A technical loading question from a new reloader.

[bill_k_lopez]

I'm trying to load some 300gr JHP bullets that I came across, but looking through the manuals got me scratching my head...


According to my Modern Reloading:

240 Grain Jacketed Bullet
ACCUR #9 Start:19.1 MAX:21.3 FPS:1500 PRS:40000 CUP

300 Grain Jacketed Bullet
ACCUR #9 Start:17.1 MAX:19.0 FPS:1257 PRS:40000 CUP

According to this, less powder can push a heavier projectile ALMOST as efficiently as it can a lighter one? Why are the max loads for a lighter projectile higher than a heavier one? My assumption is this has something to do with pressure and case size, am I at least on the right track??

Someone help me understand this better.

I also have a follow up question for this too - why are there are so few powder options for the heavier projectiles but many of those that support the heavier ones also have load data for much lighter projectiles???

Thanks.

[Bill Steele]

As you go up in bullet weight, everything else being equal you need to go down in powder to keep pressures equal. In this case, you will also usually go down in velocity, again everything else being equal.

Usually you will find less published loads for bullet types that fall outside the mainstream of use for a given caliber. That doesn't mean less powders will work, just less have been tested and published.

[G-forceJunkie]

When you change the weight of the projectile, your changing several other variables such as how much pressure has to build to to get the bullet moving, the speed at which it accelerates, the volume of space the powder is burning in, etc. This changes how fast the pressure builds up, and how long it is in the barrel. A lighter bullet will get moving forward, sooner and faster, increasing the volume of the case and barrel faster, so it takes more powder to get up to pressure in that amount of time.

[Sub95]

As you go up in bullet weight, everything else being equal you need to go with a slower powder to keep pressures equal.

Usually you will find less published loads for bullet types that fall outside the mainstream of use for a given caliber. That doesn't mean less powders will work, just less have been tested and published.

see bold.

if you used a faster powder with a heavy bullet you could have it blow up in the gun.

here is a chart to understand fast in slow powders

http://www.hodgdon.com/burn-rate.html

[sargenv]

Someone help me understand this better

This is the main reason why I tell people to get one or two good reloading books.. This question is detailed completely in several of the good manuals.. Speer, Sierra, Hornady, and the like. There is much to be learned from the loading manuals that is not really covered on even these forums.. I tend to use these forums as a secondary source.. more about "what has been your experience" as opposed to the only source for knowledge.. Please don't take it as belittling or anything like that, since this is merely advice I followed when I asked a more experienced reloader when I was just starting out.

[Bill Steele]

see bold.

if you used a faster powder with a heavy bullet you could have it blow up in the gun.

here is a chart to understand fast in slow powders

http://www.hodgdon.com/burn-rate.html

You misunderstood my post, my point was with the same powder you needed to go down in powder weight when using a heavier bullet, he was talking about published loads, with a single powder type.

[bill_k_lopez]

This is the main reason why I tell people to get one or two good reloading books.. This question is detailed completely in several of the good manuals.. Speer, Sierra, Hornady, and the like. There is much to be learned from the loading manuals that is not really covered on even these forums.. I tend to use these forums as a secondary source.. more about "what has been your experience" as opposed to the only source for knowledge.. Please don't take it as belittling or anything like that, since this is merely advice I followed when I asked a more experienced reloader when I was just starting out.

As a VERY new reloader, I only load 1 weight projectiles, with 1 kind of powder measured at the same weight within the VERY safe lower end of the minimum specifications. How my questions came about, was I found these projectiles in some of my dad's old stuff and thought this was a good opportunity to kind of expand my limited knowledge of reloading. Since I've only really looked at the 240grain projectile load specs, I just figured that there is that kind of data for all weight projectiles - but as I looked up the 300s I realized that the higher you go, the less powder options were listed. Also I compared those same powder options with the lower weight projectiles and the numbers didn't make sense to me.

I do have a little better understanding now - and I was thinking on the right track with the idea of it being pressure related. I am going to do some more reading on slow and fast burning powders, and will probably wait before loading up some of these 300s.

Thanks for your response.