Small Caliber

[Spooky]

So, I've got my hands on an old .22 air rifle barrel and was looking at making my own rifle.

I know with compressed air it's hard to get high power with a small caliber and the reasons behind that. However, after a few simulations with GGDT I'm getting some pretty poor results power wise.

When I look at .177 air rifles easily achieving 12ft/lb, why does GGDT indicate I can only just surpass this with .22 and 400 PSI.

I know PCP rifles have a bottle compressed to very high pressures, but only a small amount of this released upon firing. What sort of pressures do simple springer rifles create to accelerate pellets so quickly?

[Mr.Sandman]

Well for one thing, 22 caliber pellets are heavier and go slower. It can also be user error, post a picture so that we may better help you. What valve setup are you using and did you convert the grains to grams correctly?

[jackssmirkingrevenge]

What sort of pressures do simple springer rifles create to accelerate pellets so quickly?

The more powerful ones generate several thousand psi, and remember also that the sudden compression heats the air (as well as the detonation of lubricant in the chamber) so it's not the same kettle of fish as pneumatics.

Also note that for a given chamber size, in commercial pneumatics the 0.177 will get much less shots per fill that the 0.22 version, because you need more air to push the smaller calibre to higher muzzle energies. Simply put, bigger calibre -> more efficient. Even in spring or gas ram air rifles, if both 0.177 and 0.22 versions are sold at 12 ft/lbs, many times the spring in the 0.177 version will be more powerful.

In spite of the small difference in calibre, in terms of projectile base area the 0.177 only has 65% of the area of the 0.22 projectile, this means that for say 100 psi in the barrel the 0.177 will have less than 2.5lbs of force on it, as opposed to almost 4lbs for the 0.22

That being said, you can easily get 400 psi from a cheap shock pump and with a fast valve like say a 1/4" QEV you can achieve this sort of performance.

[Spooky]

This is GGDT's prediction, modeling a 1/2" QEV and the heaviest pellet I could find at 400 PSI.

14J = slightly over 10ft/lbs.

GGDT gives the best muzzle energy with the heavy pellet. I know that enegry will dissipate very quickly and a lighter pellet would be much better practically, it's just an example.

Barrel length is fixed, it's the length of my rifled barrel. Increasing the chamber volume has very little effect and 400 PSI is my maximum obtainable pressure. I guess that's just the limit of pneumatics?

[jackssmirkingrevenge]

I'm guessing your 40cm³ dead volume has a lot to do with it

The 30cm³ pilot volume also seems a little too high.

[Spooky]

That's the higher value suggested here when moddeling the QEV, and as I need a some space for breach loading I thought this was a realistic. Reducing the value to zero only increases the power to 20J.

[jackssmirkingrevenge]

40cm³ is equivalent to around 170cm of 0.22" tubing - that's around 4 times the total length of your barrel - how much space do you need for breech loading?

I can't see the UKSGC thread but the pilot volume also seems excessivly large, it would certainly not be that big in a properly designed launcher like copperhead prime, and if you have the pilot valve directly tapped into the QEV it could be made even smaller.

[jhalek90]

ahh JSR, you make me happy like only another man should make a man happy. Thank you for indirectly answering MY question.

But i do have a question for you.

In a nutshell, you said that a .177 cal pellet takes MORE air pressure to come up to the same speed as a .22 cal?

Dose not the weight of the projectile come into play?

Lest use some random numbers for a second...

If we have 3 cubic inches of air, at a pressure of 400 psi, assuming perfect 100% flow, simply a barrel, that the pressurized air magically appeared in, exactly 3 cubic inches behind the projectile, with the same length of barrel in front of the projectiles, lets say 3 feet. would not the .177 cal bullet leave the muzzle faster than a .22 cal??

Or am i missing something?

Thank you.
~Jhalek90

[jackssmirkingrevenge]

ahh JSR, you make me happy like only another man should make a man happy.

Er... OK!

would not the .177 cal bullet leave the muzzle faster than a .22 cal?

It would come out faster, no doubt, but it would have less energy.

A typical medium weight 0.22" pellet weights around 1 gram, while a medium weight 0.177" pellet weights about half that.

This means that if they are travelling at the same velocity, the 0.22" pellet would have twice the muzzle energy, don't forget:

Muzzle Energy = 0.5 * mass of projectile * velocity * velocity

This means that to have the same energy as a 1 gram 0.22 pellet at 500 feet per second, then the 0.5 gram 0.177" pellet has to be doing around 710 feet per second.

[POLAND_SPUD]

ahh JSR, you make me happy like only another man should make a man happy

Now you should exchange close-ups of your feet...

just make sure you're not using cheap batteries

[jackssmirkingrevenge]

Now you should exchange close-ups of your feet...

You Polish folk sure have strange ways of being intimate

[jhalek90]

... no thank you. JSR's feet do not interest me, and im sure he is not interested in mine.

ahem.

Thank you JSR, I failed to notice that you were taking about muzzle ENERGY and not just velocity.

It all makes sense to me now. except the polish obsession with feet... that will never make sense.

[Brian the brain]

You Polish folk sure have strange ways of being intimate

Ah..Europeans..



.22 barrel needs high pressure..so if you could get yourself a fridge compressor...you could enjoy it to the fullest.

Who brought those things to us BTW?
Wasn't that some crazy Polish guy??

Aaaaah!

[jackssmirkingrevenge]

Ah...Europeans...

You Dutch aren't exactly exempt when it comes to questionable intimacy

[jhalek90]

:3some: crazy dutch folk...