Weight vs FPS

[Plinkalot]

I'm trying to understand how one picks the initial FPS to tune to, particularly .22 pellets.

Is there a pickoff chart anywhere that shows the relationship between weight and best velocity?

 

[JungleShooter]

Here are some

Considerations for best velocity: ​

➊ What velocity gives the best precision (smallest groups)?
For slugs this is usually very very important, for pellets not so much.

➋ At velocities above 950fps drag will increase greatly as the pellet approaches the speed of sound (at which its precision will really get messed up).
Increased drag means more wind drift, and more pellet drop over distance.


➌ Pellet drop over distance: The faster the pellet, the less it will drop per yard forward movement.
And therefore, the longer it will fly almost level (seemingly).
And therefore, the longer the range at which vertial adjustments with the turret or reticle are not necessary — because the pellet will hit either a bit high or a bit low, but always in the kill zone of my quarry.
This range where no adjustments are needed is called PBR — point blank range.

➍ The faster the pellet (before going almost supersonic), the less wind drift.

➎ If I'm into scopecaming: the slower the pellet, the better I can film its path — it will be better visible.

➏ The faster the pellet the more air I will use per shot — the less shots I get per fill.

➐ The faster the pellet the louder the gun.

➑ There is a point where increasing velocity by only a small amount will cost me a large amount of air, and will increase the shot noise by a large amount.
And the shot cycle will become harsh, as the gun is pushed to its limits.


I'm sure I'm forgetting some factors....

Matthias

 

[Bramezy]

Lots of good info posted above there. It all depend son use and the gun you have. Those 2 factors will limit a lot or nothing. Decide what your gun is even capable of and how you want to use it and then you can tune from there. a 12fpe tune is way different than a 25fpe tune.

 

[Plinkalot]

I think I understand why there's no charts for this. I guess, on the extremes, I'm trying to tune for either most FPE or most shots per charge for the perticular pellet I'm using, or somewhere inbetween.

Do you guys then develope tunes for the different pellets you like and keep that info for reference? Can you then change back and forth between tunes without having to fine tune anything?

Thanks again.

 

[JungleShooter]

Do you guys then develope tunes for the different pellets you like and keep that info for reference? Can you then change back and forth between tunes without having to fine tune anything?

Thanks again.

An easy adjustment of power is for most PCPs rather limited to adjusting the hammer spring tension (HST).

To adjust the regulator externally, without degassing and taking the gun apart, is a feature that most guns don't offer, except for some of the most expensive ones (RTI Priest/ Prophet/ Mora, Impact, Maverick, Ghost, and some of the newer brands).

Therefore:
Making larger power adjustments is usually not possible without a mayor mechanical operation.
What you can do easily is adjust the HST so that the gun isn't wasting air when shooting lighter pellets than the previous tune (the recommended value is 5% velocity below the maximum muzzle velocity for a given regulator setting).

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It seems to me that many people who have gotten into airgunning either leave it after a while — or they fall into a rabbit hole (from which rarely anybody recovers):

They buy more and more guns, in an ever increasing variety of calibers, with the obligatory paraphernalia of scopes, range finders, chronies, tens of thousands of projectiles (in each caliber), and so on.

And with that fall into the rabbit hole — your problem of needing to tune your gun for different projectiles goes away all by itself (ask me how I know):
For shooting scenario A — you own gun A — tuned for the perfect projectile A.
For shooting scenario B — you own gun B — tuned for....
(You get the idea...)

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However, I still like to use different projectiles in a single gun.
➊ So, I tune the gun for the projectile A. Either, the projectile that is the most fussy (slugs over pellets, for example), or the one I will shoot more often.

➋ Then, I zero the gun and set up a profile for this gun—power—scope—projectile combination in my ballistic calculator.

➌ Then, I shoot another projectile B that I want to use, and note its offset from the zero of the first projectile.
This offset I enter into the same gun profile of the ballistic calculator, but as a different projectile.

➍ When I want to switch projectiles, I just change it in the ballistic calculator, and it does the rest, spitting out data for projectile B.

Works great.

Matthias



PS:
I you haven't found the rabbit hole, don't despair.
Just stick around the AGN forum for a while, and there'll be plenty of people who will show you the way. They've been a tremendous help to me!

Here's a good thread to get started in your search for the rabbit hole:

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Black Friday approaches. Post up any good deals. Arken's deals have started already. 30% off across the board. https://www.arkenopticsusa.com

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[MongooseV8]

One thing to keep in mind is that most all pellets will not like to be pushed too hard or too fast. The common fps cap recommendation for pellets is 850-880. Some pellets in some setups with some tunes will do well at faster speeds, but that is not the norm.

The air charge your pcp releases to push a pellet matters too. If the air charge is too aggressive even at slow speeds, you can disrupt flight out of the muzzle.

Some of us run very fast pellet speeds for hunting purposes, but there are drawbacks. For example my M3 Impact is setup to push 22Cal Hades at about 990fps right now. I get good groups out to about 60yds, but then the pellets veer off and really open up my groups. If I wanted to get a pellet out further I would choose a heavier pellet, slow it down, and tune for max accuracy.

Pellets are very very sensitive and have terrible ballistic properties. They can spiral through the air like a plane missing a wing, or randomly take a right turn etc. They like being lobbed gently toward your target, and can provide some terrific accuracy if you treat them right. So when deciding for a target tune and fps, its good to understand how pellets act/react.