Thread: powder and accuraccy

Ive been wondering for a while why different powders affect accuracy? Or if its actually the powder or the velocity it drives the projectile at so more a velocity thing and not the actual powder?

There are many variables that can affect accuracy, one of which is barrel harmonics. These can vary according to the burning characteristics of the powder. The theoretically correct powder will start the bullet with an even push into the rifling, even acceleration through the barrel, and ceasing the effective burn just as the bullet reaches the muzzle. A slow powder in a short to medium barrel will have a high pressure exit and possibly affect the bullet as it leaves the muzzle in a blast of still burning powder. Similarly, too fast a powder will give the bullet a violent entry to the rifling which can cause partial stripping to the bullet jacket as it starts to turn. A rule of thumb is to select a powder that gives the best combination of high velocity and low pressure with the same bullet weight and barrel length as your rifle. This means have a broad selection of loading books or a lot of time on the web. There are a lot more variables that usually have more effect of accuracy than the powder, assuming you have selected one that suits your bullet/rifle barrel combination.

It will be the burn rate as well.
Anything that can affect the initial impluse of the powder going off in the chamber and how it burns going down the barrel in conjunction with each rifles inherent harmonics when using a particular projectile.
Back when I was a fitter/turner and machined things you might encounter a piece of steel that just machined horribly.
For whatever reason it turned like shit.
Slowed down, sped up, different tips, angles, cutting fluids, cut depth ( that could be a pain I it did it on a light finishing cut), bits of wood leveled against it from the lathe bed.
If you got the barrel equivalent of that it might only group with one out of a thousand loads and just be an arse with powders having very little change

Originally Posted by blip

Ive been wondering for a while why different powders affect accuracy? Or if its actually the powder or the velocity it drives the projectile at so more a velocity thing and not the actual powder?

In my experience ( no claim of expertise here ) it's a combination of factors including a chosen powder and everything has to come together to find an accurate load. It's where handloading experimentation come in. Choose the brass, a primer and a bullet, make loads with the chosen powder and by varying the charges, if the powder proves suitable, you might find accuracy nodes within certain velocity bands. I usually expect to find an accuracy node with quite to absolutely full cases. I'm happy if this gives me a correspondingly satisfactory velocity. With another powder you may not find any accuracy node/s at all but only by experimenting do you find out. But change the bullet ( brand or weight ) and you might find another powder altogether is the one giving acceptable accuracy and velocity. Possibly a change of brass might affect the load combination as well. I don't think different primers always make such a difference but sometime do.
If starting a load development from square one I use Reloading manuals as an initial reference to decide which powders to start with. I may or may not end up using one of those listed ( although often do ) but at least the info should indicate those powders most likely to give reasonably useful loads for the different bullet weights available.

Ok good info I haven't really done to much experimenting. Maybe I've been lucky and picked a powder that worked well first time round. So has anyone done a side by side test using same pill different powder but loads that give the same velocity? was there a difference in group size?

Originally Posted by blip

Ok good info I haven't really done to much experimenting. Maybe I've been lucky and picked a powder that worked well first time round. So has anyone done a side by side test using same pill different powder but loads that give the same velocity? was there a difference in group size?

Yes, that's roughly how I do initial load development when wanting to work up a completely new load. I can't find a pic I wanted to use to illustrate this. Basically though with a new load my brass, primer, bullet are all the same. The only difference is the range of powders chosen and the charges making up the ladder. Then I shoot all at 200 yards, the sequence being one shot from one powder and the next shot being the next powder, followed by the next powder etc. until coming around to starting the same sequence again but the next lot of charges up the ladder. Velocities differ but usually not vastly. If lucky I usually find at least one powder indication good accuracy potential ( all charges of that powder shooting something resembling a decent group ) while the remainder land randomly all over the target. Thus I narrow down to the powder/s I continue load development with until, hopefully, finding the load I decide to adopt.
Here's a pic showing great accuracy potential for a .243W load I worked up. This was shot over my bench at 200 yds, each shot being a different charge of RL17 which obviously the rifle loved in combination with that case / bullet / primer.
Sometimes too you just get lucky with a particular rifle. I have two ( Tikka 30.06, Tikka 300 Blaser Mag ) that seem accurate with just about any handload I shoot with them. Makes load development very easy. All my other rifles needed more trial and error to get there but paid off in the end.

That's funny, I'm currently playing with a couple of 243s as well. The powders I've got to play with are benchmark, cfe223, h1000, imr 4064 and varget. And pills in the 75-80gn range

Originally Posted by blip

That's funny, I'm currently playing with a couple of 243s as well. The powders I've got to play with are benchmark, cfe223, h1000, imr 4064 and varget. And pills in the 75-80gn range

I love the .243W cal so much I have two rifles. Just a fantastic cal to shoot and enjoy.
Good luck with your handloading. Hoping you find the "one" load that really performs for you.

Read up on barrel harmonics

Everything else is secondary to that

Originally Posted by blip

That's funny, I'm currently playing with a couple of 243s as well. The powders I've got to play with are benchmark, cfe223, h1000, imr 4064 and varget. And pills in the 75-80gn range

I played with IMR4064 and 95 grain Nosler ballistic tips, incredible combo in the 243. I put a load together as a curiosity and had 3 powder charges loaded up at 0.5 grain increments. Third group made a one whole group with 5 fps extreme spread. 2208 goes really well too, I ended up using it with Targex 105s, very consistent, very good accuracy. H1000 I couldn't get enough powder on the case, too bulky in my Starline brass.

Originally Posted by blip

Ive been wondering for a while why different powders affect accuracy? Or if its actually the powder or the velocity it drives the projectile at so more a velocity thing and not the actual powder?

I find that theory relates to barrel harmonics. The charge that means the bullet leaves the barrel when the pressure wave is at the other end of the barrel. Speed of the pressure wave vs speed of the bullet. Or something...

How are people comparing the accuracy of one load to another ?

Naturally, we arent mostly high skill bench rest shooters so an allowance for occasional or regular shooter error seems a good idea.
There will be a certain amount of random group to group variation in diameter even with good shot delivery, so a small difference just between two x 5 shot groups may not reflect the overall precision. eg if one group is 20mm and the other is 25mm it could be the other way round next time. So perhaps we need a series of 5 shot groups with each load and that will be better than a 10 shot group because that one bad shot will taint the longer string.

One indicator I look for is when the point of impact on the powder weight ladder doesnt change much over 1 or 2gr and then I can combine say 10 or 15 shots into big group as we saw on that yellow target of 3006 K above. At the least, this shows minor errors in powder weight wont affect short range precision.

For longer range, mv sd or es will give some prediction but other variables like bullet concentricity and set will be equally relevant in affecting the amount of moa degradation as the range increases.

I think the F distribution might be a tool to compare variance between two populations but havent had time (nor capacity) to work this through. Would be interested to hear what rules of thumb others are using.

Im a pretty average shot and dont have endless supplies of powder pills primers and time. Im fairly confident I can recognize a load that has potential. Ill initially load say 9 rounds and shoot 3x 3 shot groups on the one target letting the rifle cool right down between groups. I only do 3 shots as my rifles are mainly hunters so Im not going ro be shooting long strings with them. As its cooling ive usually got something else with me as well to play with while its cooling. If its minute of a4 i wont bother and go back to drawing board if not ill tweak one thing at a time and see what it does, usually powder first. I guess if a first load shoots 4" or under ill have a play with it. Im by no means an expert but thats what I do. I guess first of all I should really do a ladder test...

sometimes..if you dont own or use a chronograph its even more simple than that...you look in manual and pick a load just a little below book max (asuming your rifle has previously been happy at about that level) or at start level and work your way up till one group looks really good and then call it quits....sometimes if previous load levels in your knowledge bank that first load will be "good enough" for what you want to do with rifle.
accuracy is a personal thing....what one person finds acceptable would cause others nightmares.the range at which one enguages targets has a lot to do with this....with my older 7.62x39mm I knew I wouldnt fire it at game over 200 yards,as not enough power to do so ethically so any load inside 2" was plenty good enough...and it was.
for head shooting bunnies that would suck.....you need an inch group at that target at whatever range...so if can still hold inch at 200..200 is headshot maximum and body shots after that...a headshot at 200 yards is a spectacular thing.