Dumb Ass Question

[BurneyCA Dennis]

What is FPE? What do I need to measure it? How do I increase it? How much do I need?
I am shooting an HW97, .22 with a 14.3 pellet. I’m sighted in at 40 yards and have a group of about 1.5 inches. My one goal is to kill pests, mainly ground squirrels. It seems the gun is less accurate on a sled than when I use a bag. Or maybe I’m the one less accurate.
Another question. I may have to move the scope as it appears it’s to far from my eye. Will I need to resight it in if I do this?
Thx for the advice.

 

[boscoebrea]

foot -pounds of energy =mass speed formula is used figure it out =weight of pellet and velocity it is traveling =fps learn the terms, they are important enough and easy enough to learn So .22, 14.3 grams,you need to know the speed it is going ,energy is used to find out the impact on target,Anyhow that is how I use it kinda like torque fps=feet per second There are charts that will have this info..

 

[Richieg]

First, there are no dumb questions....Everyone has room to learn.
FPE, Foot Pounds of Energy. Think of it as kinetic energy...how much force the pellets has when it hits whatever at any given distance.
The formula for figuring it is:
Mass in grains x (bullet speed x bullet speed) in fps, divided by 450437. Remember as the pellet travels downrange the FPE will drop as the pellet is slowing down.So the FPE will start going down as soon as the pellet leaves the barrel.
I can't comment how how much fps. it will take to kill a squirrel. All my air rifles are HP and not having enough isn't a concern of mine.
If you move your scope for closer eye relief, you will probably have to tweak it a few clicks to get it back to zero.

 

[igolfat8]

Foot Pounds of Energy.
oops, others beat me to it. Welcome to the forum.

 

[Bedrock Bob]

You need a chronograph to measure speed. It will give you the data to calculate FPE.

I also have an HW97. It shoots about 675 FPS. It's plenty on a squirrel out to 50-60 yards. But hits aren't always kills. You often have to finish the job. You will find that is true with air rifles at almost any range, depending on where the shot hits.

The proper distance from the scope is called eye relief. Get it perfect. Get the crosshairs level and plumb. Then sight it back in. Check your zero on a target often. It will move a few clicks one way or the other from day to day. Not much. But enough to miss your target.

The HW97 is a fine gun. It is very accurate and well made. Mine does not like to be rested on bags. Especially at the butt. It shoots lousy off a gun rest. But it will shoot well under an inch at 50 yards off a tripod or held in your hands. You will figure it out after a thousand shots. Just keep practicing and hold it gently. Let it recoil and don't try to control it. You will find the hold that it likes and it will amaze you how accurate it is.

 

[WorriedMan]

Pyramyd Air website has a "Calculators" section, I keep a link to FPE one. Chronograph doesn't need to be expensive, search, "Chronograph," in AGN archives, upper right page corner for ideas. WM

 

[bigmike]

Like others have said you will need a chronograph to measure velocity ( feet per second) and then plug in you pellet weight.

Airgun Calculators -

 

[Duckfish]

Get a chrony
This forum has a section called resources
Too easy
Done

 

[DesertSilver]

You will have more than enough for to kill ground squirrels. Your 97 in about on par with the Diana 34 I had back when I was going for GS. It even head shot a GS at around 85 yards one time. Extremely, extremely lucky shot on my part. Most of my shots were between 25 and 50 yards. Shot placement is far more important. Practice, practice, practice!

 

[Sawney Bean]

There is another way that you can measure your velocity without a chronograph. Download a ballistics software program like Element Ballistics, enter all the data into it regarding the pellet you are using and your scope height and then simply plug in velocities until you find one that matches your observed trajectory. So what you'll do is zero your rifle at your chosen range and then shoot groups at various measured ranges while recording their distance from your aimpoint. That gives you a plot of your actual trajectory and all you have to do is see what velocity the software says is a match for it.

 

[jking]

Yup, a chronograph, instant FPS.
My bad I thought he asked about FPS and not FPE, so thanks for all of the other great replies.

 

[delooper]

It's the kinetic energy of your projectile, measured in foot-pounds.

If m is the mass (in grams, grains, whatever) and v is the speed measured by a chronograph (in meters per seconds or miles per hour, etc) then the kinetic energy is:

E = m*v^2 / 2

i.e. multiply the square of the speed (v) by the mass (m) and divide by 2.

If your mass is in grains and your speed is measured in meters per second, this E formula would be in the units of grains * meters^2 / second^2. You'd then need to convert that into foot-pounds. You can convert between units using a lot of sources. The number E you just need to multiply by whatever appropriate constant. For example, the Wikipedia page for foot-pound says it is 1.35 joules, which is almost our units in this example. A Joule is a kg m^2/s^2, so to get the food-pound answer, we'd take our E computation, multiply by 1.35 and then multiply by however many kg there are in a grain, which the Wikipedia page says is 64.7 milligrams, so then our answer would be:

E * 1.35 * 0.0000647.

Just to reiterate, the E formula m*v^2/2 is universal, but those constants we multiply E by (the 1.35 and the big decimal) will depend on which units you use to measure mass and speed.

Since people don't like keeping track of all these details, that's why you have the on-line calculators.

 

[Bedrock Bob]

There is another way that you can measure your velocity without a chronograph. Download a ballistics software program like Element Ballistics, enter all the data into it regarding the pellet you are using and your scope height and then simply plug in velocities until you find one that matches your observed trajectory. So what you'll do is zero your rifle at your chosen range and then shoot groups at various measured ranges while recording their distance from your aimpoint. That gives you a plot of your actual trajectory and all you have to do is see what velocity the software says is a match for it.

Working backwards from actual trajectory (in my opinion) is the way to do it.

Even if you plug in your chronograph data accurately a ballistics calculator is going to be a bit off. You have to test that data on paper anyway. It just gets you close and you tweak it from there.

I have a chrono to monitor the rifles performance. I don't use it to plot a theoretical trajectory. I shoot 5 shots at a target every ten yards and figure drop in real time. When using holdover in the scope that's all you need. If you were clicking your correction and shooting off the crosshair I see how the drop calculations would help you get an extra measure of precision.

As for FPE I couldn't care less. If I wanted to hit a target with a certain energy I would work that backwards too. I'd set my chrono at the target and move out until it showed the minimum speed to make the horsepower I needed. That would be my maximum effective range. It just seems a lot more practical than fiddling with a ballistic program for my purposes.

 

[$p00kygH0ST]

The best way to visualize fpe other than just what understanding what 40lbs feels like.

You have a 40lb hammer head, it has a 1' shaft. Now imagine. A frame with a horizontal bar above your head, the bar goes through the hammers shaft. So you basically have a 40lb pendulum. Raise the hammer head 90⁰ so it swings down and forward. The impact at the bottom where the hammer would rest if it hung.. is about 40 foot pounds of energy if allowed to swing under its own gravity, now put a .22" wide bead at the dead center of the impact face. Or at least that's how it was actually demonstrated to me by my physics teacher. But with a sheet of 1/8" plastic and 1 lbs iron sphere. Now

 

[Sawney Bean]

Foot pounds of energy=velocity in fps squared times weight in grains divided by 450240

So if you're shooting 8.64 grain H&N's at 900 fps your FPE is 15.54

((900×900)×8.64)÷450240=15.54

 

[Sawney Bean]

Working backwards from actual trajectory (in my opinion) is the way to do it.

Even if you plug in your chronograph data accurately a ballistics calculator is going to be a bit off. You have to test that data on paper anyway. It just gets you close and you tweak it from there.

I have a chrono to monitor the rifles performance. I don't use it to plot a theoretical trajectory. I shoot 5 shots at a target every ten yards and figure drop in real time. When using holdover in the scope that's all you need. If you were clicking your correction and shooting off the crosshair I see how the drop calculations would help you get an extra measure of precision.

As for FPE I couldn't care less. If I wanted to hit a target with a certain energy I would work that backwards too. I'd set my chrono at the target and move out until it showed the minimum speed to make the horsepower I needed. That would be my maximum effective range. It just seems a lot more practical than fiddling with a ballistic program for my purposes.

I use ballistics software all the time to plot my holdover. If I'm really being particular about it I'll verify that it's correct by shooting groups, but in general I've had very good luck with it.

 

[alejo]

Ignorance is a bless, no offense .
Just 5 years ago I did not know about PCP’s , now my brain hurts, there’s so much info that’s impossible to remember everything however this forum is the best to learn and regret. Be safe

 

[Sawney Bean]

The best way to visualize fpe other than just what understanding what 40lbs feels like.

You have a 40lb hammer head, it has a 1' shaft. Now imagine. A frame with a horizontal bar above your head, the bar goes through the hammers shaft. So you basically have a 40lb pendulum. Raise the hammer head 90⁰ so it swings down and forward. The impact at the bottom where the hammer would rest if it hung.. is about 40 foot pounds of energy if allowed to swing under its own gravity, now put a .22" wide bead at the dead center of the impact face. Or at least that's how it was actually demonstrated to me by my physics teacher. But with a sheet of 1/8" plastic and 1 lbs iron sphere. Now

That's an interesting way to visualize it. One thing I have noticed is that momentum is a greatly overlooked factor. Kinetic energy is a function of the square of the velocity, so a small increase in velocity makes for a big increase in kinetic energy. Momentum however is directly proportional to the velocity.

When you start to consider momentum as well as kinetic energy it explains why larger and heavier projectiles with the same kinetic energy as faster and lighter projectiles seem to hit harder. I've got both a Hatsan 135 in .30 and an Air Arms S410 in .22 and the S410 is slightly more powerful in terms of energy, yet the Hatsan obviously hits harder. I was shooting both at a golf ball hanging on a string and the difference in their impact was obvious to everyone.

I also find that with firearms momentum is a much better predictor of recoil.

 

[Bedrock Bob]

I use ballistics software all the time to plot my holdover. If I'm really being particular about it I'll verify that it's correct by shooting groups, but in general I've had very good luck with it.

I visualize inches of drop on my target with a HP rifle from a dope sheet. I chronograph muzzle velocity. But i shoot targets to develop my dope sheet. I'm sure the calculator would return numbers that are very close if you fed it good data.

With the air rifle I just know the spot on the reticle that corresponds to the range I'm shooting at. So "how many inches" is not really relevant to me. I'm aiming in relation to a spot on the vertical crosshair.

I'm going to start clicking the scope to get my drop. I've never shot that way before. I have a free ballistics program that returns a drop/rise in inches and a scope with favorable turrets. I haven't mounted it on a rifle and tried it yet though. I can see how using the equipment and data can get you closer to the exact spot.

I guess I'm just a Kentucky windage and Mexican elevation type of guy. My less than stellar results with my calculator is probably my flawed input data. I just staple up targets and fling pellets until I know where to aim on the crosshair.

....and then I shoot off the wrong dot.

 

[Sawney Bean]

I visualize inches of drop on my target with a HP rifle from a dope sheet. I chronograph muzzle velocity. But i shoot targets to develop my dope sheet. I'm sure the calculator would return numbers that are very close if you fed it good data.

With the air rifle I just know the spot on the reticle that corresponds to the range I'm shooting at. So "how many inches" is not really relevant to me. I'm aiming in relation to a spot on the vertical crosshair.

I'm going to start clicking the scope to get my drop. I've never shot that way before. I have a free ballistics program that returns a drop/rise in inches and a scope with favorable turrets. I haven't mounted it on a rifle and tried it yet though. I can see how using the equipment and data can get you closer to the exact spot.

I guess I'm just a Kentucky windage and Mexican elevation type of guy. My less than stellar results with my calculator is probably my flawed input data. I just staple up targets and fling pellets until I know where to aim on the crosshair.

....and then I shoot off the wrong dot.

The ballistics software I use calculates the holdover for me in dots, but since I mostly use SFP I have to convert the dots to the correct magnification for my dope sheet. What I’ve found however is that if I use the same zero for all my rifles that the holdover is also similar on all of them. I’ve actually got about three trajectories that I have to deal with. I do a far zero of 50 yards on 80% of my rifles, but since some of those are bullpups that makes for two different sets of holdover. Then I’ve got the low velocity guns and I sight those in at 30 yards, so that’s a third one. Pistols I typically sight in at 20 yards, but since those are iron sights I don’t really bother trying to memorize the holdover on them.

I think you’ll like clicking for elevation. It really works well for precise accuracy. It’s really nice to have a zero stop though. I’ll typically set my zero at 25 yards for that.