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Burn rates...... how do they help determine which powders to choose?

3K views 2 replies 3 participants last post by  LDBennett 
#1 ·
I just found a good supply (Titegroup, CFE Pistol,Win WST) of some more pistol powder at the local Cal Ranch (a western wear/ranch supply store of all things) while all the local gun shops still cry... we can't get any powder, it's impossible to find! Perhaps I should try the local barber shop, they probably have more than the gunshops too!

Anyway, I picked up a free magazine type publication called the Basic Reloading Manual published by Hodgdon and featured tables for Hodgdon, IMR and Winchester powders. Reading through it I noticed a large table showing how powders ranked based on their burn rates. The sales clerk indicated that matching primers to certain powders based on burn rates was very important. I had never read that anywhere so came here to ask the pros....... So, exactly how does a powders burn rate play into the decision of which powder to use?

I noticed that the burn rates of three of my 223 rifle powders are ranked together; #83, #84 and #85 while the other 223 rifle powders and all of the pistol powders I have (marked with R's and P's) are all faster powders.
 

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#2 ·
That's where the reloading manufacturer's guys in the lab with their nice fancy pressure measuring setups earn their money. :)

Short explanation...
As a general rule, the faster burning a powder is the faster the pressure climbs inside the case when it's ignited. A slower burning powder creates a slower rising pressure curve.
The magic comes from marrying that concept with each cartridge/bullet combo.
Each commercial cartridge has a SAAMI or CIP pressure level standardized as it's maximum pressure. What you're generally looking for is getting the most velocity with the lowest pressure level.
That's one reason I really like to use data published with pressure levels along with charge weight and velocity. BUT...just because the lab got those pressures in their setup doesn't mean that's exactly what you'll get with your rifle due to slight variations in chamber size, barrel length, etc.

Which is why you don't see Bullseye or Titegroup loads for the .223...it would be very easy to make an extremely overpressure load (I.E. kaboom ) with a powder charge that's relatively small compared to the case capacity.
Vice versa for using a rifle powder for a handgun cartridge. You could probably never get enough BL-C2 inside a .45ACP case to get a usable velocity out of it.
If you look over some of the data for a specific cartridge and compared a powder from the fast end of it's range to one with the slow end you'll probably see the faster burners have a higher pressure peak with a lower velocity and the slower ones will have a lower pressure peak at a higher velocity...might not be a large difference but you should be able to see the trend.

Once you've got a workable range of powders that you can use in a certain cartridge, then the fine-tuning comes into play. Within the range of what the guys in the pressure lab have found to be usable powders, your rifle might work better with a faster powder or slower powder to "tune" the pressure curve and velocity for your rifle's chamber and barrel. It's all about harmonics.

If you're running an autoloader, you also need to figure your load making the right amount of pressure and the right time to ensure the action functions too.


And there are probably a whole bunch of other factors to weigh in too. These are the ones that are on the top of my head as I'm eating breakfast this morning. :)
 
#3 ·
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To start with the Burn Rate chart for you and me is relatively meaningless. We need to only use loads found in manufacturer's reloading manuals. Experimenting with reloading recipes not in manuals is extremely dangerous! The pressure testing equipment is not available to us that would assure such experimentation results in no excessive pressure combinations. All the so-called indicators of pressure using the case and primer condition after firing are too crude and unreliable.

There are in both small and large pistol and rifle primers both standard and magnum version. If the powder load is large then the manuals may recommend the energetic magnum primers to assure good ignition. For very cold environments some hunters use magnum primers to assure good ignition but they have to back the load down as the more energetic primers increase the pressures. But following the manuals keeps you safe. There is no reason for you to second guess the manuals for the selection of primers with the powders of choice. The choice of primers with powders is not one you should make using the burn rate chart as the sales person may have indicated. The pressure lab guys are the ones to make those choices. The have the tools to assure any load is safe.

Bottom line: Forget the burn rate chart. Use only manual load recipes.

LDBennett
 
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