Fast burning Powders vs. Slow burning?

My general assumption from looking at reloading charts is

Relatively slower powders (specific for the caliber in question) require more powder and produce higher velocities.

Relatively faster powders hit their sweet spot at lower velocities and usually use less powder.

The energy density between powders can vary quite a bit with nothing to do with the burn rate. But the faster powders tend to waste less of that energy.

I don't think you can mess with pressure all that much (in an autoloader) by changing your powder. No matter what powder you use, you'll end up in a fairly narrow band of pressures that work well. The charge weights and velocities you end up with may change quite a bit, though, dependent on the powder.

This is all just my own personal brand of hogwash. I don't stand by it and it wasn't the result of any testing, personal experience, or science.

The slower powders work well with longer barrels and faster will work better in a shorter barrel. Most test data is in longer barrel weapons. I use faster powder in snubby revolvers for that reason. The most accurate powder as a general rule will be one that fills most of the case. Some of the slower powders at very low pressure loads and lower charges can be position sensitive as well as they won't ignite as fast giving poor results. I am no expert but these are just my experiences. Hope this helps.

Also is there a relationship with energy per grain when comparing fast vs. slow powders?

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"Potential" for energy developed, maybe. The slower burning powders keep "pushing" the bullet longer, IF there is enough barrel to do it. The faster burning powders produce their max energy "quicker".

Sort of like pushing your car. Give it the biggest push you possible can from one spot. Measure the speed 3 feet away.
Now do it again, but give a little lighter push but keep pushing for 10 feet.
The lighter push that lasts longer will get it moving to a higher speed. At 3 feet it was slower than your "ONE PUSH", but at 13 feet it was moving faster.

Hope this makes sense.

The slower powders work well with longer barrels and faster will work better in a shorter barrel.

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Nonsense. My 30-30 revolver likes the same powders as a winchester 94. And my 9mm carbine likes the same powders as my Glock.

I keep thinking there "should" be a chart somewhere with conversion ratios for various powders. Something like 'Use 80% the weight of Powder X to get the same zing as Powder Y". It seems to me that would make sense, at least for powders with similar burn rates.

I like to use with Titegroup but I load some not very common calibers (e.g. 7.62*25) and being able to mathematically approximate/near equivalent loads (when I can't find Titegroup data) by using conversion ratios from things like Bullseye, one of the AA's, Unique or whatever might be handy....

Jerkface11, I have had some 2" barrel revolvers that are far more accurate and get a much better burn and cleaner with a fast powder like bullseye, and AA2 than persay HS6. Maybe I should have been a little more specific. I have my Glock and Super Blackhawk that do much better with Slower powders like 296, and HS6 and Bluedot. My 9mm SR9c shoots very well with bullseye. I don't think that it is as applicable to carbines and longer barrel (over 4") pistols and revolvers other than chamber pressure with the faster powders.

I agree with jerkface with the caveat that when you start getting down to 2 and 3 inch barrels the rules do change somewhat.

However in non snubby rifles and pistols the burn rate is determined by bore case ratios and pressure ratings. Bbl length doesn't figure into the mix.

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thanks for the feedback... mostly what I am thinking about is 4"/100mm barrel max, 2"/50mm min in the more robust handgun calibers....

Sig 239, 3.6" bbl.
I want to drive a 124gr jacketed bullet to 1100'/sec without spiking to pressures too high. Easily done in a 4.72" bbl.
I tried A#5 and it won't do it within load manual guidelines.
walkalong said he had success in a 3.2" bbl using n340.

Do I need a faster or slower powder than A#5?

I suspect powder characterics aren't necessarily consistent throughout their usable pressure range. Some that shouldn't work, may work. Some that should, may not.

What do you think?

I would also be interested in data on powder charge vs case capacity. Some sort of resource table with data like "recommended charge of powder Y in a 9mm load should be safe in .357 Sig even if multiplied by 1.??")

A specific target point for me is loading 125 grain copper plated HP into .357 Sig w/ Titegroup. Another would be same powder w/ 71 gr plated RN into 7.62Tokarev.

voicomp, what I've read and seen is that your idea of a ratio comparison, might work for a "portion" of the pressure range for the powders. Maybe at light loads that would work but not with more pressure; or even vice-versa. It assumes powder performance consistency throughout the burn range. I think it changes.

Important parts of what I am trying to do is guess what will reliably cycle a semi-auto action and/or make a decent plinker without excessive leading kinds of issues.

I am not looking to stop APC's, or cook up the bustiest possible banger in a particular caliber. If I want something "hot" for carry, I will buy premium factory ammo. If, God forbid, I ever have to explain shooting someone, I would be using "my stuff" only after I exhausted my supply of premium factory rounds (probably meaning the occurance of the (IMHO highly unlikely) event that the cops, courts, system, etc. have ceased to function, blah blah blah).

voicomp said:

thanks for the feedback... mostly what I am thinking about is 4"/100mm barrel max, 2"/50mm min in the more robust handgun calibers....

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It's been my experience the powder that gives you the highest velocity in a 4" barrel will also give you the highest velocity in a 2" barrel. Usually a slower powder will deliver the higher velocities with less pressure than faster powders. For example, using HS-6 in a .38 Special +P round will deliver higher velocities in both 4" and 2" revolvers than W231 without excessive pressures. Same holds true in the .357 Magnum even with a 2" barrel, W296 will deliver more velocity than HS-6 which will deliver more velocity than W231 and so on... This is from my own real life tests, not from book data and not a guess...

As a general rule, can I make the assumption that fast burning powers are better for low charges where a round will get a more complete burn, where Slower powders will give more velocity with less pressure at higher charges?

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When you say "low charges", do you mean low charge weights or low velocity loads? In either case, this is generally true.

Also is there a relationship with energy per grain when comparing fast vs. slow powders?

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Not really. Energy and burn rate are two entirely different things. A fast and slow burning powder can have the same amount of energy per grain, but the difference is the amount of time over which the energy is released.

Don

When I referred to low charges, I was thinking low grains of powder relative to the parameters I find in manuals. I usually load plinking stuff at or slightly above the minimums from the books. By using a fast-burning powder, like titegroup, I am hoping the relatively zippy powder can get mostly or totally done with the burn before leaving a short barrel. thanks!

With fast burning powders and large capacity cases you often have powder positioning issues.

Slow burning powders have a different, more gradual pressure curve. The felt recoil is also different and your gun's ability to function may be affected.

When using lead bullets, powder selection influences bullet alloy composition. If you don't figure the powder into that equation, you may lead up your barrel.

As a general rule, can I make the assumption that fast burning powers are better for low charges where a round will get a more complete burn, where Slower powders will give more velocity with less pressure at higher charges?

Also is there a relationship with energy per grain when comparing fast vs. slow powders?

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Usually. With reloading it seems there is always an "except" or "unless."

The "more velocity at lower pressures" of slower powders is most useful when moving heavy bullets.

Slow powders produce an extended pressure curve, good for long barrels. Short barrels don't do as well with slow powders. place a sheet (or a chronograph for that matter, anything...) in front of the muzzle of a few short and long barrel guns of a given caliber and you'll notice alot more unburnt powder with slow powder / short barrel. faster powder / short barrel not so much. Unburnt powder = wasted energy. What we're trying to do is maximize the area under the pressure curve. Peak pressure limit is limited by action and case strength, time is limited by barrel length. the trick is to find the combination that maximizes the area for a given barrel length / bullet wt in a given caliber. Many combinations make this a task with many answers, hence many opinions.

Some special cases like gas guns expect a certain pressure curve, enough port impulse to cycle the action but not batter it, so they have special additional requirements.

"I keep thinking there "should" be a chart somewhere with conversion ratios for various powders. Something like 'Use 80% the weight of Powder X to get the same zing as Powder Y". It seems to me that would make sense, at least for powders with similar burn rates."

We have Clark. He is a wealth of knowledge. Just ask him. I bet he has tried it & if not he well probably run it through Quick Load & give you an answer. Your second option is to buy your own Quick Load.

This is for revolvers only.
I am no expert and I am only drawing on my own experience.
I shoot and load nothing but 2 inch 357 snubbies using 38 special brass using total copper plated bullets.
I have loaded nothing but 110 and 125 grain TCP bullets over Bullseye (a fast burning powder) powder.
I have loaded the standard 4.5 grains of Bullseye and got great results for my range rounds apprx 950 fps.
It is recommended that you only go down or up 10% from the recommended load data.
I have exceeded this on the down side by a lot.
I have gone down as low as 3.0 grains of Bullseye to produce a super slow range round for my wife.
We have loaded and shot over 1000 of these rounds with no issues.
Now mind you I am shooting only 357 snubbies in 38 special brass and I would not do this with 357 brass.
I would not try this with a longer barrel gun as I would not want a squib and have the second bullet blow the gun up.
I am no expert but I do believe that you can go lower on the powder then the recommend 10% variance.
You must be mindful of the possibility of a squib round.
I would not exceed the 10% general rule on the high side for fear of destroying the gun.
I too have wanted the same nonexistent conversion chart that Voicomp ask for.
So far the only conversion chart that I can find is the information that loaders have contribute on this forum.
There are a lot of guys on this forum with a lot of great info you just have to keep asking.
Just my 2 cents

Guys, saying a slow pistol powder leaves unburnt powder in a 2" barrel is just not true. Most of the powder is burnt before the bullet even leaves the case let alone the barrel. What happens with a slow powder is, the oxygen runs out before the bullet leaves the barrel and when the bullet does leave the barrel the hot gasses are supplied with additional oxygen when they hit the air and reignite out the front of the barrel. The powder is already spent well before the bullet leaves the barrel and what you are seeing out the front of the barrel are the hot gasses reigniting, not powder burning.

the "yarchive" lead is a great link. Not super specific to the questions i was wondering but wondeful information on lots of the things i had pondered and/or probably would have eventually wondered about. THANKS!

ArchAngelCD said:

Guys, saying a slow pistol powder leaves unburnt powder in a 2" barrel is just not true. Most of the powder is burnt before the bullet even leaves the case let alone the barrel. What happens with a slow powder is, the oxygen runs out before the bullet leaves the barrel and when the bullet does leave the barrel the hot gasses are supplied with additional oxygen when they hit the air and reignite out the front of the barrel. The powder is already spent well before the bullet leaves the barrel and what you are seeing out the front of the barrel are the hot gasses reigniting, not powder burning.

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Seems like if hot gases are lit outside the gun that is wasted energy/propulsion.