+P loads, someone please explain why...

[skeeterbait]

some manufacturers designate their round as +P when another manufacturer loads the same weight bullet and declares a higher velocity but does not specify the round as +P?

Case in point:

Fiocchi Shooting Dynamics Ammunition 38 Special +P 110 Grain 730 FPS
Remington Express Ammunition 38 Special 110 Grain 950 FPS
Federal Premium Personal Defense Low Recoil Ammunition 38 Special 110 Grain 1000 FPS

Does the Fiocchi develop more pressure yet somehow drive the bullet 220 FPS slower than the Remington?

I would expect the Fiocchi load to deliver less recoil than either of the other two given equal bullet weight and slowest velocity but it is designated +P. I would expect the Federal to deliver the highest recoil yet it is declared "Low Recoil".

 

[flop-shank]

It could be different barrel lengths at play. One cartridge could be fired from an unvented test barrel and the other a vented one.

It is very possible to have higher pressure and less velocity if the manufacturer is using a faster burning powder. With fast powders the pressure rises and falls quicker and thus doesn't give the bullet as much of a sustained push. It seems counter-intuitive, but high velocity magnum revolver cartridges utilize large quantities of powders that are slow. Given an equal bullet weight, higher velocity with lower pressure is indicative that a cartridge was well engineered by having a more appropriate powder for the task.

 

[stiab]

Are you sure the numbers you are quoting are correct? I just did a search for Fioochi .38 Special 110 stats and the site quoted 1075 fps.

 

[skeeterbait]

Well the figures came from a well known reseller's website. No proof though that they were diligent in verifying their source which I can only assume is the manufacturer.

 

[skeeterbait]

stiab, your comments prompted me to research further and I located a Fiocchi product catalog. It does indeed appear that the reseller is in error as Fiocchi lists the velocity of that round as 1080 FPS. That sounds more reasonable for a +P product. Sorry for the confusion.

 

[OKFC05]

Since the PRESSURE Rating of a cartridge refers to its PEAK pressure, and muzzle velocity is proportional to the "area under the pressure curve" or INTEGRAL of pressure (work done on the bullet), it is possible to have a +P with lower muzzle velocity by using a fast powder.

However, as a practical matter, most commercial loaders and savvy handloaders save the +P loadings for the slower powders when they are trying for max velocity.

As an example of the +P loading being slower, load a +P 230gr with Bullseye in .45 ACP and then load another 230gr .45 to a max standard pressure with Unique. The Unique load has a higher MV, because the total integrated pressure while it is in the barrel is higher.

Internal Ballistics

 

[Steve C]

For factory ammo the ballistics they publish must be analyzed with the barrel length they're testing in. Remington usually says 4" vented test barrel for revolver ammo. Their velocities in my experience will be within an expected small range of variation if you take their ammo and test it over a chronograph from a 4" revolver.

Data listed on a resellers website may be from their tests out of a pistol with a shorter barrel. One can generalize a loss or gain of about 50 fps for each 1" of barrel difference from a known length.

There are SAAMI standards indicating what is the maximum average pressures for standard ammo and for +P ammo. The manufacturers do not usually load to that maximum but somewhere below. For example, the maximum .38 spl standard pressure is 17,000 psi and .38 spl +P is 20,000 psi. Using Winchester .38 spl data for their powders, a load that they say is +P generating 17,100 psi sends a 158gr lead bullet out the muzzle of a 4" revolver at the exact velocity they list in their factory ammo ballistics for the same +P 158gr Lead bullet indicating that the pressures are likely quite similar and a long way from the maximum pressure level SAAMI recocnizes for a +P load.