There are posts frequently saying that one powder gives better groups than another powder. If you load rounds with the same bullet and different powders to have exactly the same velocity how can the groups be different?
There must be something I don't understand, but it seems logical that if the muzzle velocity is the same and the bullet weight and shape are the same the groups should be the same. I can see how the pressure can be different depending on the volume of powder in the case, but if the muzzle velocity is constant the impact point should be the same.
The Sierra loading manual lists the weight of different powders to give the same velocity for the same bullet. Then they list the most accurate powder. How can that be? Since velocity is measured at the same point even the effects of acceleration are canceled out.
as I understand it..each powder is a diffrent recipe..much like Bread...while they may look the same, they are vastly diffrent. In powder while it may give same velocity, each powder burns at a diffrent rate. some faster, some slower. Imagine this, you load 3 powders so the velocity at 15 ft from the muzzle are the same...
First powder burns very fast, so fast all its powder is burnt in 1 millisec. the bullet has to travel the barrel length losing velocity the whole length. Its spin may be just a little less pronunced, affecting the accuracy.
Now powder 2 burns at 1/2 the speed of powder 1, now the bullet has substained "push" through 1/2 of the barrel. the bullet has a more stable velocity and more stable spin resulting in better accuracy.
The third powder burns at , yep you guessed it, 1/2 the speed of powder 2. now the bullet has a substained "push" through the whole barrel! the bullet exits at max velocity without having to fight friction from the barrel with out the powder pushing it.
now examine each bullet.. each started at diffrent velocitys from the chamber, due to diffrent powder dormulations.
#1 is already slowing to friction from the length of the barrel. Its inital velocity was the highest fron the chamber and starts slowing almost from the time it encounters the rifling in the barrel!
#2 is slowing some but not as fast as #1.. it had "push" through 1/2 the barrel. its flight will be longer and drop less over the same distance.
#3 exits the barrel and just then is beginning to slow to friction, since air has less drag than metal it will go further than either #1 or #2!
accuracy will depend on many factors..#1 may be more accurate at shorter ranges, and #3 at longer ranges.
while the velocity at 15 ft is the same the rate the bullet is shedding velocity is diffrent for each bullet! it all comes back to the powder "recipe"!
I may be wrong, if so others with more Knowlede and experience will step in and help us both understand this better!
I thought about rotational speed, but since it is directly related to velocity and the velocity is measured at the same distance from the muzzle with every powder the rotational speed will be the same at that point. It also seems logical to assume that acceleration or deceleration would have to be the same or the velocity would be higher or lower at the same distance from the muzzle.
Accuracy is affected by many variables: powder, bullet, primer, details of the gun configuration, the sighting aid, the rest you shoot off of, etc.. They all impact accuracy. But one is overwhelming: What the barrel does when presented with an explosion at its breech. Because it is a mechanical element with a certain mass it rings. Change the mass and it rings at a different frequency. Change how it is damped (how the furniture of the gun touches or does touch it) and the frequency changes. As the bullet leaves the barrel the barrel muzzle end is whipping about. Any change to any of the variables can change where the barrel is in space as the bullet leaves the barrel.
The idea of chasing accuracy by changing loads (bullet, power, primer, volume of powder) in effect is changing when the bullet exits the barrel and where the barrel is when the bullet leaves. Small variations in time from dead on center can create big difference in the bullet impact point because the barrel is at its greatest whipping velocity and highest acceleration or deceleration rate as it goes through the center position of the barrels motion. The most reliable accuracy results are produced when the barrel is at one extreme of position as the barrel has to stop to change directions. That is where you want the bullet to leave the barrel. We find that place by changing all the variables in an organized way to find the sweet spot. A product that helps in that regard is the adjustable position weight that Browning use to put on their barrel's muzzle. It actually worked but was a bit unsightly, at least to me. There is also a rubber donut sold for the same purpose that you adjust by sliding it on the barrel until you find the position that give best accuracy. It too works.
Different powders develop different ringing results for the barrel because the way the powder burns impacts the impulse of energy into the barrels motion. There is much more to accuracy than maintaining the same velocity of the bullet and that is why some powders are more accurate in some guns and not in others. The results for accuracy factories get with stout test barrels are only a measure of the test barrel accuracy, not necessarily the results you will get. Since their test equipment measures the pressure curve in real time they can analyze it and see if there are any problems with the burning of the powder. More complete less variable burning may mean that combo of bullet, powder, primer, load level is more stable and maybe that is their criteria for the possibility of achieving the best accuracy in your gun(??).
But it all comes down to trial and error for us to find the best combo for the best accuracy. The variables are numerous and we could test all possible combinations for years to find the best one so far. I try a few combinations and settle on the best of the tested ones. That way I can enjoy shooting instead of making it a job to find the best load for my gun. But we all get to choose what is fun and what is work. You may love the forever hunt for the best possible load for the best possible accuracy. I don't. Good enough is good enough for me.
The book "Rifle Accuracy Facts" by Vaughn is a scientific analysis of rifle accuracy with the aim to finding accuracy scientifically. The author was the supervisor of the Aeroballistics Division of the Sandia National Laboratories. It is a good read for those searching for the best accuracy understanding for a rifle with science as a background. He makes many hypothesis and tests to prove or disprove them.
A very good post LD, and dead on to boot! This is why bullet A shoots better in "your" rifle, than bullet B. Add in barometric pressure, tempreture, and humidity, and things change even more.
LD, thanks for that. It makes sense to me for the first time. I had not considered barrel harmonics, but I do know that certain harmonics in piping systems can cause catastrophic failures. I've seen pipe with a 2" thick wall whip back and forth like a rope so I can easily visualize a gun barrel doing the same thing.
In the book I referenced the author does some rather interesting tests, much much more than bedding etc.. He has the engineering background to do scientific instrumentation and to explain it in scientific terms. He goes down some blind alleys but learns from them. While some of his experiments might not be practical today to add to a gun, a gun designed around them might be awesome. In general, it is food for thought.
Amazon doesn't have it but some source that specializes in gun books may.
i do ladder tests for each powder i want to work up a load for.
for instance.
in my rem 700 30-06 using about 5 ( or more ) different powders.. i found imr 4064 at 46.5gr for my projectile gave me best groups.
varget ( forget the charge ).. was right on the heals.
I chose those 2 as i could do a lower charge and get better groupings. that is not to say i could not get good groupings with other powders. just i found i could use lower charges with 4064 and varget. lower charge = more relaodings per can of powder.
i don't chase velocity. i know some do. I chase accuracy and grouping.
it don't matter how fast it is if you miss. If you hit the bullseye.. even the minimum load / published velocity is fast enough! It isn't a race between you and another shooter to see which guys projectile hits the target the fastest from pulling the trigger at the same time. I do know htere are timed shooting events. but muzzle velocity is way low on the list of a time eater.. the human operating the gun is at the top of the list.
You may have to search out used book stores that handle gun books. If you can't find it maybe I can do a synopsis of the book for you. Copying it is forboten (copy write issues).
It is not a recipe for making a gun accurate but a study in things that impact accuracy. Some are applicable today and others are not practical today but may be in the future.
A more extensive search leads to a reference to Precision Shooting Magazine as the publisher, located at 222 McKee St, Manchester, Conn 06040. A little more searching leads to a phone number, 860-645-8776 for that address. And a bit more curiosity provides a picture of the building.
If someone who is not at work right now would like to call the number, I'd love to find out where to get the book.
You can go to the reading room of the Library of Congress and read it there. They say they have two copies. Too bad you can not access it via the internet as a .pdf file (even for a fee would be acceptable but no luck). My search turned up nothing too. It is a 14 year old book. I don't even know if Harold R Vaughn is still alive (??).
Here's a follow up question - I've been told that chrome lined barrels are inherently less accurate than non-lined barrels. Why is this? I would think the chrome lining would make the barrel stiffer and less prone to movement when a shot is fired.
Also no 2 rifles will react to your load the same-that's why asking for "pet loads" is really an exercise in futility but may help you when you tweak them.A good example-I have 2 consecutive serial# Savage 110FPs-both 1/10 bull barrels,same trigger and stock work.Both LOVE 168-180gr bullets BUT 1 will print 3/4" groups all day long using CT Ballistic Silvertips at 2500fps-other will print 2" will same load-it will print 3/4" at 2650fps with exact same load except for powder grs.One of my 6.5x06 loves IMR4350-the other loves H3841-pretty much identical bull barrel Mausers...I haven't found this in handguns,only rifles...I've been told chrome lining rifling doesn't contact rifling as well,but I don't know.
I think(!!) the reason chrome barrels are less accurate is because it is impossible to get a uniform thickness of chrome plated inside the barrel. The tight spots make the bullet fit loosely in the less tight spots.
I use to restore vintage MX race bikes. The fork tubes were usually rusted. The fix was to re-chrome them. But that was not enough. They were hard chromed then precision centerless ground to the right diameter. That's tough to do on barrel bores.
Chrome plating of barrel bores is done to ward off rusting in jungle or high humidity environments. Beyond that I think it has no other purpose. If it was an accuracy enhancer then Bench Rest shooters would do it but they NEVER do.
Also done because of corrosive primers. When you build a gun designed to be fixed by a peasant with a rock (AK), letting the bore rust away because said peasant did not clean it is not a good plan.
I've read that chrome plating made the barrels much easier to clean and also made them rust resistant. I wonder why they don't chrome the inside first then cut the lands and grooves? If they did it that way it would avoid the inconsistent diameter.
Also done because of corrosive primers. When you build a gun designed to be fixed by a peasant with a rock (AK), letting the bore rust away because said peasant did not clean it is not a good plan.
AR barrels are chrome lined today for US military use and the US military quit using corrosive primers in the early 1950's, long before there even was an AR. The stated military purpose is for jungle warfare to avoid the high humidity from corroding the bore. If you live in a humid environment then chrome lined barrels make sense. Otherwise a good steel like Chrome Moly steel is fine.
As for making the barrel bore chrome plated and then doing the rifling, Chrome is very hard and not that easy to machine other than by grinding. For a corrosion resistant bore the way to go is an all stainless steel barrel. Chrome is the main ingredient alloy metal that makes stainless steel corrosion resistant. Various additional amount of chrome in the stainless steel make the material increasingly more resistant to corrosion and less magnetic.
LDBennett
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