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

 

[Dougfirtree]

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

Yeah, this is what I’d like to learn more about and get more comfortable with. And it’s more or less what I do, but it still helps to have confidence in where the window of safe powder charges is for the COAL you are using. Which is going to be different from the range in the published data that has a different COAL. So you can make an educated decision about what charge to start with. That was the crux of my question; whether there are formulas/rules of thumb for estimating that.

 

[Dougfirtree]

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

Or to say it more concisely, work up to pressure signs from where? And how did you determine that starting charge?

 

[Dougfirtree]

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

Yeah, this I understand. I’ve been reloading for years (though I genuinely appreciate the concern). I think I didn’t describe my question very well. See my responses to Brockel above.

 

[N2TRKYS]

I use Nosler’s tested COAL in their data. I always start at a grain or half a grain below their listed max charge. I have no idea the distance to my lands and do not care how far they are. I don’t do seating depth tests. I’ve never had a reason to. I also have zero desire to ever touch the lands with my seating depth.

Book COAL has always been very accurate for me across over a dozen rifles.

 

[brockel]

Or to say it more concisely, work up to pressure signs from where? And how did you determine that starting charge?

I do things different than most. I start 2 grains below max. Say book max says 60 grains. I load one at 58,59,60,61. If 61 doesn’t show pressure I’ll load one at 62. Then once I find pressure I back off a grain and load 3. If those 3 show potential I load 10 and see what it will do. I don’t play with seating depths or powder charges. If the load doesn’t shoot this way I switch powders or bullet. Just how I do things.

 

[sclancy27]

I just load to max mag length and start a grain or 2 under and work up.

So, if book max is 43 gr.

Load 2 @ 41, load 2 @ 41.5 etc. Until I get to 43 gr. I shoot them for a group. If the group is good and I find a velocity I like w/o pressure I load up a bunch and move on with my life.

 

[Drake4]

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

This

 

[Lasiocarpa]

Unless you first find pressure at a shorter COAL, and then jamb the bullet into the lands with the same load, you shouldn’t cause any pressure issues by altering your seating depth.

 

[grizzly63]

While it is true that I find most of my best loads near the max, not every rifle is the same. I tend to start in the middle of the powder ranges and work up .3 or .4 gr at a step. In my experience roughly 1 in 4 likes lower powder charges.

 

[Wolfshead]

I find my most accurate load, working up from usually around 20% below max, while checking for pressure signs. I’m too chicken to go over max charge by grains, usually moving in .2-.3 grain increments.
I usually start length around what the book says for COAL.
If my load then is accurate enough then I leave it alone. If I feel I can tighten up the groups a little then I measure my mag length and start working up towards that in like 0.010s and see if I can tighten them up.
Usually I’m able to get a good enough load out of book COAL.
One thing I do, do, is once I get an accurate load, I measure CBTO, and then use that as my measurement from that point on.

 

[Frequently Banned Troll]

I’m surprised to not hear of rifles blowing apart in folks faces more often ..

 

[Sheltowee]

I’m surprised to not hear of rifles blowing apart in folks faces more often ..

Local range at Fort Carson got stood down for a good while after some yahoo deconstructed a .338 Lapua next to his face.

For what it is worth, the only gun I've blown apart was a Glock shooting factory ammo.

 

[Alpine01]

As others have said, I don't get too concerned about COAL. I find where the bullet I am working with touches the lands and then back off 15 or 20 mils as my starting point. I will go 50 mils for monos. I start 2 grains below max recommended based on powder vendor and bullet vendor data then work up to max charge in 0.5-gr increments; loading 5 rounds at each level. I chrono every group, check for pressure signs, and evaluate group size to find a promising range to further refine, usually centered around one particular load. Then I will load another 5 groups that start 0.2-0.3 gr below and increase in 0.1-gr increments and repeat the velocity, group size and pressure signs testing. I have very rarely gone back to tweak how far off the lands I am (and thus COAL) unless I run into feeding/extraction issues during this testing. I also bump my shoulders back 2 mils during full-length resizing. Seems to work as I have several loads for my 308 and 7mm RM that are well under 1 MOA and are consistent over several hundred rounds at the final load variables. I find both of my rifles shoot best just under max book load. Just my $0.02.