Powder burn rate conundrum

[stubbicatt]

All, while looking for a suitable load for 357 magnum, now that my 2400 is gone, I discovered that Longshot is only 2 places "hotter" on the burn chart, suggesting that it is nearly equivalent.

Burn Rate Chart reference.

However, when researching loads using 158 grain bullets, the starting charge was 7.3 of Longshot, and 8.5 grains max. The starting load of 2400 is not printed on Alliant's website, but a max of 14.5 grains is listed. For comparison, 8.5 of Longshot is max while 14.5 of 2400 is max loading for this cartridge/bullet combination.

This makes no sense to me, seeing as it is nearly equivalent on the burn rate chart. The only thing I can think of is there must be a relatively HUGE jump between these two powders, demarcating a gap between slow pistol and fast rifle powders perhaps?

I'm ok following the recipes etc., so that's not an issue. What confounds me is the nearly twice the weight of 2400 to max out compared to the Longshot.

Anybody got a good explanation?

ETA: Anybody have any hands on experience with Longshot and cast 357 magnum loads they care to report?

[jwrowland77]

Different burn properties of the different powders plain and simple.

I try not to look at burn charts too much because if you look at three different charts, you'll get three different rankings listed.

I try not to understand since I don't have the lab equipment to test it.

[Sevens]

I definitely don't have an explanation but if you dig up different "burn rate charts" from different sources, you will often see how things vary, which is yet another clue that these charts simply aren't all that useful.

I have a few loads I have run in .357 Magnum with Longshot and I have chrono'd them as well but all were jacketed bullet loads.

[math teacher]

Burn rate is not a constant. It varies somewhat with different cartridges. Powders with similar burn rates may require vastly different loads. The data should never be interchanged.

[T. O'Heir]

"...max of 14.5 grains is listed..." Reduce by 10% for the starting load. Pretty standard.
Burn rate charts are all the same. Difference is what powders are included. Powders 'higher' on the list are not hotter, they burn faster the lower the number. The burn rate has nothing to do with the amount used. One powder will have larger grains than another.

[GJSchulze]

You are making the assumption that powders have the same density and same energy content. This is simply not true. As I understand it, burn rates are determined by shape of the powder kernel and any burn inhibitors. The active ingredient is nitrocellulous and/or nitroglycerin. For instance, 4.0 gr of Power Pistol for a 147 gr 9mm bullet takes up half the case, while 3.2 gr of Titegroup takes up 1/4 to 1/3 of the case (hence my squibs, so I don't use Titegroup anymore). Both loads have the same velocity.

In addition, burn rates are relative to each other and not absolute. Charts differ from each other as do load recipes because the don't all use the same barrel for testing.

So you can use burn rates to find alternative powders to use, but you still have to work up a new load starting at minimum. Don't get hung up about recipes being inconsistent; they just are. You must also be aware that high density powders (those that take up less volume) are likely to have a small spread between min and max. Titegroup had a spread of about .3 gr while Power Pistol has a 1.0 gr spread. If you've ever seen how few kernels make up .1 gr, you'd be very careful about weighing. If you are new to reloading I would stay away from such high density powders until you've had sufficient experience. This pertains to handguns and more so to low volume cases.

[Shotgun Slim]

I was studying True Blue as a new powder to try and when I compared it to Accurate #5 in some recipes in the Western Powder loading guide it loaded like a slower powder under some bullets and a faster powder under others. It occupies different spots on burn rate charts so obviously there is no cut and dried to that. Point is: burn rate charts are ok for rough reference but for sure use the manufacturer's load data to be safe.

[Nick_C_S]

seeing as (Longshot) is nearly equivalent (to 2400) on the burn rate chart.

How do you know?

Just because Longshot is #53 and 2400 is #55, doesn't mean that they are "nearly equivalent." Their burn rates can be very different. I can assure you - and as you alluded to - that the burn rate chart is not linear. Some powders adjacent to one-another will have nearly the same burn rate. Others may have huge differences. Furthermore, burn rates vary considerably, depending on who's doing the testing. I've seen lots of burn rate charts. When you compare any two, contradictions abound.

And as GJSchulze stated:

You are making the assumption that powders have the same density and same energy content.

He's right on the money.

Bottom line, you're comparing apples n oranges.

I have no experience with 2400 or Longshot. I load a lot of 357 Magnum; but I almost never use propellants so slow. If I'm loading 158gn lead, I'm using Unique or HS-6. If I'm loading 158 JHP's, I'm using Power Pistol or AA7. The only exception is if I'm loading for my 8-3/8" barrel beast (rare), I'll reach for the slow burning W296.

What would be helpful is if you told us your ammo purpose, and the specific bullet used (lead or jacketed). Also, why did you select Longshot? Did you buy some; or are you still contemplating a purchase?

[Sevens]

Burn rate lists/charts are phenomenal tools for:

opening up discussions in handloading forums... and precious little else.

FWIW, Longshot is a useful powder in .357 Magnum and I won't speak for the OP, but can tell you why I ended up trying it in .357:

Bought it specifically for chasing velocity in 10mm. It does that well and meters great. A natural handloading curiosity made me say "good stuff, get 8 pounds, where else can I try it?"

In .357 (and .44 Mag), it makes loads that "feel" more like true magnum loads, distinguishing itself from middle of the road (Unique/Universal) type loads and it does so at -far- lower charge weight than my favorite slow burners like 2400 & AA#9. It runs out of gas and falls short in battling for 'top velocity' but they are strong enough to run my Coonan 100% of the time, which Universal will not.

It's a fine powder and one that would be a "must have" at my bench.

[mehavey]

Burn Rate is only one element of how the chemical energy is released
in modern powders/cartridges:

- Explosion Heat/Potent'l (energy density)
- Specific Heat Ratio (change in energy per unit mass/per unit temperature rise)
- Burn Rate (fuse speed)
- Progressivity (change in burn as pressure increases)
- Progressivity Limit (where things flatten out)
- Factor B ("Fudge Factor")
- Density (of the propellant -- 'fluffy' vs 'mud')

Blue VolksWagon ≠ Blue Peterbilt

[mehavey]

8.5 of Longshot is max while 14.5 of 2400 is max...

When things actually begin to happen after primer strike, LongShot and 2400
react as two very different propellants:


In the end, this is an area-under-the-pressure-curve problem.
And the inputs to the equation for the curves are very different

{Edit: Sorry, but QuickLOAD's copyright holder, NECO, has expressly denied permission for anyone to use graphs from their software on Internet forums. The raw data is not copyrighted, though, so you can export to Excel and make your own graph from it.}

[stubbicatt]

Thank you all for your input.

I too bought Longshot for use in 40 and 9mm, and it has performed well. I rarely shoot those calibers anymore, and have been in search of a substitute for 2400 as I cannot seem to find any hereabouts.

Since I have the 8 pounder of Longshot, I thought to look to see if it would work well in 357 magnum, sort of middling loads, shooting 160 grain Lyman "big groove" RNFP bullet. It seems there are load recipes available to use in this application. However, the pressures it generates, even at starting load, seem very high according to the Hodgdon website loading data, which puts me off a bit.

My other powder which I have in depth is WW231, with a small amount of WSF. I can find some 231 data for 357 mag which will achieve the moderate performance I seek, so perhaps I will try that instead of the Longshot. Perhaps I will try a SR4756 if I can find some locally. It seems to be a pretty good choice for what I have in mind, with lower pressures for moderate velocities.

Again, thanks for your good hearted suggestions.

[TimSr]

If the amount used was based on burn rate, Trail Boss would be even more interesting to explain.

[mehavey]

STUBBICAT:

If you look at Hodgdon's 38Special+P loads for Longshot, you'll see a 5.5gt/17ksi load.... about perfect for starting point of lead bullets.

I don't have QuickLoad access right now, but this is where it shines. Barring having actual QL data, kicking the load to 6.0gr to make up for the extra 357case volume/upping pressure to 20ksi (BN 12-13ish) would be my suggestion.

You want that fast rise in pressure for lead bullet to seal the bore quickly,

[mikld]

Burn rate charts only tell you if one powder is faster than another. The burn rates are not linear. Number 50 may be faster than number 51 (just random numbers), but you don't know by how much! 50 and 51 may be right next to each other on a chart but that's only because there may not be a powder that fits between them. They could be similar in burn speed, or they could be waaaay different...

Trying to think of a good way to explain this. Say you had 60 men in a room and rated them by body weight. The lightest man was 125 lbs. and the heaviest was 220, and they were numbered from 1 (for the 125 pounder) to 60 (for the 220 pounder). Number 5's weight may be 150 lbs. but number six may not be 151 lbs., he could be 180 lbs, as our "chart" only tells us number six is heavier and not how much heavier...

[mmb713]

Longshot should be quite useful in 357 Magnum. It will never get you up to H110/296 velocities but it will get you higher end mid-level loads, probably better than SR4756, which has been discontinued. Good luck finding any of that. WSF, which I recently saw on my LGS's shelf, should work well too. If you want better magnum performance from a 2400 substitute keep your eyes peeled for AA#9, Enforcer or 4227. For moderate velocity loads anything from Unique up to Longshot on the burn rate chart will get you where you want to be.

[Lost Sheep]

GJSchulze hit it first. Quickness ((Burn rate) is not closely related to energy density.

You may see non-proportional relationships among

1) weight energy density (Energy per unit weight, influenging the powder charge weight)

2) volume energy density (how full the case will be)

3) burn rate.

The relationships are complex. This is why we rely so heavily on manuals listing loads that have been thoroughly tested in laboratory settings where people are protected against catastrophe.

Lost Sheep

[black mamba]

I have used a lot of Longshot in both 44 mag and 45 Colt, and in loading those two great cartridges it is closer in burn rate to Herco or Power Pistol. Regardless of the chart, Longshot is a good deal faster than 2400.

[stubbicatt]

Thanks guys. A lot to digest, for sure. I like the analogy of Mikld about the weights of guys in the room. That makes sense to me.

Mehavy, that is good advice about obturation. I learned from Taylors that the groove diameter is .355", so I'm *pretty sure* that obturation shouldn't be quite the issue it might be in a .358 or so bore.

Since the lowest charge weight of Longshot has pretty high pressures associated with it according to the manufacturer's website, I have abandoned that number.

Fortunately, the other day, I found 2 pounds of 2400, so I reckon I'll be in clover for awhile. Now to find my bullet mould and cast up some slugs. This is very exciting times. The Uberti is a very pretty rifle, and the fit and finish is very good, with only the wood at the rear of the fore end a little proud of the front of the receiver/frame where it meets up. Who knows, maybe it is supposed to be like that.

I had intended to fire a few jacketed rounds through the barrel to make sure it was pretty smooth, but I reckon not, now that I've learned that bore diameter is .355 inches. Should be swell for cast boolits, but I'm reluctant to shoot the jacketed bullets through a tight bore like that.

I reckon my 20 to 1 or wheelweight alloy ought to be a good choice.

I like the rifle just fine, only the trigger pull is pretty stout at what seems to be about 8 pounds or so. It does break clean, so that is a plus. Perhaps I'll find a good local gunsmith who can bring that down to about 4 pounds or so, and keep the clean break. Too, I'm thinking a Marbles tang sight, since I don't see well enough anymore to get a clean front sight using the standard, barrel mounted, buckhorn-style, rear sight.

It is nice to be excited about something again.