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 Posted: Thu Apr 15, 2010 3:21 pm |
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| SEE IT LIKE A NATIVE |
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| rsterne wrote: |
There is a very long, involved thread on this forum about using heavy pellets in springers.... The argument is that every springer above "pop-gun" power (for sake of argument like target rifles which are all under ~550 fps) gets at least SOME of it's power from combustion of a thin film of lubricant spread along the walls of the tube by the previous stroke of the piston.... Note, not "detonation" or "dieseling" which is destructive.... but a "controlled burn"....
When you put in a heavier pellet, the pressures in the chamber rise to a higher level before the pellet starts to move (more momentum).... and eventually, with a heavy enough pellet, the pressure will rise to the point of detonation or dieseling.... This "explosion" IS detrimental to the gun, causing piston bounce, spring re-compression (to the point of kinking it) and seal failure.... There was a recent thread showing damage to an RWS-350 which may have been caused by this phenomenon.... The damage to your rifle begs the question if it suffered a similar fate....
I'm still not sure I buy all the arguments on this subject.... but there seems to be enough anecdotal evidence to support it.... The conclusion of that thread was that "medium powered" springers (in the D-34 power range) shouldn't use pellets above about 9.5 gr. in .177 or 18 gr. in .22 cal.... "Magnum" springers should be designed to handle the heavier pellets, but even there, the upper limit would appear to be about 11.5 gr. in .177 and 21 gr. in .22.... Pellets heavier than that are designed for use in high-powered PCPs....
Bob |
Now we are getting somewhere ! I wonder how much pressure is developed in my springer ? I would guess about 250 -300 psi ? at most ! I also wanted to say that my gun was showing signs of trouble latching before a tried the heavy pellets ! I believe the damage to my gun resulted from the uncontrolled firing whenwhen the barrel was returned to battery position !After it fired a couple times without pulling the trigger I cocked it without loading a pellet to troubleshoot and the gun fired unloaded ! It looks like the sear is worn slightly but I dont know what it looked like new ! Also this gun only has about 200 rounds through it total !Maybe 20 were 16 grainers ! By the way the 16 grain pellets were very accurate 3 shots inside a dime at 50 ft . Kevin |
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| Posted: Thu Apr 15, 2010 5:20 pm |
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| rsterne |
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You might be surprised at how high the pressures go in a Springer....
Bob |
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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count! |
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| Posted: Thu Apr 15, 2010 6:23 pm |
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| fritz |
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That might just explain how thick the metal of the tube is?
I think I read somewhere the chamber pressures can exceed 50,000psi. IIRC a .223 Rem should top out at 45,000psi. |
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"I never set out to be wierd, it was always everyone else who called me it" -Frank Zappa
Speed is impressive, accuracy is deadly.
It's not that I'm not a people person, it's just that I'm not a stupid people person. |
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| Posted: Thu Apr 15, 2010 6:48 pm |
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| rsterne |
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| Quote: |
| I read somewhere the chamber pressures can exceed 50,000psi |
I would seriously doubt that figure.... A piece of 1" steel tubing with a 1/8" wall (ie only 3/4" ID) is only safe to about 4000 psi with a burst strength of 16000.... A 1.25" OD with a 1/16" wall (1.125" ID) has a safe working pressure of 1500 psi and burst at 6000.... The second example is pretty typical of a springer chamber tube....
It might be possible for the pressure in the transfer port to go above what is safe for the tubing.... provided that the pressure is isolated from the tube walls by the breech end (where the transfer port is) and the piston and seal.... I would be very doubtful if normal chamber pressures in a springer ever exceeded 5000 psi.... but that is a total guess....
If you look at it another way.... It takes about 1 cu.in. of air (at 1 Bar) for each FPE of energy delivered to a pellet in a PCP.... If we take 25 FPE as the upwards limit for a springer.... that means a chamber of 25 cu.in.... that is maybe twice as big as they actually are.... so it might be reasonable to assume that the peak pressure might be double that of a PCP.... A gun like a Disco produces that much power with only 2000 psi.... double that and you get 4000.... I offer that in support of the above guess....
Bob |
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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count! |
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| | | | | | | | | I wish I was better at Physics | | | | | |
| Posted: Fri Apr 16, 2010 1:54 pm |
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| SEE IT LIKE A NATIVE |
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| I am measuring the stroke on my gun and it appears to have a 4inch stroke with about a 1 inch bore thats about 3.14 cubic inches if the final volume is 1/8 inch that is about 32 to 1 compression ratio ! I think that works out to about 470 psi this is assuming the cylinder is closed which it isnt because it is open to the port of the gun barrel ! Which is obstructed by the pellet ! Kevin |
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| Posted: Fri Apr 16, 2010 3:26 pm |
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| rsterne |
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As I said before.... the THEORY is that a large percentage of the performance of a Springer is due to combustion.... I've heard as high as 65-70%.... The pressures in a cylinder of an engine are a LOT higher than the compression ratio times 14.5 psi.... 9:1 compression would only yield 130 psi....
The end space in your springer is likely LESS than 1/8".... It may approach zero with light pellets.... Again, in theory, the pellet doesn't move until the piston has moved to the end and is actually rebounding.... depending on pellet weight and a hunderd other factors....
Bob |
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_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count! |
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| | | | | | | | | you know I am gonna end up with this thing in peices !! tryi | | | | | |
| Posted: Fri Apr 16, 2010 9:06 pm |
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| rsterne wrote: |
As I said before.... the THEORY is that a large percentage of the performance of a Springer is due to combustion.... I've heard as high as 65-70%.... The pressures in a cylinder of an engine are a LOT higher than the compression ratio times 14.5 psi.... 9:1 compression would only yield 130 psi....
The end space in your springer is likely LESS than 1/8".... It may approach zero with light pellets.... Again, in theory, the pellet doesn't move until the piston has moved to the end and is actually rebounding.... depending on pellet weight and a hunderd other factors....
Bob |
You are right about the combustion pressure being very high !If we added 1 or 2 drops of fuel between shots I could believe it , but without adding fuel the combustion can only happen for the first few shots after the gun was lubricated ! With regards to the pressure developed if the volume is halved the pressure is doubled ,so if we take my 1/8th inch space and devide it by 2 we get about 900psi at 062 inches and 1800 at .031 inches , and 3600psi at .0155 inches .7200psi at .0075 inches ! now we are talking serious pressure !! This pressure applied to the area of a .177 inch pellet .works out to be .44136 pounds of force working on our 16/7000 pound mass pellet . Ok from here I am over my head ! I havent done any physics in 20 years or so and dont know how to calculate velocity from this ?? Help ??!! Kevin |
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| Posted: Fri Apr 16, 2010 9:16 pm |
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| rsterne |
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The THEORY is that the piston leaves behind a very thin film of lubrication each time you fire the gun.... That film combusts the next time you fire and is replaced by the movement of the piston seal.... Testing a gun in a nitrogen atmosphere significantly reduced the velocity....
Hey, it's not MY theory.... but it certainly has lots of believers.... 
NOTE:.... we're not talking dieseling (detonation) here.... just combustion....
Bob |
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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count! |
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| Posted: Fri Apr 16, 2010 9:24 pm |
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| sniper |
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well here's a parallel... a car engine "combusts" (controlled explosion)
it should never diesel (detonate).......  |
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I believe in gun control,
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| | | | | | | | | you know I am gonna end up with this thing in peices !! tryi | | | | | |
| Posted: Fri Apr 16, 2010 9:35 pm |
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| SEE IT LIKE A NATIVE |
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| rsterne wrote: |
As I said before.... the THEORY is that a large percentage of the performance of a Springer is due to combustion.... I've heard as high as 65-70%.... The pressures in a cylinder of an engine are a LOT higher than the compression ratio times 14.5 psi.... 9:1 compression would only yield 130 psi....
The end space in your springer is likely LESS than 1/8".... It may approach zero with light pellets.... Again, in theory, the pellet doesn't move until the piston has moved to the end and is actually rebounding.... depending on pellet weight and a hunderd other factors....
Bob |
You are right about the combustion pressure being very high !If we added 1 or 2 drops of fuel between shots I could believe it , but without adding fuel the combustion can only happen for the first few shots after the gun was lubricated ! With regards to the pressure developed if the volume is halved the pressure is doubled ,so if we take my 1/8th inch space and devide it by 2 we get about 900psi at 062 inches and 1800 at .031 inches , and 3600psi at .0155 inches .7200psi at .0075 inches ! now we are talking serious pressure !! This pressure applied to the area of a .177 inch pellet .works out to be .44136 pounds of force working on our 16/7000 pound mass pellet . Ok from here I am over my head ! I havent done any physics in 20 years or so and dont know how to calculate velocity from this ?? Help ??!! Kevin |
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| Posted: Sun Apr 18, 2010 8:48 pm |
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| Quack |
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| Well with all that being said, I just popped a coon at 5 yards in the head about 3 hours ago with the Diana Model 54 (.22) and it went SPLAT! Stone dead! So how does that work in the theory? Oh, crossman premier pellets. |
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Quack Kills |
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| Posted: Mon Apr 19, 2010 10:05 am |
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| SEE IT LIKE A NATIVE |
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| Way to go quack !! So how fast was the pellet going and how much did it weigh ?? Kevin |
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| Posted: Tue Apr 20, 2010 8:54 pm |
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| Quack |
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| Apparently they are 14.3 gr and it the gun is rated at 850 fps. Yeah, it was my first coon with an air rifle, just destroyed it! Anyways sorry for jumpin in on the technical/theorical posts I was just a little excited and pleased with myself! I do perfer my Model 34 .177 for birds though, just need a barrel... |
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Quack Kills |
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| | | | | | | | | good shooting ! | | | | | |
| Posted: Thu Apr 22, 2010 12:58 pm |
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| SEE IT LIKE A NATIVE |
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| It is gonna be a few monthes before I dedicate any new airgun funds ! by then I should have a better idea of what I reallly need to get the job done ! It seems obvious that I should be looking for a .22 cal gun at around 850 to 950 fps ! Until then I guess I will just have to lay off them ! The only air gun I have felt is my 1377 crossman ! I t is fun but I dont think it has enough power to even try on a racoon ! Kevin |
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| | | | | | | | | Re: good shooting ! | | | | | |
| Posted: Thu Apr 22, 2010 1:19 pm |
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| Mark5043 |
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| SEE IT LIKE A NATIVE wrote: |
| The only air gun I have felt is my 1377 crossman ! I t is fun but I dont think it has enough power to even try on a racoon ! Kevin |
Absolutely..I wouldn't even consider the 1377,for that task.The price of a-lot of PCP set ups have become quite reasonable......... 
My Discovery,is my go to PCP for critters...light,compact,and just about the perfect little field gun IMO.Put in a little time on stock refinishing etc,and they can be handsome as well....also price can't be beat for what you get.With help from guys like rsterne,and yourdaddyjoe etc,they can be made beastly....  |
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