Powder Burn Rate effects

[rickOshay]

Being relatively new to reloading, I have been trying a variety of powders for the 123gr AMAX trying to reproduce the commercial Hornady ammo.

PA-Allen posted nice data on his favorite loads and had a brief discussion with longdayjake on the effects of burn rate and barrel length:

http://www.65grendel.com/forum/showthread.php?51-Some-of-my-best-loads-with-chrono-data

I wanted to add my observations based on a 16" barrel and eight powders. The data in the chart below were obtained using 123gr AMAX loaded into new Horndady or Lapua brass with REM 7.5 primers at temperatures between 80 - 88 degrees.



When viewing this graph from left to right, the order of the powders match very closely to the Hodgdon Powder Burn Rate chart:

http://www.hodgdon.com/burn-rate.html

H335 > XBR8208 > TAC > AA2520 > VARGET > WIN748 > BL-C(2) > CFE223

I do realize the the burn rate order is different depending on the source of the data.

The faster burning powders achieve higher velocities with lower charges in a 16" barrel.

I took the liberty to plot PA_Allen's data for his 20" barrel for the 120 gr Nosler Ballistic Tip:



According to the Hodgdon chart the burn rate order would be: H335 > TAC > AA2520 > RL15

So the trend is not as pronounced in PA-Allen's data.

[Hoot]

Nice job!

Thanks for taking the time to do all that work.

Hoot

[PA_Allen]

Exexllent! If you want, You can add a couple of data points for 8208 and the 120 NBT to my data plot from this thread:

http://www.65grendel.com/forum/showthread.php?1124-XBR-8208-range-results-for-100-and-120-gr-NBT

Thanks for taking the time to make the plots.
Best,
PA Allen

[rickOshay]

If you want, You can add a couple of data points for 8208 ...

Here is the updated graph. XBR does not fit as well. However, I would guess that if I had loaded 28.5 gr, it would have given velocities greater than H335 - based on the slope of the line.

[rickOshay]

223 Load Summary

Here's the data from my 20" .223 using 69gr SMK. I did not have CFE223 at the time.

Here XBR is faster than H335, and the slower powders are getting higher velocities - albeit with higher charges.

Also, it appears that the H335 and XBR data show the beginnings of curving off at the higher loads, indicating approach to a maximum.

[Bennybone]

pine cone to pine tree, come in pine tree.........

I have been looking at the posted charts and as a new reloader (been doing my own for a year) I feel like I am not seeing the forrest for the trees.

Can someone shed some light on this from the following perspective(s):

---A pattern can be observed across all charts that as you add powder you are going to see a shift in the next data point up and to the right (more charge = more velocity).---
+++Why then does the line of data points stop when it appears as though there would be more room for powder in a case+++
I assume that burn rate and pressures are the answer but I don't know this for sure

---With the assitance of a line drawn through the average across data points, a pattern can be seen that some lines intersect the actual data point while other lines have data points off to one side or the other---
+++Does this indicate a powders consistency i.e. purity as it relates to performance+++
I assume that we all would like to use a powder that behaves consistently, when plots aren't on the line could it be construed that the powder is more volatile? i.e. erratic?

---Each chart above is specific to a barrel length / atmospheric conditions / a particular bullet weight---
+++Can any assumption be made relative to accuracy nodes or what powders would yeild an effective use beyond the bullet weight plotted? In other words once you plot for a specific weight of bullet across all powders can you overlay a grouping (accuracy) chart and make any determination of sweet spots consistent across all powder charges and then can you theorize what powders would be most effective (velocity) and accurate to a higher or lower bullet weight based on burn rate results.+++
I assume those who have reloaded for years can do this on the fly based on experience

Anyhow, hats off to this community and kudos to members such as yourselves who take the extra time and expend the extra effort to make notes and charts such as this.

I feel like I am missing the decoder ring to unlock the secrets of the data.

I am sure I could read a book or take a course on simple and advanced ballistics however I am a product of Generation X - (stereotype alert) we seek instant gratification and answers without investing the necessary time and efforts when we probably should...

Thx for listening and if I didn't make sense in my questions/assumptions let me know so I can try to clarify.

BB

[Dogue]

Benny, the simple answer is that it's possible to have the bullet exit before all the powder can burn, especially with slower powders and shorter barrels. You can also use the charge-to-speed relationship to find you are getting close to running over pressure. If you're seeing an avg increase of say 50 fps from load to load while working up (assuming you're increasing the powder charge by the same amt for each test load) then you notice loads start gaining minimal speed then you are likely getting to the edge of safe pressures. This isn't a failsafe since the only true way to gauge pressure is with fance, expensive equipment, but it can be a good indicator or high pressure. That's why it's best if you can use published data as a guide and work up your loads...but that's not always possible with so many powder and bullet combinations out there so we start looking for other signs to keep us from going over the edge.

[Bennybone]

What is the rule of deciphering charts such as these and equating it to powder burn rate?

High velocity and low charge weight = fast burning

vs

high charge weight and moderate velocity = slow burning

If not for the original posters link to Hogdons burn rate chart I wouldn't have known what powder is fast or slow burning based on the charts alone.

BB

[rickOshay]

What is the rule of deciphering charts ........

Remember that not all burn rate charts give the same ranking. I plotted the data according to the rank given by Hogdgon, and it seemed to fit my data.

I am new to reloading as well, and am trying to get from the 10,000 ft view to the 1,000 ft view. My understanding was that the faster burning powders would give higher velocities in shorter barrels. My data seems to fit that.

I limited my range of charge weights to be well within safe pressures based on commercial data and what has been posted by members of this forum.

[rasp65]

Benny, the simple answer is that it's possible to have the bullet exit before all the powder can burn, especially with slower powders and shorter barrels. You can also use the charge-to-speed relationship to find you are getting close to running over pressure. If you're seeing an avg increase of say 50 fps from load to load while working up (assuming you're increasing the powder charge by the same amt for each test load) then you notice loads start gaining minimal speed then you are likely getting to the edge of safe pressures. This isn't a failsafe since the only true way to gauge pressure is with fance, expensive equipment, but it can be a good indicator or high pressure. That's why it's best if you can use published data as a guide and work up your loads...but that's not always possible with so many powder and bullet combinations out there so we start looking for other signs to keep us from going over the edge.

Dogue The fact is all those powders will be burned in the first few inches of the bullet travel. Propellants have their own oxygen in their chemical make-up and it reacts very quickly. Muzzle flash is a reburn of the hot gases when they hit the air. That is why a pressure curve peaks at a point close to the case. It is a common misconception that shorter rifle barrels need faster powders. While these charts are interesting powder manufacturers measure burn rate with a device they call a closed bomb.

[Bennybone]

Good stuff, things I can look up later!

[rickOshay]

Relative burn rate can be calculated as a function of velocity, bullet diameter, and charge weight by:

RBR = Velocity x Diameter(^2)/weight

Using this for the data in the top chart, I get these results:
H335=5.9, TAC = 5.8, AA2520/XBR8208=5.7, Varget=5.5, WIN748=5.4, BL-c(2)=5.2