Why does powder matter ?

[Hammer]

Assume the same rifle, brass case, bullet, primer, case prep, etc.

Assume no wind and a skilled shooter.

Assume that two very similar powders have had loads worked up to the same average velocity.

Why should one powder give any different accuracy than another powder ?

 

[billmo]

Burn rate will play a large roll in barrel harmonics and chamber pressure.

 

[Hammer]

Let's say burn rate is very similar...

 

[billmo]

I guess the balance of the equation then would boil down to the consistancy of the powder due to resistance to temp changes and I seriously doubt that you would stumble onto two different powders that would deliver the exact same barrel harmonics. I have worked up loads for hunting rifles in the past with more than one powder and have both powders perform pretty much equally well, but never identical. In my experience it is not difficult to use more than one completely different combo as far as powder, primer, brass, bullet, etc. to realize acceptable accuracy for some particular rifles. On the other hand, some rifles are hard to find one combo that works really great with until some degree of changes are made within the rifle to try and wring the whole accuracy slug out of it.

 

[Tommie]

Powder kernel shape will play into it as well. Let's say you have two loads worked up with powders of similar burn rate, but one powder is extruded and the other is spherical. Typically,but not always) the extruded powder load has the potential for a small accuracy advantage because of it's bulkier shape - i.e. the case is more "full". Many people find that their guns shoot well with 100% capacity loads ... or even compressed loads. It is easier to load a case to 100% capacity with extruded powders while still remaining within pressure limits. Conversely, if a 100% capacity load with extruded powder seems to be shooting ok and displays mild pressure but still is not grouping as well as the gun is capable of, a switch to spherical powder of similar burn rate can sometimes allow a slightly heavier powder charge,again, due to greater load density) and push the velocity and barrel harmonics into the next accuracy node.

Tom

 

[Clark]

People who think that one powder is better than another could pass a lie detector and really believe it, but none usually have controlled and normalized data to support it, just like every other superstitious ritual involved in handloading for accuracy that is too much work to really check out.

 

[EricStecker]

Hammer,

Verifying that two powders are producing exactly the same pressure and velocity is something few can do accurately to begin with. If you had a Utopian situation where everything were exactly the same then it might not matter but how often does that actually occur.

Powders vary lot to lot to such a degree that some will change places on the burn rate chart. Since we know this to be true,that's why no two loading manuals are the same) then the process to make powder is not under as much control as accuracy oriented hand loaders would like,all powder comes from three places so you would thing that they would be more similar but it must be harder to produce then one might imagine).

Keep in mind also that within manufacturing you will have variables that need to be controlled. How well these variable are controlled will determine in large part the degree in which something is consistent. If they did their job right then powder A can be very consistent while powder B might have been run with less concern for tight control and not be as consistent.

Clark is correct that few have the ability to actually verify this and it is unlikely that you could find a given combination that is exactly the same using any different components,bullets, primers or powder).

Regards,
Eric

 

[mikecr]

RSI might have in-depth ideas about this, given all the combinations they've measured.
http://www.shootingsoftware.com/pressure.htm