Finding optimum burn rate?

[NotSoFast]

I've been thinking lately about how I would go about finding the optimum burn rate, a burn rate that would burn all the powder inside the barrel, yet not so fast that it would cause an early pressure spike and possible damage. The trouble is, not having a whole lot of experience in reloading, I don't know where to start.

Let's say I start with a .40 S&W in a Glock. I do know I would start with the powders listed in the popular manuals. I have three I rely on, Hornady, Lyman, and Hodgdon. From there I would think I would want to not only chronograph the shots, but also somehow determine that all the powder is burned for a particular type powder.

My question is, with the tools I have available as an amateur, or could reasonably afford, how can I determine the powder that finished its burn just as the bullet leaves the barrel? And of course, if I am using a longer barrel, how to adjust for that.

I would also be interested in determining this for my rifles as well, one at a time.

Three things have brought this on. One is the Speer Short Barrel ammo, Two is the acquisition of a Glock 35, and three is wanting to come up with a powder that doesn't have a lot of visible flash in the dark.

I'm looking forward to learning more.

Chuck

 

[helg]

You need an internal ballistics program, which models powder burning and accelerating bullet inside a barrel. Among the programs there are QuickLoad, Sierra Internal Ballistics and several others.

Smokeless powder burns fast at the beginning of the process. In a handgun, which is loaded in the way that 100% powder is burned exactly when bullet leaves the barrel, 95% of the powder is burned when bullet did yet not pass even half of the barrel. Therefore, load with 100% burn with the bullet still inside is not the best for performance.

If you give your bullet caliber, length, weight and type (lead, jacketed), powder type and barrel length, I will give you internal ballistics estimated results for different powder loads, which include muzzle speed and %powder burned while bullet in inside.

 

[D. Manley]

Just MHO but while a complete burn is not a bad thing, its not something to be overly concerned about. Keep in mind that within a caliber, the slower burning powders still produce the highest velocities even, in short barrels...albeit, with the accompanying muzzle flash thrown in.

I think I understand where you're going but in the example of Speer's Short Barrel ammo, it's more a function of the bullet weight & design being optimized to perform within a given velocity window. Using their bullet and load data you can achieve essentially the performance level.

Muzzle flash is only partly due to a powder's burn rate. Some very fast powders still have significant flash. FWIW, Ramshot's Silhouette provides the highest velocities with the lowest amount of flash of anything I personally have seen. Full powered loads display no appreciable flash when shot indoors. It's a fantastic powder for 9MM and although I've not yet used it to any extent in .40, so far it's been very good.

 

[Walkalong]

a burn rate that would burn all the powder inside the barrel, yet not so fast that it would cause an early pressure spike

Sounds nice, but, like D. Manley posted, it doesn't quite work like that.

 

[NotSoFast]

Thanks for the idea. I hadn't thought of internal ballistics programs. I'll look into it.

 

[NotSoFast]

I understand Speer did change the powder for their SB ammo. The bullets are the same as loaded in their regular barrel ammo with the exception of being more completely burned in the shorter length barrels.

I've heard that Ramshot Silhouette works best for lowering flash. I haven't tried that yet. I'll have to see if my local dealer can get some in.

And you may be right that powder fully burned in the barrel may still give a decent flash. I'm sure it would differ for each powder/barrel/bullet combination and there are a LOt of those. This may just be a study in futility where I need to go back to speed and accuracy and not worry about the rest. lol

 

[bluetopper]

Two words..........Power Pistol.

 

[kelbro]

I would think that the crimp would be another variable that would be hard to model.

 

[helg]

crimp would be another variable that would be hard to model

QuickLoad has a parameter "Shot Start (Initiation) Pressure" for this. There are recommendations what to set it to for different types of bullets. While the exact number is unknown, playing with various numbers for the parameter gives a good idea how it affects results.

 

[243winxb]

Find the caliber you want to work with. The bullet weight your using. Then look at all powder. Pick the powder with the highest velocity and lowest pressure. The Hodgdon site is great for this. Looking at the 40 S&W 180gr HDY XTP SR4756 looks good to me. Unless its a type O on Hodgdons part, seems the one to pick. This is where another source of data is need.

 

[jpwilly]

^^^
For Example the 155gr Hornandy XTP using Longshot a slower powder gives more velocity with less pressure:
155 GR. HDY XTP Hodgdon Longshot .400" 1.125" 7.5 1129 24,900 PSI 9.3 1283 31,900 PSI
155 GR. HDY XTP IMR SR 4756 .400" 1.125" 7.9 1139 25,900 PSI 8.4 1223 31,300 PSI
155 GR. HDY XTP Hodgdon HS-6 .400" 1.125" 7.7 1035 26,500 PSI 8.5 1137 33,200 PSI
155 GR. HDY XTP Winchester AutoComp .400" 1.125" 7.0 1109 25,800 PSI 7.8 1223 33,800 PSI
155 GR. HDY XTP Hodgdon Universal .400" 1.125" 5.7 1056 23,900 PSI 6.2 1138 31,800 PSI
155 GR. HDY XTP Winchester WSF .400" 1.125" 6.2 1070 26,100 PSI 6.8 1159 32,500 PSI
155 GR. HDY XTP Winchester 231 .400" 1.125" 5.0 937 22,900 PSI 6.0 1103 33,000 PSI
155 GR. HDY XTP Hodgdon HP-38 .400" 1.125" 5.0 937 22,900 PSI 6.0 1103 33,000 PSI
155 GR. HDY XTP IMR SR 7625 .400" 1.125" 6.4 1087 26,800 PSI 7.0 1153 30,800 PSI
155 GR. HDY XTP IMR PB .400" 1.125" 5.2 1030 28,100 PSI 5.7 1084 32,400 PSI
155 GR. HDY XTP Winchester WST .400" 1.125" 4.6 957 25,400 PSI 5.3 1039 32,500 PSI
155 GR. HDY XTP Hodgdon Titegroup .400" 1.125" 5.4 1058 28,400 PSI 5.9 1139 31,700 PSI
155 GR. HDY XTP IMR 700-X .400" 1.125" 5.2 1054 26,600 PSI 5.8 1138 33,700 PSI
155 GR. HDY XTP Hodgdon Clays .400" 1.125" 3.6 854 23,300 PSI 4.0 942 30,900 PSI

 

[Ky Larry]

Shouldn't accuracy and reliablity be your first concern? I really couldn't care less if all the powder is burned in the barrel. I understand your concern about muzzle flash but not about burning all the powder inside the barrel.

 

[ranger335v]

"..how I would go about finding the optimum burn rate, a burn rate that would burn all the powder inside the barrel, yet not so fast that it would cause an early pressure spike and possible damage. The trouble is, not having a whole lot of experience in reloading, I don't know where to start."

Ignore all the theoritical stuff, you don't have enough data and, even if you did, it's mostly worthless to reloaders anyway. Which explains why no one even tries to provide all the esotoric info it would require to compute!

Where to start? Just use your loading manual's listed charges and test the accuracy of the efforts. After all, that's why we buy the books! They do know what they're doing and they aren't going to give us bad data so we don't need to duplicate their efforts. Use the powders they suggest, keep the ones that work best because THAT will give you the "optium" loads for your weapon.

Rarely will any charge be totally consumed in any barrel, it's not that simple. If you want low muzzle flash and blast, stick to slow speeds and minimum charges of fast powders. Higher bullet speed requires more of slower powders, and that makes for flash and blast. And leaves more unburned powder.

 

[Redneck with a 40]

JP, I load 40 S&W with Longshot, good stuff! Good thing I've got 4lbs of it, can't find it anywhere right now.