Is FPS change always linear?

[Webster]

Mostly.

Mostly.

My testing shows a strong linear relationship. For example, the chart below, with each test shot being .4gr higher than the last. This is single-shot data and would be smoother with multiple shots averaged at a given charge weight. I've done multiple tests like this with rifles, different powders, always linear. Don't know about handguns.

View attachment 1709898

Having said that, I'm told that the curve will flatten near the top of the permissible charge weight. I don't push things high enough to see that.

A chart like that looks a lot different if you plot five shots at charge. Plot each shot not an average. I don't care what charts look like. As long as the groups are round and small I am happy.

 

[Oldbloke]

Mostly.

Mostly.

My testing shows a strong linear relationship. For example, the chart below, with each test shot being .4gr higher than the last. This is single-shot data and would be smoother with multiple shots averaged at a given charge weight. I've done multiple tests like this with rifles, different powders, always linear. Don't know about handguns.

View attachment 1709898

Having said that, I'm told that the curve will flatten near the top of the permissible charge weight. I don't push things high enough to see that.

Yep, close enough to linear. More data would provide a better graph. Those bumps could simply the result of variations such as case capacity or powder charge discrepancies.