Does Temperature Affect POI?

[19 Turkeys]

Interesting read from Sierra Bullets.

Steve W.

[260 Striker]

Steve, Thanks for the link. Interesting read.
At our June match the temps were at 90 degrees or maybe a tick or two higher. Using the same load I have used for years in my 260 Striker I was hitting about two to three inches low on the turkeys and rams using my normal holds. I didn't know if it was me or just the conditions of the day but this article makes me suspect my ammo was shooting to a higher velocity and shooting lower at the farther targets. Something to remember for the next match on a hot day.

[Alvin]

Interesting article Steve. Thanks! I do remember competitors carrying insulated coolers at the Internationals in years past to keep their ammo cool. I have noticed a change in POI with my .22 rimfires due to heat at times.

[gibar]

I guess that no one here has noticed that powder companies ARE producing temperature insensitive powders(probably will never be 100%). Good article on this on accurateshooter.com. Scroll back on the daily bulletin topic. Article 8/24/16

[david bradshaw]

Interesting read from Sierra Bullets.

Steve W.

Steve,
Simple question. Beyond the obvious "Yes," difficult to answer. (Thanks for posting connection to the Sierra report.) In the early days of steel shooting, most firing lines were open to sun and rain. In the heat of summer, sun beating down, a barrel starts to heat on the first bank. At temperatures above 90-degrees fahrenheit, and especially at 100 degrees and above, the combustion-warmed barrel seems to hold the heat while targets are set. Some folk laid a damp towel over the barrel at the cease fire. Others directed a small battery powered fan at the opened action of a single shot. A few shooters covered revolvers with a damp towel. Most of us just prayed the scorching barrel would hold ZERO. The idea of the wet towel struck me as a good way the shrink the chilled side of the barrel.

Later, as stainless steel came in, I noticed that it heated more slowly than blue, yet took longer to cool off. This observation was later confirmed by Bill Ruger, Jr., during development of the .357 Maximum. We took a break one afternoon to pour forth with a pair of select fire Mini-14's. The blue was a AC-556K, with 13" barrel. "K" as a Ruger suffix denotes "kurtz," German for "short." The other was stainless, a KAC-556. "K" as a Ruger prefix denotes "stainless."

We shot both guns full auto, hot enough to where you had to hold 'em by the magazine and the trigger started to burn your finger. The stainless Mini 14 heated a bit more time to heat up, and considerably more time to cool down. Today, one could repeat that powder burning escapade with laser thermometer and note actual temperatures. As a footnote, while there were no malfunctions of any kind, we noted erosion of the flash hiders.

Optical rules of iron sight shooting apply to Point of Impact. The old rule of High Power marksmanship applies to handguns: "Sun high, shots high. Sun left, shots left." The sun tends to pull POI. The rule is not without confusion. Example: the sun is on your left, and it lights up the left wall of your rear sight notch. To even the light on both sides of the front sight, you unconsciously shift the blade towards the light----left. In this instance, sun on your right pushes POI left. To read a sight picture in the open is more difficult! Overall, bright sun will raise POI, while that big cloud passing overhead will depress your Point of Impact.

The pig @ 100 meters is the silhouetter's friend; the pig is the roadmap to sight adjustments for turkeys and rams. The rule applies big time for shooting a revolver in the wind.

As to actual POI shift caused by barrel heating, the individual gun trumps theory. The target is the final arbiter of accuracy, and to get there the first step is a consistent sight picture.
David Bradshaw