Weight vs Volume

[David W.]

Well in any of my MLs I would expect a one ounce load to produce enough smoke to be visible from weather satellites, a rain of unburned powder granules which could ignite on subsequent shots, and a recoil which would discourage subsequent shots. :hmm:

:rotf: :rotf: :rotf: :thumbsup:

 

[hanshi]

Of course some of us use 3f for virtually everything just to simplify matters. There will be only a slight variation going from 3f to 2f but the variation is real. Along the same lines locks such as the Large Siler need only be primed with 2-3 grains 4f while the big locks such as the English round face locks can use twice that.

 

[Joel/Calgary]

When using FFFg, it is general rule of thumb to reduce the volume by 10% over FFg. That is because the finer the granulation will build up more pressure because of the faster burn rate.

This rule of thumb is cited by a lot of people cite nowadays, but things can vary quite a bit with the individual firearm & load. When I first got interested in BP in the '60s, the most common rule of thumb was to increase charges by ~1/3 going from 3Fg to 2Fg (which is equivalent reduce by ~1/4 going from 2Fg to 3Fg - the ratio is 3:4) to get the same velocity. This was with references ranging from the 19th century into the '50s, and naturally varied with bore size, barrel length, and other such variables. Whenever I examine the data in loading manuals and the like, where both granulation are tested with the same barrel & projectile, I find charge differences between 3Fg and 2Fg ranging from something less than 10% to nearly 50% to get the same velocity, but the average increase is in the 1/4 to 1/3 range. Naturally, the pressure is higher with 3F. Getting the same velocity does not necessarily give the same POI - barrel harmonics, recoil, and such can come into play - which may be why the 10-15% rule-of-thumb seems to work so frequently. Accuracy is a separate matter. As has often been said, accuracy may or may not be significantly different with different powders. Every gun has its own preferences, and some are fussy while others are not.

Regards,
Joel

 

[Golfswithwolves]

This is an interesting discussion! From another angle too: what about switching payloads of shot in a smoothbore? Should a shooter make shot loads of #5 shot that weigh the same as his load of #6 shot, or should he use the same volume of either size shot. :hmm:

 

[Joel/Calgary]

This is an interesting discussion! From another angle too: what about switching payloads of shot in a smoothbore? Should a shooter make shot loads of #5 shot that weigh the same as his load of #6 shot, or should he use the same volume of either size shot. :hmm:

That depends on what you want. If you take the easy way and not adjust the volume, the #5 will weigh a bit less, so you'd lose some pellets and gain a bit of velocity, but the effect will be much less significant than going to the same volume of much larger shot, like #2 or BB. I don't know if you know the principles involved, and I'm a slow typist, so I've copied & pasted something I wrote in a previous discussion.

Regards,
Joel


How much shot a measure will hold depends on the aggregate density of the shot - for lead (and its alloys), it's usually given as approximately 7 times denser than the powder, depending somewhat on the alloy. This is apparently the density of hexagonally-close-packed uniform spheres composed of lead alloys with bulk densities of 10.75-11.25 g/cc, depending on alloy, and is independent of shot size (36% porosity, IIRC). That should calculate to 6.9-7.2 g/cc, with most shot alloys in the 7.1-7.2 range. All comparisons I've seen of shot and powder in real-world measures actually come out with shot less than 7 times the weight of the powder because the shot are not perfectly packed in the measure. The dimensions of the measure STRONGLY affect how much shot actually fits in - especially with larger shot. Because of the effects of the geometry of the shot against the sides of the measure, larger shot will not pack as well as smaller, so it will weigh even less in a given measure, and the smaller the diameter of the measure, the greater will be the effects of shot size on charge weight. (I've heard this called "boundary effect" in a discussion of packing.) A shot measure is comparatively fat to minimize the boundary effects on packing and be more consistent with different sizes of shot but with some loss in precision, while a powder measure is skinny to allow more precise measurement of the much finer gunpowder because the boundary-effect differences are much less among different granulations of powder.

Picture a layer of shot in the measure. In the middle, the shot is likely close to that perfectly ordered hexagonal packing, but around the edge, there will be places too small for a shot to fit, so there is less shot in the layer than a perfect hexagon of the same cross-section, or, alternatively, of a circle drawn over a wide perfect layer of hexagonally packed shot. The larger the cross-section of the measure compared to the size of the shot, the greater the portion of the area that will have shot in dense hexagonal packing (roughly proportional to the area of the measure, or to the diameter squared) and the smaller the portion with some "missing" shot (roughly proportional to the circumference, or to the diameter [directly, not squared]). Similarly, the larger the shot, the wider the boundary region with some "missing" shot for a given diameter of measure, and the lower the weight for that layer. The actual 3-dimensional geometry is more complicated, but the same principles still apply.

 

[necchi]

Wow! That made me dissy.
That's an awfull amount of thought put into the simple act of pouring the right amount of shot down the barrel to get a good group with the powder charge your using.

geez, I wonder if those clay pigons I bust at the vous know I only rap the barrel once after I pour the shot in? :haha:

 

[Joel/Calgary]

Wow! That made me dissy.
That's an awfull amount of thought put into the simple act of pouring the right amount of shot down the barrel to get a good group with the powder charge your using.

geez, I wonder if those clay pigons I bust at the vous know I only rap the barrel once after I pour the shot in? :haha:

Well, that's the theory. The practice is, if I don't have enough pellets in a (pick a measure setting) of the size of shot I want to use, I'll up the measure an eighth, maybe check the weight or maybe not, adjust the powder accordingly, and shoot a couple of patterns to check. Or maybe just use a smaller shot size.

What's this rapping the barrel after ya pour the shot?

Regards,
Joel