powder usage

[NO-GO]

Is there a simple explanation why 55 gr. bullet in. .243 takes more powder than a .22 to get same speed? Just looking thru sierra manual and noticed the difference. Thanks

 

[Larryh128]

It's all dependant upon the volume of the case & the size of the hole in the case (mouth).

 

[necchi]

Then a .22 what?

 

[bheadboy]

you have to get the chamber pressure up to the point it will push the bullet x fast. to do that the size of the case increasing, requires more powder burning to get the pressure for the velocity, the dia of the bbl opening also increases the exaust pipe for the burning powder, bigger means more powder

Bob

 

[Kingfisher]

Bearing surface will also come into play. A 55. gr 6mm likely has less bearing surface than a 55 gr. .223 thus generating less resistance. The decrease in resistance lowers pressure, so you've got to add more powder. This is certainly more obviously when you're comparing one bullet weight in a chambering to another bullet weight in the same chambering, like a 180 gr. in a 30.06 vs. a 165 in a 30.06, but the same rules still apply.

 

[treeman]

a 22 bullet that weighs 55 gr has more bearing surface than a 6mm bullet weighing 55gr. I don't know what 22 cal cartridge you are looking at but if the case was the same except for bullet dia. that is how it would work.maybe you are looking at 22 br vs 6mmbr??

 

[NO-GO]

than a 22-250
larger bore o.k., still looking, 55gr. 22-250 /748 33.2gr. to get 3,300 fps, 6ppc 55gr. 748 30.5grs. to get 3,300 fps. I am guessing that case size has to do with pressure also?

 

[riverwolf1]

WoW! so I guess the different burn rate of powder has nothing to do with all of your therorys since its the single item that was not in any of your posts!!

 

[mac86951]

It's all dependant upon the volume of the case & the size of the hole in the case (mouth).

Physics time...

Powder makes the expanding gasses (certain volume over certain time). This creates the pressure that works on the base of the bullet and brass case, within
the volume of the case and bullet/chamber as the bullet passes down the barrel.

Differing bullet diameter, with total pressure over time being the same, the larger bullet will move slower. Case volume being larger, same again. Case being bigger, the force to expand the brass to the chamber will need to be greater, meaning less force pushing bullet down the barrel. Friction surface of bullet to barrel is different too, larger bullet, MIGHT have more friciton thus again taking more force.

I know I am missing at least a hundred more factors that come into play to develop a truely accurate model of what is occurring. Example, think of what happens when a bullet has to Jump to the lands in terms of volume and in terms
of momentary gas leak. It goes on from there.

 

[jonbearman]

When dealing with this question,think of it a different way.With a heavy bullet(mass) you actually need a lesser charge to build the pressure to where you want it,the lighter bullet moves easier with less resistance and nedds a stiffer charge to equal the effect of the lighter bullet. It is simple really.The physics of an explosion so to speak is the direct opposite to pushing a car,the heavier car the more power to move it,the light car requires less power to move it.

 

[NO-GO]

Well maybe no easy answer, I have no theories on this just noticed differences and wondered why. I think I'll just follow the book and leave the heavy thinking to someone else. thanks