minimum and maximum fps

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miatamama

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Jan 2, 2018
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erie Pa. usa
Hi! Guys, I now have access to a chronograph. I can now adjust my power. I have read that a 177 pellet should be kept below a certain speed to keep it stable. What would that speed be for outdoor shooting? I also need to know what the speed for shooying 10 meters in my basement should be. Any info will be appreciated. JC Schardt

What speed should I not go over and what should I not go under?
 
For basement shooting, the 10m guys use wadcutter pellets and usually keep them in the range of 450 to 650 fps. The claim is wadcutters get real unstable above 750 fps.

For the outside shooting, the pellet is the determining factor for velocity vs. stability. Regardless you want to keep it below the speed of sound. Crossing over that threshold really upsets things, or so I am told.

Enjoy.
 
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Depends on what type of pellets you are using. The three commonest types in .177 would be a wadcutter, a medium weight domed pellet weighing between 7.9 grain (Crosman Premier) to 8.4 grain (JSB Exact and its variants) and heavy domed pellets typically weighing 10.3-10.5 grain (JSB exact heavy, Crosman Premier Heavy etc.).

Domed Pellets: The rule of thumb is that the drag force on dome shaped pellets dramatically increase at about .8 of the speed of sound, i.e about 900 fps(roughly). So a safe upper limit should be 850 fps. In my personal experience there isn't a lower limit except those imposed by rules of competition or to save on power in a pcp. However if you are shooting past 20 yards it's good to have at least 7-8 fpe energy to avoid too much wind drift. This can be a good lower limit and that would translate to about 600-650 fps for domed pellets. 

A very good power level for .177 for less than 45 yards is about 12 fpe with 7.9-8.4 grain pellets where you should maintain a speed of 825 fps for 7.9 grain and about 800 fps for 8.4 grain.

Wadcutter: If you are shooting a wadcutter pellet it's best to stay indoors and save on power by shooting at 5.5-6 fpe(energy) as in 10m competition. So about 550-600 fps with typical wadcutters. It's best not to shoot wadcutters outdoors. 


 
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For normal pcp with CZ and LW barrel the important thing is the blast or turbulence behind the pellet. As you know pellets are self stabilized and they don’t need as much as bullet spin rate so they’re GS (gyroscopic stability) could be under 1.

But most of the air rifles have turbulence when pellet leaves the barrel. So normaly in Miller equation we want to make it higher than 1. In the other hand if you exactly know what are you doing you can keep pellet speed around 400fps which mean pellet stability is under 1 but because of low turbulence they will fly dead straight.

In ST barrel things are little bit different so if you use fx airgunes keep pellet speed around 270 to 280 m/s. I heard twist rate in fx is about 1:44 to 1:75.

I will send miller equation when I get home. For most of the guns keep them between 1.2 to 1.8.
 
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Ok

S=(30*M)/((T^2)*(D^3)*L*(1+(L^2)))

F=(V/2800)^(1/3)

Sg= S*F

S: gyroscopic stability

M: weight in grain

T: twist rate in inch/D

D: diameter in inch

L: length of pellet/D

V: Velocity (fps)

For JSB pellet in 0.22 length is 0.295 inch

Example= A 0.22 Cricket shoots 18.13 grain JSB with the speed of 880 with 1:16 twist rate. Calculate Sg

S=(30*18.13)/((16/0.22)^2*0.22^3*(0.295/0.22)*(1+(0.295/0.22)^2))= 2.573

F=(880/2800)^(1/3)=0.680

Sg= 2.573*0.68=1.75

As you know pellet speed for cricket is up to 880 because after that pellet become hight stabilized. but lowest speed for cricket is 200fps with Sg= 1.07.

For HW100 with 17.8:1 twist rate and JSB 18.13

920fps Sg=1.44 and 350fps Sg= 1.03

For Fx with 1:63.9 and JSB 15.89 and 918fps

Sg= 0.098

If you use longer pellet like Metalmag with 0.4 inch length your Sg nearly become 1 with 16:1 twist rate and because of that cricket shoot them well unlike other guns like fx
 
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The above numbers are right. 450-600ish for indoor 10m max - and thinking wad cutters or you could naturally just shoot say JSB at full power & waste air-



Will depend on your rifle naturally. Possibly more so at high power than low due to increased harmonics/et al.

If your still using a Gauntlet I would suggest after deciding your desired speed use 2 different bottles. You may be able to go down to the 450psi range and hit 450+fps, and, shoot all day long on a fill then no tinkering just a 60 second swap back to full power. I've got an 1,100 pro-top on mine and plan on setting the factory bottle/reg down to something low.

Are shooting a .177?



John

also wadcutters at maybe 600max are the very best of all bird feeder defense rounds
 
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Thanks for all the feedback. It looks like if I keep the low at 550 to 600 and the high to 850 I should be ok. Yes I am shooting a 177 gauntlet. Before the mod I cleaned 4 clay birds in a row at 85 yards just by sighting 3 dots high on my scope. I is still right on at 10 meters. After I chrony it I will try again and see if it is still on at 85 yards shootimg at 850. Am I on the right track with this. Oh! I shoot the Crossman destroyer as my wad cutter and Crossman pointed or Crossman hollow point as a domed. This is what is available locally

miatamama
 
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