Author Topic: Internal/external ballistics for Pellets/Bullets (Read 1849 times)

Nvreloader · « **on:** July 08, 2017, 03:12:25 PM »

Guys
This is a new post for several questions that were being discussed in "the next Big thing in PCP's.

The following info is what I have been playing with, for the .172"/.224" Bullets and .177"/.220" Pellets etc.

I don't know the barrel Bore cross sectional area for the 17/22 cal pellet rifles is, so my calculations are off,
as I know the 22 cal pellet and .177 pellet rifle bore area is smaller, than RF/CF bbl Bore X sectional bbl areas/spec's etc.

I used .222" Bore X sectional of the 22 LR RF bbl, of .037293 sq inches.

The .224" CF Bore X sectional barrel area is .03889 sq inches,
and the .172" CF Bore X sectional barrel area is .022859 sq inches.

I hope that Bob will show the correct spec's etc, as he is the AR GURU.

LOL
As I am still in the 1st grade.

I had a choice of which Shot Start (initiation) pressure to use, which is the force required to start the pull out and engraving of the bullet,
so I will post both of the start PSI of "O" PSI and 146 PSI, for both the Bullet and Pellet choices posted.

I used a 3000 psi as Max psi used for all calculations in both caliber examples.

Here is what I came up with for the following Bullets and pellets,
I kept the same standards thru out, ie,
24" bbl length, 3000 psi for pressure,
.220 cal bbl Bore X sectional area of .037293 sq inches, for .220" cal pellets,
.224" CF bbl Bore X sectional barrel area is .03889 sq inches, for .224" Bullets
.172 CF bbl Bore X sectional area of .022859 sq inches, both pellets and bullets.

.172 cal bullet, 20 gr bullet, with a BC of .185 and SD of .097 at of 1000+ fps,
.224 cal bullet, 35 gr bullet, with a BC of .109 and SD of .100 at 1000+ fps,

.220" cal, 29gr Eun Jin Pellet, 24" bbl @ 3000psi, "O" start psi, with a BC of .xxx and SD of .xxx
start ===@ 5" bbl travel==10" bbl travel=15" bbl travel===20" bbl travel===24"
870 fps = 845 fps ======804 fps ====745 fps =======622 fps======0 fps
3000 psi=1058 psi =====493 psi ==== 309 psi ======= 220 psi =====170 psi

Same as above with 146 psi start
856 fps ==831 fps ======791 fps ====713 fps========616 fps =======0 fps
3000 psi ==1006 psi =====477 psi ====299 psi ========215 psi ======164 psi

35 gr VMax .224 Bullet, 24" bbl, @ 3000psi, O start psi, with a BC of .109 and SD of .100
start ===@ 5" bbl travel==10" bbl travel=15" bbl travel===20" bbl travel===24"
870 fps = 845 fps ======804 fps ====745 fps =======622 fps======0 fps
3000 psi=1058 psi =====493 psi ==== 309 psi ======= 220 psi =====170 psi

Same as above with 146 psi start
799 fps ===773 fps ======739 fps ====687 fps========576 fps =======0 fps
3000 psi ==1006 psi =====984 psi ====464 psi ========281 psi ======159 psi

These are SWAG's,
as I am not sure I have the calculator set up right, for PSI values x distance etc.

I will post the 17 pellet/bullet info later, along with the friction reduction coating of bullets/pellets etc.

Thoughts, suggestions or Ideas?

Tia,
Don

rsterne · « **Reply #1 on:** July 08, 2017, 07:22:36 PM »

I'm not 100% sure what you are trying to calculate, but I presume it is the velocity as the pellet/bullet travels along the barrel, and then the muzzle velocity?....

There is, unfortunately, no standardization between various airgun barrels.... Most companies don't even publish the dimensions.... Lothar Walther do, so I will give you those to use as a basis, they will be within a few thou of others....

.177 cal LW.... land = 0.176", groove = 0.182"
.22 cal LW.... land = 0.215", groove = 0.221"
.25 cal LW.... land = 0.248", groove - 0.254"

Generally the groove diameter is used to calculate the bore area, so that would be 0.026 sq.in. for .177 cal.... 0.038 sq.in. for .22 cal... and 0.051 sq.in. for .25 cal.... I see no point in using more than two significant figures when there is a variance between manufacturers....

I'm not sure why you chose 146 psi for a starting pressure, but using that value, the force on the pellet would be 3.8 lbs. for .177 cal, 5.5 lbs. for .22 cal and 7.4 lbs. for .25 cal.... I personally think those values are high, you could test them by chambering a pellet and placing a rod of known weight against it and then adding weight until the pellet started to slide....

It looks like you are trying to present the velocity and pressure as the pellet moves along the bore.... However, the numbers go in opposite directions?.... In your first example (29 gr. @ "0" psi), I presume you are predicting a muzzle velocity of 870 fps, but a muzzle pressure of only 170 psi?.... I can pretty much tell you that those two numbers (assuming I am reading your data correctly) are mutually exclusive.... ie if you are getting 870 fps, the muzzle pressure will be a lot higher, and if you have a residual muzzle pressure of only 170 psi, you won't get a 29 gr. pellet to 870 fps, starting with 3000 psi in a 24" barrel....

I would assume you are using a program designed for PBs to do airgun calculations.... and if that is the case, I think you will find they are too different to produce reliable results.... For a start, you need to factor in the reservoir (plenum) volume, and the valve dwell, to calculate the pressure profile as the pellet moves down the bore.... Here is generic example....

This chart shows what happens to the pressure when you have drastically different reservoir (plenum) volumes.... In all 3 cases, the valve dwell was the same....

Bob

Nvreloader · « **Reply #2 on:** July 08, 2017, 09:16:35 PM »

Quote from: rsterne on July 08, 2017, 07:22:36 PM

I'm not 100% sure what you are trying to calculate, but I presume it is the velocity as the pellet/bullet travels along the barrel, and then the muzzle velocity?....

Bob
I was playing around with the PB ballistic program to see if I could get it to work with the AR ballistic etc.

.220" cal, 29gr Eun Jin Pellet, 24" bbl @ 3000psi, "O" start psi, with a BC of .xxx and SD of .xxx
start ===@ 5" bbl travel==10" bbl travel=15" bbl travel===20" bbl travel===24"
870 fps = 622 fps ======745 fps ====804 fps =======845 fps======870 fps
3000 psi=1058 psi =====493 psi ==== 309 psi ======= 220 psi =====170 psi

Same as above with 146 psi start
856 fps ==831 fps ======791 fps ====713 fps========616 fps =======0 fps
3000 psi ==1006 psi =====477 psi ====299 psi ========215 psi ======164 psi.

This programs shows the above info,
@ 3000 psi, the max fps for the 29gr pellet would be 870fps, after the first 5" of pellet travel,
the psi would be 1058psi and 845fps, etc, etc etc, for each 5" of bbl travel, until the pellet left the muzzle,
@ 856fps with 170psi remaining at the muzzle.

There is, unfortunately, no standardization between various airgun barrels.... Most companies don't even publish the dimensions.... Lothar Walther do, so I will give you those to use as a basis, they will be within a few thou of others....

.177 cal LW.... land = 0.176", groove = 0.182"
.22 cal LW.... land = 0.215", groove = 0.221"
.25 cal LW.... land = 0.248", groove - 0.254"

Generally the groove diameter is used to calculate the bore area, so that would be 0.026 sq.in. for .177 cal.... 0.038 sq.in. for .22 cal... and 0.051 sq.in. for .25 cal.... I see no point in using more than two significant figures when there is a variance between manufacturers....

I'm not sure why you chose 146 psi for a starting pressure, but using that value, the force on the pellet would be 3.8 lbs. for .177 cal, 5.5 lbs. for .22 cal and 7.4 lbs. for .25 cal.... I personally think those values are high, you could test them by chambering a pellet and placing a rod of known weight against it and then adding weight until the pellet started to slide....

I only had a choice of these 2 start psi values, "O" or 146 psi, so I did both,
I do believe that 146 psi it too high also, but not sure which would be the better start psi etc.

It looks like you are trying to present the velocity and pressure as the pellet moves along the bore.... However, the numbers go in opposite directions?.... In your first example (29 gr. @ "0" psi), I presume you are predicting a muzzle velocity of 870 fps, but a muzzle pressure of only 170 psi?.... I can pretty much tell you that those two numbers (assuming I am reading your data correctly) are mutually exclusive.... ie if you are getting 870 fps, the muzzle pressure will be a lot higher, and if you have a residual muzzle pressure of only 170 psi, you won't get a 29 gr. pellet to 870 fps, starting with 3000 psi in a 24" barrel....

I would assume you are using a program designed for PBs to do airgun calculations.... and if that is the case, I think you will find they are too different to produce reliable results.... For a start, you need to factor in the reservoir (plenum) volume, and the valve dwell, to calculate the pressure profile as the pellet moves down the bore.... Here is generic example....

This chart shows what happens to the pressure when you have drastically different reservoir (plenum) volumes.... In all 3 cases, the valve dwell was the same....

Bob

Thanks Bob,
I see that this ballistic program will not work with/for AR, etc.

I'll go stand in the corner while learning more,

Tia,
Don

rsterne · « **Reply #3 on:** July 09, 2017, 08:30:50 AM »

Not putting your efforts down, Don.... and I'm not familiar with the program you are using.... However, I suspect it starts with a small, finite volume for the "chamber" and works from there....

Bob

Nvreloader · « **Reply #4 on:** July 09, 2017, 10:17:21 AM »

Thanks Bob
No problems,
When I state, "I'll go stand in the corner again",
means "Hey you dummy, you need to learn more", ie, Jokes on me.

Yes, you are correct,
I can set the volume of the chamber to whatever capacity, I want to use.
There is over 13+ different parameters I can set/change etc.

I was hoping that I could use this program, I am not going to read 200+ pgs of formulas,
figure them out and then set it up, with what little I would probably use it with my AR's.

Tia,
Don

rsterne · « **Reply #5 on:** July 09, 2017, 11:53:43 AM »

If you can set the volume of the chamber to whatever you want.... Try using 1 cc per FPE, just as you might for the plenum size.... ie for a 30 FPE gun, use 30 cc (1.83 CI) for the chamber volume (there are 16.4 cc per CI).... Leave the starting pressure at 146 psi, that is probably closer than using zero.... The residual pressure at the muzzle should be much higher, because your chamber is now twice the barrel volume (.22 cal. 24" of 15 cc)....

Since there is no way to "close" the valve, your answer should be what would be predicted using a "dump shot", ie keeping the valve open until the pellet exits the muzzle.... but it would be interesting to compare your results to Lloyd's spreadsheet, which produced that graph....

Bob

ncrary · « **Reply #6 on:** July 10, 2017, 08:41:29 AM »

I am so glad there are guys like you two. I was trying to make sense of what you are talking about and it is Greek to me. While I do have an advanced degree, I assure you it is NOT in mathematics.

However, it is interesting to try and follow these discussions. Who knows, I might even learn some math.

Nvreloader · « **Reply #7 on:** July 14, 2017, 10:40:17 AM »

Thanks Bob

Sorry for the late replys,
Internet went down again and had several VA Dr appt's etc.

I set up the spec's, for 3000 psi, 27.80 grs max, PSI runs,
I am not sure I did the formulas correctly etc.

3000 psi start
@ 5" = 2297 psi, @ 10'' = 1245 psi, @ 15" = 818 psi, @ 20" = 599 psi, @ 24" = 442 psi,
FPS
@5" = 641 fps, @ 10" = 852 fps, @ 15" = 957 fps, @ 20" = 1025 fps, @ 24" = 1072 fps.

IMHO, I don't think this ballistics calculator will work very well, for AR's,
built for and work very well on PB's.

Tia,
Don

rsterne · « **Reply #8 on:** July 14, 2017, 11:51:45 AM »

Don, the velocity profile looks reasonable, but the pressure profile doesn't make any sense to me.... What chamber volume did you use?....

Bob

Nvreloader · « **Reply #9 on:** July 14, 2017, 02:00:18 PM »

Bob

If i figured out everything OK, $:-\$
I used 27.80 max grains H20 for chamber volume @ 3000 psi max?

Tia,
Don

rsterne · « **Reply #10 on:** July 14, 2017, 03:05:58 PM »

hmmmmmmmm.... There are 15.43 grains per gram, water weighs 1 gram per cc, so 27.8 grains is only 1.8 cc of chamber volume.... I would suggest you use 30 cc to simulate a normal plenum on a 30 FPE PCP..... That would be 463 grains of water chamber volume.... Bet it doesn't go that high?....

Bob

Nvreloader · « **Reply #11 on:** July 14, 2017, 08:12:23 PM »

Bob
I'll take an Ice cold Diet Coke, Thank you,

I can go up 5646+ grs case capacity.

I sure messed up figuring that capacity out, Huh,

been over 50+ yrs since I HAD to do that type of figuring,
I am kinda rusty etc. LOL

Here is a 22 cal 35 g Horn
3000 psi=24" bbl

3000 psi start
@ 5" = 2949 psi, @ 10'' = 2776 psi, @ 15" = 2503 psi, @ 20" = 2283 psi, @ 24" = 2086 psi,
FPS
@5" = 559 fps, @ 10" = 907 fps, @ 15" = 1139 fps, @ 20" = 1312 fps, @ 24" = 1455 fps.

Tia,
Don

rsterne · « **Reply #12 on:** July 14, 2017, 08:32:53 PM »

Well, now we know that calculator isn't giving the right results for airguns....

Using Lloyd's calculator, 30cc plenum, 3000 psi and 24" barrel.... .22 cal with 35 gr. bullet.... even at 100% efficiency with a dump shot I get "only" 1215 fps muzzle velocity, and a residual pressure of 1974 psi.... so now you are on the other side.... BTW, typical PCPs run about 60-80% efficiency....

I have no idea how that program is doing the calculating.... but IMO it's pretty much not worth spending more time on it....

Bob

Nvreloader · « **Reply #13 on:** July 15, 2017, 05:33:44 AM »

Bob
Thank you for your time and trouble leading me down the Dark Side pathway.......

You are right,
I had to play around with it just to see, learned some info, etc.

On this Lloyds calculator, where can I buy this program?
I have hear you mention it several times etc.
I take it, he is a AR Guru?

Tia,
Don

rsterne · « **Reply #14 on:** July 15, 2017, 08:45:12 AM »

Lloyd Sikes is the owner of AirGunLab, and the designer of the Crosman Rogue ePCP.... His spreadsheet is Proprietary, and I am fortunate enough to have a copy.... It is not generally available to the public....

Bob