What happens when you load pistol powder in a rifle cartridge?

[motoman98]

Smokeless powder is by definition a propellent, whereby a comparative "push" is acting on the bullet. That is when a proper balance of bullet weight and diameter, cartridge capacity and the burning rate of the powder is provided to accellerate the projectile with appropiate pressure. So when that part of a loading "recipie" is wrong, ie. a powder with much too fast a burning rate is used, something closer to an explosion occurs,(an unsafe pressure spike) rather than a controlled burn to achieve a given velocity.

 

[bolus]

Smokeless powder is by definition a propellent, whereby a comparative "push" is acting on the bullet. That is when a proper balance of bullet weight and diameter, cartridge capacity and the burning rate of the powder is provided to accellerate the projectile with appropiate pressure. So when that part of a loading "recipie" is wrong, ie. a powder with much too fast a burning rate is used, something closer to an explosion occurs,(an unsafe pressure spike) rather than a controlled burn to achieve a given velocity.

Thanks, sounds similar to how running lean on an engine can cause detonation and blow a hole in a piston

are +P rounds more powder or do they have faster burning powder or is it different per manufacturer?

 

[Steve M]

As someone not familiar with reloading, does the pistol powder burn faster? What property gives it the power to blow a rifle apart compared to the same weight of rifle powder?

Considering that, could you overbuild a large caliber rifle to shoot rounds with pistol powder to make it more powerful?

An ideal powder for a firearm is one that as it burns it quickly builds to maximum pressure then keeps it there as the bullet travels down the barrel then exhausts itself the moment the bullet exits the barrel. In a pistol you have no choice but to use a fast burning powder to get the most out of that 3-5" barrel but in a rifle you have 16"-26" to get things up to speed so a slower burning powder is ideal as it keeps the pressure up for a longer time.

The burn rate is controlled by physical shape and coatings. If you break up the sticks of a rifle powder into granules you will alter its burn characteristics and possibly cause a dangerous over pressure.

The powder used was 40.5gr of Titegroup under a 120gr bullet in a 7mm-08. A maximum 9mm loading of Titegroup under a 124gr bullet is 4.1gr and develops a max pressure of 32.7kpsi. Now if you'll indulge me in a little math:

Pressure = Force * Area and Area = π * radius^2 so we can rewrite as Force = Pressure/Area = Pressure/(π * radius^2)

Area of the base of a 9mm bullet is 0.09954 in^2
Area of the base of a 7mm bullet is 0.06335 in^2

Therefore it takes 1.57 times more pressure to exert an equal force on the base of a 7mm bullet as it would on a 9mm bullet. And since Force = mass * acceleration we know that for the same weight bullet the 7mm would accelerate more slowly given the same pressure behind it as a 9mm bullet. To be fair, the max pressure for a 9mm is 35,000 psi while the 7mm-08 is 61,000 psi.

So not only did he had 10 times the maximum full load for a 9mm cartridge, but he put it under a smaller bullet that needs more pressure before it will start moving. The bullet moving is what causes pressures to drop and a firearm to fire instead of explode. That bullet had no chance to get out of the way before the powder was consumed.

Now it is possible that from a pressure point of view a loading of perhaps 6gr of Titegroup would be safe in a 7mm-08, but it would be consumed while the bullet was still in the barrel and you would get very low velocities.

I have no idea what kind of pressures it built up, but yes, you could in theory build a firearm heavy enough to handle the charge. But you'd only be able to make use of a 5" barrel on your very expensive truck mounted rifle and it would serve no useful purpose.

+P simply means that the ammo and firearm are built to a higher pressure limit than normal. You typically see this with older handgun cartridges such as 9mm, 38 special, and 45 Auto that run at low pressure compared to modern designs. The standard 9mm is allowed to reach 35,000 psi but a 9mm +P is allowed to reach 38,500 psi. typically this is done by adding more powder but I suppose it could also be done by using another powder that wasn't a good match for the firearm at standard pressures.

 

[bolus]

Thanks, awesome explanation. Very interesting.

 

[rick benjamin]

Relatively speaking...

Faster burning smokeless powder pushes lighter bullets
Slower burning smokeless powder pushes heavier bullets

Then...
The same smokeless powder used in a .38 revolver (125 gr bullet) and a .45 1911 pistol (230 gr bullet)
is also used in a 12 gauge (437 gr slug) load. Amount of powder varies.

Science, Chemestry, Art, Experience
Smokeless powder burns rapidly when combustion gasses are contained in the barrel chamber.
The same powder burns slower when un-contained as in an open tuna can.
Rapid is different than Exploding (shattering).

 

[bolus]

Yes, sounds very similar to tuning an engine (of which I know just enough that if I tried it I'd blow up my engine)

 

[deadshot2]

First clue that something wasn't right should have been that the "powder was meetering well with the granules not causing the powder measure to ztick or drop irregular charge weights.

First sign yoy AREN'T using Varget.