Muzzle Velocity and Powder Choice

[BJung]

I recently thought of Nodes and Powder Choice but have no experience with it. Has anyone switched powders for a specific firearm with the same other components and discovered that the new pet load has the same muzzle velocity? I'm thinking that like a tuning for with the same strike, the powder will find the same Node based upon the firearms construction. If true, then person can find new petload with a different powder sooner if they have a chronograph.

[Bart B.]

Nope, never done that. While different powders may produce the same velocity, barrel time is typically different. The bullets will leave about a different place on the bore axis angle as it whips vertically that may not shoot slower ones at higher angles than faster ones.

Bullets should leave on the bore axis up swing at the correct angles to compensate for bullet drop at target range.

[kilotanker22]

Reloader 16 and H-4350 give me the same velocity with the same powder charge when using the same components in one of my creedmoor rifles. Although Bart's message definitely rings true. I have a point of impact shifts when switching between the two loads

[BJung]

Thanks. Very interesting ( to me )

[hounddawg]

if what you are asking is if certain bullets appear to like a certain muzzle velocity then yes. The thread I am doing on the 80 Berger shows the groups tightening up at around 3010 FPS with my best group so far at 3110 and the best group so far at 3139 FPS. My research on this bullet showed me that other shooters had success at 3150 FPS using VV N135 and Federal 205M's. Different primer, powder, and twist barrel twist rate but the groups tightened at about the same FPS. I am using IMR 8208 XBR and CCI 450's to get there. The 8208 is a tad faster than the N135 so weight wise I need just a touch more than I would N 135 to get to 3150

[BJung]

No, this is not what I was asking but I have been curious about what you are researching. For example, I recently found a pet load for my .357mag using Blue Dot and it was the same as the pet load other Shooters recommended. I've been reading the standard muzzle velocity for the SKS and have wondered if my pet loads for three different bullets (Speer, Barnes, and Hornady) with the same powder will have the same muzzle velocity and the muzzle velocity the standard military round was designed for. I will know when I make the test.

Thanks for mentioning your research.

[Bart B.]

Although different powders will have different burn rates and charge weights can be adjusted to produce the same muzzle velocity for a given bullet, barrel time across all will not be the name.

The barrel muzzle axis will vibrate at the same frequency for all powders, but bullets will leave at different angles. The difference can be fractions of an inch at 100 yards.

If two identical bullets shot from a 308 Winchester at the same angle have a 50 fps difference in muzzle velocity, the slower one will strike about 1/10th inch lower than the faster one at 100 yards.

I don't think the smallest few-shot group for a given charge weight best represents the accuracy one can count on. It's near impossible to repeat. Remember you do your part for every group you and your stuff shoots.

[BJung]

Bart. Can you clarify your last statement. I don't quite understand what you meant. To me, you're stating that you might find a load that makes a small group but it can't be repeated because of the Shooter.

Your first comment sounds like the results of the earlier research conducted with the Barnes bullets . To add, test loads with different powders, producing the same muzzle velocity can find the same Node, yes?

I was looking at an old target last night and was comparing prints and muzzle velocity that identified the Nodes of my rifle to the Ken Waters' pet load using the same model rifle and cartridge size as mines. I'm using R22 and he was using H4831. Same bullet. I was astonished to discover that the muzzle velocity of one of those bullets that fell in that Node was 1 fps different from his pet load! Maybe it's luck. I don't really want to conclusively believe it and will make a retest. But-as most of us might agree-the journey is as satisfying as the result.

[Unclenick]

In principle, when you load several powders to the same velocity, the fastest burning powder will produce the shortest barrel time, while the slowest burning powder will produce the longest barrel time. This is because, when producing the same velocity, these loads are producing the same muzzle energy. When the same muzzle energy is produced for the same amount of bullet travel distance down the barrel, the average force against the base of the bullet had to be the same for the whole trip. A fast powder gets to that average with a higher peak pressure and lower muzzle pressure than the other powders produce. The slow powder gets to that average with a lower peak and higher muzzle pressure than the other powders. Compared to slower powders, the higher peak of the fasted poweder increases acceleration closer to the breech end of the barrel, while the lower pressure approaching the muzzle adds less acceleration, so a bigger portion of the final velocity was picked up nearer the breech end causing the bullet to start out faster down the rest of the barrel, shortening the time it takes to reach the muzzle.

As Bart explained, that will change where the muzzle deflection phase is, and a change not only in group size but in POI typically accompanies the powder change.

If you are lucky, you may find a load that works well in a number of different barrel lengths, and with the different muzzle velocities and barrel times those different barrel lengths produce. This can happen if the change in barrel time for a load and the change in barrel length happen to coincide with the resulting change in barrel bending and deflection phase. This seems to be the case with Federal GM308M ammunition, as an example. It is what Dan Newberry calls a "chocolate ice cream load", the name being premised on the idea everyone likes choclate ice cream. You might be interested to read his pages.

[BJung]

I could be wrong but I try to envision the barrel whipping around like a wet noodle caused by the pressure behind the bullet. I envision a fast burning powder creating a bulge at the receiver than the barrel whipping around until the bullet leaves the muzzle. Then, there's the slower burning powder that creates a bulge throughout the length of the barrel and a less violent whip. If I am correct, while there is a climb in printed bullets as the powder load increases, the faster burning powder prints a larger pattern than the slower burning powder. I have not experimented enough to notice this but have you?

I once read that a barrel whips around in a figure 8 pattern. If so, than the faster burning powder would create a larger figure 8 as the whip is more violent and the slower burning powder creates a smaller figure 8..

[BJung]

btw. Thanks for the homework guys.

[Bart B.]

Originally Posted by burbank_jung

I once read that a barrel whips around in a figure 8 pattern. If so, than the faster burning powder would create a larger figure 8 as the whip is more violent and the slower burning powder creates a smaller figure 8..

Barrel dynamics

https://www.varmintal.com/amode.htm

There's other vibration links on the shooting home page above this one.

A slower burning powder creates a smaller figure 8 of the muzzle axis? Gotta look that up.

Most of the barrel vibrations are in the vertical plane. It's caused by the recoil force centered on the barrel axis that's above the rifle's center of mass. It's line of fire relative to the line of sight is also effected by how we hold the rifle evidenced by the fact that several people shooting the same rifle and ammo will have different zeros on the sights. I've seen a 2 MOA spread across 4 people shooting the same 30 caliber magnum in team matches. No wonder those tiny groups shot in benchrest disciplines are made with free recoiling rifles resting on bags untouched by humans except for a finger on their 2 ounce trigger.

When we shoulder a rifle resting on bags atop a bench as we grip it with our hands to shoot a group downrange, that group's size reflects how much we change the rifle and ammo's inherent accuracy. There's no guarantee the smallest groups are solely due to the rifle and ammo's precision. Same thing about the largest groups.

[BJung]

Uncle Nick. I started reading Dan Newberry's page. That made me sad. I thought I had everything dialed out using the ladder tests.

Here's a question. I found old targets from over 10 years ago using the ladder test. The Node found from the ladder test by using a horizontal line drawn across to find the optimal load was very close or in the same range as Ken Waters' Pet Loads. However, I will add that the POI of the two or three consecutive charges that were horizontal were close. Maybe this is the OCW?

I'll try a different way. I'll shoot three ladder tests at one large target. I'll use bingo marker dots to record each string with a different colors. I poke the holes with the marker. Bingo markers are at the dollar store. After the string, the load with the best cluster is the OCW, right? If they are on a horizontal line. Even better!

[Bart B.]

Here's pressure curves for two different powder burn rates:

https://images.app.goo.gl/ryFc5bfKrKrKBawLA

[Bart B.]

Originally Posted by burbank_jung

Bart. Can you clarify your last statement. I don't quite understand what you meant. To me, you're stating that you might find a load that makes a small group but it can't be repeated because of the Shooter.

It's seldom repeated because of all the variables.

The odds of repeating a few-shot smallest group are slim. All the variables in ammo, rifle and human will occasionally add up producing a huge group. Or they'll cancel each other out and produce a tiny group. All the others fall in between. Single groups of at least 20 shots start having a 90% probability of representing what all shots of the next few hundred will group. They typically get larger as the barrel wears out.

Once you've shot a tiny group, shoot 5 more with the same ammo and shot count.

Ever seen the group size spread across several made by a shooter in a benchrest match? Compare the warmup groups to the match groups for a few different people. Which ones are smallest? Largest?

https://internationalbenchrest.com/r...-match-results