What Ftlbs Can One Expect From a 10" Barrel?

What Ftlbs Can One Expect From a 10" Barrel?

Joined: March 17th, 2007, 1:07 pm

August 11th, 2011, 7:59 pm #1

Im planning on building a super short carbine using a 2250 as the base. Can anyone guesstimate what power I might get from a standard 2250 with a 10 inch barrel?

Also with a modified valve what power and shot count am I likely to acheive again with a 10 inch barrel?
Last edited by Brit. on August 11th, 2011, 7:59 pm, edited 1 time in total.
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Joined: November 28th, 2002, 6:26 pm

August 12th, 2011, 1:38 am #2



Steve
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Joined: March 1st, 2002, 12:22 am

August 12th, 2011, 3:22 pm #3


Even though the barrel is ~29% shorter than stock?

 


dr_subsonic's pneumatic research lab

the Lunatic Fringe of American Airgunning
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Joined: November 28th, 2002, 6:26 pm

August 12th, 2011, 5:06 pm #4

...even though it's only 50% as long.

That's with the stock tune, and gas-thrifty vs gas-hogging DIY tunes might show different results, of course. But no more info than barrel length, 90% is my guess.

What's yours?

Steve
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Joined: March 1st, 2002, 12:22 am

August 12th, 2011, 5:24 pm #5


at first blush.....about 71%

but, after I posted that, it occurs to me that there are other factors in play with changes in barrel lenght. shorter barrel means less friction or drag on the pellet...

And the whole pneumatic propulsion thing can, at time (har, most of the time) be counterintuitive, which is part of why I'm hedging/waffling on the 71%.

your 2240 example indicates a shortening of 50% only reduces MV by 20%. Definelty nonlinear and counterintutive.

Flashing back to some research you did as the ramp up to the AC efforts, are we back to most of the energy given to a pellet being developed _very_ early on in its travel trhu the barrel.


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the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
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Joined: March 17th, 2007, 1:07 pm

August 12th, 2011, 7:08 pm #6

So if my maths is correct and assuming a standard 2250 gives around 8ftlbs energy. I sould get around 7.2ftlbs with a 10" barrel before any valve mods?
Last edited by Brit. on August 12th, 2011, 7:09 pm, edited 1 time in total.
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Joined: November 28th, 2002, 6:26 pm

August 12th, 2011, 9:16 pm #7

at first blush.....about 71%

but, after I posted that, it occurs to me that there are other factors in play with changes in barrel lenght. shorter barrel means less friction or drag on the pellet...

And the whole pneumatic propulsion thing can, at time (har, most of the time) be counterintuitive, which is part of why I'm hedging/waffling on the 71%.

your 2240 example indicates a shortening of 50% only reduces MV by 20%. Definelty nonlinear and counterintutive.

Flashing back to some research you did as the ramp up to the AC efforts, are we back to most of the energy given to a pellet being developed _very_ early on in its travel trhu the barrel.


dr_subsonic's pneumatic research lab

the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
...is the fact that pressure usually drops rapidly as the charge expands behind the pellet.

So the energy contributed by the last inch of bore is generally much less than the energy contributed by the first inch, simply because the pressure - and therefore the push - behind the pellet is higher near the breech than near the muzzle.

Steve
Last edited by pneuguy on August 12th, 2011, 9:18 pm, edited 1 time in total.
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Joined: November 28th, 2002, 6:26 pm

August 12th, 2011, 9:17 pm #8

So if my maths is correct and assuming a standard 2250 gives around 8ftlbs energy. I sould get around 7.2ftlbs with a 10" barrel before any valve mods?
Steve
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Joined: March 1st, 2002, 12:22 am

August 12th, 2011, 9:48 pm #9

...is the fact that pressure usually drops rapidly as the charge expands behind the pellet.

So the energy contributed by the last inch of bore is generally much less than the energy contributed by the first inch, simply because the pressure - and therefore the push - behind the pellet is higher near the breech than near the muzzle.

Steve
if you have more of the variables

oh so much to learn.....


dr_subsonic's pneumatic research lab

the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
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Joined: June 5th, 2006, 12:49 am

August 13th, 2011, 2:09 am #10

at first blush.....about 71%

but, after I posted that, it occurs to me that there are other factors in play with changes in barrel lenght. shorter barrel means less friction or drag on the pellet...

And the whole pneumatic propulsion thing can, at time (har, most of the time) be counterintuitive, which is part of why I'm hedging/waffling on the 71%.

your 2240 example indicates a shortening of 50% only reduces MV by 20%. Definelty nonlinear and counterintutive.

Flashing back to some research you did as the ramp up to the AC efforts, are we back to most of the energy given to a pellet being developed _very_ early on in its travel trhu the barrel.


dr_subsonic's pneumatic research lab

the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
Remember that friction is proportional to the normal force and in the airgun's case
the normal force decreases with barrel length because pressure decreases
and to some extent because the rotational acceleration decreases.
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