I am new to benchrest shooting and I have only been reloading about 4yrs. so I still by some standards am a rookie.This being said I have a question( I hope not a real dumb one) Why is it that the 30BR uses H4198 and the 6BR uses n-135 or varget or to be more tech. a much slower powder?
A question about powders ?
- Thread starter fatalbert
- Start date
Ah yes, the voodoo science of internal ballistics - expansion ratio, bore capacity, all that good stuff.
Given the same case volume, the smaller the bore the slower the powder.
The same amount of gas would be generated in two identical cases with different caliber bullets. The one with the smaller bore is trying to push this gas against a tighter constriction thus creating a higher pressure. To counteract this boost in pressure, a slower powder is used.
Albert, I like your personal motto. Shows a realistic outlook on life.
Given the same case volume, the smaller the bore the slower the powder.
The same amount of gas would be generated in two identical cases with different caliber bullets. The one with the smaller bore is trying to push this gas against a tighter constriction thus creating a higher pressure. To counteract this boost in pressure, a slower powder is used.
Albert, I like your personal motto. Shows a realistic outlook on life.
Thanks for the response,I appreciate the patience you guys have with us rookies and the learning curve.I understand the pressure part of the issue with the smaller cal. but isn't it pretty much common pratice to reduce the powder charge in the case? I'm don't mean to argue I'm just trying to get my head around this.I appreciate the approval on the motto, I've tried all my adult life not to take myself to seriously and at times to poke fun at the folks I know who are way to serious about everything.I think a little well placed humor works wonders in some very tense situations.The secret to that is knowing when and where to ask that age old question--- Are we having fun yet? :
Rifle cartridges seem to be most accurate with a powder charge between 90% and 100% capacity. Reduce the charge too much and you have powder lying in the case at different locations relative to the primer which can cause variations in pressure and hence lower accuracy.
This is a real problem with cast bullet loads in rifle cartridges. Various methods such as kapok filler holding the powder against the primer have been used with small charges of fast burning powders. Others prefer larger charges of medium burning rate powders such as IMR 3031 to bulk up inside the case.
With slow burning powders reduced charges have been known to cause "unexplained pressure excursions", lawyer talk for a blown-up gun. A reduced charge that you think would produce a lower pressure in fact produces over-max pressures. But, not every time. This phenomenum is so unpredictable that the wise policy is to use a powder that loads 90% to 100% with safe pressures and you don`t have to worry about mysterious pressure excursions or variations in pressure between shots.
This is a real problem with cast bullet loads in rifle cartridges. Various methods such as kapok filler holding the powder against the primer have been used with small charges of fast burning powders. Others prefer larger charges of medium burning rate powders such as IMR 3031 to bulk up inside the case.
With slow burning powders reduced charges have been known to cause "unexplained pressure excursions", lawyer talk for a blown-up gun. A reduced charge that you think would produce a lower pressure in fact produces over-max pressures. But, not every time. This phenomenum is so unpredictable that the wise policy is to use a powder that loads 90% to 100% with safe pressures and you don`t have to worry about mysterious pressure excursions or variations in pressure between shots.
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