What's your rule of thumb for changing COAL?

[Dougfirtree]

When you're working with load data that has a different COAL than you'd like to use, what's your rule of thumb for adjusting where you start with powder charges (or where max is apt to be)? In other words, if the load data is based on a 2.73" COAL and you'd like to use 2.8", how do you alter the powder charge for start/max loads? I feel like I'm generally able to look at different sources and make an educated guess about a safe place to start, but I'm wondering if you have a more concrete formula, etc?

 

[grizzly63]

Don't make it harder than it has to be. Start 10% below max and move up until you are happy with accuracy or you hit pressure signs. Make sure your mag and chamber will accept 2.8 first.

 

[Dougfirtree]

Don't make it harder than it has to be. Start 10% below max and move up until you are happy with accuracy or you hit pressure signs. Make sure your mag and chamber will accept 2.8 first.

Understood. But my question is, 'how do you determine what max is if you're changing the COAL from the data (since COAL affects pressure)?'

 

[cgasner1]

Understood. But my question is, 'how do you determine what max is if you're changing the COAL from the data (since COAL affects pressure)?'

Heavy or sticky bolt or sign on the back of the brass. You may wanna do some more reading or get someone that has some experience to give you a hand. It doesn’t take much of a bump to build a lot of pressure

 

[Chingon]

If going from 2.73 to 2.8 inches, I'd start at book max. But I live life on the spicy side. Safe answer is to drop one grain from max and work your way up in hot weather.

Edit - I would also not be doing this without knowing where the lands are. If you are pushing the bullet into the lands then you might have a bad day following internet advice.

 

[cgasner1]

If going from 2.73 to 2.8 inches, I'd start at book max. But I live life on the spicy side. Safe answer is to drop one grain from max and work your way up in hot weather.

Edit - I would also not be doing this without knowing where the lands are. If you are pushing the bullet into the lands then you might have a bad day following internet advice.

Even knowing where your lans are if your playing with these high bc bullets I’d recommend getting the tools to measure the o dive on the bullet and not just the tip so your getting a accurate measurement

 

[brockel]

I pay zero attention to book COAL. Kiss the lands and back off a tad or load to fit mag. Work up to pressure signs. Book data is just guidelines not rules