SIG SAUER P320 CO2 Air Pistol Muzzle Velocity Update

When we reviewed the SIG SAUER P320 CO2 air pistol recently, we were a little disappointed at the Muzzle Velocity achieved in the test. And so, it’s fair to say, was SIG SAUER.

The manufacturer claims “up to 430 FPS”. In the HAM test, we actually achieved an average of 347 FPS for a 10-shot string.

Now, Muzzle Velocity is not a very important factor for firearms replica air pistols like the SIG SAUER P320 CO2 air pistol. It’s not weighted highly in our test review scoring and around 350 FPS is actually plenty when shooting pellets, as this gun does.

But the question remains, why did the HAM test give FPS figures that were so far below that claimed by the manufacturer?

As it happens, I traveled to the SIG SAUER headquarters in New Hampshire recently and I took the SIG SAUER P320 CO2 air pistol we tested with me. (There will be a separate story about the visit in HAM quite soon). This gave us the opportunity for SIG specialists to inspect the pistol and for us to sit down together and understand what might have caused the difference.

What we found can be summarized as:

1. Differences in the pellet weighs used.
2. A minor issue with the gun itself.
3. Temperature difference in test environment.

If these factors are all taken into account, HAM’s calculations are that the SIG SAUER P320 CO2 air pistol tested by HAM will achieve the claimed 430 FPS Muzzle Velocity at a temperature of 88 degrees F, as follows:

347 FPS – HAM Test Muzzle Velocity

+ 20 FPS – Due to different pellets

+ 18 FPS – Due to minor valve issue

+ 1.7 FPS Per degree Fahrenheit due to test temperature effect

= 430 FPS – Manufacturer’s claimed Muzzle Velocity would be achieved at 88 degrees F

Here’s the details…

1. Difference in Pellet Weights.

SIG SAUER tests their ASP airguns – reasonably enough – using their own pellets. To be precise, using the SIG SAUER 5.25 Grain Match Ballistic Alloy Pellets.

Hard Air Magazine uses H&N Field Target Trophy Green 5.56 Grain alloy pellets as the lightest ones in our standard test suite.

In our original test review, the highest average Muzzle Velocity was 347 FPS for a 10-shot string using the Field Target Trophy Green 5.56 Grain pellets at 64 degrees F.

Shooting SIG 5.25 Grain pellets at the same temperature, 64 degrees F, gave an average of 367 FPS for a 10-shot string.
The pellets used for their performance claims by SIG are 0.31 Grains lighter than the lightest HAM test pellets. That’s about 6%. The difference in Muzzle Velocity was 20 FPS.

So, we have HAM Test Muzzle Velocity + 20 FPS.

2. Minor Issue With the Gun.

Once at SIG SAUER, the airgun team there determined pretty quickly that the SIG SAUER P320 CO2 air pistol tested by HAM was actually a pre-production model. Production guns have a very slight change to the valve.

SIG SAUER technicians swapped a new “production” valve into the HAM test gun and we tested again. The increase was 18 FPS with identical pellets and at the same temperature as before.

Here we have another + 18 FPS compared to the HAM test numbers.

3. Temperature Differences.

It’s long been known that all CO2-powered airguns shoot with different Muzzle Velocities at different ambient temperatures. Hotter means faster, at least until a phenomenon called “valve lock” occurs – generally somewhere above 90 degrees F.

In previous experiments with QB78-type air rifles, I had found that the difference due to temperature was 2 FPS per degree Farenheit. In other words, if a QB78 air rifle shoots 600 FPS at 65 degrees F, the same gun with the same pellets will shoot 640 FPS at 85 degrees F, PURELY DUE TO THE DIFFERENCE IN TEMPERATURE.

Obviously the same phenomenon would apply to CO2 air pistols such as the SIG SAUER P320 CO2 air pistol. The question is: how much?

So, I tested our SIG SAUER P320 CO2 air pistol with the same pellets and same valve but at two different temperatures: 62 degrees and 72 degrees. This difference of 10 degrees in ambient temperature caused an increase in Muzzle Velocity of 17 FPS.

Clearly this difference indicates that the Muzzle Velocity of the SIG SAUER P320 CO2 air pistol increases by 1.7 FPS per degree Farenheit. This equates very closely to the results I found in the past with CO2-powered air rifles.

This means that, had the HAM test been undertaken at a temperature of 88 degrees Fahrenheit, the Muzzle Velocity would have been just at the claimed 430 FPS.

The calculation for this is as follows:
88 – 62 degrees = 26 degrees difference. 26 x 1.7 = 44 FPS.

So that’s it! The numbers do substantiate the manufacturer’s claim for the SIG SAUER P320 CO2 air pistol. However, differences in test temperature, pellets used and a minor valve issue caused the much lower test FPS found in Hard Air Magazine testing.

SIG Sauer P320 CO2 Pistol, Metal Slide, Coyote Tan
SIG SAUER P320 Pellet Pistol, Coyote Tan