What data do you use for determining "useable shots"? Is it how many shots before refilling the air tank, a FPS range, a FPE range, accuracy group size ? Thank you.
How do you determine "useable shots"?
- Thread starter Dan B
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With an unregulated gun most people will pick an acceptable extreme spread of velocity. What goes into picking that range will depend upon your situation. If you're shooting in your backyard, a 50-60 fps extreme spread may be acceptable. It's very helpful to actually plot your velocity data and look for a point in the graph where your velocity starts to decrease rapidly. Most unregulated PCPs will have a "curve" to this graph, but some may have linearly decreasing velocity (these guns typically get very few shots per fill). A more simplistic alternative is to just look at your POI as you shoot. Once this starts to change noticeably that would be the end of your shot string.
With a regulated rifle, it's a bit easier to figure out; you stop shooting when your air cylinder pressure roughly equalizes with your regulator pressure (assuming that you know the reg pressure). This is the point at which the velocity will start to become inconsistent.
With a regulated rifle, it's a bit easier to figure out; you stop shooting when your air cylinder pressure roughly equalizes with your regulator pressure (assuming that you know the reg pressure). This is the point at which the velocity will start to become inconsistent.
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For my unregulated Marauder, I like to see a 4% ES or less for up to 35 yard shooting. 2% for 50 and beyond. The data I use is a shot string from 3000PSI down to 2000PSI (recording shot velocity for every shot and pressure every 5 shots or so). With that data, I can find the pressure range where I have that 4% or 2% ES. Fill to the max of that range (say 2800PSI) shoot down to the pressure that ES ends at (perhaps 2100PSI). Gotta have a chrony though.
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For target shooting, all the shots within the desired grouping at the distance I want to shoot at, as long as it can punch through the target card, or knock over the target/spinner or whatever I am shooting at.
For hunting, all the shots I can accurately place where I want to on the quarry and the distance I am shooting at, provided it has sufficient power to kill cleanly.
Easier to manage with my regulated rifles, but not really more difficult with unregulated once tested over the chronograph to understand the shot curve, and also on target for accuracy.
For hunting, all the shots I can accurately place where I want to on the quarry and the distance I am shooting at, provided it has sufficient power to kill cleanly.
Easier to manage with my regulated rifles, but not really more difficult with unregulated once tested over the chronograph to understand the shot curve, and also on target for accuracy.
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@DeanB I think the application matters here. Let’s look at this shot string in the photo below.
This is a hunting rifle that I use to take deer. State regulations stipulate that an air rifle used to hunt white tailed deer need to generate a minimum of 215 FPE. So for that purpose the first three shots are useable.
Aside from that, for other animals or target shooting, I’m looking at bullet drop and the amount of fps shed per shot. When the fps per shot increases from the longest trend, to me that’s an indicator to stop. If the projectiles are dropping drastically or I have to use a large holdover compared to previous shots, I stop and top off the reservoir. Is this the best method? Probably not, but it works for me.
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fill your gun to mfg recommended max operating pressure.
Place your target /bullseye at a distance where your ZERO'd your scope....
begin shooting and count each and every shot
when you begin to see a distinct and noticeable change in accuracy (bad thing) stop shooting
Take note of # shots you took before things went south.
You now have what i consider the number of useable shots from a fill.
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You nailed it in your question - you have to define what it means for you . . .
Most of the advice here has been geared towards measuring your shot data, and then applying a specific definition of usability onto the results. I think the key factor here is to look at it in terms of the word "useable" in the context of how you want to use your gun. You'll get a different answer based on what you feel your use case is. For example, I have an unregulated .22 50 FPE Daystate Air Ranger that I have tuned to shoot at ~30FPE, and it is quite efficient since I fabricated a really cool internal SSG for it - and it has a ~500cc bottle on it. It is a very accurate gun in the sweetspot of the shot curve and still quite accurate outside it if you know the holdover. I did all the chrony testing and plotting to know how the gun shot, and thus I know my usable shots from it based on what I am using it for:
1) Shooting for accuracy with a hand pump: about 20 shots, as that allowed me to fully refill in one pumping session of 50 strokes. All shots in a tight ES.
2) Shooting for accuracy with a tank: about 30-40 shots, with an ES only a smidge worse than above (no worries on time to refill)
3) Shooting for highest accuracy from a bench: after the first ten shots (assuming starting from a full fill), about ten shots, then "blip" about 100 psi into the gun from the tank that I just keep tethered to it. Very tight ES shooting one mag right from the sweetspot of the shot curve, then reload, "re-air", and repeat.
4) Plinking for fun - easily 100 shots. Overfill about about 150 psi above my normal fill point, then keep shooting - the SSG keeps the shot cycle in control with no hammer bounce, but the ES degrades more but it is fun. ES is probably about 8-9% like this, but it is just plinking . . .
Bottom line, usable shots depends very heavily on what "usable" means . . . . and yes it is easier with a regulated gun, as it is best to refill when it gets down to the regulator's set point, or very soon after that.
Most of the advice here has been geared towards measuring your shot data, and then applying a specific definition of usability onto the results. I think the key factor here is to look at it in terms of the word "useable" in the context of how you want to use your gun. You'll get a different answer based on what you feel your use case is. For example, I have an unregulated .22 50 FPE Daystate Air Ranger that I have tuned to shoot at ~30FPE, and it is quite efficient since I fabricated a really cool internal SSG for it - and it has a ~500cc bottle on it. It is a very accurate gun in the sweetspot of the shot curve and still quite accurate outside it if you know the holdover. I did all the chrony testing and plotting to know how the gun shot, and thus I know my usable shots from it based on what I am using it for:
1) Shooting for accuracy with a hand pump: about 20 shots, as that allowed me to fully refill in one pumping session of 50 strokes. All shots in a tight ES.
2) Shooting for accuracy with a tank: about 30-40 shots, with an ES only a smidge worse than above (no worries on time to refill)
3) Shooting for highest accuracy from a bench: after the first ten shots (assuming starting from a full fill), about ten shots, then "blip" about 100 psi into the gun from the tank that I just keep tethered to it. Very tight ES shooting one mag right from the sweetspot of the shot curve, then reload, "re-air", and repeat.
4) Plinking for fun - easily 100 shots. Overfill about about 150 psi above my normal fill point, then keep shooting - the SSG keeps the shot cycle in control with no hammer bounce, but the ES degrades more but it is fun. ES is probably about 8-9% like this, but it is just plinking . . .
Bottom line, usable shots depends very heavily on what "usable" means . . . . and yes it is easier with a regulated gun, as it is best to refill when it gets down to the regulator's set point, or very soon after that.
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I agree that for regulated guns the usable shots pretty much end when you go off the regulator but it's a good idea to shoot it down some and see what it does. My P35-25 is tuned to almost 50 fpe using 34 grain JSB pellets. I only get 25-30 shots until I go below 150 bar where the reg is. But my velocity does not go down 20 fps until I get to 100 bar. So I can really get about 40 usable shots from it. Accuracy and POI do not change when it goes off reg.
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Hi Dan,
You have received a lot of good information in the responses above…
…I’m going to tie this into accuracy and distance - to give you a reference point.
Assuming a typical air gun distance of 30 yards and assuming that you are shooting within typical 840-880fps velocity range (typical USA velocity)…
With those assumptions, you will about a 1/8” vertical PoI shift with a velocity spread of 25fps. I’ve got hundreds of targets to support this.
Here are some targets and shot strings to support this - using an unregulated rifle and two different pellet weights (15.89 and 18.13). (For reference the 10-ring on this target is 1/8” diameter)
You will note from the shot strings that velocity does not drop off linearly - and this applies to both regulated and unregulated - as you can often squeeze a few more shots from a well tuned regulated rifle AFTER the reg set point, but below the reg set point it is essentially an unregulated rifle.
Chrono a shot string with your rifle and note where Shot-to-shot velocity starts to drop much more quickly (say 5fps drop per shot). Note you rifle fill pressure at that point. You would likely want to refill just before you get to that fill pressure.
Hope this helps,
-Ed
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WOW!!! All the information response is like attending an Airgun seminar!! I will print this. Thank you very much.
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Here's what I did with my Revere .177 cal unregulated rifle. I filled the gun to max capacity of 250 bar and it cooled a bit to 240 while setting up for the test. I ran 13 shot magazines over the chrono and recorded the pressure reading after the end of each magazine. I also shot each magazine in one target at 10M to see where the POI dropped off. It was during the 9th magazine that the shots started to drop off which was around 825 fps with 10.3 gr AA pellets. For general plinking, I think over 100 useable shots are there. If you want to be a little more in control, then I would shoot it from 200 down to 130 bar giving you a nice flat velocity curve around 900 fps.
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Knowing your equipment and purpose would help.
I was looking for info like this when I bought my first PCP. The folks here at AGN told me that I needed a chronograph to troubleshoot and see issues.so I bought an FX pocket chrony.
My use was plinking, and I was very dissatisfied with my new rifle. It was unregulatd, and the point of impact would fall for each shot. The chrony just showed the same thing in fps.
Studying it, I found that the model I had came with an adjustable hammer tension that could be set lighter so that hammer didn't release as much air. The higher the gun pressure, the harder it is for the hammer to open the valve. This is the principle used to regulate an unregulated gun, as well as one of the building blocks of adjusting a regulated gun.
With a lighter hammer weight, less.air is released, so you start with a lower fps.
As the pressure drops, the hammer over comes it releasing more air, increasing fps to a max point, and then the pressure and fps drop.
My goal with this info was to to get the highest shot count in the optimum accuracy range.
The fps change was pretty great here so, what if I wanted to hunt ?
There are about 8 shots at the top of the string at the highest power level with a good fpe. More fpe could probably be had with more adjusting, but the shot count would likley drop, and it is almost a full mag at the current setting.
So I would have to note the pressure of the gun at the point where those shots start and set that pressure, then I would have one mag of the most consistent and powerful shots that the gun is capable of.
Its all in the soup ingredients.
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