Accuracy: fast burning powder vs slow burning powder

[243winxb]

The powder that has the closest to 100% burn rate, before the bullet exits the muzzle, may be the most accurate.
My guess.

 

[jelenko]

But, that's not always the powder that has a high fill ratio.

 

[357Mag]

All -

Howdy !

Ballistician Homer Powley has told us....

Recoil
" The peak pressure [ in a rifle ] is expressed in pounds per square inch. Multiply the pressure by the area of the bore to find the force, in pounds exerted on the bullet and the gun in opposite directions.

This peak force is reached in an ordinary rifle approximately 600-800 micro-seconds after burning begins and lasts only a few micro-seconds. A micro-second is one-millionth of a second. Meanwhile the gun has recoiled only something like 1/16" inch during the time required for the pressure to reach its peak. "

With normal loads only about 99% of the powder burns inside the gun and the rest goes out of the muzzle in the form of splinters; you can tell them when you find them. All of the powder that is going to burn has done so at the place of peak pressure which is only a few inches in front of the chamber."

The above comments by Powley were found in his " Powley Papers " that were printed in the " Guns & Ammo 1974 Annual ". Mr. Powley included lots of other data, and graphs for things like " Peak Acceleration in a 10 lb gun " ( example ). Too much for me to pass along, especially his math formulas that featured special symbols/ characters. The point of peak pressure can be calculated.

With regards,
357Mag

 

[SeabeeKen]

I had a Savage 110 in 243 that shot single hole groups with a Hornady 100 interlock and 35.5 gr Of IMR-3031. It loved that load and took countless deer. Case fill was about 75-80% but it sure was accurate

 

[dellet]

Way to many variables to have anything more than a general statement, that will only be true sometimes.

Bore size, bullet weight and case capacity will change your "truth"

In 22 K Hornet or 218 Bee I will argue that 1680 is more accurate than 296 or Lil’gun at the same velocities, but often different “nodes” with the “slower” powder creating a load that exits the barrel sooner.

With 300 BLK, I will argue that faster powders for bullets under 150 grains are more accurate, and slower powders with bullets over 150 grains. Bullets in the 145-165 grain range could go either way.

45-70, 38-55 might differ if shot off the bench or off hand because of recoil impulses, or rifle weight.

Cast bullets and copper solids also change the game at times.

Can we throw subsonic loads into the mix?

I love the discussions and insights from so many very knowledgeable people here, but sometimes the focus is very narrow. I had no idea how many “absolutes” I have been on the wrong side of during my shooting/loading time. It took a while to figure out that many of the “absolutes” argued may only apply to a few cartridges or shooting styles.

But what do I know, I think neck tension is how big of a flair I put in a case neck to keep it tight in the chamber when I seat the bullet .060” in front of the case.

I’m not saying there are no universals, just fewer than we might think. Just because I don’t shoot the most accurate cartridges known to man, or distances over a mile, doesn’t mean I can’t use the techniques, or apply the science. It just means I shouldn’t be surprised if the results are different or backwards.

 

[SeabeeKen]

Another situation I've seen lately, during the last 6 months I've been doing a lot of testing of Hammer Hunting bullets in several cartridges. The owner of the company had said that slower powders worked best due to much less bore friction and engraving pressures. I've found this to be quite true. For instance, my 250AI shot tight groups with low numbers with IMR-3031. The same was true of my 284 Win with IMR-4166. These powders also produced top velocities as opposed to 4350 and 4831 class powders. Using GRT, Ive been able to find more efficient powders which give me amazing accuracy and numbers as opposed to blowing 15-20% out the bore as a fireball. IME

 

[darkangel_r2]

@darkangel_r2 that illustrates part of my point.

There are some patterns to what we are calling state of the art accuracy performance, but there may or may not be agreement when we throw in Midrange, Long Range, F-Class, Highpower, etc.

That is true. I posted that point to support the OP's point. There is a general trend in centerfire shooting disciplines where the faster the powder and less time the bullet spends in the barrel the lower the dispersion on the target. The bc of the pill being launched is a limiting factor on effective range for these rifles. This would explain why chambers like 6br family are competitive across so many different ranges. Moderate bc for mid and long range but comparatively fast burning powders and comparatively short barrel times.

There are calibers with better ballistics and similar recoil to the 6br family but they rarely stack up favorably. I think this is a contributing reason as to why.

It would even be difficult to get a consensus on what constitutes a "fast" or "slow" powder in a given context.

Maybe. I bet each discipline at each range could just list their top competitors calibers and loads and you would get a faster powder favored curve for each caliber.

We can model internal ballistics to a degree, but then it falls to real results to calibrate a model well enough to be able to either mirror those results or go even farther and predict the next ones.

I'm fairly certain we can accurately measure both position of the bullet in the barrel vs time and consistency of the pressure curve with p-trace or similar software. I think in a previous thread you told me you had done this yourself.

If a particular context gets nailed down to a standard, you can have a decent debate on the concept of which powders will tune for accuracy better than others.... maybe....

True. But I don't think this question was about particular powders and more about a general trend.

 

[Beiruty]

All -

Howdy !

Ballistician Homer Powley has told us....

Recoil
" The peak pressure [ in a rifle ] is expressed in pounds per square inch. Multiply the pressure by the area of the bore to find the force, in pounds exerted on the bullet and the gun in opposite directions.

This peak force is reached in an ordinary rifle approximately 600-800 micro-seconds after burning begins and lasts only a few micro-seconds. A micro-second is one-millionth of a second. Meanwhile the gun has recoiled only something like 1/16" inch during the time required for the pressure to reach its peak. "

With normal loads only about 99% of the powder burns inside the gun and the rest goes out of the muzzle in the form of splinters; you can tell them when you find them. All of the powder that is going to burn has done so at the place of peak pressure which is only a few inches in front of the chamber."

The above comments by Powley were found in his " Powley Papers " that were printed in the " Guns & Ammo 1974 Annual ". Mr. Powley included lots of other data, and graphs for things like " Peak Acceleration in a 10 lb gun " ( example ). Too much for me to pass along, especially his math formulas that featured special symbols/ characters. The point of peak pressure can be calculated.

With regards,
357Mag

Today, we have advanced internal Ballistics that you play with it to visualize what Poweley stated.
I highly recommend the free GRTools.

 

[RegionRat]

I'm fairly certain we can accurately measure both position of the bullet in the barrel vs time and consistency of the pressure curve with p-trace or similar software. I think in a previous thread you told me you had done this yourself.

Yes, I was able to track projectiles from the chamber to traveling down the bbl using a reflector and the right frequency radar.

When combined with pressure data, we had a fair idea of internal ballistics from ignition to the muzzle.

The G forces on projectiles are incredible. Then they asked for sensors on shells and the real fun began.....