JSB 18.13 pellet at 950 fps for best accuracy?

I need to try some more 100 yards shooting. The heavier pellets like the JSB Monster Redesign might possibly be better for further distances, although their ballistic coefficient isn't hugely higher than the 18s. Both are excellent designs though.

The wind has been pesky where I live here in Alabama lately as the seasons change. The least air movement has been right at dusk. There's around a thirty minute time period when the wind stops while there is still enough light to see well enough to shoot. There is 100 meter indoor range in my county not too far from home but it's an expense that I don't want to go there.

KodiakJac said:

After reading this Hard Air Magazine article The External Ballistics Of Diabolo Pellets and watching this Ted Holdover YouTube video Pushing the Velocity of .22 Pellets I'm wondering if we should be testing the .22 JSB 18.13 pellet in the 950 to 960 fps range for maximum accuracy at 50 or even 100 yards?

I've been shooting firearms all my life, but other than shooting BB and pellet guns as a kid, I've only been shooting airguns seriously for about 2 years. And when I got started with airguns, I fell into the 880 fps crowd for the .22 18.13 pellet pretty quickly, as that seemed to be the consensus velocity I kept reading about.

So, is 880 fps really the sweet spot for the .22 JSB 18.13 pellet at 50 or even 100 yards?

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I'm shooting mine at 970 out my FX Impact MKII Power Plenum regulator set at 75 bar with 700mm barrel. Anyone else shooting then at high velocities??

I have great accuracy out to 100yds when wind is cooperative. I shoot JTS 18gr at 915fps. No specific reason just where it landed when started tuning and left it there. Had good results at 960fps but not near as good as 915fps. This was 5 shots when wind had died down at 100yds. So I don't think destabilizing with the 18gr is really a thing unless your tune isn't really dialed in with them. Been shooting them for years with good results with different guns. Wind is the only factor.

Generally I've found when shooting Diablo pellets FAST !!! the slower barrel twist rates do better and also allow for further distances before pellet spirals if it does at all. Slugs don't care for slow twist rate barrels, but pellets sure seem too

And YES, there are always exceptions or stand out results for either school of thought or discovery.

Motorhead said:

Generally I've found when shooting Diablo pellets FAST !!! the slower barrel twist rates do better and also allow for further distances before pellet spirals if it does at all. Slugs don't care for slow twist rate barrels, but pellets sure seem too

And YES, there are always exceptions or stand out results for either school of thought or discovery.

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The difference between slugs and pellets is down to the different stabilization methods they use, slugs being gyro stabilized and pellets being aerogyro stabilized.

The other problem with shooting pellets at faster speeds is that if there is any wind, the wind drift will start to increase.

The theory that makes the most sense to me is that pellets destabilize because the rotational spin from the twist rate times the velocity gets too large relative to the forward velocity. Forward velocity falls faster than rotational velocity so the instability occurs at distance. Some also report instability is more likely in windy conditions. My one gun that likes 18 grain pellets prefers H&N Baracudas. I shoot them at 900 fps but I haven not tried that gun at longer range yet. I think it's twist is 18 to one so the rotational speed would be relatively high. My guess is it will retain reasonable accuracy to 100 yards but I won't know until I try it.

JimD said:

The theory that makes the most sense to me is that pellets destabilize because the rotational spin from the twist rate times the velocity gets too large relative to the forward velocity. Forward velocity falls faster than rotational velocity so the instability occurs at distance. Some also report instability is more likely in windy conditions. My one gun that likes 18 grain pellets prefers H&N Baracudas. I shoot them at 900 fps but I haven not tried that gun at longer range yet. I think it's twist is 18 to one so the rotational speed would be relatively high. My guess is it will retain reasonable accuracy to 100 yards but I won't know until I try it.

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It's not really instability that is the problem, it is having too much stability that causes the problems.

Ballisticboy said:

It's not really instability that is the problem, it is having too much stability that causes the problems.

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Is over-stabilizing changing the orientation of the pellet on the way to the taget..going nose-up?
more drag and less bc?
seems like any wind would throw it off

I guess it makes sense to call too high a rotational velocity for the forward velocity "over stabilization" but I don't know how this clarification increases our understanding of what is going on, when it occurs, and why it occurs. If we agree it is the rotation velocity for the forward velocity that causes issues at times, then what we call it doesn't really matter to me.

My suggestion is that the maximum velocity is thus a function of the twist rate of the barrel. Higher twist barrels need lower velocity than slower twist barrels is my theory. That seems to fit the examples people have given.

JimD said:

I guess it makes sense to call too high a rotational velocity for the forward velocity "over stabilization" but I don't know how this clarification increases our understanding of what is going on, when it occurs, and why it occurs. If we agree it is the rotation velocity for the forward velocity that causes issues at times, then what we call it doesn't really matter to me.

My suggestion is that the maximum velocity is thus a function of the twist rate of the barrel. Higher twist barrels need lower velocity than slower twist barrels is my theory. That seems to fit the examples people have given.

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Because over stabilization results in well understood behaviour of any projectile using gyroscopic stability. Gyroscopic over stability makes projectiles sluggish to change their orientation so that yaw wave lengths become over long, giving yaw induced side forces time to give significant changes in position. This results in spirals and increased group sizes. Similarly, if muzzle velocities get too high, pellets begin to lose aerodynamic stability on leaving the muzzle due to the changes in airflow with Mach number. The loss of aerodynamic stability causes increases in gyroscopic stability, which again make the pellet slow to try to correct any yaw or yaw rates which all pellets get from the barrel. In this case, the gyroscopic stability can initially reduce as the pellet slows down, but the damage will already have been done to the group size, and the gyroscopic stability will always be higher than for a slower muzzle velocity.

The size of the problems will depend entirely on the detailed pellet design.

Miles,

Berger bullets says over stabilization is a myth for rifle bullets. Maybe not for pellets I guess. They say it can be an issue for artillery shells but not rifle bullets.

But still empirical evidence says it happens so I guess you are right, at least about what pellets do. Thanks.

Jim

JimD said:

Miles,

Berger bullets says over stabilization is a myth for rifle bullets. Maybe not for pellets I guess. They say it can be an issue for artillery shells but not rifle bullets.

But still empirical evidence says it happens so I guess you are right, at least about what pellets do. Thanks.

Jim

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Shows how much Berger bullets know about artillery shells then. The biggest issues are with what is called proof shot for artillery guns, which are just high drag metal cylinders used to test charges, and some designs of tank practice rounds, usually tubular rounds. In high angle fire, artillery rounds can wobble a bit at the vertex, but they soon settle down on the way back down again and never really get to angles high enough for major problems. To me, over stability is when things start going sideways like I have seen proof shot do, not when they start to wobble a bit.

Normal rifle bullets will not have huge problems, as they do not go high enough in the air in normal use. You would get it if firing near vertically, and tubular rounds have been suggested for rifles, which would have the same problems as the tank rounds.

manabeknives said:

Is over-stabilizing changing the orientation of the pellet on the way to the taget..going nose-up?
more drag and less bc?
seems like any wind would throw it off

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It will make the pellet more sluggish in following the curve of the trajectory, and the dynamic instability of pellets will give some increase in yaw also. Drag will increase but not significantly until angles get up to around 6-10 degrees, by which time you will have missed the barn, never mind the barn door.

Severe wind gusts can induce bigger yaw angles as the pellet tries to turn into the new airflow direction.

All I can add is that my Cricket Carbine, with 17.7" twist, is shooting 18.1 gr FX pellets at 928 fps avg and at 100 yards in fairly calm days can do just over an inch with me at the trigger, even though I'm waiting for the calmest of days to improve on that. So, for this combo, it is extremely accurate.

The overstabilization is an interesting theory. My FX Dream Tac also shoots 18.1 gr FX pellets well at 100 yards, with the short (380mm I believe) barrel. I don't know what the twist works out to be in a smooth twist X barrel, but if it is slower, relative to velocity, then all this makes sense. I have seen one of my .177 rifle spiral at close range when I cranked the speed up a lot, so now we're making sense. I knew it happened, just never gave much thought to actual cause, beyond velocity.