Rookie question, why the variance in data for same weight bullet?

CoronaCA · Monday at 6:16 PM

Hi all, so in my WSM I have always shot the Amax, 168gr, with 67.0 gr of IMR4350. The max in the Hornady manual for a 168 is 67.6, but in the Nosler manual it is 66.0 for their 168gr. I sure there are valid reasons, but maybe not. In short, why can't I use 67.0 for the 168 ABLR, which is what I was using for the Amax same weight. I will follow the manual for Nosler but just curious. Or do I start at say 65.0 and go up in .2 increments looking for pressure signs. Kinda new at the advance stuff, be nice! Nick

hunter24605 · Monday at 6:42 PM

Always start low and work up, to many variables for a loading manual to account for. The reason you see different max charges for similar weight bullets goes back to variables. Different H2O capacities in brass brands, lot to lot variations in the powder, etc. Two different bullets may be of similar weight and design, but there are differences in jacket materials, core hardness, different bearing surfaces lengths, all of which contribute to differences in pressure, some will reach peak pressure before others. Also each barrel is its own creature. Best practice is to follow the golden rule of start low , work up. Starting at or near max is a recipe for disaster. I had a tikka 270 WSM and it reached max around book starting loads. I never got it anywhere near a max load. I would bet most around here have a similar story.A chronograph is your best friend. Take your time, ask a lot of questions and you’ll be golden.

gerry · Monday at 9:11 PM

The above post covers it very well. Start low and work up watching for high pressure signs and you'll be good.

NYDAN · Tuesday at 4:43 AM

Hunter24605 has given you good advice. Other variables that contribute to variations between manuals include different lots of powder (which can vary by up to 10%), different primers (which have different brilliance), different C.O.A.L. Always start low and work up. As Hunter stated, a chronograph is an excellent tool to use for developing loads.

Personally, I don't intentionally keep going up until I see pressure signs. There is some correlation between pressure and velocity. That correlation between pressure and velocity is different from rifle to rifle. One rifle may reach maximum rated pressure at a lower velocity than another rifle. I generally figure that once I reach the top velocity for a book load, I have reached the maximum pressure I want to go to. For example, let's say that a book lists 2950 feet per second with bullet xyz and 65 grains of 123 powder. Once I see 2950 fps I stop going up even if I am only at 64 grains of powder. However, if I am only getting 2880 fps at 65 grains, AND I DON'T HAVE ANY PRESSURE SIGNS, I may go up in powder charge until I reach 2950 fps. However, I seldom do that since I often get excellent accuracy at loads less than maximum.

Good luck with finding a load for your rifle.

Aussie Wanderer · Tuesday at 5:18 AM

All barrels aren’t created equal and depending on the cartridge, some gain more from extra length. I know from my own experience, sometimes playing with a cartridge using similar weight projectiles and different powders creates a better understanding of how things work. Some really good advice above, but don’t be afraid to experiment within the bounds of safety.

DrMike · Tuesday at 7:24 AM

You have been given excellent advice. Tickling the dragon's tail in hopes of 25 fps more velocity is a game that can quickly lead to disaster. Data published by reputable powder/bullet manufacturers has been pressure tested in their firing system. Each change from that precise system introduces a potential change in chamber pressure and/or velocity. Ultimately, increased pressure will not mean increased velocity because the firing system begins to yield to the pressure.

Guy Miner · Tuesday at 8:03 AM

CoronaCA said:
Hi all, so in my WSM I have always shot the Amax, 168gr, with 67.0 gr of IMR4350. The max in the Hornady manual for a 168 is 67.6, but in the Nosler manual it is 66.0 for their 168gr. I sure there are valid reasons, but maybe not. In short, why can't I use 67.0 for the 168 ABLR, which is what I was using for the Amax same weight. I will follow the manual for Nosler but just curious. Or do I start at say 65.0 and go up in .2 increments looking for pressure signs. Kinda new at the advance stuff, be nice! Nick

It's a great question which I think most of us ask ourselves time to time.

Hunter24605 did a great job with the answer. There are a LOT of reasons why data differs from bullet to bullet, source to source.

I look at the loading manuals and published data as a guide. Be careful, enjoy crafting your own custom ammo and using it.

Merry Christmas! Guy

RL338 · Tuesday at 8:10 AM

hunter24605 said:
Always start low and work up, to many variables for a loading manual to account for. The reason you see different max charges for similar weight bullets goes back to variables. Different H2O capacities in brass brands, lot to lot variations in the powder, etc. Two different bullets may be of similar weight and design, but there are differences in jacket materials, core hardness, different bearing surfaces lengths, all of which contribute to differences in pressure, some will reach peak pressure before others. Also each barrel is its own creature. Best practice is to follow the golden rule of start low , work up. Starting at or near max is a recipe for disaster. I had a tikka 270 WSM and it reached max around book starting loads. I never got it anywhere near a max load. I would bet most around here have a similar story.A chronograph is your best friend. Take your time, ask a lot of questions and you’ll be golden.

This