air requirements per shot, per caliber

This information has to be very specific there can be no, "regardless of hammer weight, port size ect." because it all matters. The information IS brand and gun and tune specific for a single caliber, projectile type and weight, barrel type and length, fill pressure, operating pressure, hammer weight, spring pressure, port size, plenum size and more and this is to get the info on just one gun, in one caliber, at one tuning level.

FX has a page that has some of the information you desire on just one gun here.

https://fxairguns.com/rifles/the-impact/

They have this info with the stock components and a factory tune. Scroll down to see the fps/fpe of each caliber. There is another chart elsewhere that will give the regulator settings to get these power levels.

I expect there are similar pages for different guns and brands of guns available although not every maker will be so kind. So unless the factory has included this information or someone has kindly posted it up for the specific gun you have in mind it is difficult to say what the end result will be.

Still I expect there are mathematical equations that would get you in the ballpark with a given pressure, port size, projectile weight somewhere out there. I just can't find them.

Bob Sterne has part of the equation for you here

https://www.gatewaytoairguns.org/GTA/index.php?PHPSESSID=f49244b8d82f1958c82b2f1900aafba5&topic=163044.msg155818337#msg155818337

The .22 caliber is way more efficient than the .177 so you have a plus going for you right from the beginning.

Now after all of that I finally understand what you are saying and sorry I have not helped allot.

I found this I think it is what you are looking for.

Speed = sq root ( (2 x length of pipe x PSI x pi x r2) / mass)

Where pipe = barrel and r = .5 of the pellet diameter mass = pellet weight I think this is how it werqs

Now after all of that I finally understand what you are saying and sorry I have not helped allot.

I found this I think it is what you are looking for.

Speed = sq root ( (2 x length of pipe x PSI x pi x r2) / mass)

Where pipe = barrel and r = .5 of the pellet diameter mass = pellet weight I think this is how it werqs

But now we haven't addressed the plenum volume and I does not know how to do that. I can say however it will need to be very BIG.

So you want to take the Impact made for a max of 75FPE to 211+FPE then? Ouch that gonna hurt!!

rsterne also Bob Sterne on the airgunguild has allot of information on plenums and about different builds you might want to look him up. He says 1cc per fpe on the plenum

https://airgunguild.com/index.php?pretty;board=ask-bob;topic=plenum-size.0

1/2cc to 1FPE capability is closer than 1cc per FPE equation, at least with most of my PCPs. That said, I don't really believe that math is linear for all PCPs. Some designs are more optimal than others in that regard.

@biohazardman I get that it may be gun specific, but the Impact, with it's one platform, can easily tune and have four different caliber configurations. I am wanting to add a fifth caliber to the lineup! I want to put a .308 barrel and probe into her and I want it to push the slugs out at 950+ fps. But I don't want to experiment with buying a new barrel and sizing it to the gun if there isn't enough air pressure to push an NSA .308 99 grain (or higher) slug out of the current configuration. I've got the high power mods to drive the hammer and flow the air in .30 caliber, I just need to know how to figure out if that will be enough air (or how much I may need) to push a slug that's twice as heavy at the same slug speeds.

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I'm sorry but what you are saying is not making sense to me. Why ad a .308 barrel to the mix if you have a .30 cal. already and the tune for it. They are the same and both require 7.62 ammunition. Don't you mean .357? Biohazardman is correct in his estimation, doubling the projectile weight and maintaining the same velocity is a big ask. I doubt that a tune like that would be possible in an Impact no matter how much air you feed it.

How fast are you shooting .30 caliber slugs right now? I don’t think you would see a noticeable increase in FPE by modding to .308. Especially if you are already pushing the limits of the gun with mods. 

I'm going to offer up my non-scientific thoughts on the subject.

In the OP you say .177 to .22. There I would think you would benefit from the increase because, as mentioned earlier, .22 is more efficient than .177. Moving from .30 to .308 and trying the get that much power from the heavier slug is going to be a challenge, right size plenum an TP or not. I'm not a pro at mods yet so maybe the FX can be taken there, but a 3x the stock power I see you running into reliability issues.

I also want to address the plenum size equation. I'm just not fully on board with either the 1/2cc or 1cc per 1 FPE. It just never adds up to me. As a for example I'll take one of the most efficient airguns I own, the Leshiy. Without really pushing it I can get 50fpe from a .30 44.75gr pellet. Using the equation I would need a plenum of 25cc to get that power, yet the full air tube on the Leshiy is 40cc so there is no way the plenum is larger than maybe 10cc. I can get 8-10 regulated shots at this power. I guess what I am getting at is this equation seems like it would be specific to each and every gun.

I would agree that plenum volume and barrel length would go hand in hand as you'll need more volume to continue accelerating the pellet/slug the full length of the barrel. 

Overall there probably is a lot of science and math behind it, but most of these conversations seem very subjective.

I'm going to offer up my non-scientific thoughts on the subject.

In the OP you say .177 to .22. There I would think you would benefit from the increase because, as mentioned earlier, .22 is more efficient than .177. Moving from .30 to .308 and trying the get that much power from the heavier slug is going to be a challenge, right size plenum an TP or not. I'm not a pro at mods yet so maybe the FX can be taken there, but a 3x the stock power I see you running into reliability issues.

I also want to address the plenum size equation. I'm just not fully on board with either the 1/2cc or 1cc per 1 FPE. It just never adds up to me. As a for example I'll take one of the most efficient airguns I own, the Leshiy. Without really pushing it I can get 50fpe from a .30 44.75gr pellet. Using the equation I would need a plenum of 25cc to get that power, yet the full air tube on the Leshiy is 40cc so there is no way the plenum is larger than maybe 10cc. I can get 8-10 regulated shots at this power. I guess what I am getting at is this equation seems like it would be specific to each and every gun.

I would agree that plenum volume and barrel length would go hand in hand as you'll need more volume to continue accelerating the pellet/slug the full length of the barrel. 

Overall there probably is a lot of science and math behind it, but most of these conversations seem very subjective.

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The leshiy has a 20.5 cc of plenum 

Ok first you ask about changing barrel from .177 to .22 and would it have enough powerful to get the same speed with a .22 from a .177. Then you jump to .30 and .308. That's a big set up. Stock impact can not even push the 50gr to 950 without mods. I know some guys can mod their impacts to push 50gr to about 950 but that is pushing its limits. And now you want to push a 99gr to 950? Dude. The impact ain't a super power house gun that will do 200 plus foot lb. If you want power, get an Texan. The impact had its limits when talking about power. It cant be mod to shoot 200, 300, 400. Etc ft lb. For some miracles you achieve these power levels, the internals of the impact are not made to handle that amount of abuse. Something will give. And when you mod these hpa pcp beyond its limits, someone gonna get hurt.

Ok first you ask about changing barrel from .177 to .22 and would it have enough powerful to get the same speed with a .22 from a .177. Then you jump to .30 and .308. That's a big set up. Stock impact can not even push the 50gr to 950 without mods. I know some guys can mod their impacts to push 50gr to about 950 but that is pushing its limits. And now you want to push a 99gr to 950? Dude. The impact ain't a super power house gun that will do 200 plus foot lb. If you want power, get an Texan. The impact had its limits when talking about power. It cant be mod to shoot 200, 300, 400. Etc ft lb. For some miracles you achieve these power levels, the internals of the impact are not made to handle that amount of abuse. Something will give. And when you mod these hpa pcp beyond its limits, someone gonna get hurt.

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I believe that 200FPE would be the upper limit of a modded MKII. I wouldn't want to shoot it with that much power though. I am pretty anxious to see what the .35 model is capable of, but I'm not hopeful of it becoming a Texan.

@2fast2furious I used the .177 to .22 as an example of going up in caliber only because, like the .30 to .308, it is a relatively small percentage of increase in bore size. I should edit that so people aren't so freaked out. Going from a .30 slug to a .308 slug is more of a gain in projectile weight than bore size, relatively speaking. The bore and weight obviously need more air, and going through those calculated steps to see if it is even feasible keeps people safe.

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You missed my point. There is no difference in bore size from .30 to .308. They both use 7.62 mm projectiles. It is not a relative percentage increase in bore size, they are the same. A .30 cal. JSB pellet is 7.62mm diameter and so is 308 Winchester, 30-06,30-30 or any other .30 cal powder burner. What advantage do you expect from rebarreling with the same calibre?

The problem also between going from .177-.22 and .30-.308 is it's a big percentage difference. .177-.22 is 24% increase in size. .300-.308 is a 2.67% increase....not even comparable really. 

PS I'm a dairy Farmer my math could be off but should make sense

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I believe that 200FPE would be the upper limit of a modded MKII. I wouldn't want to shoot it with that much power though. I am pretty anxious to see what the .35 model is capable of, but I'm not hopeful of it becoming a Texan.

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I agree, 200 PFE is the upper limits as the platform is now (with mods to secure the barrel and probe). The calculation does come to that PFE as well, if the air can push to those speeds. I too am wondering what the new .35 will have in store for us. It will definitely be beefed up.

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You're no kidding. I've had to torque the hell out of my barrel set screw when I have my MKII turned up, otherwise it moves forward an inch or so! And that is just with 65cc's of total plenum volume at 150bar

IMHO...The impact platform does not produce enough power to even the lightest of .308 projectiles to the velocity you are wanting. Seek a true big bore platform for this kind of happiness.