Understanding 22 LR Ammo specifications

[mainegrw]

So I started looking at the SAAMI specs for rimfire cartridges recently, and noticed that all of the 22LR rounds listed all fall under the same maximum pressure rating, despite having different listed velocities, bullet weights and bullet designs. I assume then that velocity becomes a factor of powder burn rate, bullet weight, and shape.

That said, considering that chamber pressure is (at least it's my understanding) the major factor in the cycling of a rimfire action, what makes high velocity ammo i.e. Mini Mags more reliable in some actions than standard velocity?

Further, if the chamber pressure remains the same, how is it that high velocity ammo is capable of inflicting damage to certain firearms that standard velocity ammo does not? This is where my research began, actually, with regards to using high velocity ammo in an old High Standard Model B.

What else am I missing in the equation?

Sent from my SM-G965U using Tapatalk

 

[OKFC05]

SAAMI Max Avg Pressure numbers are a limit, not a required performance spec, i.e., "Do not exceed"

 

[shouldazagged]

SAAMI Max Avg Pressure numbers are a limit, not a required performance spec, i.e., "Do not exceed"

Beat me to it.

 

[mainegrw]

Gotcha! So with the maximum allowable pressure being 24,000 psi, what would the average chamber pressures be for standard velocity and for High Velocity 22 LR? Does that data exist somewhere?

Sent from my SM-G965U using Tapatalk

 

[rockquarry]

I tried standard velocity ammo (CCI) in an early 1940s Model B, but don't recall if it functioned reliably with this ammunition. However, the gun has had a steady diet of high velocity ammo for well over fifty years. Is high velocity ammo not recommended for such pistols?

 

[Jellybean]

.22 rimfires do not function by chamber pressure, they are recoil operated.

The recoil from "standard velocity" ammo is less than that from "high velocity" ammo and firing high velocity ammo in a gun designed for low velocity ammo will cause damage due to excessive recoil, i.e. weakened recoil springs and/or frame/slide battering.

"Recoil" is the momentum of the case pushing up against the bolt face and would be equal to the velocity times the weight of the bullet and propellant. Some newer pistols are designed for high velocity ammo, which would have problems functioning with low velocity ammo. Some, such as the Jennings J22 are designed for the Mini-mags and even have problems shooting some high velocity ammo.