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Some info on velocities required for certain fpe

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Some info on velocities required for certain fpe

Unread postAuthor: beastmode986 » Mon Jul 09, 2012 12:00 pm

Yesterday i did a little bit of research on air rifle pellets and what velocities are required for a certain muzzle energy. I decided to make my target muzzle energies 45 ft lbs , 55 ft lbs , and 63.5 ft lbs because i wanted to do a little test for a few reasons 1. the fpe gives me extra power for destroying more junk i have lying around2. personal interest, I just wanted to get some info for future project goals.
Heres what i got


.177 cal pellets

a.crosman hunting pointed 7.4 grains
b.crosman destroyer 7.9 grains
c. Winchester pointed 9.68 grains
d.eun jin 16.1 grains

velocity required for 45 ft lbs

a.1654.6 fps
b.1601.4 fps
c.1446.7 fps
d.1121.8 fps

.22 cal pellets
a. bee man silver bear hollow points 12.65 grains
b. crosman hunting pointed 14.3 grains
c. H&N baracuda round nose 21.14 grains
d. Eun Jin pointed 32.4 grains

velocity required for 55 ft lbs

a.1399.1 fps
b.1315.9 fps
c.1082.3 fps
d.874.23 fps

.25 cal pellets
a.H&N spitzkugel pointed 24.85 grains
b.H&N baracuda round nose 31.02 grains
c.Eun Jin 43.2 grains

velocity required for 63.5 ft lbs
a.1072.65 fps
b.960 fps
c.813.5 fps
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 09, 2012 12:14 pm

Supersonic velocities are difficult to achieve with air guns, so unless you plan on going hybrid aim for the 800-900 fps range.

Also note that for a given energy, a smaller faster projectile will generally penetrate deeper than a larger slower one, even though it will make a smaller hole. And unless you're using a rifled barrel, heavyweight pellets will rarely stabilise from a smoothbore barrel.
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Unread postAuthor: beastmode986 » Mon Jul 09, 2012 6:02 pm

good to know thanks alot!

why are supersonic velocities harder to achieve with air? i have always wondered but never bothered to ask anyone

also couldent someone use co2 to acheive a higher velocity? or would a gas lighter than oxygen such as helium make the projectile go faster?
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Unread postAuthor: ramses » Mon Jul 09, 2012 8:01 pm

beastmode986 wrote:good to know thanks alot!

why are supersonic velocities harder to achieve with air? i have always wondered but never bothered to ask anyone

also couldent someone use co2 to acheive a higher velocity? or would a gas lighter than oxygen such as helium make the projectile go faster?



Gases don't like to move faster than their speed of sound, so the projectile essentially outruns the propellent gas.

CO2 has a higher molecular weight than N2 (the primary component of air, not oxygen as you suggest), and so would be an inferior propellant gas. Helium would be ideal, since it is the lightest gas molecule. (Hydrogen is diatomic)
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 10, 2012 12:05 am

As above, you want to use low density gas for best performance, and in this regard CO<sub>2</sub> is possibly one of the worse candidates.

Remember that force = pressure x area

A 0.177" projectile has roughly half the base area of a 0.25" projectile, to achieve the same power you need to double the pressure. If it's ft/lbs you're after, the bigger the bore the better.
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Unread postAuthor: DYI » Tue Jul 10, 2012 8:16 am

Helium would be ideal, since it is the lightest gas molecule. (Hydrogen is diatomic)


Just a quick correction, dihydrogen gas (~2.02g/mol) is much lighter than helium gas (~4g/mol). Helium sees a lot of use because it is easier to work with. Its lower heat capacity is also useful in some regards (it is a better buffer gas for hybrids than hydrogen gas).

I'm not too sure what this topic is here for - I see no question or point of discussion in the first post.
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Unread postAuthor: beastmode986 » Tue Jul 10, 2012 11:32 am

DYI- I made the post because i thought the information could possibly help someone who wants to know what velocity there projectile needs to travel at to have a certain muzzle energy.The info might help people in future projects as well.

jsr and ramses- wouldent i need some sort of special equipment in order to say put like 300psi of helium in an airgun ? What would i need???
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 10, 2012 11:48 am

DYI wrote:I'm not too sure what this topic is here for - I see no question or point of discussion in the first post.


It's a thinly veiled cry for help ;)

jsr and ramses- wouldent i need some sort of special equipment in order to say put like 300psi of helium in an airgun ? What would i need???


You're not going to get it from the atmosphere, it floats away :) you need to buy the gas in cylinders, it's commonly sold to fill balloons.

http://www.ebay.com/itm/Disposable-Heli ... 460525fec7

You'd want something at higher pressure to decant from though.

Personally I would go for HPA, various options from stirrup pumps to fridge compressors through to paintball supplies.
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Unread postAuthor: beastmode986 » Tue Jul 10, 2012 11:53 am

true , but would i be able to mix helium and air for better performance? i can get propane tank sized cylinders at party city for 30$
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 10, 2012 11:56 am

Theoretically it can be done, but it won't be the same benefit as pure helium, probably more trouble than it's worth. Any idea what pressure those tanks are at?
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Unread postAuthor: POLAND_SPUD » Tue Jul 10, 2012 12:31 pm

i can get propane tank sized cylinders at party city for 30$
IIRC they are basically like propane cylinders... so my guess is that they are rated to like 300 psi max

EDIT
found them -> http://www.balloonheliumtank.com/dispos ... um-tank-3/

uhmm ok should have noticed that jsr had posted a link to them too :?


Anyway what are we really talking about ? Do you want to build a gun yourself or merely mod a commercial airgun ?

I've read that some ppl mod their QB78 to run on air instead of CO2 and such setups achieve MVs higher than 60m/s or so
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 10, 2012 12:38 pm

260 psi is not much...
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Unread postAuthor: beastmode986 » Tue Jul 10, 2012 1:27 pm

well i am going to build another gun very very soon im not sure about the output pressure on the helium tanks though

My goal for my next project is something powerful and has alot of recoil i dont think i should move onto hybrids yet though. i dont want to start a new thread or talk about it in this one though.....
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Unread postAuthor: Gippeto » Tue Jul 10, 2012 1:57 pm

POLAND_SPUD wrote:I've read that some ppl mod their QB78 to run on air instead of CO2 and such setups achieve MVs higher than 60m/s or so


I should bloody hope so. :lol: 1000+fps is quite do-able...but rather wasteful of the air charge.
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Unread postAuthor: POLAND_SPUD » Tue Jul 10, 2012 2:30 pm

lol I meant 'MVs higher by X'

Gippetto don't you have a QB78 (or 79) ?
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