Can Outside Temperature Affect Cartridge Velocity?

by
posted on November 29, 2011
bs_2015_fs.jpg (21)

Can Temperature Affect Bullet Velocity and Point-of-Impact?

The Myth: Outside temperature does not affect the velocity of rifle cartridges, therefore point-of-impact remains the same regardless of temperatures.

The Expert Deferral: On page 241 of the NRA Fact Book, Mr. E. H. Harrison writes: "Temperature has a marked effect on both velocity and pressure. ... Especially does temperature affect pressure....The matter of temperature effect on velocity is simpler. For the IMR powders, each change of temperature of one degree Farenheit changes the muzzle velocity by 1.7 fps in the same direction. Thus, and increase in the temperature of the powder amounting to 20 Farenheit could be expected to increase theMV by 34 fps.

... It should be borne in mind that ammo exposed to the direct rays of the summer sun will reach a temperature much higher than that of the surrounding air. A temp withinthe ammunition of 130 Farenheit or even considerably more would not be unusual under such conditions.... Even worse is the condition within the baggage compartmentof an automobile, especially onof dark color, exposed to the desert sun of one of our southwestern states.

... It can be taken as a generalrule that factory ammo and moderate handloads will give no trouble due to temperature effects, if the ammo container is kept shielded from the direct rays of the sun."

The Practical Meaning: If you sight in your.243 Winchesterbefore deer season in 40-degree weather then go prairie dog hunting in the100-degree summer heatwhere your cartridges are exposed to the sun (reaching 130 degrees inside the cartridgecase), expect an increase of around 136 fps.

In a .243 Winchester 100-grain load thathas a MV of 2850, expect a point-of-impact shift of-2.5 inchesat 300 yards (From 14 inches low at 300 yards with a 100-yard zero to 11.5 inches low in the heat) when shooting at that prairie dog. *Note thatan outside temperature of 100 degreesalso plays a small role on velocity in terms of atmospheric pressure and that is factored above.

The Conclusion: The myth is busted. Extreme temperature changes to ammoDO effect velocity andtherefore point-of-impact. But for reasonable ranges atmoderate temperatures, huntersshouldn't be overly concerned.

Latest

What To Do When Elk Wont Respond To Calls Lead
What To Do When Elk Wont Respond To Calls Lead

What to Do When Elk Ignore Your Calls

Shooting a bull as it comes stomping to your calls is an adrenaline rush, surely, but you need to be ready for silence. Here’s how to work your calls on low or mute.

Conservation Policy Recommendations in Seventh Edition of Wildlife for the 21st Century

The American Wildlife Conservation Partners (AWCP)—comprised of the nation’s top 52 sporting-conservation organizations, including the NRA—released its Wildlife for the 21st Century, Volume VII (W-21) on Sept. 11.

Wisconsin Wolf Ends Opening Day Hunt

On Sept. 21, opening day, a group of young waterfowl hunters made their way to their blind in Wisconsin slightly before 4 a.m. Sunrise wasn’t due for more than two hours, but while they waited one of the young hunters in the group thought they heard a deer approaching.

Montana FWP Releases Final Statewide Grizzly Bear Management Plan

Montana Fish, Wildlife & Parks released the final Statewide Grizzly Bear Management Plan today, wrapping up an extensive public process analyzing how the state intends to manage the iconic species while it’s federally protected and after it is turned over to state management.

Review: Maven B.7 8x25 Binocular

The Maven B.7 is an ultra-compact, pocket-sized binocular that uses modern light transmission technology, phase correction and contrast, resulting in a very respectable optic in a concise package.

Review: CVA Cascade SR-80

The Cascade SR-80 is a versatile Scout Rifle designed for close-range, quick target acquisition hunting.

Interests



Get the best of American Hunter delivered to your inbox.