Effects of lightening the slide

[Guy Neill]

There seems to be a trend to lighten the slides on 1911 (and other) handguns. As you would expect, removing weight from the slide results in increased slide velocity and further travel by the time the bullet leaves the muzzle.

 

Looking at the changes while reducing the slide weight an ounce at a time gives these sorts of results. The gun weight is taken as 2.44 pounds before weight is removed, regarding the free recoil energy (FRE).

 

This is based on a 230gr 45 bullet with a muzzle velocity of 830 fps with 5.0gr of powder.

 

Weight Removed	Slide Weight	Slide Velocity	Slide Movement	Gun FRE
Ounces	pounds	fps	inches	Ft-lbs
0	1.058	25.8	0.140	6.51
1	0.996	27.4	0.149	6.68
2	0.933	29.2	0.158	7.05
3	0.871	31.3	0.170	7.05
4	0.808	33.8	0.183	7.25

 

Not, maybe, a significant change, but there is also the argument that various holes in the slide allow dirt and debris access to entering the gun.

 

[zzt]

You lighten a slide to reduce reciprocating mass.  As you lighten, you increase the weight of the recoil spring.   So, the increase in slide velocity is not as great as you depict.  Nor is the slide movement.  A heavier spring increases the preload.

[Guy Neill]

While this example neglects spring and friction forces, when added those (16 lb recoil spring and 23 lb mainspring) for the full weight slide, it reduced the slide motion by 0.006".

 

Changing from the 16 lb recoil spring to a 22 lb recoil spring for the lightest slide listed saw the slide motion reduced by 0.009".

 

[shred]

Is this a computation or real-world data?  What is the "slide movement" number?  Distance with the slide and barrel locked together?   Seems like they wouldn't want to separate until the bullet exits and the pressure drops.

 

 

[outerlimits]

no way this is real world.  ill take reduced reciprocating mass all day.

[Guy Neill]

The initial weight is the slide and barrel locked together.

 

The slide motion is how far the slide has moved at the time the bullet exits the barrel. Bercovitz and my values matched neglecting friction and spring forces (0.140") for the values used.

 

When I originally calculated this, I found adding the friction and spring forcers changes the slide motion to 0.134". That's right at the general statements I've seen over the years that the slide moves about an eighth of an inch at the time the bullet exits. Barrel ramp-down occurs after the bullet exits.

 

There are still many that do not believe the slide moves at all before the bullet exits. It clearly does move when viewing high speed videos - and exploring the physics.

 

[outerlimits]

38 minutes ago, Guy Neill said:

The initial weight is the slide and barrel locked together.

 

The slide motion is how far the slide has moved at the time the bullet exits the barrel. Bercovitz and my values matched neglecting friction and spring forces (0.140") for the values used.

 

When I originally calculated this, I found adding the friction and spring forcers changes the slide motion to 0.134". That's right at the general statements I've seen over the years that the slide moves about an eighth of an inch at the time the bullet exits. Barrel ramp-down occurs after the bullet exits.

 

There are still many that do not believe the slide moves at all before the bullet exits. It clearly does move when viewing high speed videos - and exploring the physics.

 

add into that the effects of changing the firing pin stop angle.  I have an old steel gun where my smith took the FP stop and angled it to mate with the disconnector rail.  course it also had only one barrel lug-he machined off the first lug completely.  unlocked quite fast!

[Nolan]

1 hour ago, Guy Neill said:

The initial weight is the slide and barrel locked together.

 

The slide motion is how far the slide has moved at the time the bullet exits the barrel. Bercovitz and my values matched neglecting friction and spring forces (0.140") for the values used.

 

When I originally calculated this, I found adding the friction and spring forcers changes the slide motion to 0.134". That's right at the general statements I've seen over the years that the slide moves about an eighth of an inch at the time the bullet exits. Barrel ramp-down occurs after the bullet exits.

 

There are still many that do not believe the slide moves at all before the bullet exits. It clearly does move when viewing high speed videos - and exploring the physics.

 

 

 Here's a photo of yours truly taken by Ray Soloman showing this exactly.

 

 

Close up

 

 

Nolan

[Guy Neill]

Great photo!

[RangerTrace]

So I had an enlightened moment today.  I've been shooting nothing but Staccatos for the last three months in various forms.  I received my XL today, a 5.4" 9mm variant.  It shoots so soft, I actually prefer it to the XC which is a 4.4" comped gun.  I will give actual weight numbers, later, but the dot never moved out of the A zone.  It was amazing.  

[GrumpyOne]

6 hours ago, Guy Neill said:

Great photo!

It is...but the bullet has already left the barrel. Here is a video at 73k FPS showing the bullet leaving the barrel, before ANY motion of the slide.

 

https://youtu.be/7y9apnbI6GA

 

And another video, from Larry Vickers, showing the same thing.

 

https://youtu.be/jig-RvZr1OM

[LHshooter]

2 hours ago, GrumpyOne said:

It is...but the bullet has already left the barrel. Here is a video at 73k FPS showing the bullet leaving the barrel, before ANY motion of the slide.

 

https://youtu.be/7y9apnbI6GA

 

And another video, from Larry Vickers, showing the same thing.

 

https://youtu.be/jig-RvZr1OM

Well, they say a picture is worth a thousand words. Those 2 videos are terrific and very educating. Thanks for sharing.

[zzt]

Thanks Grumpy.

[shred]

In the Mythbusters video you can see the combined barrel and slide have started to move backwards relative to the dust cover before the bullet exits.  Not much but it's there.

 

It can be hard to see on high-speed videos because there's also a recoil component and much of the time the pistol being filmed is hand-held so it's moving around.

 

As soon as the bullet leaves, the pressure in the barrel goes rapidly to ambient as does the load on the upper lugs and then things start clicking and clacking.  I suspect this load and associated friction might play more of a factor than calculations suggest.

 

[Jim Watson]

Physics and engineering mechanics are very fine, but so much of the choice of gun and ammo boils down to feel.  Does it shoot "soft", does it shoot "flat"?  What number to optimize for a gun that feels right?  

[Guy Neill]

Stopping the first video at the 0.11 second point, the bullet is exiting the muzzle. Backing up to the 0.10 second mark clearly shows that the slide has moved between the 0.10 and 0.11 marks.

 

The black background isn't the best for seeing details, but examining the two marks will show the motion.

 

Thanks for posting the vids. I still need to look at the second one.

 

 

 

[Nolan]

2 hours ago, shred said:

As soon as the bullet leaves, the pressure in the barrel goes rapidly to ambient as does the load on the upper lugs and then things start clicking and clacking.  I suspect this load and associated friction might play more of a factor than calculations suggest.

 

 

Agreed.  That's a SVI long heavy dust cover and full weight slide in the photos.  My records show this was back in the daze of 180gr MG JHP and 4.8gr of Clays for 172pf with IIRC an 11lb recoil spring for Limcat's Best of the Best match.

I tried a lot of different bullet weights, powders, and springs and this was the softest, lowest muzzle flip combination for that pistol.

This photo was pretty much full muzzle flip for that combination.  I'm leaning hard right and bending, squatting to shoot under a no shoot I think.

 

Nolan

Edited December 9, 2023 by Nolan

[Guy Neill]

In the second video, at the 0.40 - 0.41 second mark, you can see that the slide has moved just before the bullet exits.

 

[zzt]

34 minutes ago, Guy Neill said:

In the second video, at the 0.40 - 0.41 second mark, you can see that the slide has moved just before the bullet exits.

 

 

Nonsense.  At the very beginning of the 38 second mark you can just see the nose of the bullet peeking out the front of the muzzle.  The slide has not moved.  Moving slightly ahead in the 38 second frame shows the bullet half out of the barrel.  The slide still has not moved.  Click ahead again and the bullet is at the end of the muzzle.  Click again and the bullet is out and you can see the bright flame front.  The slide still has not moved.

 

Two more clicks and the bullet is out by an inch.  Still no slide movement.  You are correct in the slide has just started to move at 40, but the bullet is long gone.  All of this is easier to see if you go full screen with the video.

[shred]

The barrel and slide are going to be moving together until they unlock at the very least.  Most of the Vickers super high-speed is not useful because you can't see anything except barrel and slide so have no reference point until they separate.

 

In the Mythbusters video, play at 1/4 speed, then click on the timeline at about :10-- after ignition but before the bullet comes out and leave the mouse there.  Wait for the bullet to just before it pokes out, then click again to jump back to :10 and watch the slide jump a little while the frame doesn't.

 

 

 

[zzt]

In the Mythbusters video, the slide has started to move even before the bullet becomes visible.

 

In the Vickers video, it has not moved until the bullet is completely out of the barrel.

 

So, both sides of the argument are correct sometimes.  I wonder what counts for the difference, other than recoil spring weight.

[Guy Neill]

I see nothing in either video that has the slide not moving by the time the bullet exits. It can't be one way one time, and different the next time.

 

It takes the bullet some 0.0009 seconds to traverse the bore. The slide cannot stand still for that time and suddenly start moving later.

 

Perhaps the video time scales differ a bit, but I don't see the bullet exit until the 0.42 mark - after the slide has moved in the 0.40 - 0.41 marks.

[shred]

I've noticed several high-speed videos of cutaway 1911s show odd looking lockup dynamics.  I suspect missing a lot of lug area and structural integrity changes things somewhat.

 

It's also common that cutaways are made from otherwise defective guns.

[zzt]

42 minutes ago, Guy Neill said:

Perhaps the video time scales differ a bit, but I don't see the bullet exit until the 0.42 mark - after the slide has moved in the 0.40 - 0.41 marks.

 

Go back and look again.  The bullet is out at the end of 38 and the beginning of 39.

[Guy Neill]

0.38 * 0.39 is a different shot than 0.40 - 0.41