For colder winter/fall increase powder load by 0.1 grain.
For hot summer days at Raton, NM reduce powder load by 0.1 grain.

To adjust your seater just prior to the competition:

Colder low pressure systems: turn in Weber breech seater rod (to shorten length) by 1/4 turn to see if it tightens. Do again to see if group gets tighter.

Hotter high pressure systems: turn out the Weber breech seater rod (to increase length) by 1/4 turn to see if group gets tighter. Do again to see if group gets tighter.

Each rifle needs to be assessed by testing to determine the correct adjustments needed to fine tune. And of course you need to figure out the correct powder load and specific breech depth to determine if you are close to the sweet spot before you can fine tune. You can use your adjustable seater to fine tune back to that sweet spot as temperature, relative humidity, and elevation change.

Great points Boats I also get on the Internet and look at the detailed weather predictions the night prior to and the morning of the match. 

In the Military Sniper Training handbook in regards to Humidity it is stated when the humidity goes up the impact goes down; when the humidity goes down the impact goes up. Since impact is affected by humidity, a 20 percent change in humidity equals about one minute as a rule of thumb.

I would assume if one has the ability to convert this information into velocity loss and velocity gain it could be helpful in regards to what direction the powder charge would need to be adjusted to help one stay in tune?

I might as well throw this into the pot while I am at it. One of the top bench rest shooters in this game told me that once you have your rifle sighted in for a no wind condition and assuming you have a scope that will not change its point of impact in transit or other wise it is simple matter of adjusting your powder charge the morning of a match until it impacts back into the previous setting which should have been the center of the 25 ring to be in the right tune.

After reading my own posting on the increase and decrease of the impact point with a change in humidity his method truly does makes since. Due to my never ending load development and the daily changes associated with it I have not been in a position to try his method. 

J.Louis

Jack,
I don't disagree with thoughs basics but, there will be times when the gun stops grouping well. Then you do have to at least try adjusting your powder charge to bring it back in and it's the easiest variable to deal with, too. Primers come next. 

I use fixed length BSer's so, I never have to worry about it getting out of adjustment. I've had that happen when I first started this game and it almost drove me crazy. I would mess with the breech seating last (assuming it shot well before) as a way to get a gun to come back in.

There are so many variables in the load and rifle that, the more you shoot, the more you learn about the basics and your rifle in particular.

Frank

Quote:

John, such a true statement!  Unfortunately, the majority of Schuetzen and BPCR shooters haven't read the books detailing the time and results that they wrote in the 1800's and early 1900's!
For instance, how familiar are folks with the works of Metford - Mann - Noble - Hudson and even Harry Pope to name a few?

I have followed this thread with great interest and was starting to feel like an egg. Then JackHughs comes along and hits the nail on the head. 
I feel like he does; I hardly ever change my powder charge, never my seating depth. If your gun shoots good and your group opens up it's because of the condition that you can't see. While you're pissin' around "tuning" your load the condition has come back to "normal" and you think you've done something. When my gun starts shooting badly I go have a sandwich.

When using my Hoch .32 Miller short, the cases are all preloaded with a wad on the powder.  Perty tough to change the powder charge. 

When reloading a single case I would change the powder charge if it got very hot out.  Doubt I would have time to do any fine tuning on a sighter target during a match.  From a clean barrel theres usually three to five shots on my sighter target. Then I go to record.  

                          Joe.