To get the optimum accuracy out of a PCP what's a good standard deviation on a 16 or so shot string? I was thinking 2 or less would be good but I may be wrong. What are you guys seeing that works the best?
What's a good standard deviation for optimum accuracy?
- Thread starter LSS152
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I think it's good if I'm under 5 fps. I noticed you still get great groups if your speed doesn't deviate more then plus or minus 5 fps from your average.
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It depends on your distance mostly. The further you are shooting there should be less deviation in velocity. Use Chairgun to plug in some numbers and decide how much drop (variation in velocity) are you willing to accept.at a certain distance.
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SD of 2fps? that's more than perfect.
Don't go too crazy over ES or SD numbers they will make you mad, a gun with 20fps ES can shoot MOA all day long with the right ammo, also don't cheat yourself with 16 shoots string unless that's all you get out of the full fill, you want to know what gun is doing over whole fill, the other day I got ES of 0fps (over two shoots
) and 60fps over 60 shoots if that makes sense.
One more thing, always blow your first shoot after filling the gun or the next day when you starting a new session.
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Don't go too crazy over ES or SD numbers they will make you mad, a gun with 20fps ES can shoot MOA all day long with the right ammo, also don't cheat yourself with 16 shoots string unless that's all you get out of the full fill, you want to know what gun is doing over whole fill, the other day I got ES of 0fps (over two shoots
) and 60fps over 60 shoots if that makes sense.One more thing, always blow your first shoot after filling the gun or the next day when you starting a new session.
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I get 17 shots out of a MK2 Compact 30 Cal with 44.5gr hybrids. My last 17 shots were average of 901, SD of 5FTS, ES of 14FPS, 79.5 FPE at 85 degree day. 74 degree day with 17 shots I was average of 903, SD of 2FPS, ED of 8FPS, 82 FPE. The POI was the same and the group size was the same. No change in tune between strings also.
+1 on blowing first shot. If I don't I will almost always get a weird first shot. Happens on my Airforce Talon also. Doesn't happen on my Cricket 2 however. I fill slightly above 250BAR on the impact and blow off first shot and sit right around 250 and the shots do well after that, just doing the blow off will improve my SD and ED.
+1 on blowing first shot. If I don't I will almost always get a weird first shot. Happens on my Airforce Talon also. Doesn't happen on my Cricket 2 however. I fill slightly above 250BAR on the impact and blow off first shot and sit right around 250 and the shots do well after that, just doing the blow off will improve my SD and ED.
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If you have a fairly consistent string going and then have one or two shots that are crazy numbers, say 30 or 40 off that make no sense, do you delete those shots and consider those are a whacky pellet or two?
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Don’t let OCD consume you. That’s obsessive chronograph disorder. After a good base tune I let my targets determine if I need to revisit the chronograph. Living over a chronograph can make a guy never be satisfied and contribute to lead poisoning. Just remember this, if your gun isn’t shooting bad, why waste pellets or slugs shooting at nothing.
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I have only had that problem once I have fallen off the regulator and didn't notice for a few shots. That is why I know I get 17 shots with 44.5gr. These guns are so well done that they will shoot consistent for a few shots off regulator before they get squirrely. 30-40 FPS deviation before that would point me to a warranty issue or possibly a really terrible tune. This is why the OG guys tell you to write the factory tune down before playing with it so you can get back to "zero" if you totally mess up.
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There's a short answer: None.
But.... Even with no standard deviation you will not be excluded from other accuracy factors: wind, small difference among pellets/slugs, humidity on air, your self and your pulse....
Notwithstanding good PCP's are super accurate there are still external factors that can take your shot out of destination. Even with same fps among pellets.
But.... Even with no standard deviation you will not be excluded from other accuracy factors: wind, small difference among pellets/slugs, humidity on air, your self and your pulse....
Notwithstanding good PCP's are super accurate there are still external factors that can take your shot out of destination. Even with same fps among pellets.
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My .177 taipan usually stays within 10-15 fps es, within a wide hammer setting. But it seems not to be the es, but rather the average speed itself which decide if it is accurate or not. My gun with factory reg pressure was more accurate at low 800 fps, than 900+ fps. Even the Es or sd was rougly the same. Had I upped the speed above 1000 fps, getting closer to the max speed of the gun, the Es would probably be even tighter, but the grouping would be bad, simply because the pellet would go to fast.
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Don't worry about it, unless the target tells you there is a problem. Example, you have that perfect rifle that shows a 0 SD. But, it's a crappy barrel, and shoots all over the place. Conversely, a rifle shows a SD of 10, but it's a great barrel, and shoots tiny groups out to 50 yards or so. Is that a problem?
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Well said, my friend!!!
I got a gun that can shoot MOA at 50Y with 40fps ES and a gun that will do 3" groups with 10fpsm ES at 50Y, moral of the story, put your chrony away if a gun is shooting good just leave it the way it is.
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+1
At 100 yards an average pellet shooting at 900 fps with an ES of around 30 fps (SD of about 10) will be about +/- 0.4" above/below POA. That's +/- less than half an MOA. That's a pellet. Higher BC's will tend to minimize that. Single digit SDs are, as said elsewhere, "better than perfect". For field purposes an SD which is less than one percent of the average muzzle velocity is probably more than "good enough". Precision shooters will not find that acceptable, but they are trying to hit flies at a hundred yards...
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