Changing light conditions.

[JeffinNZ]

Team.

Yesterday I was shooting my caplock MLer at 100m. The day was cold and heavily overcast. My group was looking very good for the first two shots and then as I loaded the 3rd round of the group the sun burst through and lit up the target like a Xmas tree. I grinned to myself and thought of the old local adage "light's up, sights up" and sure enough the next two rounds landed an inch apart but about 2.5 MOA low.'

Is a 2.5 MOA change in POI to be expected with such a large change in light using open, buckhorn style sights?

[44man]

Yes, imagine what it does at 500 meters. It is not your sights, it is the bending of light from the target to you and you do not see the target where it really is anymore.

[sundog]

That adage, Jeff, is more universal than local. Light up, sight up. Light down, sight down. Just as bad to contend with as boiling mirage. Maybe worse, as light changes can be VERY subtle.

[HeavyMetal]

When I worked for Millett for a short period of time in the early 80's we had a range day as part of the sales training.

During the range time the sales manager pulled out a piece of card board about 3' X 3' and used it to cast a shadow from several different angles across a shooter that was firing a Mini 14 with iron sights.

Sure enough he could move the group 3 or 4 inches in any direction he wanted by casting a shadow on the shooter from a specific direction.

I had known that light conditions would move groups but had never seen it demonstrated to this effect before, it was an eye opening for those in the group who had no idea.

It also suggested to me that if I wanted to hunt in darker woods with iron sights I should sight my rifle in under the same light conditions if possible.

[JeffinNZ]

Thanks guys. Just need reassuring. I was rather pleased that I predicted the results prior to the shot going down. Guess I have learned something after all.

[Echo]

The way I learned it, the sun pushes the group. Sight in in the morning, start the match, and if the sun goes behind a cloud, the group will move toward where the sun was...

[44man]

Light on sights does have an effect but it is in how you see the light gap and top alignment. It is the least problem and can be almost no problem if you blacken the sights. Shiny sights that glare are the worst.
A quality sight like a Micro, etc, just about stops it but a Ruger sight is bad. We tried for years to get Ruger to put better sights on their guns with no luck. The first flat top's had good sights.
We never had it bother us shooting IHMSA because we smoked sights, mirage and wind was nasty though.
Heat rising from the barrel was a problem.