22 rifle giving ammo warning.

I have never seen anything like this before The Keystone 22 in Varmint profile is warning against using Stinger ammunition. http://www.ozgunsales.com/listing/79234/keystone_pt_precision_chassis_16_5_22lr.html

Has anyone seen this before or know the reason behind it?

Pinched straight from that most trustworthy and respected source - Wikipedia

The CCI Stinger was the first hyper-velocity .22 LR cartridge, and provided a significant increase in velocity and energy over standard rimfire rounds. The Stinger case is longer than that of the long rifle; about .702 in (17.8 mm) versus .613 in (15.6 mm) for the long rifle, but the plated hollow point bullet is lighter and shorter at 32 gr (2.1 g), giving the same overall length as the long rifle cartridge. This longer case can cause ejection problems in some guns. A powder with a slower burning rate is used to make the most use of the length of a rifle barrel. Most .22 long rifle powders increase velocity up to about 19 in (480 mm) of barrel. The powder used in the Stinger increases velocity up to the longest .22 barrel length tested by the NRA, 26 in (660 mm).[22]

Hm interesting. I have used them in my Anschutz without any problems. I have problems with the Winchester HP ammo in that once I chamber a round the only way it is coming out is by being fired. It is obviously being jammed into the lands. The case ejects fine once it has been fired. I dont recall having the same problem with the Stinger.
I was a bit disappointed when I bought my first pack of them learning that the increase in speed was really made possible by the lower bullet weight. I haven’t done the sums but I would think the energy would be nearly the same as standard velocity.

Surprisingly to me yes.
22LR Muzzle Energy: 22lr muzzle energy is measured in foot pounds to determine the destructive potential of the bullet. The 22lr muzzle energy is the kinetic energy of the bullet as it leaves the muzzle. Generally the heavier and faster the bullet the more damage it will do to the intended target. As you can see the CCI Stinger Ammo has a higher initial muzzle energy but at 200 yards the Remington Golden Bullet 36 gr has a much higher kinetic energy and more killing power at that distance. Look at the 22lr ballistics table to compare the muzzle energy at various distances.

Found this online. The second value in the muzzle column is the kinetic energy at the muzzle.

Makes sense seeing that Ek is 1/2mv^2. If the velocity is doubled, it needs to be a quarter of the original weight to have the same energy.