Heat of explosion vs. Burn rate

[Doom2]

So, how is the HOE number useful at all?

In this case it is useful in internal ballistics calculations. That is a whole science unto it self. Look up "internal Ballistics" on WIKI to learn more. In terms of usefulness in reloading without a program such as Quickload (an internal ballistics program) it serves no purpose. With a program such as Quickload it can be used to predict pressure and velocity as a function of time, geometries, powder and barrel length.

 

[Barrelnut]

Good thread.

I was under the impression that one could use the HOE to help determine powders that would help with longer barrel life. I have seen a few charts and list over the years that allude to this. For example H1000 in a 300 RUM will give better barrel life than Retumbo. Because H1000 has a rather low HOE.

 

[Trnelson]

Good thread.

I was under the impression that one could use the HOE to help determine powders that would help with longer barrel life. I have seen a few charts and list over the years that allude to this. For example H1000 in a 300 RUM will give better barrel life than Retumbo. Because H1000 has a rather low HOE.

No doubt that a thermally cooler powder will have a slower rate of throat erosion. As previously reported, outside of Quickload predictions HOE doesn't mean much to the average guy reloading, especially if they are using a commercially made SAAMI or CIP spec rifle shooting a published load combination. I'm not anyplace near an expert on interior ballistics, I'm interested in the math and variables that contribute and have read some articles. If someone is using a wildcat chambered rifle trying to 'make something work' in terms of powder and bullet selection then they better keenly understand how HOE can relate to expansion rate and the resultant pressure curve. Specifically with a given case volume and bore diameter ratio. Good thread guys!

 

[BallisticsGuy]

Good thread.

I was under the impression that one could use the HOE to help determine powders that would help with longer barrel life. I have seen a few charts and list over the years that allude to this. For example H1000 in a 300 RUM will give better barrel life than Retumbo. Because H1000 has a rather low HOE.

It is a factor but that's going to be doped by the burn speed and both of those will affect the suitability of the bulk density for the case capacity and bullet weight at hand. None of the 3 factors should be really considered in exclusion of the others. It's nonsensical to do so since none of those by itself is enough to make any informed decisions about much of anything.

One needs to integrate all 3 functions which will provide in the end a pressure over time curve and a temperature over time curve. If you take the result of that function integration and run it inside a new equation which includes frictional coefficients, barrel length and such then you could make a good fist of approximating the expected velocity. That's how QL does it.

The above said: If the powder is still burning (ie transitioning from a solid to a gas) down substantial lengths of the barrel then the throat is unlikely to see the as high of a flame temperature as it would if the combustion were to convert the solids to gasses closer to the chamber. I've seen some very reliable reports and am doing a project right now to experimentally validate it for myself.

 

[tbrice23]

Which is evident that even though H50BMG has a higher HOE than RL33 my barrel is MUCH cooler after a shot.

 

[Mikecr]

Accurate barrel life can be rule of thumb predicted pretty accurately(with rational assumptions). Inaccurate barrel life is endless..
The trick here is knowing accuracy to begin, so that you know it just left.

Amount of powder, with it's heat potential, and pressure, taken to bore size, are key. Another is cleaning. And of course greatest contributor is shot rate.
This 'accurate barrel life' spreadsheet was developed with decades of input from IBS competitors(those detecting accuracy step change right to the relay/shot count): http://accurateshooter.net/Blog/barrellife2013oct.xls

 

[tbrice23]

Mike, did you take out the moly option?

 

[Mikecr]

Yes I removed Moly. Added 'Extending Adj %', which is for future KNOWN adjustments (like melonite treated (once known), or some special coating).

I removed moly, even though it's latent heat of vaporization cools burning, because anyone less than an expert in managing moly use, likely reduces barrel life.
This, leading to failed tests.

 

[Doom2]

Limiting throat erosion is influenced more by peak pressure/temperature and that is a function of load more than heat of explosion. Double base powders (those containing nitrocellulose and nitroglycerin) do typically have higher HOE and higher temperature. Faster burning powders will also typically eroe throats faster. But the best way to extend barrel life is to stay away from max loads, especially if you don't need the velocity. Beyond that, don't overheat the barrel.