200 vs. 230gr .45 ACP's

[Unclenick]

All 3 shot to the point of aim elevation wise

That's typically the case with the same bullet weight, even in a revolver. POI doesn't change appreciably with the load—a little, but not a lot. It's because a lighter charge, though it doesn't recoil as hard, will apply that recoil for a longer time before the bullet clears the muzzle. It's not exact compensation, but its close enough for most folks.


Mal,

If the slide didn't move at all, there would be no momentum in it to cycle the gun after the bullet left. Once the bullet was gone it would just sit there. Not moving at all would also mean the slide was locked to the frame, so the muzzle would rise more during the time the bullet is in the barrel, like a revolver does.


David,

On a full-size 1911 the slide and barrel weigh about a pound. At 352 ft-lbs ME, the bore experiences and average recoil force of 977 lbs plus about 3-5% more to overcome friction, so about 1000 lbf (pounds force). The barrel time for the 230 grain ball to produce that ME with that average force at its base is about 0.77 ms, so acceleration will be:

1 lb = 0.0311 slugs and 1000 lbf / 0.0311 slugs = 32,174 ft/s².

So slide velocity at the end of 0.00077 s will be 0.00077 × 32,174 ft/s² = 24.8 ft/s.

Since the slide started at 0 fps, the average velocity will be 12.4 ft/s and the distance traveled will be 0.00077 seconds × 12.4 ft/s will be 0.0095 ft or 0.114 inches.

That assumes no other sources of load on the recoil, but in fact, there is a bit. The cocking of the hammer, the spring-mass compressed in that sub-millisecond period. Friction between slid and frame. Unlocking force will produce some too, so actual motion might be closer to 0.1 inches with that hardball load.

 

[JohnKSa]

Since the slide started at 0 fps, the average velocity will be 12.4 ft/s and the distance traveled will be 0.00077 seconds × 12.4 ft/s will be 0.0095 ft or 0.114 inches.

Yup. The bullet and the slide both start at zero fps and by the time the bullet exits the bore, it is going at muzzle velocity and the slide is going about 25fps.

I used a WAG of the max slide velocity (velocity at bullet exit) instead of the average velocity of the slide while the bullet is in the bore. My number will therefore overestimate the slide movement. The 0.114" number should be more accurate than the 0.2" figure I provided.

 

[74A95]

With all this talk about slide speed, folks might find the information at the link below of interest.

http://www.shootingtimes.com/editorial/recoil-spring-rate-affects-timing/99604

 

[JohnKSa]

From the article:

"...it was clear that the recoil phase was not dramatically different between these spring weights when using the same ammunition. The slide moved much slower when going forward..."

Interesting. So while the cycle time was slowed with the weaker spring, the main change occurred during the FORWARD travel of the slide--the portion driven by the recoil spring. The slide speed during the rearward travel of the slide was not changed dramatically by changing the recoil spring strength.

 

[Unclenick]

I think that makes sense. With an average force of about 1000 lbs during the barrel time that imparts momentum to the slide, whether you have a recoil spring with two or four more pounds of force opposing it is a difference that will be lost in the noise.