Working on a .30/.25 cal MSP/ACP, Info useful??

[DavidS]

I have done a bit of testing and now I am designing a .30 and .25 cal MSP/ACP from scratch.  The MSP verient will have a 7.25cc valve air chamber, and the ACP versions will have a 14.5cc valve air chamber.    The exaust valve will be a pull open (kind of like on the Daisy 901/880/22X/22sg), with an initeral hammer similar to that on the Crosman AirRifles.   The trigger group is to be inspired by that of the 13xx Crosmans though with the known deficiencies corrected.

The onboard pump will be similar to all of the known MSP air rifles with a check valve going to the air chamber similar to that used in the Crosman MSP's though made of steel and using an O-Ring to form seal with a mass forward to minimize the inlet port volume, the piston will be a guided Flat Top piston similar to those used in the Daisy MSP's.

The effective pump volume will be 8 inches long by 0.75 inches in diameter equals aprox 58cc.

For the barrel I will try all twist rates from 1:14 through 1:18 to determine the best balance of power and accuracy for this design.   The twist rate is to be determined.

The above should give enough information with out giving away the design completely.

I ask for any aid of information before I get to far into this project.   Any thoughts that may be of use in the design are very much wanted.   Also any ideas for operation simplicity that may be of use.

I AM MAKING THE ENTIRE AIR RIFLE FROM SCRATCH, ONLY O-RINGS WILL BE PREMADE.

Once I have made two or three and tested them in the field for a year, worked out all of the bugs, I do intend to make these for sale to other AirGunners.  Though do to liabilities I will have to make some arangement with an existing vendor, and require an agreement of no liabilaty in order to do so (money/money thanks to laweyers ).

[farmerjoe99]

sounds cool!What are your hoped-fore specs?
will be interested to see how it comes out
Have fun and take lots of pics
Joseph

[rsterne]

5cc Air Resovoir with a seperated shot air chamber of aprox 0.7cc

Way too small for a .177 cal, let alone a .357.... A .357 barrel 20" long would have a volume of 2.0 cu.in. (33 cc)....

8 inches long by 0.75 inches in diameter equals aprox 7.21cc.

A pump with a 0.75" bore and an 8" stroke is 3.53 cu.in. (58 cc).... You need to be more careful with your arithmetic....

I will try all twist rates from 1:14 through 1:18

Way to fast a twist rate in .357 cal, an 18" twist would handle a bullet over an inch long and over 250 gr., and a 14" even longer and heavier....

You need to start with a pellet weight and velocity in mind (and hence an FPE level) and then work from there....

Bob

[DavidS]

5cc Air Resovoir with a seperated shot air chamber of aprox 0.7cc

Way too small for a .177 cal, let alone a .357.... A .357 barrel 20" long would have a volume of 2.0 cu.in. (33 cc)....

I posted from the ratios that I had written down, and I made notable arithmatic errors last night.   I do thank you though.

8 inches long by 0.75 inches in diameter equals aprox 7.21cc.

A pump with a 0.75" bore and an 8" stroke is 3.53 cu.in. (58 cc).... You need to be more careful with your arithmetic....

Ok.   I do make some dumb mistakes some \times,    Thank you, I will look back at notes as I was half asleep last night when I made the post.

I will try all twist rates from 1:14 through 1:18

Way to fast a twist rate in .357 cal, an 18" twist would handle a bullet over an inch long and over 250 gr., and a 14" even longer and heavier....

You need to start with a pellet weight and velocity in mind (and hence an FPE level) and then work from there....

Bob

Ok I was thinking of moving around the 1:16 rate used in most small cal AirRifles.   I do thank you I will look at more twist rates as I cut barrels.

[DavidS]

I have made corrections to the original post showing the correct volumes.

• aprox 58cc pump volume.
• Aprox 45cc main air chamber volume
• Aprox 9cc shot air chamber volume

Also I may try twist rates all the way up to 1:20 to see where the balance is for the barrel.

@rsterne:
Thank you for your corrections.   I have everything volume wise written down as a ration of the pump volume and I was half asleep and made some notable mistakes in calculation last night.

If you look at my current avatar: it is a picture of my back yard.  What you do not see are the wheel chair tracks from me running around collecting wood for fire, and collecting stones to reinforce dug in areas of the mountain side, and collecting my prey for dinner a couple times a week.   I live 100% off the grid as far as utilities and water are conserned and about 90% off grid as far as food so there is a lot of work on some days (especialy as we have not lived here long so still setting things up).  No excuses just saying I do get tired at the end of the day.

Thank you again.

[DavidS]

sounds cool!What are your hoped-fore specs?
will be interested to see how it comes out
Have fun and take lots of pics
Joseph

Well I hope to get around 750FPS out of it with a 120 grain bullet for around 149.9FPE.   As to what I actualy get we will see.

Though the desigh is fairly simple as it is inteded to be easy to manufacture and maintain.

[fortyshooter]

Maybe I'm missing a lot....but how will you get 750 FPS from a 120 gr. bullet from 1200 psi. ?
That's just about the FPS of a 130 gr. .38 Special Winchester target ammo out of a 4-5 inch barrel of course.
If it works I'd be interested in a double barrel version! 

[rsterne]

I would suggest that before you start work on this project, you read over this thread....  http://www.gatewaytoairguns.org/GTA/index.php?topic=57828.0

In there are some reasonable limits for PCPs which are possible, although difficult to obtain.... Without going into all the math, a .357 cal running on 1200 psi with a 24" barrel could, in theory, reach about 120 FPE.... To do so would require bore-size porting and efficiency better than what has been achieved by any of the PCP gurus so far, and it would require that 1200 psi to be pushing on the pellet for at least the first 12" of bullet travel, in other words a very large reservoir, not a small dump valve where the pressure drops during the shot.... Your 9 cc shot chamber would only have 1200 psi pushing the pellet at the instant you pull the trigger, by the time the pellet has travelled 12" down the barrel the pressure will have dropped to 375 psi.... I can say with confidence that even 120 FPE is completely out of reach using 9 cc at 1200 psi....

Regarding twist, you need to realize that the twist rate in inches goes up with caliber, so you need a much slower twist in .357 cal.... My 127 gr. boattail is stabilized perfectly in a 26" twist, and a flat based bullet, shorter bullet, or roundball can use an even slower twist.... The .35 cal JSB Exact pellets (79 gr.) are only 0.423" long and would be quite happy in a 40" twist barrel....

While I commend your enthusiasm, trying to produce such an unusual airgun to be marketed requires a much better understanding of the basics than what I see in your posts above....

Bob

[farmerjoe99]

not to tear-down the plans for a .357.
but what kind of power could he get in .25?
Then you could use either factory pellets or
Mikes slugs/bullets.if you can get a 37gr pellet moving
700fps+ would be in the 45fpe range which would
interest me ...just a thought 

What kind of format are you thinking
long rifle?if long barrel helps you could make it
a bullpup format.

[DavidS]

Maybe I'm missing a lot....but how will you get 750 FPS from a 120 gr. bullet from 1200 psi. ?
That's just about the FPS of a 130 gr. .38 Special Winchester target ammo out of a 4-5 inch barrel of course.
If it works I'd be interested in a double barrel version! 

To be honest I will be happy with anything better than 400FPS = aprox 42FPE.     I the 750FPS is more a dream and would probably require over pumping to around 2400PSI maybe more.

Though in testing I will make sure that the design can withstand at least 3000PSI as this gives a good safety margine (using hydrostatic pressure testing) and is able to shoot with 2400PSI though I will set the saftey release valve for 1400PSI and recomend not to exceed 1250PSI fill pressure on the final version.

I could have been a bit more clear above that it would be nice to see 700FPS out of extreme operating limits not out of normal operating conditions.

[DavidS]

I would suggest that before you start work on this project, you read over this thread....  http://www.gatewaytoairguns.org/GTA/index.php?topic=57828.0

In there are some reasonable limits for PCPs which are possible, although difficult to obtain.... Without going into all the math, a .357 cal running on 1200 psi with a 24" barrel could, in theory, reach about 120 FPE.... To do so would require bore-size porting and efficiency better than what has been achieved by any of the PCP gurus so far, and it would require that 1200 psi to be pushing on the pellet for at least the first 12" of bullet travel, in other words a very large reservoir, not a small dump valve where the pressure drops during the shot.... Your 9 cc shot chamber would only have 1200 psi pushing the pellet at the instant you pull the trigger, by the time the pellet has travelled 12" down the barrel the pressure will have dropped to 375 psi.... I can say with confidence that even 120 FPE is completely out of reach using 9 cc at 1200 psi....

Ok fair.   I admit that I did not run out the math all of the way and took some short cuts.    I like to see what it will do real world.     Also I was thinking that the 700FPS may be possible with an overfill to 2400PSI which I failed to mention above, for normal operation I will be happy with 400FPS, for that matter even 350FPS would be usable in most cases.

Regarding twist, you need to realize that the twist rate in inches goes up with caliber, so you need a much slower twist in .357 cal.... My 127 gr. boattail is stabilized perfectly in a 26" twist, and a flat based bullet, shorter bullet, or roundball can use an even slower twist.... The .35 cal JSB Exact pellets (79 gr.) are only 0.423" long and would be quite happy in a 40" twist barrel....

As far as twist rate goes all I have are some old tables for black powder guns.   As I do not see these being verry accurate for AirRifles and I do not have the information needed for the math I am going on what seems to make sence to me.    If you can provide the equations as well as how they were derived I would be happy ot updat everything to be more accurate for AirRifles.

While I commend your enthusiasm, trying to produce such an unusual airgun to be marketed requires a much better understanding of the basics than what I see in your posts above....

Bob

I admit that at this point I am taking some shortcuts on the math I still feel that it is quite doable.   Also I do not have any aplicable information on the equations and there dirivation for the calculation of twist rate for AirRifles so I am only able to guess.   Thus far I have only made .22 cal and .25 cal barrels for AirRifles and those only to experiment with twist rates.  The .22 and .25 cal barrels are also what made it clear that the info for black powder twist rates is of no use for AirRifles.     Integration is simple with the aid of a simple BASIC interpreter or even a rewrite in C so do not worry about the equations scaring me, there is nothing dificult in math .

I do thank you for your aid.

Do you realy think that 400FPS at 1000PSI shot chamber pressure with a 9cc chamber and an 24 inch barrel is unrealistic?   If so I am interested in your information so I may look at it a bit more closely.   And the same question for a 9cc chamber at about 2200PSI for 700FPS with a 24 inch barrel?

I guess I should go ahead and run out the math.   Time to update my internal balistics program to deal with larger calibers.    Also the information on the twist rate calculations will help to make my internal balistics program more accurate.

Also as you are quite good with this kind of thing I would ask about the application to .30 cal and .25 cal with the exact same power plant specs.   I ask as I would like to also use this power plant for .25 and .30 cal once it has proven itself in .357.     For my personal use I like the idea of .25 and .30 over that of .357 any way.

Thank you again.

[DavidS]

not to tear-down the plans for a .357.
but what kind of power could he get in .25?
Then you could use either factory pellets or
Mikes slugs/bullets.if you can get a 37gr pellet moving
700fps+ would be in the 45fpe range which would
interest me ...just a thought 

What kind of format are you thinking
long rifle?if long barrel helps you could make it
a bullpup format.

I am thinking about implementing it as a carbine with a 24 inch barrel.

For my use I am going to also be implementing .30 and .25 cal versions of it.   I was thinking that in the big cal AirRifles there is nothing practacle out there so it would be nice to fill the need.    I have not done any of the math for .30 or .25 cal as of yet so I can not comment on the potential.

[Nomadic Pirate]

Buy yourself a Crossbow , LOL

I'm afraid but you're all over the place, those pumpers barely make enough power on small bores, you're .357 idea I would confidently say is a waste of time

[rsterne]

Twist calculator:  http://www.geoffrey-kolbe.com/barrel_twist.htm

400 fps with 120 gr. = 42 FPE, that's a long way from 150.... Yes, possible with 1000 psi in a 24" barrel with a 9 cc dump valve.... Using a 79 gr. pellet about 480 fps or so @ 1000 psi, or using 1200 psi about 530 fps....
Same setup in .30 cal with 45 gr. pellet about 560 fps @ 1000 psi, or 610 fps @ 1200.... In .25 cal with a 25 gr. pellet, about 630 fps @ 1000 psi, or 690 fps @ 1200....

I would recommend that with such limited power available you forget the idea of using bullets and stick with the JSB Exact series of pellets, those are the weights I used in the above estimates.... Hope that gives you some idea what to reasonably expect....

Bob

[rsterne]

Same data at 2200 psi, 9 cc chamber, 24" barrel....

.357 cal 120 gr. 590 fps 92 FPE
.357 cal 79 gr. 700 fps 87 FPE
.300 cal 45 gr. 800 fps 65 FPE
.250 cal 25 gr. 900 fps 45 FPE

All the above are estimates using Lloyd's Internal Ballistics Spreadsheet....

Bob

[DavidS]

@rsterne:
Thank you cor that prety much matches my calculations.   That makes me a bit more confident in my internal balistics program .   That also helps me in that I know that the mods for larger cal are correct.   Also note that there will never be a drop all of the way to atmospheric do to the adjoining air chamber so while it should act close to a full dump it will be slightly more effecient.

As to the issue of barrel twist:
The program you pointed me to gives the same results as the black powder tables I have and noting a veriation in them versus .22 and .25 AirRifles is there a more correct calculation for AirRifles?   I would guess that the calculator may get me in the ball park, though I would rather get the correct calculations.

[rsterne]

Also note that there will never be a drop all of the way to atmospheric do to the adjoining air chamber so while it should act close to a full dump it will be slightly more effecient

.
No idea how that will occur, as you have to close the valve to prevent it, dump valves don't do that....

RE Twist, I have no idea why you feel that you need a faster twist for air rifles, if anything it can be even slower because of the drag induced stability of the diabolo (waisted) pellet shape.... I know of no formulas or twist calculators that allow for that, but as I said it's even slower.... Applying that program to air rifles seems to work quite well, IMO, to determine the slowest twist usable for a given length pellet, which is the critical dimension....

Bob

[DavidS]

EUREKA:
I finished running the math, and wish I had done so before posting the thread.    I will be going for a .30 cal MSP with a full dump valve of 7.25cc.    Yes I know that is a bit small for a dump valve with .30 cal, though I believe the results will be good.

I will also do some testing in .25 cal with the same power plant.

Also I will make an ACP version in a more traditional way with a single air chamber of 14.5cc.  This is more along the lines of how Crosman MSP's are converted to ACP, and will likely only give 3 to 5 good shots before needing to be pumped back up.

Also note that there will never be a drop all of the way to atmospheric do to the adjoining air chamber so while it should act close to a full dump it will be slightly more effecient

.
No idea how that will occur, as you have to close the valve to prevent it, dump valves don't do that....

The idea was not a traditional full dump valve, though rather a valve that is opened by the dwell of the hammer and closed by the valve spring after the hamer recedes.

Now kind of a mute point with the change in concept resulting from calculations.   See above in this post.

RE Twist, I have no idea why you feel that you need a faster twist for air rifles, if anything it can be even slower because of the drag induced stability of the diabolo (waisted) pellet shape.... I know of no formulas or twist calculators that allow for that, but as I said it's even slower.... Applying that program to air rifles seems to work quite well, IMO, to determine the slowest twist usable for a given length pellet, which is the critical dimension....

Bob

I am going to follow my Black powder rifling tables and test different rates starting at what is recommended for black powder of the same cal and power.  I think that will start me close enough.

[DavidS]

Buy yourself a Crossbow , LOL

I'm afraid but you're all over the place, those pumpers barely make enough power on small bores, you're .357 idea I would confidently say is a waste of time

As method of operation is the same, I assume that you do not think that PCP's are any good for large cal either?     That is what you are saying as operationaly an ACP Pumper is a PCP, it is just a matter of the correct chamber volume, pressure, and pump volume (the last to minimize the number of strokes to refill).

Also my compound bow is always with me when hunting, or wandering the property for any reason (as a defence against agressive wild animals, if ever needed).   It is faster to noch an arrow and let it to its target than it is to load a pellet .

[Matt15]

How much would they cost?