Powder grain size effects on velocity

I did a search but couldn't find anything specific on the subject: has anyone performed tests on the effect of powder grain size on bullet velocity?
I mean something as loading
- the same gun
- with the same load (in grains)
- of the same powder brand
- with the same bullet (type and weight)

but different powder grain size.
Like using a .36 cap and ball Navy, then load say 20 grains of FFFFg Swiss powder with a round ball, then 20 grains of FFFg Swiss powder, then 20 grains of FFg Swiss powder, no test with Fg which is probably way too coarse, and measure the average velocity for 10 shots.

Or, perhaps for more consistent results, a single shot pistol or musket or rifle.
Common sense tells us that increasing grain size should cause velocity to decrease on a short barrelled firearm such as a revolver or single shot pistol, but how much with each grain size change?
What would happen on a musket (starting with FFFg up to Fg) using the same load (consider that it must be safe to use with the finest grained powder)?

Well if measuring by volume and not weight, the finer powders should shoot faster because the smaller grain size will allow for less air space in the measure and therefore more powder.... At least in my mind, I've not done any chronograph testing on that subject.

Contact the NMLRA ( National Muzzleloading Rifle Association email: [email protected]) and get a copy of the Association's magazine "Muzzle Blasts" from September 2022. The Bevel Brothers have an article in that edition regarding velocity variation with grain size that might be helpful to you in response to your question.

Lyman black powder load book has that type of info. Several on here say if you use 2f then which to 3f, reduce your powder charge by 12-15% for same FPS. That is using the powder manufacturer. Switching makers is pretty well tested on here as well. Swiss vs goex vs schutzen vs elephant etc.

The Lyman book, the second edition has those tables. However none of the powders used in 1984 (?) are presently available. GOEX, Curtis and Harvey, and Elephant are long gone. Pyrodex was under development.

Black powder burns from the outside to the inside. Smaller grain sizes burn faster than larger grain sizes. But while smaller grain sizes can give an initial higher pressure it all depends on the barrel caliber and barrel length. A larger caliber rifle typically does better with larger grains which give a slightly longer burn time to achieve best velocity. A pistol or revolver can benefit from smaller grain powder. But, depending on the gun, all the granulations will work. Certain guns will prefer exceptions to the rule.

When I shoot 30gr of Goex VS 30gr of 777 there is a big difference.
So as I figure out how to keep the smoke from covering the gates Im gonna chrony the 44 again.

Grenadier1758 said:

The Lyman book, the second edition has those tables. However none of the powders used in 1984 (?) are presently available. GOEX, Curtis and Harvey, and Elephant are long gone. Pyrodex was under development.

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To true , but it does show there can be differences in velocity between makes and granulation size . I have found that there can be considerable variations of both velocity and accuracy within different manufacturing batch numbers of the the same make and granulation

I did a little of my own testing between my home made 3f and 4f powders. I shot 8 shots of 50 grains of each through my Traditions Deerhunter rifle and got an average of 1167 fps with the 3f and 1206 fps with the 4f. These groups were shot on the same day within an hour of each other.

I don't claim this to be any kind of scientific research. I was just curious about how much the difference might be.

If measured by volume, finer grained powders have more mass in the same powder measure. That’s one factor to consider.

I rely heavily on my chronograph. My main purpose is to document a load so that I can re-create it regarding accuracy if I need to switch something. In other words, if a great load gets 1500 FPS and I can no longer get whatever component (same brand/size ball, patch material, lube, priming powder, cap, ... etc.) I find reproducing the same velocity often produces the same accuracy.

With that in mind, I used the same brand powder (Goex) in two granulations (3F and 2F) in two different rifles. One rifle is a .54 with 29" barrel and the other is a .58 with 32" barrel, both percussion. Loaded with the same measure of powder by volume and the same components, the average on both rifles was the same for 3F as it was for 2F.

I repeated above but with Scheutzen powder. While the velocity was different, the same results between 3F and 2F occurred.

Using the same experiment with a flintlock, the 3F was consistently higher velocity in both brands.

So based on the questions in the OP, I have done some experimenting and I've concluded that between 3F and 2F there is not much difference, all other things being the same, in percussion rifles. With flintlocks, the 3F seems to produce a higher average velocity than 2F of the same amount and brand.

I did not try any other granulations or any other brands of BP or substitutes in the rifles.

In BP revolvers, I have noted distinct differences in velocity from different granulations and that includes 2F, 3F and 4F of the same brand. I tried several brands, including substitutes. Interestingly, in some cases the finer granulation was not the one that provided the highest velocity.

Several factors can affect velocity in muzzleloaders. Some include compression of the powder when seating the ball, the effectiveness of the seal between patch and ball. the length of the barrel, and condition of the bore. TDM was correct when he said that black powder burns from the outside in. The reason that 3F usually generates higher velocities is that it has more surface area in an equal volume than 2F and thus burns the powder faster. The more rapid burn generates gas faster which usually results in a higher peak pressure in a shorter amount of time compared to 2F. Two F takes a bit longer to reach its maximum pressure which will usually be lower than the pressure generated by an equal volume of 3F. The weight of the ball affects the rate of acceleration so the amount of time/energy required to reach whatever muzzle velocity the charge will generate in a given barrel can also be affected by barrel length. In most cases a longer barrel will generate a slightly higher velocity than its shorter companion. Smaller calibers accelerate faster and can take full advantage of the burn curve of 3F. Very large calibers sometimes produce better results with 2F because the charge is still generating increasing amounts of gas when the ball exits the barrel. One element that is often overlooked in load discussions is breech pressure generated by finer granulation powder, particularly using 4F as a charge in the barrel. Its a good idea to "proof" the barrel before testing heavy loads. This info and $6 will get you a cup of coffee in most coffee shops.

I think I would hesitate before using 4f for anything but priming a pan.

I don't believe 4f is going to blow your gun up though. Black powder only generates so much pressure.

Take a look at these charts on Triple 7, specifically the heavier weight bullets in the 50 cal loose powder like the Hornady385 grain HP-HB or heavier conicals with heavier powder loads

It would seem with a heavier projectile, finer grain doesn't translate into higher velocities. There seems to be some kind of wall (or break point if you will)

i tried my homebrew for this. what i found was ffff produced a more noticeable "crack" when loaded with just thumb pressure on the rod.
accuracy was dismal in the .54. ff and fff gave good results.
what did amuse me was if i thumped the ball/patch with the rod until the rod bounced i had a heck of a time igniting the charge. my story is it compressed the ffff into a pellet without the angular grain to catch fire. I had to pick the vent repeatedly to make it work.

deerstalkert said:

i tried my homebrew for this. what i found was ffff produced a more noticeable "crack" when loaded with just thumb pressure on the rod.
accuracy was dismal in the .54. ff and fff gave good results.
what did amuse me was if i thumped the ball/patch with the rod until the rod bounced i had a heck of a time igniting the charge. my story is it compressed the ffff into a pellet without the angular grain to catch fire. I had to pick the vent repeatedly to make it work.

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That sounds quite reasonable and correct. No place to catch a spark!

So according to the Lee powder dipper capacity chart (used for their powder scoops for metallic reloading), "Black Powder" with no manufacturer listed ranges from 13.9 grains *weight* for 1cc volume for 1Fg to 14.7gr (2Fg), with 3F and 4F at 14.9 and 15.9 grains weight for the same volume. Smaller grains will burn faster, raising pressures faster and then because there is more in an equal volume, higher if given enough time.

If pushing higher end loads, back off. Safe, and a great excuse to shoot more.

I’ve tested different manufacturers powders by weight over a chronograph while looking for a node, level velocity changes yet different weight charges in order to achieve a more consistent group size at various distances.

It’s very true that Swiss produces the highest velocity for a give weight charge no matter the caliber size.

And yes 3Fg vs using 2Fg can and will produce a higher velocity for a given weight charge depending on the powder used and caliber diameter.

In the end for me personally I prefer accuracy and repeatable POI vs velocity alone. If it won’t hit where you’re aiming then you’ll be better off tuning it to where POA and POI are the same even if it’s only going 1,550 fps.

The rifle will tell you what it likes just as the bullets flight never lies.

Smaller grain reaches it's peak pressure faster. When the projectile has moved the height of the powder column, the volume has doubled and harder to maintain the same pressure. So powder that is slower to peak pressure is safer, all other factors being the same.
There's quite a few variables that can affect time to peak pressure including composition and construction of the powder as well as grain size.
I have heard of people using 4f as a main charge with acceptable results but I would advise treading carefully with that.
If the peak pressure exceeds what your barrel can withstand, it'll let you know. Outside of testing facilities you might not find where you are until your gun chooses traumatic disassembly.