.45 ACP and Pressures

[Rod Snell]

Rod

Are there any references to compare medium and fast burning pistol powders being related to felt recoil (kind of an abstract term I guess).

First, the calculated recoil is more if the powder charge is greater, so fewer grains of a fast powder produces less recoil.


http://www.handloads.com/calc/recoil.asp

However, this is not the whole story. The RATE (first derivative) of momentum transfer makes the recoil feel "sharper."

Think of a large sledge hammer being swung in just a gentle arc against your outstretched hand, not enough to hurt. Your hand is for sure going to be pushed out of the way, but relatively slowly. Now consider a tack hammer swung hard enough to have the same momentum as the sledge; it is going to be moving a lot faster, and your hand is going to receive the momentum very quickly: it will HURT! We talk a lot about energy of projectiles, but momentum is the quantity conserved in a collision.
http://en.wikipedia.org/wiki/Recoil

That's why those 12oz guns leave your hand numb with just a moderate load.

FELT recoil, or what the shooter can tolerate. is highly subjective and I don't know how to quantify that.

 

[NikatKimber]

Rod

Are there any references to compare medium and fast burning pistol powders being related to felt recoil (kind of an abstract term I guess).

Loaded to the same PF I much prefer faster powders for USPSA (as do most others shooting non compe'd guns). This seems to be true for 45/40/9/and 38 super (non compe'd gun). The sights track better and it "feels" as if there is less recoil (the gun may just be behaving differently though). Is there anything looking at pressure curves vs. slide speed (or some other variable) that may explain these differences. Or is it all in my head?

Thanks for the read!

Rod's pretty much got it.

I'll see if I can explain it slightly differently.

The velocity of the bullet depends only on the amount of energy expended on it during its time in the barrel.

However, for a brief period after, if the propellant has not completely burned up, the pressure inside the barrel will not instantly go to zero. Think rocket here. Now I'm not familiar enough with pistol powders to know if they mostly burn completely or not. But, given what you are saying, similar velocity, but more felt recoil from the slower powder, sounds to me like it is not burning completely before the bullet leaves the barrel.

So the faster powder is burning completely, achieving the velocity with no extra energy being wasted. Where the slower powder is still burning, thus releasing energy, after the bullet has left.

First, the calculated recoil is more if the powder charge is greater, so fewer grains of a fast powder produces less recoil

 

[338Shooter]

It's all about impulse. Impulse is defined as the integeral of the force vector from a time 1 to another time 2. With a fast powder you get a spike of pressure which acts on the surface area of the back of the bullet (force) for a short time. With a slower powder you get a smaller force for a longer amount of time. If a fast powder and a slow powder are used to drive the same bullet to the same velocity the impulses will be equal in both cases, but the time windows will be different. The slower powder will peak the pressure more near the muzzle, this high pressure gas can jet out after the bullet increasing felt recoil with Newton's third law similar to rocket engines. If this is the case the same energy was delivered to the bullet, but there is more energy left in the form of the jet of gas causing more perceived recoil. As you know, the slower powders are used in compensated guns to be able to harness this gas and limit muzzle flip.

I believe the slower powders are used to achieve higher velocity because the peak pressure can be equal to the faster powders, but for a longer duration thus a higher impulse and a higher velocity.

 

[technetium-99m]

You guys are referring to the barrel acting kind of like a rocket engine with the high pressure gas rushing out at the muzzle and thus increasing recoil right. I guess I can buy that reason.

 

[338Shooter]

Yeah, with the slower powders there is more pressure in the barrel with the bullet leaves it. This depressurization and any powder still burning will act like a rocket at the muzzle.

 

[ldp4570]

less calculus, more blowing **** up!

YEP!!! When they are done with propellants, then we can talk explosive train. It ain't rocket science. OOOOHHHHH my head hurts!!!!! Every type has its own speed.

 

[walker]

I've been reloading .45 ACP for a while now with 4.8gr of Titegroup under 230gr lrn & jhp's. One thing about that powder is that the velocities are a bit slower than other powders but the pressures seem to run a bit more. Question for you all. Do higher pressures help in the functioning of a semi-auto? With the 4.8gr I estimate velocities are in the 780fps range. Not blazing speed by any means but my 1911 likes 'em and functions like a champ.

They can help or hurt, depending on what your gun likes. My 1911 will cycle anything but is more accurate with a med velocity round. Some guns, like most Berettas have to use a hot load. Just depends on the gun and the shoter.
If you just want to try something different, load 4.2gr of RedDot for 230gr LRN with a CCI 300 LP. This load is a little lower pressure and a little higher velocity than the TG. I load leads only but it will work for the J's just as well.
Also, some primers create higher pressures than others. I use Federals on my 357 loads but step down the charge to keep the pressures down.

 

[ByrdC130]

Good read and thanks for the info folks.