Air Usage
I made a setup so I could get psi per shot today. Gauge is +- .25%. I got a little time and have been asked this a few times.
My Airgun time has been cut back a lot to spend more time with my family. So sorry for how long things are taken for those that are waiting for things from me. This is something I do in my spare time. My day job is bad enough when I work. My average day is 14 hrs min.
Here is the numbers I got in .25 and .257 with 62 ci tank plus the fill hose.
.25 were 63 gr hunter supply and .257 was 74 gr Lyman 420.
I didn’t try for a curve. I was just after usage.
Here is how it looks on the gun.
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Caboose
Believe me,sniping based on calculations but air usage is another parameter and i think all these are bullshits…the most important thing is trial and errors than theory.
For me it is better to make a testing system and experimenting .
A testing valve with an adjustable inlet wheel (like Air Arms or Fx),and a testing breech with an adjustable wheel in order to play with ports behind or next to the valve…also a quick release system to fit different barrels,springs,hammer etg..
Porting and valve diameter is more important for me for a perfect performance…even.010″ less or more in diameter could be a huge difference especially for consistency.
Every part on that system should be visible and adjustable…Other words,imagine a condor without a frame on a chassis without the parts being apart .
If you want power forget pre-chamber.Anything works like a baffle affect negatively for a normal velocity with heavy slugs.
Air must keep its elasticity as much as possible,and flow must be directed straight to the port and not under control.
Pellet guns up to 100ft/lbs are another story.
wow… lots of math… good thing I’ve started to like math again!!! What I’m really after is, how big of a pre-chamber would be good to use for your valve doug? 100cc? more? just use the stock tank? I’m trying to get away from the stock tank, and I’m hoping that the pre-chamber won’t be too long. not sure of size (O.D./I.D./Wall) or material yet. I’ll have to write down this math stuff and do my own figuring… Just for fun.
Thanks. I was just curious. I know the .25 is wasting some. But to get those kind of number that’s what it takes with a short barrel (24″).
The .25 at 3300 psi was 1033 fps with 63 gr.
The .257 at 3300 psi is right around 1100 fps right know. I just didn’t turn up the PW enough and that’s why shoot 2 is higher than 1.
I have a 34″ .25 barrel. I didn’t plan on using all of it. That was what showed up when I ordered a 30″.
I’m happy with my .257. 😀
.25cal
1st shot.. if you shoot without bullet (free flow)normally you must spent 68.8psi for the first 2 feets supposed that the valve is already closed once the bullet leave the barrel(i m saying that because it is impossible to calculate the valve timing for more accurate calculation ) ..but..with a loaded bullet your pressure being 52psi less, concerning the starting fill…That means you spend about 16.5psi outside which is ok.
Also your first shot remove .834cf compressed air from your bottle starting from 3100psi .
.257 you released 59psi to the atmosphere…this is not what i call air usage but not so bad at all on that power.i believe a slightly longer barrel(33″-34″) will brought the ideal result on same setting. i mean better air usage and greatest velocity without touch anything on the rifle.
air capacity removed from air reservoir was 1.080cf compressed air starting from 3200psi
Please dont make me calculate between other 5 shots…i have to go to sleep….if you want i can pm you the rest.
62 ci
what is your air reservoir capacity?
What are your thoughts on how much air is used? .25 is 24″ and .257 is 32″.
Lets say we have a .22 barrel 24″in lenght..this is .3cu/ft of volume at free atmosphere.
according the Boyle’s Law it is Va = pc Vc / pa
where
pa = atmospheric pressure (14.7 psia, 101.325 kPa)
Va = volume of the gas at atmospheric pressure (cubic feet, cubic meter)
pc = compressed pressure (psi, kPa)
Vc = volume of the gas at compressed pressure (cubic feet, cubic meter)
Now lets say for a 200 bar filling we have Va=3100 x .3 /14.7=63cu/ft for the barrel volume under 200 bar pressure.
but…. the same be valid for the tank
so…for a 62cu/ft tank it is
3100 x 62 /14.7=13.074cu/ft
Once you did try this calculator and find the air pressure drop.
where cfm
if your rifle shoots at 900fps that means 900 x 60sec(1min) =54000 ft/min …so if the barrel is 2ft the maths are 200/54000=.0039
its easy…imagine the barrel bore like a cylinder and volumetric with a calculator like this.
but you have to add 60-70% (160-170% overall volume)of the result (depending the caliber)because during the pellet/bullet movement ,the distance between pellet and valve increased and pressure drops a little bit while the valve has already closed and air find more area to its passage before exit from the barrel.
if it keep opened then we do not have an air usage and spend a good amount of air to the atmosphere although pressure remaining as it is from point A* to point B* …However no backyard friendly when this happened and shot count suffered dramatically.
*point A=next to the pellet feeding prode
*point B=barrel edge
So If I’m looking at this right- the .257 with your settings is only using 345 psi of air for six shots… divided over six shots is 57.5 psi per shot… but how would that equate to cc’s of air? Weird question, and I’m not even sure you could convert it, considering one’s pressure, and one is volume. Poop… GOOD INFO TO HAVE THOUGH!!! Thanks Doug!! :8:
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well, considering my original idea was to use the factory tank as a stock, but hook up a larger tank via remote to have more available air- you’re saying this would be a bad idea? isn’t this the same idea as a pre-chamber but on a larger scale? I do get what youre saying though- air wants to flow, so let it. I guess I’ll have to compromise and just use the factory tank, and hook it via remote… no sense in messing with something that already works, right? Doug! any news on your valve sets and availability?