Longevity of .40 vs. 9mm pistols

[Cee Zee]

If you got that impression from anything I wrote, I certainly didn't intend to make THAT claim! Perhaps you're misireading earlier comments by others?

Actually it was something that occurred to me that might be the case based on the nature of physics as I know them. The momentum of the larger caliber .45 certain accounts for much of the felt recoil but physics being what they are a lighter bullet driven at a higher speed should have the same reaction as a heavier bullet driven at a slower speed. The thing is the .45 is said to have less pressure so I don't see how it can have more recoil to be dealt with. Yet I know it does from experience. I just don't know why and I haven't really heard a good explanation for why that's true.

But the 45ACP bullet has 39% more momentum.

Why is that true? The KE and the weight are obviously the reasons but I suppose what makes me wonder is that I haven't done these calculations in 40 years and the weight conversions make it difficult. I could spend a day figuring it out again or I could ask someone who knows. I put in my time explaining this stuff to others way back when but that's been many moons ago and a lot of my marbles are off their tracks now if you get my drift. I just didn't want to go through learning to do the equations again I suppose. They aren't all that hard if your brain hasn't grown lazy but my thinking has been about other subjects for a long time now. Yes I see the explanations here but I'd still like to see the actual math involved and I believe it's actually going to be pretty complicated so to heck with it. I'm gonna forget that I asked.

have never heard about other calibers and certainly not about a .45 version

Maybe the source I read on the subject was wrong but I thought they made a few in .45 ACP. I could be wrong again. Every source I've looked at today says it was only 9mm., .30 caliber and .22 caliber that made up the choices. I read the stuff about there being some .45 variants quite a while back and of course they could have been wrong about it. Probably was it seems. I'm having a bad thread it seems.

 

[bc1023]

The P220 was first built in .45. A 9mm version soon followed.

Not at all. It was a 9mm. It was Sig Sauer's first handgun and was built to replace the Sig P210.

The 45ACP version came later for the American market.





Edit: I see this was already corrected.

 

[Cee Zee]

Not at all. It was a 9mm. It was Sig Sauer's first handgun and was built to replace the Sig P210.

The 45ACP version came later for the American market.

The first P220 model was sold to the Swiss army in 1975. It was a 9mm. In 1976 the .45 version began being sold in the US. That first year they also sold .38 Super and 9mm versions in the US market but not after that year.

 

[JohnKSa]

The thing is the .45 is said to have less pressure so I don't see how it can have more recoil to be dealt with.

Recoil is not dependent on pressure. It is dependent on muzzle momentum based on the principle of conservation of momentum.

Why is that true?

Momentum is mass times velocity. There are some conversion factors if you want to get the actual momentum values, but that's not necessary if you just want to compare the muzzle momentum of two different cartridges since the conversion factors will be the same in both calculations and will cancel in a comparison.

To do that just multiply the bullet weight times the muzzle velocity for each cartridge and compare the two numbers.

It seems to me that whatever method is used to slow the slide down to a stop is going to take the same energy either way. So why is it that using a heavier spring will wear out the slide stop faster?

Assuming that the recoil momentum of the slide is sufficient to bottom out the recoil spring (and it will be unless the spring is so strong that it keeps the gun from operating properly), then the amount of force applied to the slide when it is pushed back into battery is mostly dependent on the strength of the spring. There is some rebound velocity from the slide bouncing off the frame at the end of its rearward travel, but the spring plays the major role in terms of determining the forward velocity of the slide as it returns to battery.

So a stronger spring means more force applied to whatever stops the slide as it returns to battery.

 

[GLOOB]

Why is that true? The KE and the weight are obviously the reasons but I suppose what makes me wonder is that I haven't done these calculations in 40 years and the weight conversions make it difficult.

JohnKSa answered this exactly the way I would have, but allow me to elaborate. Momentum can be expressed as kilogram-meters per second. Or pound-feet per minute. Or ounce-miles per hour. It really doesn't matter, since we are just making a comparison.

If you were so inclined, you could express momentum in grain-feet per millisecond. This happens to be the unit of measurement used for the power factor in an IPSC event. The formula is (bullet weight in grains * velocity in feet per second)/1000. So power factor is really just momentum expressed in grain-feet per millisecond. Power factor isn't derived from momentum. It isn't a function of momentum. It IS momentum. 168 pF = 168 grain-feet per millisecond. It makes sense that power factor is a measure of momentum, because this is the most objective measurement of recoil that is available. Competitors can get there any way they choose; some guns/individuals might shoot faster with a heavy for caliber bullet going slower, and some might prefer a lighter bullet going faster. If the momentum of the bullet is the same, the total amount of recoil will be objectively the same.

When I say that a 230 grain bullet at 750 feet per second has 39% more momentum than a 124 gr bullet @ 1000 fps, it's a simple ratio. (230*750)/(124*1000). The units all cancel, so they don't matter. No conversion needs to be done. The result is 1.39. A percent is 1/100th. Move the decimal place over by two spots, and you have 139%. The 45ACP bullet has 39% more momentum than the 9mm bullet, in this specific example.

Kinetic energy is easy to get. KE is 1/2 mass * velocity squared. The lighter the bullet, the higher the energy you can reach for the same amount of recoil. If power factor was based on kinetic energy, competitions would be dominated by rinky dink lightweight bullets, e.g. 50 grain 9mm bullets doing mach 2.

 

[Cee Zee]

When I say that a 230 grain bullet at 750 feet per second has 39% more momentum than a 124 gr bullet @ 1000 fps, it's a simple ratio. (230*750)/(124*1000). The units all cancel, so they don't matter. No conversion needs to be done. The result is 1.39. A percent is 1/100th. Move the decimal place over by two spots, and you have 139%. The 45ACP bullet has 39% more momentum than the 9mm bullet, in this specific example.

That's the thinking that was eluding me. I know physics pretty well or at least I did at one time. The math was always easy enough for me. But I was looking at it more complicated than it needed to be. I was stuck on the idea that the same amount of pressure was being applied to both the .45 bullet and the 9mm bullet. I thought about the weight of the bullet being a factor of course but for some reason my brain was locked onto the idea that the momentum would be equal because the pressure was equal. Obviously I left out part of Newton's second law, the part about the mass. You'll understand when you're older. I heard that a lot when I was a kid. It comes back on you. People don't understand how these senior moments hit you. But they will when they start getting them.

 

[mavracer]

KE really doesn't have any place in gun discussions sure it's there but it's meaningfullness is skewed.
While energy must be conserved it can change form from potential>heat>kinetic>heat.
What yo need to realize is the KE of a handgun is really insignificant.
Momentum also must be conserved but it doesn't change form which is why a 45 recoils more than a 9mm and why a 40 is going to cause more wear on a gun than a 9mm.