choosing a powder charge?

[6.5marinediesel]

I tend to struggle with this every time I want to try new bullets or powder combo.[smilie=b: first reason the load manual doesnt have my exact bullet. or second the the data's not listing the same weight bullet i plan on loading. Then finally if the book list my weight of bullet and the powder i plan on using but the bullet composition is different from mine.

So id like to understand where you pick a safe starting point. Obviously i cant go by a burn rate charts if my powders not listed for the caliber.

Bullet... i get that you could use FMJ load data for cast bullets. but still dont understand how you find a starting point. but what if your bullet weights differ?

I recently got a good deal on the new shooters world powder, now their load data on line seems to be a bit of a contradiction if you deep dive it. or maybe im just thinking about it to much.

I have a bunch of 358-125RF cast bullets id like to load in .38 special.

If your load data only as 158gn LRN where would you start with a charge?
or if the load data has 125gn xtp, FMJ, or TMJ bullet again where to start?

I know this is practically basics if reloading. but im not into experimenting outside the book. but it seems that with whats available on the market and whats printed isn't always going to match.

thanks for any help/ knowledge its appreciated

[JSnover]

I look for the powder first. If you can't find load data for it and don't know where it is in the burn rate chart, get data from the manufacturer. Then you can start with whatever bullet is close to yours. Start near the low end and work up carefully.

[tazman]

JSnover is correct.
Also, it helps to have a chronograph available during testing. Since you have an idea what velocities you are looking for, the chrono will tell you when you get near the expected max velocity or if you have exceeded it.
It will also tell you how consistently your loads perform.

[dragon813gt]

As a note, XTP's have their own specific load data. Their bearing surface is different which is why their data is different. I do not use their data for anything else. If there is no data for the specific weight bullet you want to load then call the powder manufacturer. It's different if there are weights above and below what you have. It's easy to determine a starting charge in this scenario.

[GhostHawk]

Going UP in bullet weight causes increased pressure. So if I am looking at making a big change I start pretty low on the powder side.

Jacketed for lead swap I do not worry about as much. Lead slides down the bore easier, less drag, so lowered pressure not raised.

You do need to be careful and not lower certain rifle powders. IMR 4350 for example likes a full case. You could be setting yourself up for a problem by lowering it significantly.

4895 on the other hand is pretty tolerant.

Anytime I want to make changes I try to look for corroborating data. I may look at a similar caliber with similar case space to see what it does with a 20 grain increase in bullet size. Such data not to be taken as gospel for your caliber, more as a general trend. If you up bullet weight by 20% you probably need to drop powder charge by 20%

Reduce variables to the absolute minimum possible.

I always trust data from an established load manual over everything else.
When in doubt, buy another manual.
I recently spent double what it originally sold for to get a copy of the Lyyman cast boolit handbook #3 with all the Red Dot Recipes.

Worth every penny.

But even then when it says I can put 4.5 grains of Red Dot under a 125 grain cast boolit I do not jump straight to 4.5. I try 4, then 4.3, then 4.4.

Generally speaking one of the lower charges is going to be more accurate by far than the highest.