Is there empty space in a casing?

jsergovic

question

If powder brand A says use 4.7 grains and brand B says use 8 grains, what's up with the difference in empty space in the casing. Is there empty space in a casing?

Bert H.

Hello jsergovic...

In most cases, yes, there is empty space inside the case. However, that space in most cases (pardon the pun[:D]) is not linear due to the differences in the physical shape of the powder grains. The only time empty space in a cartridge is a serious concern, is with blackpowder cartridges... and you don't want any empty space then. Generally speaking, the faster the burn rate of the powder, the fewer grains are needed/desired.

Bert H.

Real Men use a SINGLE-SHOT!

TRAP55

Sometimes, sometimes not, sometimes it's compressed. Depends on type of powder.What fills a box up, a pound of lead or a pound of feathers? It can make a difference in a large capacity case, in accuracy, if there is too much air space the powder can sit forward in the case away from the primer flash hole. Hope this makes sense, it's past my bedtime.

Iconoclast

Jim,

A: often. The difference you see between 4.7 & 8 gr of powders is largely due to the difference in burning rate. Volume difference is typically not a factor in pistol powders - the granules are uniformly on the small side, while in rifles you will see loads for ball powder and an IMR stick powder which occupy significantly different spaces. Further, in handgun rounds the air space is typically not an issue because of the limited limited case capacity. As you get into this, you will find powder / bullet combinations which work best in *your* piece - this is a function of the internal ballistics as they relate to the physical characteristics / idiosyncracies of a particular firearm.

"There is nothing lower than the human race - except the French." (Mark Twain) ". . . And DemoCraps" (me)

jsergovic

quote: It can make a difference in a large capacity case, in accuracy, if there is too much air space the powder can sit forward in the case away from the primer flash hole. Hope this makes sense, it's past my bedtime.


Yes, this and all the replies answered my questions. I knew there must be some interstitial space between the grains, but is one powder was more "potent" than another, and occupied less space in the case, in that particular case, the powder could be up against the bullet rather than against the primer...or lying evenly along the bottom of the case...like a snake in a sewer...

TRAP55

Jim, A good loading manual, Lyman, Speer,Hornaday, etc., Has already taken out the guess work. Look at the loading tables, compare powder, velocity, and chamber pressure.My personal choice is the best velocity with the lowest pressure. I've never found a load in the books that didn't work. I have found that every gun will prefer a specific load to itself. Never start with the max. recommended loads. Work your way up. Never reload when you are tired ,stressed out,or in a hurry, and you won't make any mistakes. With a little practice, you'll find your reloads better than factory. Enjoy!

Contender Man

The problem becomes most noticable in pistol rounds when the loader is trying to make up low power loads, say for Cowboy shooting, in the larger cases. Then you can have the problem of uneven ignition between rounds and this will certainly show up in the accuracy side. Lastly, with too light loads there is the danger of having a round not clearing the barrel. I try and encourage folks to not go below the minimums in the load manuals and to use filler material in the larger cased rounds. And if your loading BP, you must use filler!



If you only have time to do two things so-so, or one thing well ... do the one thing!

JustC

Yes,..there is space inside a case. the amount of space (or in certain instances,..the lack of space) depends, as Iconoclast stated,.on the burn rate of the powder. Faster burning powders,.have a much sharper pressure curve. That curve being the time in which the load reaches full pressure during ignition. Faster powders,..will "spike" quickly and gradually drop as the bullet travels the rifling. Slower powders,..need longer to fully ignite and reach full pressure,..thus they have a more gradual pressure curve. For any given weight of bullet,..their is only so much +/- of any powder which can be ignited in "X" space before too great a pressure results in failure,..or two little pressure due to powder rate too slow for the caliber, results in poor velocity and powder fouling. If you shake a factory loaded round,..you will quite often hear the charge shake around inside,..this is because the manufacturer feels that to be an acceptable load with their chosen propellant,..with a comprominse of pressure in a range the lawyers approve of,..while yielding acceptable accuracy.

All but the slowest powders (H870, Retumbo, H5010, WC872, the vightavouri 2N series) will be a less than 100% load. If you look at the right hand side of the manual I sent you,..you will see the column for "load density". That percentage pertains to the amount of internal case volumne occupied by that particular powder charge. A 100% load would fill the case,..to the base of the bullet. HTH

why chase the game when the bullet can get em from here?....
Got Balistics?

jsergovic

The deeper I get into that Nolser book the more I realize it's a gold mine.

For my 357 snubbie, I want a faster-burning powder because full pressure buildup has got to take place rather quickly if i want a fully-powered projectile.

Very interesting. Also, most loads come nowhere near 100% load density, although the Remington Maximum (357) with 24.3 gr. of RL7 under a 180 gr. bullet will produre 1690 fps w/ a load density of 110% (compressed).

Sounds pretty ripping fast from a handgun.

heavyiron

All answers are basically correct. But,the real answer is powder density. That is the mass of powder per volume powder. Confused? Compare aluminum to lead. Pound per pound the mass is identical. But if you have 1 cubic centimeter (cm^3) of lead and 1 cm^3 of aluminum (a different volume) the mass is not the same and lead will weigh more per volume.

Generally, fast burning powders have smaller grain size to facilitate a faster burn. Because the grains are smaller more grains fit in a given size cartridge case. Therefore the density (weight) is greater per volume.

This is exactly the basis for the volumetric powder measure used by many of the reloading companies. Powder charge is determined by volume not weight.

jsergovic

Got it.

A smaller grain will expose more of it's surface, per mass, to the surrounding environment.

(A similar condition limits the size of individual cells ... they can only get so big because the increased mass of the cell has only so much surface area thru which to receive interaction, nutrients, etc).

v35

For best accuracy,the choice of a bulky powder that would give you high loading density is preferred.
Very low loading density has resulted in destructive detonations in cases as the 25-06.