So, Do the big cased cartridges we all love burn ALL the powder contained? I'm talking the STW, the RUMs and Weatherbys and bigger. OR, does some of that powder exit the barrel unburned? If you say yes, do you have proof? WHY isn't it burned? Shouldn't the newer powders available have addressed the problem if it existed? Also, if all powder is not burned, does it accelerate throat erosion? I've heard some "experts" expound upon this while bashing big magnums. What do you guys know? mtmuley
Unburned Powder in Big Cases, Right?
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Michael Eichele
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I have experienced "unburned" powder exiting my muzzle with one rifle. This was a factory 30-378 with a 26" barrel.
What was the proof? It was unburned kernals of powder inside and stuck in the plastic lense of my chronograph. After that, I shot through some cardboard at close range. You could see where the kernals went through the cardboard.
Yes it is real and does exist.
Some remedies include using a faster powder or less of the powder you are using, using a longer barrel and a proper twsit for the bullets used.
Burn rates change a bit depending on how heavy a bullet is or isnt, primer type, bullet to twist ratio, temprature, bore quality and probably more variables than you or I am aware of. All of these things go into how the powder will react in a given barrel. Some powders in a given situation will not burn fully in a large magnum. This makes it hard to predict any results without experimentation. It seems that when powder isnt burning efficiently, the necks are very black as well as the primer pockets. When you get it right, things appear much cleaner.
Bear in mind none of the above is scientifec proof. Just notes and thoughts from tens of thousands of rounds fired using a wide variety of calibers, bullets, powders and primers.
steve smith
Well-Known Member
I've found that one very important facor in finding unburned powder is whether or not the load was producing high enough pressure. Large charges of very slow powder in a fairly small case will produce these results. My 45LC with H110, even at max loadings, consistantly leave powder in the barrel, while top loadings in my 460 S&W rarely leave any. Only difference here is chamber pressure
As for finding it in a very overbore cartridge, well that entirely depends on how high or low the charge weight is, the burnrate of the powder, the weight of the projectile, as well as the barrel length.
A large amount of slow powder pushing a light for caliber bullet out of a short barrel will almost definitely leave unburned powder.
Using the slowest burning powders I could get my hands on (namely WC 872, IMR 5010, H-50BMG,) and loading to top velocities in my 30" barreled 270-300Rum rarely left any unburned powder in the barrel. Come to think of it, I never really noticed any unburned powder at any charge weight, with most exceeding 100grs. I'll attribute that to the barrel length.
As for finding it in a very overbore cartridge, well that entirely depends on how high or low the charge weight is, the burnrate of the powder, the weight of the projectile, as well as the barrel length.
A large amount of slow powder pushing a light for caliber bullet out of a short barrel will almost definitely leave unburned powder.
Using the slowest burning powders I could get my hands on (namely WC 872, IMR 5010, H-50BMG,) and loading to top velocities in my 30" barreled 270-300Rum rarely left any unburned powder in the barrel. Come to think of it, I never really noticed any unburned powder at any charge weight, with most exceeding 100grs. I'll attribute that to the barrel length.
MagnumManiac
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This is my belief, some powder types will burn far more efficiently than others. I agree with Michael Eichele, it's true, it happens some of the time.
An easy fix if it's happening with a single base propellant is to switch to a double base propellant that is slightly slower ie: switch H4831sc to RE22 for example.
The reason it's not burned is because the pressure hasn't risen fast enough to allow peak pressure to be reached, as you know as pressure increases so does the burn rate, and so as pressure is increased further more powder is burned quicker.
Throat erosion is caused by a 'plug' of unburnt powder moving from the brass case to the chamber throat, which is larger and longer in big cases than small ones. It acts very much like the glass beads in sand blasting on the barrel steel, and the more powder that is not burnt on initial ignition the worse it's effects will be.
Single base powders seem to be the worst for this, I'm not sure why, I think it is because double base powders release their energy quicker than single base powders, but switching to either a ball powder or double base extruded powder seems to prolong barrel life.
So to answer your question about big cases not burning all the powder, yes and no, it depends on your choice of powder and also loading technique, which by this I mean 'packing scheme' of your selected powder. If you slow drop the powder for a tighter pack or use the swirl charge method, you will get more uniform ignition and the powder will burn correctly, and lessen the chance of the 'plug' forming.
Cheers.
MagnumManiac.
gun)
If your spewing unburnt powder....get a longer barrel or faster powderWith enough of slow burning powder you can make any case have a less than 100% burn rate.
That will stop the problem of spewing unburnt powder out the barrel, but the throat erosion due to unburnt powder can't be eliminated unless you shoot a VERY fast powder! A powder fast enough to burn in your case would NOT be appropriate for these calibers!
edge.
steve smith
Well-Known Member
Now, switching to a slower burning powder will increase the duration of peak pressure (you will get there later but stay there longer), but if you're not hitting peak pressure to begin with, moving to slower powder would exacerbate the situation. If you're not reaching peak pressure, increasing the charge weight could be the answer, but if you're limited by the case capacity then you need to go to a faster powder.
One thing to keep in mind is that the peak pressure (ie; max pressure) in your cartridge may not be enough to burn the powder efficiently. Namely using H110 in a 45lc. I'm pushing things to max, but my max isn't high enough to get a complete burn.
LouBoyd
Well-Known Member
Have you ever considered the actual life of a high power rifle barrel. I'll use the 7mm STW with a 26" barrel as an example with a 180 gn bullet at 3000 fps. If you allow that it will give 1000 useful shots thats only a lifetime of 1.27 seconds. The time the bullet is in the bore per shot is only 1.27 milliseconds.
Shooting high performace rifles is hard on bores. I really coiuld care less whether all of the powder burns or not. What matters is the pressure curve which is generated.
Desirable pressure curves
1. achieve a desired muzzle velocity.
2. don't exceed rated chamber pressure,
3. give repeatable burn rates resulting in low velocity spread. That usually means case fills in the 95 to 100% range.
4. as a tie breaker give lower muzzle pressure than other loads.
Nohwere on that list is long barrel life.
If I want more barrel live I choose a smaller capacity cartridge.
I consider 1000 shots, maybe even 500 reasonable life in a hunting rifle barrel. I'd prefer 5000 in a target rifle which I shoot a lot. Barrels however are an expendable item. They rarely cost more than the ammo it takes to burn them out so they're not the major cost of shooting.
Shooting high performace rifles is hard on bores. I really coiuld care less whether all of the powder burns or not. What matters is the pressure curve which is generated.
Desirable pressure curves
1. achieve a desired muzzle velocity.
2. don't exceed rated chamber pressure,
3. give repeatable burn rates resulting in low velocity spread. That usually means case fills in the 95 to 100% range.
4. as a tie breaker give lower muzzle pressure than other loads.
Nohwere on that list is long barrel life.
If I want more barrel live I choose a smaller capacity cartridge.
I consider 1000 shots, maybe even 500 reasonable life in a hunting rifle barrel. I'd prefer 5000 in a target rifle which I shoot a lot. Barrels however are an expendable item. They rarely cost more than the ammo it takes to burn them out so they're not the major cost of shooting.
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Michael Eichele
Well-Known Member
Bingo!
The short bbl life in a hyper mag has more to do with the pure quantity of powder in the case and the heat and shock associated with it.
