Amount of Propellent Burnt

[59FLH]

I run what-ifs with QL for:
Fastest powder that fills the loaded case at SAAMI max pressure with lowest muzzle pressure for barrel length.

My muzzle pressure goal is ~8Kpsi or less, an attribute I noticed of successful underbore cartridges.
I believe this goal provides for efficient powder burn, clean muzzle release of bullets, and eliminates secondary pressure spiking.
I'm not a suppressor shooter, but I can picture this as something to mind there as well (esp. for semi-autos).

Added; no matter the barrel length, if you keep adding powder, pressure and velocity will go up. But, so will muzzle pressure.

Likewise, right or wrong my thought process as well. Thanks.

 

[Dmagna]

People have suppressors, you can't because of ordinance, that seems like politics. You mention the popularly of over bore cartridges and short barrels.

How does that explain 100% powder burn and it's effects?

When running a suppressor you have to be really careful of your burn %. Can't too much of a fireball into the can, it can't take it. So with the trend of shorter barrels you have to ride the fine line of powder burn and case fill. Case fill and is what gives you good ignition, big overbore magnums will always have some powder being unburnt.

I didn't say anything about politics, you did.

I use a powder that gives me best case fill and SD/ES with my rifle.

 

[59FLH]

I use QL. I would say I like to see it burned by 80% of barrel length, but really as long as it calculates full burn within the barrel I'm ok.

Mike, no bash, what is your experience with this theory that works for you?

When running a suppressor you have to be really careful of your burn %. Can't too much of a fireball into the can, it can't take it. So with the trend of shorter barrels you have to ride the fine line of powder burn and case fill. Case fill and is what gives you good ignition, big overbore magnums will always have some powder being unburnt.

I didn't say anything about politics, you did.

I use a powder that gives me best case fill and SD/ES with my rifle.

Dmagna, understood, shooting suppressed is a factor I had not considered thanks for the reply. My apologies for the politics jab.

 

[JiminAZ]

Might be helpful to note the distinction between completing the powder burn and completing the expansion/cooling of burn-generated gasses

The incandescent flash at the end of our barrels often isn't "unburned powder". It is completed burn gasses escaping the barrel that are still hot enough to incandesce.

 

[Mikecr]

Yeah it's not like we're wasting powder really. But we need consistent pressure, and it helps to have the powder burning completely inside the barrel (ideally, most in the chamber). This takes bottling the charge in the chamber, so that it's confinement is constant through the burn. Any unburned powder slug traveling with the bullet will burn differently and inconsistently.

 

[Seabeeken]

That's great, how does the 100% burn affect velocity and accuracy? Care to share the science?

338 rcm doesnt hold enough slower powders to get the speed i wanted so i tested a number of powders and ran many grt simulations Before testing. The hammers like faster burning powders so thats where i worked with it.. in grt i was looking for 96-100% case fill and Same amount of propellant burn all while trying to achieve 3000 fps. Most of my 2520 and tac loads worked very well. Im testing leverevolution tomorrow as grt shows it hitting 3000 but we will see if the accuracy is there. I did hit 3000 with A-4350 and 185 tsx but im sure it was a bit over pressure but no visible signs on the case. Ive learned to stick to ball powders with the rcm to get the most out of it. Is there a science? I dunno, i just try to work with powders and burn about 100% for efficiency. My 284 and 257ai love imr-4166 and give me impressive speeds and accuracy. With all this said, keep in mind im shooting light hammers and barnes tsx, not cup and core bullets. Just my experience in my rifles. I seldom shoot slow powders anymore. ymmv

 

[59FLH]

338 rcm doesnt hold enough slower powders to get the speed i wanted so i tested a number of powders and ran many grt simulations Before testing. The hammers like faster burning powders so thats where i worked with it.. in grt i was looking for 96-100% case fill and Same amount of propellant burn all while trying to achieve 3000 fps. Most of my 2520 and tac loads worked very well. Im testing leverevolution tomorrow as grt shows it hitting 3000 but we will see if the accuracy is there. I did hit 3000 with A-4350 and 185 tsx but im sure it was a bit over pressure but no visible signs on the case. Ive learned to stick to ball powders with the rcm to get the most out of it. Is there a science? I dunno, i just try to work with powders and burn about 100% for efficiency. My 284 and 257ai love imr-4166 and give me impressive speeds and accuracy. With all this said, keep in mind im shooting light hammers and barnes tsx, not cup and core bullets. Just my experience in my rifles. I seldom shoot slow powders anymore. ymmv

Does where in the barrel length you hit 100% powder burn have an effect on your speed and/or accuracy?

 

[QuietTexan]

Yeah it's not like we're wasting powder really. But we need consistent pressure, and it helps to have the powder burning completely inside the barrel (ideally, most in the chamber). This takes bottling the charge in the chamber, so that it's confinement is constant through the burn. Any unburned powder slug traveling with the bullet will burn differently and inconsistently.

You're exactly correct, bottling the charge in the chamber is very important because pressure affects the burn of discrete kernels of powder - it's physics, Gay-Lussac's Law states that the pressure of a gas at a constant volume is directly proportional to the temperature. Meaning higher pressure = hotter temps. Hotter peak temps will burn through kernels faster, so hitting the correct, highest pressure in the chamber does more for having a consistent burn than any amount of barrel length. That's why a pistol length barrel will hit 80% or better of maximum possible velocities for a chambering from the longest possible barrel; the most meaningful mass of powder is burned very early on because of 60k+ chamber pressures in any decent modern round.

QL shows the point in the burn where peak pressure is reached. Running one of my N565 300 RUM loads pressure peaks at 65000psi when the bullet is at 3" of travel, and goes below 30k PSI by 14"of travel.

Velocity pickup from a longer barrel is "free" in the sense all that velocity was already paid for in the chamber and the longer barrel is keeping the bullet on the wave longer. There's a 14% velocity pick up by doubling barrel length with that 300 RUM load meaning the last few inches barrel, while still helpful, are returning a significantly smaller benefit that the first 14 inches. @Ernie made this very good point in another thread that if a shooter needs to hit an arbitrary velocity for a bullet then short barrels can get you there - because 80-90% of velocity comes from the chamber burn. A 300 RUM in a 14" will still outrun a 30-06 in any length because the first few inches of the barrel are all it takes to burn the most significant amount of powder.

I still run long tubes for the free velocity on most of my rifles because I don't care about how they'll pack down, but I have multiple 8-16" barreled SBRs and just got my first bolt action pistol. They're a fun distraction from my mega-thumpers projects.

The incandescent flash at the end of our barrels often isn't "unburned powder". It is completed burn gasses escaping the barrel that are still hot enough to incandesce.

That's right, primary flash is the wavefront of the hot ejecta gasses hitting cooler air, the gas is hot and visual light is a form of radiation. There's no secondary flash from re-combustion in the ejecta after oxygen exposure from a rifle because there's more than sufficient oxygen in the case and volume in the barrel to consume all the propellant.

Very short revolvers and SBRs will occasionally shoot sparks - those are partially consumed kernels that can't burn fast enough in low pressure to be completely consumed. They don't show up as a fireball of consumed kernels but unburned gasses because the surface area of the kernel never burned through.

 

[akmtnhnt]

Does where in the barrel length you hit 100% powder burn have an effect on your speed and/or accuracy?

I don't find that to be relevant to accuracy. And I haven't noticed a coincidence between complete burn length and velocity, except that if you're not getting 100% burn in the barrel, that's never a powder that's producing the most velocity for what you have.
I go for velocity first, then optimize timing finding the most accurate I can with that, then play with seating depth until I settle upon something.

 

[akmtnhnt]

338 rcm doesnt hold enough slower powders to get the speed i wanted so i tested a number of powders and ran many grt simulations Before testing. The hammers like faster burning powders so thats where i worked with it.. in grt i was looking for 96-100% case fill and Same amount of propellant burn all while trying to achieve 3000 fps. Most of my 2520 and tac loads worked very well. Im testing leverevolution tomorrow as grt shows it hitting 3000 but we will see if the accuracy is there. I did hit 3000 with A-4350 and 185 tsx but im sure it was a bit over pressure but no visible signs on the case. Ive learned to stick to ball powders with the rcm to get the most out of it. Is there a science? I dunno, i just try to work with powders and burn about 100% for efficiency. My 284 and 257ai love imr-4166 and give me impressive speeds and accuracy. With all this said, keep in mind im shooting light hammers and barnes tsx, not cup and core bullets. Just my experience in my rifles. I seldom shoot slow powders anymore. ymmv

I've found if you're seating pretty deep into the case due to length restrictions, ball powders take up so much less volume than stick, you can still get enough in there to get the pressure up and most of your velocity back.

 

[Seabeeken]

Does where in the barrel length you hit 100% powder burn have an effect on your speed and/or accuracy?

I try to keep burnout as near to the end of the barrel as I can when selecting powders but to answer your question, not that I can tell. With the RCM case, there are only a few powders that will be a perfect fit with respect to speed. My rifles all shoot .5 moa or better, with a couple shooting under .1
The 338 RCM is what got me looking into the efficiency of powder burn.

 

[Ernie]

When selecting a powder from a choice of multiple powders how much of a factor is 100% burnt by the time the bullet exits the barrel?

If it is a factor, at what point along the barrels length is desirable?

I realize there exceptions to every rule and who gives a darn if the load is accurate and it kills, but for those of you who have an understanding of this phenomenon in ballistics is there a rule of thumb, theory, or fact?

I never really concern myself whether it's 100% burnt, by the time the bullet exits the barrel.
I am just going for a performance level.
You guys are too smart for me.