Accuracy & Powder

[1_pointer]

I was wondering how powder affects accuracy? It is obvious to me how different bullet affect accuracy. The different construction etc. 'interacts' with the rifling differently and thus can change where the bullet goes (this is correct, right?). On the other hand, how does powder change where the bullet ends up. I can see how different powders can change the velocity of the bullet and therefore have an indirect effect on accuracy, but is that the only affect? Do the burning rates of different powders, given that the propel the bullet at the same velocity, change the harmonics of the barrel an thus change accuracy? Just wondering.

BTW- What would you suggest as a good(light) load for shooting 'yotes with a .338?

Thanks for any and all advice that you can give.

 

[Calif. Hunter]

Good questions, 1-pointer! I wish I knew all the answers. I "assume" that you are somewhat correct in your statement that the harmonics of the barrel are affected by the burning rates. Perhaps it also has to do with the rate of acceleration of the bullet, the rate of twist of the rifling and the uniformity of all the parts involved. If a rifle LIKES a certain powder, though, that is more important than the uniformity of the powder charges (within reason.) I don't know, honestly. In general, though, it often works out that certain calibers like certain powders. such as the .223's affinity for H-335, BLC-2 and IMR-4895. (There are always other powders that work well in a given rifle, but some powders just work well in some chamberings "almost" always. It's that "almost" part that keeps it interesting!)

When you consider all the factors involved in a shot being fired...it's amazing that we getit right as often as we do. The amount of heat or spark of the primer, the rate of ignition of the powder, the thickness of the brass, the space available in the catridge case for expansion, the amount (if any) of crimp, etc. all work together to create what we hope to be an accurate round.

 

[danr55]

Boy, did you launch a big canoe this time. There are three words that describe accuracy in load applications. CONSISTANCY, CONSISTANCY, and CONSISTANCY.

Your statement about barrel harmonics is more correct than you would think. Each time you pull the trigger on a live round, you start a controlled explosion. How well that explosion is controlled determines, in part, how accurate that load will be. The concisitancy of the pressure spike in the chamber will determine how well the rest of the components work together. Certain powders burn at different rates and create different amounts of pressure. As with any pressure problem, the more volume you have that is free, provided you are not working in a vaccuum, the better you can control the consistancy of the pressure rise. So compressed charges will tend to burn more consistantly than charges that leave a lot of room in the case. That also is partially the reason that some light charges of fast powder in heavy calibers can be extremely dangerous.
As the bullet travels down the barrel, the barrel will oscillate in an eliptical pattern counter to the twist of the rifling. The amount of control you have over the point in that arc where the bullet exits the muzzle will determine the accuracy of that load. The "sweet spot" load will cause the bullet to accelerate and the barrel to oscillate at the same rate each time. Different powders, like any pressure problem, will create different amounts of shock related to the expansion. Finding the one humms is the trick.
There are lots of things that will contribute to consistancy. Anything that relates to the pressure equation will effect the consistancy of the pressure rise. Rate is one of those contributors. Powder determines that rate.

 

[MLM]

Hi 1pointer, Heck I have had a good load go bad on me just by changing primers! Let alone powders, seating depth is another. Oh lord what a boat load we opened here! Then we can go into every rifle even the same make and cal. not shooting the same load as the other ones! They may be close but , I have yet to find one load that is good in every 223 I own! But we still keep trying , besides that is the fun part, we love to tinker.
Mike Murphy

 

[Nodak Hunter]

Here's a system I use to find a good load for about any suitable powder/bullet combo:

I load up "pressure testers", one cartridge for each load, starting at what I think will be 10% below max, and work my way up to, and a grain or two past estimated max, in .5 grain increments. They are al seated .030" off the lands. I fire them all at the same target, noting where each individual bullet strikes, and sketching the progress on a duplicat target at the bench as I go. I also log the velocities of each shot, and stop when I get to max velocity, or get high pressure signs.

Usually, there will be two or three shots that group close together. This gives me an idea of what charge the particular rifle "likes" for this powder. If the velocity is lower than what I deem necessary, I try another powder and do the same thing over. If the velocity readings are where I want them to be, I go back to the loading bench for phase II.

I now load up one cartridge for each charge between the high and low charges that grouped close together using .2 grain increments. I take these to the range, and do the same thing again. The two shots closest together are going to probably be the most accurate loads for the rifle, irregardless of seating depth. Time for phase III.

I load up six rounds each of the two loads that grouped closest together, and head for the range. I shoot two individual three shot groups with each load, and measure the average group size. The tighter one is now my "pet load", and will be the subject for future tweaking. This is when I can fiddle with seating depth, different primers, whatever.

It seems like a lot of work sitting here and reading it, but in reality it's worked more quickly for me than any other method I've tried. I think what I'm determining with this method is where the barrel position is closest to either 12 o'clock or 6 o'clock when the bullet exits. Those are usually the postions where the most consistency can be found for bullet placement.

 

[danr55]

Nodak makes an interesting point. He stated that 12 o'clock and 6 o'clock are the best for accuracy. I would think the 3 o'clock and 9 o'clock would be best since those are the smaller arcs in the elipse.

Guess I need to do some more research.

 

[Nodak Hunter]

Honestly, Dan, I don't really know at what position on the clock face a rifle shoots most consistently, but I read long ago some guy stating that 12 o'clock was the most desireable. The theory was that at 12, there was less chance of the barrel contacting the stock due to the barrel heating up, or the stock absorbing moisture.

I have no way to verify this, and am not particularly worried about it myself, since I can't see where the barrel is in it's movement when the bullet exits. I can only observe where the bullets land with certain powder charges, and adjust my loads accordingly.

 

[danr55]

Not intended as a rebuke buddy. You just made a statement that I had never given any thought to. It's one of those things that I just "Assumed". So now, you've given me a purpose again. I have something that I need to research and get an answer for. I can understand how that may be true for small arms in wood stock and it makes sense. I wonder about larger caliber weapons with no stock. Now I gotta go find out.

 

[GilaMonster]

All of the above affect accuracy. In my experience, a charge of powder that fills the case without excessive pressure will genarally generate the highest velocity and produce better accuracy from most rifles. There are many theories concerning why, and what to do if the results aren't to your liking. Remember most are just theories. The exception to the above would be rifles with extremely short barrels. In these cases, usually a faster burning propellant will create higher velocity and generally better accuracy because the slower propellant will not burn completely. The secret, in my experience, is matching the propellant with the barrel length. Thus larger volume cartridges require longer barrels in order to achieve good accuracy with the slower burning propellants. Now, everything else must be tuned properly to achieve the optimum performance from your firearm as was discussed above. I made part of my living building custom hunting rifles for 6 years and held an "ammunition manufacturing license" to build ammo for resale. I've been handloading (notice I didn't use the word "reloading") for over 25 years. This has been my experience, but I'm sure someone else will have something else to add. That's what is so great about handloading, it's like a big science experiment, and not everyone comes up with the same results. Mostly, everything is theory.
Load, Shoot, and Enjoy!
As far as exploding "yotes" with the wonderful 338, I would suggest one of the light X bullets available from Barnes with a charge of IMR 4064 or a powder in that general burning rate class. That's where I would start.

<FONT COLOR="#800080" SIZE="1">[ 07 November 2001 15:59: Message edited by: GilaMonster ]</font>