to a point. IIRC the optimum for a Crosman 2250 is 18" barrel. Past that the gain isn't really worth it. There was some test data kicking about on the net, but can't recall exactly where.

[bighit]

Yesterday I made a comment about a longer barrel being more efficient with air in a precharged airgun and that got me thinking. I have danced around this subject but today I’ll tackle it head-on. What is the difference between a short and long barrel in an airgun?

Spring guns like shorter barrels
Gerald Cardew and his son, Mike, wrote in their book The Airgun from Trigger to Target about an experiment to determine the maximum length a spring-gun barrel should be. When they performed this experiment in the 1960s , the low-powered .22 rifle they tested got its maximum velocity by the sixth inch of barrel. After that, the pellet was coasting. After 25 inches of barrel, the pellet began to slow from friction.

Today’s spring guns are more efficient, and the barrel length required for maximum acceleration is closer to 10 to 12 inches. Caliber makes a difference, as well, but it’s not that big a difference. So, spring guns favor shorter barrels over longer ones. Accuracy is not affected by barrel length as I pointed out in the posting on May 26, Are longer barrels more accurate?

CO2 & pneumatic guns like longer barrels
No conclusive tests have been run on this, to my knowledge, but I can easily prove that gas guns like longer barrels. An AirForce Talon SS shoots a .22 caliber Crosman Premier pellet at 830 to 850 f.p.s. when set to its highest power seting. Exchange the standard 12-inch SS barrel for an 18-inch optional barrel, and the top speed will be 925 to 940 f.p.s. with the same pellet. Exchange that for the 24-inch optional barrel and the top velocity climbs up to 1,000 f.p.s. with the same pellet. These results all use the same base gun and air tank, so the only thing that changes is the barrel length.

Notice that the top velocity doesn’t increase as much going from the 18-inch barrel to the 24-inch barrel as it does going from the 12-inch to the 18-inch. That’s because the additional six inches of barrel after 18 inches don’t add as much as they do after only 12 inches.

The proof of greater speed with a longer barrel in a CO2 gun is seen in the quoted velocity for the Walther CP 88 with a 4-inch barrel compared to the Walther CP 88 with a 6-inch barrel. There is a gain of around 30 f.p.s. from the additional two inches of barrel.

What does it mean to you?
When shopping for a PCP, a longer-barreled gun will be the most efficient. If two guns of the same make get the same velocity and energy, the one with the longer barrel should get a few more shots per charge. A CO2 gun will be faster in the long-barreled versions. Compare the velocities of the S&W 586-4 with the S&W 586-6 to see what I mean.

And, now you also know that when the velocity given for a short-barreled CO2 gun is the same as for a longer-barreled version of the same gun, the velocity for one barrel length has been given for both models. Simply compare that gun’s stated velocity with that of a similar gun to discover whether the short- or long-barreled model’s velocity was quoted.

[clarky]

Longer barrels definitely make a difference on PCP and C02 performance, but springers are different and barrels that are too long can tend to slow down the pellet. John Bowkett did some tests with a spring rifle and published his findings in one of the magazines.

Baz

Believe it or not Johns findings suggested 11 inches as being the peak length for power in the springer and that was realised in the Air Arms Woodsman at the time....i wonder if he had a hand in the design or if they just went with his findings but the Woodsman had an 11 inch barrel.
Regardless the Woodsman matched my longer barreled Hi power, operating with the same cylinder and internals but running a 14 inch barrel.
John suggested a marked tail off after 17 to 18 inches and longer lock times, hence the then trend for carbines.
This trend past with springers though....it upset balance, increased noise and required extra manufacturing costs for muzzle weights or silencers.....pretty much returning these carbines to the original length...

[Geezer]

Yesterday I made a comment about a longer barrel being more efficient with air in a precharged airgun and that got me thinking. I have danced around this subject but today I’ll tackle it head-on. What is the difference between a short and long barrel in an airgun?

Spring guns like shorter barrels
Gerald Cardew and his son, Mike, wrote in their book The Airgun from Trigger to Target about an experiment to determine the maximum length a spring-gun barrel should be. When they performed this experiment in the 1960s , the low-powered .22 rifle they tested got its maximum velocity by the sixth inch of barrel. After that, the pellet was coasting. After 25 inches of barrel, the pellet began to slow from friction.

Today’s spring guns are more efficient, and the barrel length required for maximum acceleration is closer to 10 to 12 inches. Caliber makes a difference, as well, but it’s not that big a difference. So, spring guns favor shorter barrels over longer ones. Accuracy is not affected by barrel length as I pointed out in the posting on May 26, Are longer barrels more accurate?

CO2 & pneumatic guns like longer barrels
No conclusive tests have been run on this, to my knowledge, but I can easily prove that gas guns like longer barrels. An AirForce Talon SS shoots a .22 caliber Crosman Premier pellet at 830 to 850 f.p.s. when set to its highest power seting. Exchange the standard 12-inch SS barrel for an 18-inch optional barrel, and the top speed will be 925 to 940 f.p.s. with the same pellet. Exchange that for the 24-inch optional barrel and the top velocity climbs up to 1,000 f.p.s. with the same pellet. These results all use the same base gun and air tank, so the only thing that changes is the barrel length.

Notice that the top velocity doesn’t increase as much going from the 18-inch barrel to the 24-inch barrel as it does going from the 12-inch to the 18-inch. That’s because the additional six inches of barrel after 18 inches don’t add as much as they do after only 12 inches.

The proof of greater speed with a longer barrel in a CO2 gun is seen in the quoted velocity for the Walther CP 88 with a 4-inch barrel compared to the Walther CP 88 with a 6-inch barrel. There is a gain of around 30 f.p.s. from the additional two inches of barrel.

What does it mean to you?
When shopping for a PCP, a longer-barreled gun will be the most efficient. If two guns of the same make get the same velocity and energy, the one with the longer barrel should get a few more shots per charge. A CO2 gun will be faster in the long-barreled versions. Compare the velocities of the S&W 586-4 with the S&W 586-6 to see what I mean.

And, now you also know that when the velocity given for a short-barreled CO2 gun is the same as for a longer-barreled version of the same gun, the velocity for one barrel length has been given for both models. Simply compare that gun’s stated velocity with that of a similar gun to discover whether the short- or long-barreled model’s velocity was quoted.

Is think that is basically right. From my recollection, the Cardew tests on an HW35 topped out at 7-8 inches, not 6.

A relevant factor, for springers, is the added accuracy advantage of forward weight.

And I distrust all published manufacturers' velocity figures. They are at best a rough guide to the real world, at worst an over-optimistic, lawyer-driven, version of a best-case scenario with alloy or plastic pellets.

[bighit]

Is think that is basically right. From my recollection, the Cardew tests on an HW35 topped out at 7-8 inches, not 6.

A relevant factor, for springers, is the added accuracy advantage of forward weight.

And I distrust all published manufacturers' velocity figures. They are at best a rough guide to the real world, at worst an over-optimistic, lawyer-driven, version of a best-case scenario with alloy or plastic pellets.

I just copy and pasted the link I put up earlier