I know case capacity,and bullet weight/ length play parts in powder burn rate desired as well as rifle twist. What I have trouble with is when to go faster or slower in burn rate when I don't get the results I want. I didn't have this trouble before I got online and started seeing guys use powders that might not normally be recommended for a certain cartridge.Or guys twisting the very last bit of speed or accuracy. I guess so many newer powders has not helped things either.

Let me give a couple of my examples. First up is my new .270WSM.

I am getting sub MOA groups with H4831sc and Nosler 140 grain NBT's but not at max loadings so not at top velocity. Now I know there are several powders both faster and slower known to work for this cartridge but do I go slower or faster? Are there rules so to speak or just flip a coin?

Don't get me wrong I don't need max velocity I am just trying to learn how to decide what way to go if that is my goal.

Another example is my .257AI. So many ppl said R22 was their go to powder for the .257 and .257AI especially with heavy bullets. I got no accuracy with R22 or other slow powders. My sweet load came with IMR 4895.

Again I know every barrel is different but everyone has to have an idea what way they want to go next. I am hoping that I gain something here other than the SWAG system.

I generally tinker with Quickload to find the powder I want to use...I look for the powder that gives me over 90% fill ratio and over 95% powder burn and I go from there....generally loads that fill the case and burn the powder completely are very accurate. Within reason I'm not concerned with velocity at all, I want accurate first and fast second....I don't shoot over 200 yds so it's not a priority for me.

Guess that works if you have Quickload. However I do not.

I never think of burn rate, I have paid for manuals so experts could make that decision for me. If it looks good in the book data, I will try it.

Prior to Quickload I tried to follow the same criteria using my manual....I looked for the powder that used the most...that will give you the best fill ratio in most cases....I'm a fan of compressed loads.

Powders like Varget in 223 where you here that nice crunch with a load are the ones I like the best...no worry of double charges, no worrying about powder position in the case,....

I like loads that are slightly compressed for my rifles. If I load to this density and don't hit the targeted velocity that I'm looking for I will step down to the next faster burning powder to see if it will meet my expectations for velocity and accuracy.

When I hunt is very wide open and velocity is a friend, tempered with accuracy, to get flatter bullet flights that end up hitting more stuff.

Normally, I like powder charges that fill or nearly fill the case. If a max charge is a compressed powder charge, I will take that too, but they don't HAVE to be compressed. I will usually start with one of my "preferred" powders for a similar case size and shape. For many years, I would use whatever powder was the absolute best for each given cartridge, no matter how small the difference was. That lead to me having 20-30 different powders in my inventory at all times. I have since started trying to combine cartridges to shoot the same powder. It doesn't always work that way, in that some of my rifles have been flat stubborn, and want what they want, but I have managed to overlap several cartridges to use the same powder. Easier for me. Those that do overlap, and volume warrants, I buy 8 pounders instead of 1 pounders to save some $ on components.

For my belted magnums, my first powder of choice is always IMR 4350. If I can get that to work, great. If not I keep moving on. Case in point, my 338 win mag, and 375 H&H both use this powder. When I got my 257 Wby mag, it would not shoot this powder successfully with the bullet I wanted to use. So that rifle gets RL-22. I tried RL-25 in it, but it didn't shoot as good a groups. Others have the opposite experience with those 2 RL powders. Go figure. I also use IMR 4350 in my 30-06 hunting load. I use W-760 in my 308 and my 243. I use BL-C2 (the last of my old milsurp stash-almost gone) in my 223, but when it runs out I will go to H-380 and I use that in my 22-250 as well. I use H-4831sc in my 6.5x284, and nothing else I shoot seems to like that powder over another, but the 243 is close. I use IMR 4064 in my 257 AI, 257 Rob, and my 375 JDJ.

Not sure if that's any help at all. If I was starting off dry, with no powders, I would look for a powder that fills, or very nearly fills the case and comes with max velocity at max pressure in my load data book. It is at least a starting point. Play with seating depth and primers also. Try several different bullets normally before abandoning your "try" powder for another. Then start over again with new powder.

I have several rifles with "sweet loads" that are not near "max" pressure. That happens too, and most of the time, I'm more concerned with max accuracy, then max velocity.

Thank you for the answers so far. So far I am pretty much on the same path as you guys except in the fact I have to buy some slower powders. This .270WSM is only my second "magnum" the other being a .300 Winny. It shot 165 grain bullets great with IMR4350. When I went to 180 grain bullets I had to move to H4831sc and then tried R22 because so many recommended it. Looks like I need some of the newer slower powders and Retumbo looks like it will be what I try first. I really try to stick with IMR and Hodgdon powder if possible. No reason just what I started with.

As far as the 257AI try H-414 powder.

Ive usually had pretty good luck going with what is generally accepted as an appropriate powder (burn rate) and comes close to filling the case. Im not a big fan of compressed loads, but they dont bother me either and I like half full loads much less.

I started with my 257 AI with IMR 4350 and the results were such that Ive just ran with it, I would like to try a couple slightly slower powders though. I find it rather bizzare that your pet in that caliber is with such a fast powder..

Someone opined in another recent thread that there are generally two schools of thought in reloading. One reaches for top velocity 1st and accuracy 2nd whilst the other says damn the velocity and and considers accuracy paramount.. I expect this is somewhat true and also has a bearing on powder selection. Naturally most of us building a hunting load want it all..

Sometimes I simply try what happens to be on my shelf at the time that seems a suitable powder. For instance I have a couple lbs of old Rlr 12 that needs a home so Im going to try some practice loads with it for my 358 and see what happens..

Another consideration that fits in the picture somewhere is the barrel itself in regards to dimensions. A heavier "bull" type barrel is usually not as susceptable to "bad vibrations" (hormonics) and thermal changes. A slender-skinny barrel tends to have problems with all of the above. The heavier barrels will tend to be less finicky. With lighter thinner barrels it is anybody's guess. In my limited experiences the faster powders in relation to bore - capacity tend to upset these vibrations a bit more often. They are a bit more violent at ignition and lift off time so to speak.

The reason I mention this is (as has been posted several times before) I have a 7X57 in a Rem. 700 Mountain rifle. It has a very thin 22" "coach-whip" type barrel. Many here at AR forums suggest powders in burn rate of H-414/W760 for the little 7mm. I started with those powders and had less than acceptable results. At best, accuracy was fair with good velocity at 100 yds. and poor to terrible accuracy at 200 yards. Long story short I ended up with 50 gr. of RL-19 behind 150 gr. bullets. The barrel had other issues as I have posted on the G-Smithing forum but the slower RL-19 powder seems to have balanced the barrel out the best. Even before having the barrel handlapped I was getting great TO fair and acceptable accuracy at both 100 and 200 yards more often than not along with 2650+/- vel. @ the muzzle.

IMHO, (keeping in mind bore size to capacity of case) in a lighter and thinner and/or longer barrel, a slower powder should be tried. In a stockier fatter barrel it probably won't matter that much.
But as they say; Never say Never.

Each rifle has it's range of powders that are suitable. Faster burning powder is usually giving better velocity with lighter bullets. Slower burning powder usually gives better velocity with heavier bullets.

I tend to stick with powders not so bad for velocity loss when the temp drops. I pick a bullet weight then look for book data for both heavier and lighter bullets than I am trying to load.

I want some margin each side of my load. I work up for best accuracy and will not settle for less than MOA (inch groups).

If I get all those things together I have a load to hunt with and it's good for 300 yards more or less and from 70 F down to minus 20 F.

I discovered this little known fact many moons ago.
If a single base powder didn't perform in either accuracy or velocity, I would look to a similar burn rate double base powder, 9 times out of 10 it would give all the desired results that the single base powder failed to achieve.

I would also start with the powder that the load data indicated was giving the highest velocity, whether it was single or double base.

Now I go to the double base powders first up and, I include powders of a slower burn rate than what might be recommended in most manuals, this has worked out for me in most of rifles that may be slightly 'overbore', which in this day and age is a meaningless term really, with all the ultra slow powders available to us.

BTW, I would definitely give W760/H414 a go in your 257Ackley, you might just be surprised at the velocity this powder will give you!

Cheers.

Well, I don't have QL but I do have a rather large library of load books. And the rule of thumb I was given when I first started reloading was to start with a powder that gives good performance and spans several bullet weights in it's utility. If you don't get your desired results you can change bullet weights or makers. If your results are still unsatisfactory, you can try faster and slower powders that have the potential of giving you the performance window you're looking for. This is why reloaders have so many half cans of powder sitting around.
I don't think there is any "rule" about going to a faster or slower powder to get where you want to go.