Comments on: Sierra Test Reveals How Velocity Varies with Ammo Temperature

By: Aziz

Aziz — Fri, 09 Sep 2016 09:58:15 +0000

Thank you. Your explanation makes sense. I’ve noticed it myself during load development but could not figure out why faster velocities sometimes printed lower. Now I know.

By: Kester B Rice

Kester B Rice — Thu, 08 Sep 2016 20:20:03 +0000

Changing the velocity of a round changes the time that the bullet leaves the muzzle (barrel time). So the faster round left the muzzle when the barrel harmonics had the muzzle at a lower point in its cycle of vibrations. That is why a faster round would shoot lower. You can change the point of impact of a round by changing bullets and powders but keeping the same velocity due to changes in barrel times.

By: Aziz

Aziz — Sat, 27 Aug 2016 11:27:30 +0000

What I found really interesting (and a little confusing) is that the fastest ammo printed lower than the rest – how did that happen? Wouldn’t the POI at a given distance shift upwards as the velocity increased?

By: Neil

Neil — Thu, 25 Aug 2016 12:23:50 +0000

Temperature testing of ammunition is standard military practice. Normally, for NATO countries, in three zones: -40C, +21C and +63C (-40F, +70F +145F). The average velocity (well pressure really) in each region used in the various ballistic tables and fire control systems.

By: Jim Miller

Jim Miller — Thu, 25 Aug 2016 12:03:49 +0000

Excellent test. I think this is of value considering so many venues, competition take place in the summer. We’ve all learned to protect our ammunition from heat. The problem is during competition keeping ammunition at a specific temperature range is most unlikely.
Maybe the real value is testing your specific load and realizing the impact the choice of powder makes.