Internal Ballistics Calculations Help

[TK 1985]

Hi guys, building a lightweight 6.5 Creedmoor with a 20" barrel on it.

My question is as follows: Are there any programs or ballistics tables which will show me the percentages of a certain powder burned within "x" length of barrel as well as pressure curves?
With the shorter barrel I will be using, I believe ideally that I would like to have 100% burn by 18" of barrel length, not to mention peak pressure around that point.

If someone could point me to said programs/resources, or just point out if I am flawed in my thinking, then I would appreciate it.

 

[MagnumManiac]

Hi guys, building a lightweight 6.5 Creedmoor with a 20" barrel on it.

My question is as follows: Are there any programs or ballistics tables which will show me the percentages of a certain powder burned within "x" length of barrel as well as pressure curves?
With the shorter barrel I will be using, I believe ideally that I would like to have 100% burn by 18" of barrel length, not to mention peak pressure around that point.

If someone could point me to said programs/resources, or just point out if I am flawed in my thinking, then I would appreciate it.

Firstly, peak pressure occurrs within 2" of the chamber, on average, and no rifle powder of the correct burn rate is going to fully burn within the barrel, no matter the length, within reason.
Quickload will give you an IDEA of what you MAY get, but, a chronograph will tell you a lot more for your trouble.
Many will tell you QL is the 'bees knees', I had it, and a pressure trace, they NEVER corresponded to each other, no matter how much tweaking was performed. QL, may, or may not get you close, if you want to spend the money, go right ahead.

Cheers.
gun)

 

[TK 1985]

I appreciate the input on your experience with quick load, I was considering it. I guess I used wrong terminology with a couple things.
Yes I understand peak pressure and the majority of the burn happens within a short period. I guess I'm trying to find a powder that I can get the most percentage of the powder burnt before it exits the barrel.

 

[Engineering101]

TK 1985

QuickLoad will tell you directly pressure curves and how much powder is burned in the barrel IF you calibrate it to your rifle and load by doing a few things - like measure the H2O capacity of your fired brass and fire loads over a chrono and use that info to calibrate the burn rate of your lot of powder. You also have to tweak the "weighting factor" and a few other things. Frequently even when doing these things QuickLoad will be predict significantly lower pressure than you actually get. You can tell this by looking at published load data where a pressure barrel was used and thus the pressure developed by the load is known. If you are getting the published velocity, you are also getting the published pressure. Unless you are curious and like to mess with stuff just for the sake of doing it and have $150 to burn, I suggest that you don't worry about internal ballistics.

On the other hand, as was mentioned by MagnumManiac, a good chrono provides very valuable info. That is something you should consider buying way before QuickLoad. You can pick up a CED Millenium 2 for a few hundred bucks. They work very well if you align them properly. I've used one for years.

 

[TK 1985]

I do have a chronograph, so it seems like I'm overthinking this. Basically just go out, shoot, see what happens and record the data.

Thank you guys for the input

 

[Mikecr]

Frequently even when doing these things QuickLoad will be predict significantly lower pressure than you actually get. You can tell this by looking at published load data where a pressure barrel was used and thus the pressure developed by the load is known. If you are getting the published velocity, you are also getting the published pressure.

This is not valid. For one, what is 'published' means nothing locally, much less w/resp to local use of QL.. We're not shooting with their proof barrel, or their particular lot of powder.
You CAN calibrate with QL(once you know how), and then the predictions are valuable. Especially for wildcat cartridges.

It is possible for higher pressure than predicted, even with calibrated QL. A strain gauge can show this as secondary peaks further down a bore. But it's not a prediction error, it's a problem. You've put together a mess to get their.
Keep in mind though, strain gauges have to be calibrated, just like QL. Until then both purely relative.

 

[TK 1985]

Yes the secondary, that's what I meant. Ideally you want that to spike a little before the end of the barrel, correct?

 

[MagnumManiac]

In almost every instance I have ever checked side by side, a shorter barrel will still get it's highest velocity with the same powders that get the highest velocities in a longer barrel.
Some will protest and say that their xxx rifle with 20" barrel PREFERRS a faster powder, this may be true, but preference doesn't mirror performance.
It is a common misconception that a short barrel requires faster powders than a long barrel, simply isn't true.
I know people who NEVER use a slower powder than Varget in their 30-06 because it's accurate, but slow!!

Cheers.

 

[TK 1985]

I do appreciate the input. I am learning quite a lot.

 

[elkaholic]

I agree with MM above. You may get a little more muzzle flash with slower powders, but generally, a given powder will give top velocity over a few inches of barrel length difference. You will never get ALL of the powder to burn in an 18" barrel no matter what you use. I would think something like RL17 might give you close to top velocity, although I have never had a Creedmore.......Rich

 

[TK 1985]

So then wouldn't a faster power that produces less flash while getting you there be ideal?

 

[elkaholic]

So then wouldn't a faster power that produces less flash while getting you there be ideal?

Possibly, but I would go first and foremost with what gets you the velocity that you want coupled with good accuracy. Also, many factor in temp stability, etc.........Rich

 

[TK 1985]

I know IMR has the new Enduron powders which are supposed to be very temp insensitive. How do the old standbys hold up to temperature' 4064, 4895, 4350, etc?

 

[elkaholic]

I know IMR has the new Enduron powders which are supposed to be very temp insensitive. How do the old standbys hold up to temperature' 4064, 4895, 4350, etc?

H4350 is an extreme powder, and 4895 might be too?