Burn rate, charge weight, barrel length?

S

Shadow9mm

New member
So I have been reloading for a while. I am trying to understand how several things inter-relate.

Burn rate
charge weight
barrel length

How does one understand which powder and which charge weight is optimal for a cartridge and or barrel length. In general one would expect to simply be able to choose the powder with the highest velocity in the manual, however most of the manuals I have don't list barrel lengths, or they are longer or shorter barrels than what I have.

For example. In my case I am loading for 38spl currently.
158g Hi-Tek coted SWC
Powders I have are HP-38 and Power Pistol
2 pistols
357 mag chamber 6in barrel
38spl +P chamber 1.8in barrel

My plan was to shoot a start and a max charge of each (already worked up from start) in each barrel length. My hope was to understand from this how efficient each powder in each barrel length by velocity increase from start to max in each barrel length.

I am currently loading up a test batch 6rnds each, hoping to test tomorrow. Curious to see how it plays out and whether I can learn anything, or whether its a dead end. All loads within published data.
 
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In general, the powder that gives the highest velocity will do it in almost every barrel length. But if you have a very short barrel and a very slow powder, the muzzle flash and recoil make it less than ideal. You can go to a faster powder, get nearly all the velocity of the slow one, and have a much more pleasant load to shoot and control.
 
Very roughly, very very roughly..
The faster the burn rate, the less the charge weight. The lighter the bullet, the faster the burn rate.

.357 Magnum is one of only a few straight wall pistol cartridges that benefit from longer barrels, right out to carbine length. It’s a very high pressure round, for a handgun.

The trick to finding maximum load is to find the right modern article done by a reputable hand-loader to find the latest optimal load for exactly your bullet, case and primer.

Then have a good strong gun that you inspect regularly. Going overpressure by a few percent won’t make your pistol in to a cherry bomb. But even under pressured, the risk is not zero.

Here is my advise from an old fart- for .357, there is no significant advantage to pushing the load. Ease up, you’ll worry less and whatever you hit is still in a world of hurt.

.38 special is a little different on account of history.

My reloading manual from 1958 has data for “regular” and “good strong revolvers”. There always was “+p”, it’s just now we have a name for it.

If your pistol can handle +p loads, again, you’ll rest easy knowing you’re not at the bleeding edge of max load, and ain’t nobody going to tell the difference between the loads.

Shot placement is the dominating factor.
 
the 38spl is P+ rated I updated the original post to reflect it. Both guns are Rugers so they are sturdy.

I'm not trying to push to the bleeding edge. I'm just trying to better understand and figure out a way to test to find which powders are burning the most efficiency and in what charge weight zones in my barrel lengths.

Ideally My goal is to have the 158g SWC coming out of both guns at 950 fps, but I know that may not be possible with the snubbie. I also want to know if it is worth working separate loads up to optimize for barrel lengths.
 
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In past experiments by others, I've seen a faster powder produce lower average velocity but smaller velocity variation than a slower powder did in the snubby, and the slowest round produced by the slow powder, despite the faster average velocity, was slower than the slowest fast powder round due to its wide velocity swing. This suggests a lot of variability in how much unburned slow powder is ejected from the short barrel, while the fast powder can finish burning in the short distance involved. YMMV.
 
My experience is more with rifles, but to a point it applies to handguns too. With rifles, the powder that gives the best speeds from a 26" barrel will also give the best speeds with a 16" barrel. Although the 16" barrel will be significantly slower. There is no advantage to using a faster burning powder in short barreled rifles.

This is because even the slowest powder will completely burn in even the shortest legal rifle barrel. Having a longer barrel gives the pressure generated by the burning powder more time to accelerate the bullet.

But in handguns with much shorter barrels a faster burning powder could be an advantage with shorter barrels.

Within the same cartridge slower burning powders give best results with bullets that are heavier for caliber while faster burning powder is usually better with the lighter bullets. For example H4350 is an excellent 30-06 powder with bullets 150-180 gr. But if you choose bullets heavier than 180 gr, and even right at 180, a slower burning powder is needed to efficiently shoot those bullets. So bullet weight also influences which powder is best
 
jmr40 said:
My experience is more with rifles, but to a point it applies to handguns too. With rifles, the powder that gives the best speeds from a 26" barrel will also give the best speeds with a 16" barrel. Although the 16" barrel will be significantly slower. There is no advantage to using a faster burning powder in short barreled rifles.

This is because even the slowest powder will completely burn in even the shortest legal rifle barrel. Having a longer barrel gives the pressure generated by the burning powder more time to accelerate the bullet.

But in handguns with much shorter barrels a faster burning powder could be an advantage with shorter barrels.

Within the same cartridge slower burning powders give best results with bullets that are heavier for caliber while faster burning powder is usually better with the lighter bullets. For example H4350 is an excellent 30-06 powder with bullets 150-180 gr. But if you choose bullets heavier than 180 gr, and even right at 180, a slower burning powder is needed to efficiently shoot those bullets. So bullet weight also influences which powder is best
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So with rifles, in general, all powders are getting a full burn, but there is less time for the bullet to ride the pressure wave.

with handguns, due to the shorter barrel, you have to be more careful to select a powder that will get a full burn due to the short barrel length.

And with cartridges usually the faster powders in the range are better for the lighter bullets, and the slower ones better for the heavier bullets.

How does one determine if one is getting a full powder burn in a handgun cartridge other than looking for a fireball?

in one instance I tried AA #7 in a 9mm loading out of a 4in barrel, 115g bullet, start was 7.6g, max of 8.4g. however after 8.0g there was zero velocity increase, actually a slight decrease. so could one assume that the powder was not getting a full burn and that 9mm powders, for the selected bullet weight need to be, in general, faster burning? or that it may perform better with 124 or 147g bullets?

So is it possible to select an ideal powder based off burn rate for a given cartridge and bullet weight, or an ideal bracket within the burn rate chart?

The main issue i see with reloading data is barrels that are too long, or no length listed. with pistols short barrels this could significantly impact ones ability to get a full burn.

Testing today. will try and get results posted tonight.
 
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Shadow9mm said:
in one instance I tried AA #7 in a 9mm loading out of a 4in barrel, 115g bullet, start was 7.6g, max of 8.4g. however after 8.0g there was zero velocity increase, actually a slight decrease. so could one assume that the powder was not getting a full burn and that 9mm powders, for the selected bullet weight need to be, in general, faster burning? or that it may perform better with 124 or 147g bullets?
Click to expand...

I haven't seen A#7 plateau. Velocity has increased from 8.7 to 10.2 grains (from a 4.6" barrel).

After a while, chasing the 'efficiency' of a powder can be pointless. The usual goal is velocity and accuracy. If a slow powder does what you want it to do, does it really matter whether it is efficient or not? I get some of the best accuracy in 9mm from A#7. And high speed, too!
 
Ballistic Efficiency is the portion of a powder charge's energy that is successfully converted to its bullet's muzzle energy. So, BE=ME/E of charge, expressed as a percentage. Obviously, for a given load, it will vary with barrel length.

Let's suppose you have a rifle powder with 4000 J/g of chemical energy and you use a 50-grain charge (3.240 grams).

3.240 g × 4000 = 12960 J.

1 joule is 0.7376 ft-lbs, so this is:

12960 × 0.7376 = 9,559 ft-lbs

If the muzzle energy is 2900 ft-lbs, then

BE = 2900 / 9,559 = 0.3035 = 30.35%


Shadow9mm said:
So with rifles, in general, all powders are getting a full burn, but there is less time for the bullet to ride the pressure wave.
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Not really. First, as board member Hummer70 pointed out long ago if you put a white sheet out in front of a rifle firing point, you collect a lot of unburned powder particles. You can collect them up into a pile, when you have enough, and put a match to the pile and it ignites and burns up. While a rifle has a longer barrel, the powders are much slower burning and when the bullet passes the location at which peak pressure occurs, commonly an inch or so into the bore, then the pressure starts to drop and temperature and pressure go down with it, slowing the powder burn even more. The powder that was shoved down the bore with the bullet is often still lighting up at that point. It exits after the bullet along with the muzzle blast. Once outside, it is surrounded by combustion product gases and can go out as happens with a squibbed-out charge. Typically, overbore guns throw away more powder than the more efficient shapes.

Rife 24" barrel times are usually in the low 1's of milliseconds. Handguns are typically half that (4" 357 Magnum) to just under 1 ms (5" 45 Auto 230 grain bullet over 5 grains of Bullseye), so the barrel time is normally longer in the rifle. In both instances, as long as there is more pressure than is needed to overcome bore friction, the bullet keeps accelerating in proportion to the force from that pressure less the friction-overcoming force.

BE with fast pistol powders can approach 50%. I don't think I've ever seen it over 35% for a rifle, with some of the overbore rounds below 15%. A lot of energy goes into heat and muzzle blast with those rounds. IIRC, Hatcher put the 30-06 at about 30% with military ammo using assumptions that match some of those in the SAAMI paper on calculation recoil energy. That agrees very well with QuickLOAD and GRT.
 
The load below falls within the listed .38 Special +P load data listed in Winchester's 15th Edition Reloader’s Manual for W540. W540 and HS-6 are one and the same, being made by St. Marks Powder, Inc with just different labels on them. Since it's their powder, and Hodgdon has never made a powder, IMHO they are in a better position to know load data.

Ideally My goal is to have the 158g SWC coming out of both guns at 950 fps, but I know that may not be possible with the snubbie. I also want to know if it is worth working separate loads up to optimize for barrel lengths.
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Shadow,

You likely won't be able to get 950fps out of a .38 Special with a 1.8 inch barrel with a 158gr SWC using a safe load. I did testing with what is known as "the FBI Load" several years back. The very best load I found was 7.0gr of HS-6 with a 158gr SWCHP, which gave me 940fps out of my 2.5 inch snubbie. Regardless, I would consider using this load for both your handguns. Having ammo interchangeability between your 2 handguns would be a good thing.

Don
 
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Since that load is above Hodgdon's published +P load, unless you have it in load data manual, the board warning needs to be included at the top of your post. I am putting it in. If you know of a reliable standard data source that includes it, then feel free to remove the warning.
 
So I did make it to the range today. Here is the data I got. I had a few chrono problems today. Clouds were moving and I was going from shade to bright sunlight. Even with the sun shades the chrono was not happy and I had several round that would not read, and I had 1 set that read at 150fps with some other ammo I was using to try and diagnose the problem. I attempted to get 6rnds per test group.

HP-38 Start 3.8g
1.8in barrel, 664fps, sd 35.95, es 69 (only 3rnds chrono problems)
6in Barre,l 746fps, sd 50.82, es 89, (6rnds)

HP-38 Max 4.3g
1.8in barrel, 726fps, sd 13.44, es 19 (only 2 rounds, chrono problems)
6in barrel, 841fps. SD 22.78, ES 60 (6rnds)

Power Pistol Start 4.8g
1.8in barrel, 741fps, sd 14.01, ES 34 (6rnds)
6in barrel, 866fps, sf 9.04, ES 26 (6rnds)

Power Pistol Max 5.4g
1.8in barrel 806fps, sd 9.63, ES 25 (5rnds chrono problems)
6in barrel 954fps, sd 11.0, ES 29 (6rnds)
 
The BB specs are pretty impressive. The Power Pistol results are what I assumed would be about the limit, but, obviously, there are more powders to try. I note that Hodgdon's highest velocity in +P 38 Special is with CFE Pistol followed by IMR Blue. I've not tried either powder, personally, but the Hodgdon data doesn't support them getting what BB is getting out of their loads. BB may have a proprietary powder.
 
My only issue with Hodgdon load data is the barrel lengths. 38spl and 38spl+P with a 7.7in barrel? 357 mag with 10in barrel....

I have never tried ether of those powders either. I have looked at CFE Pistol a couple times now, will have to grab a pound to play with...
 
SAAMI has standardized two pressure and velocity barrel lengths for many revolver cartridges. One is a 4" barrel with a 0.008" vent slot to mimic revolver barrel-to-cylinder gap. The other is a longer barrel with no vent meant to mimic a single-shot handgun. The latter has its length measure from the breech face, the same as a rifle or self-loading pistol barrel would be. The former is the actual barrel and forcing cone length, so it is longer by the maximum cartridge length plus the gap, if you want to compare its length to the single-shot barrel length.
 
Quote:
Originally Posted by USSR View Post
You likely won't be able to get 950fps out of a .38 Special with a 1.8 inch barrel with a 158gr SWC using a safe load.

Buffalo Bore does it.
Click to expand...

I have long questioned Buffalo Bore's listed velocities. There is nothing that requires them to accept SAAMI pressure standards.

Don
 
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