Any Advantage for Heavy or Long Slide with Red Dot

Hi All,

I was wondering if the benefits of a heavy slide or a long slide are negated if you slide mount a red dot to the pistol. The slide mounted red dot would provide the mass similar to the heavy slide reducing recoil, and increased sight radius from the long slide would not be relevant to the red dot.  Any opinions?

Best,

Joe

You could make it heavy enough to turn it into a reliably single shot pistol, or require to raid ballpoint pens for recoil springs.

FWIW, I think heavy slides were an outdated, wrong step down the evolutionary trail.  The basic concept seems okay; increase inertial mass in order to slow down unlocking of the barrel, decreasing recoil.  Sounds good so far, but keep in mind that the 1911 is recoil-operated; it needs some recoil to work.  Too much mass, and the gun won't cycle.  

Furthermore, in my opinion, once the barrel unlocks and tilts down, I want that slide to move as quickly as possible to move fully to rear and moving going forward as quickly as possible so the gun is ready for the next shot.  I think the better approach is to increase the mass of the barrel (with a bull barrel, barrel weight or compensator).  That way, when the barrel and slide are locked to together, you enjoy the benefit of increased inertial mass decreasing rearward acceleration of the slide, but once the barrel is unlocked and pulled downward, the mass of the inertial mass of the slide is effectively greatly reduced.  I'd also prefer to reduce reciprocating mass as much as possible (by lightening the slide) to reduce that feeling of a huge block steel moving slowly back (causing the gun to pivot rearward) then slamming forward (causing the gun to pivot forward).  Ideally, I'd prefer to have a very light slide move quickly to the rear, then quickly forward, causing as little rearward or forward rotation of the gun as possible.  You can get a sense of this by taking a wadgun with a slide-mounted dot, firing a few rounds, then taking the dot off and firing a few rounds.

Admittedly, there are some potential trade-offs.  A light slide with a heavy barrel with relatively higher slide velocity is probably harder on the barrel lugs.  But with the lower volume of rounds and lighter loads typically shot in bullseye vs. other games like USPSA/IPSC, it's probably not a big deal.

Anyhow, just my philosophy.  Others might have different opinions.

The purpose of the heavy slide was to slow down the slide to reduce the muzzle flip from when the slide hits the rearward end of its travel. There is no way the recoil spring can absorb all that energy. From start to finish the energy absorbed in the recoil spring is about 12 inch pounds. The slide at unlocked has about 5. 9 - 6 foot pounds, or an order of magnitude more. So the idea was to slow the velocity of the slide which would allow the slide to bottom at a lower velocity and lower energy.

What gives the slide its velocity is the bullet momentum

200gr x 700 fps / 7000 gr(slide weight, approx) = 20 fps slide velocity

Slide energy = 1/2 x m x V x V
m = w/32.2

So Energy is .5 x 1/32.2 x 20 x 20. Which is about 6 foot pounds. When the slide hits the recoil spring plug that energy lifts the muzzle. It doesnt slow down much maybe to 12 fps.

Add 1/4 pound (1800 grains) to the slide the slide velocity drops to 16 fps. And the free energy at unlocked is just below 5 even with more mass.

Not that these are “back of the envelope” level... there are delays from the hammer being re-cocked and losses due to the friction of the parts, etc.

I'm under the impression Jim Clark coined the phrase "Heavy Slide" when Bomar sight ribs were added to a slide vs the original plain front/rear sights. They were all steel ribs and added quite a bit more weight. The longslides were welded up slides to add additional 1" of slide length and then a longer heavy rib. So cyclic rate does slow down with additional weight added to the slide. Today's new aluminum optic rails and optics weigh close to what a Bomar rib weighed.
I'm of thr opinion a poorly fit barrel allows increased slide velocity. A properly fit barrel will slow down the slide. If you look at majority of M/HM shooters they are all shooting aluminum rib and optic (slide mounted) on 5" slide. They choose that because they like how the pistol recoils and goes back into battery; its a feel thing. They rarely shoot frame mounted optics or longslides. Longslides aren't as forgiving at 50 yds as 5" pistols. Longslides were originally used for longer sight radius as well. 
So I believe there is an advantage to slide mounted optics and 5" government length slides. 
Jon

Wobbley wrote:The purpose of the heavy slide was to slow down the slide to reduce the muzzle flip from when the slide hits the rearward end of its travel.  There is no way the recoil spring can absorb all that energy.  From start to finish the energy absorbed in the recoil spring is about 12 inch pounds.  The slide at unlocked has about 5. 9 - 6 foot pounds, or an order of magnitude more.  So the idea was to slow the velocity of the slide which would allow the slide to bottom at a lower velocity and lower energy.

What gives the slide its velocity is the bullet momentum

200gr x 700 fps / 7000 gr(slide weight, approx)  = 20 fps slide velocity

Slide energy = 1/2 x m x V x V
m = w/32.2

So Energy is .5 x 1/32.2 x 20 x 20.  Which is about 6 foot pounds.  When the slide hits the recoil spring plug that energy lifts the muzzle.  It doesnt slow down much maybe to 12 fps.  

Add 1/4 pound (1800 grains) to the slide the slide velocity drops to 16 fps.  And the free energy at unlocked is just below 5 even with more mass.

Not that these are “back of the envelope” level... there are delays from the hammer being re-cocked and losses due to the friction of the parts, etc.

I think you're a bit low on the slide weight with a rail and optics.  But aside from that, all of the above assumes a constant mass and constant velocity throughout the slide's travel.  However, the mass of the moving parts (barrel and slide locked together) is reduced dramatically when the barrel is unlocked and pulled out of the way of the slide.
While very simplified, consider this hypothetical.  Assume you have two guns whose combined slide and barrel mass is identical:

Gun A:  Traditional slide mount wadgun with a 1.5lb slide/rail/optic and a 0.5lb bushing barrel.
Gun B:  Non-traditional frame mount bull barrel wadgun with lightened 0.75lb slide and a 1.25lb bull barrel and compensator.

For the initial travel, the effective weight of the mass moving rearward is the same.  However, once the barrels unlock from their slides, things change dramatically.

Lets calculate the Force of Impact at the end of slide travel from the point the barrel unlocks.  To keep things simple, let's assume a constant slide velocity and that the distance the slide has to travel after the barrel unlocks is 2".  Force of Impact = Slide or Kinetic Energy/distance).

200gr * 700 fps ÷ 14,000 gr (Gun A: slide+rail+optics+bushing barrel, or Gun B: slide+bull barrel and compensator, approx mass)  = 10 fps slide velocity.
Converting all that to SI (easier for me): 0.0129598kg * 213.36m/S ÷ 0.90718474 = 3.048m/S

So now that we have the slide velocity (3.048m/S), lets calculate Force of Impact (F = (0.5 * m * v^2) ÷ d) after the barrels have unlocked from their slides...the big difference between Gun A and Gun B is going to be the mass of the slide assemblies as they continue to travel rearward.  

For Gun A:  (0.5 * 0.6803890kg * 3.048m/S^2) ÷ 0.0508m = 62.215N or in pound-force, about 13.986lbf.
For Gun B:  (0.5 * 0.3401943kg * 3.048m/S^2) ÷ 0.0508m = 31.107N or in pound-force, about 6.993lbf.

All other things being equal, the Force of Impact when the slide on Gun B reaches the end of it's travel should be about half of that of Gun A.

Well, mechanics of impact deal with momentum and coefficients of restitution. Not so much impact force. As for the weights, I was comparing a steel “Bomar” rib to a ribless slide.

But when a slide is stopped at the end of its travel, the force to do so is a lot higher than 14 pounds. An accelerometer can also tell you that. If it was only 14 pounds the frames wouldn’t batter. The key to understanding this is to assume that there is little velocity gain after unlock, and from watching high speed videos I’m reasonably certain that no appreciable slide velocity gain happens.

I'm thinking that people like the feel of a heavy slide no matter where the weight comes from.  Red dot won't make a shooter of someone with poor trigger control.  The red dot advantage is really for guys with bad eyes.  Before Pascarella won Camp Perry back to back with red dots every body shot heavy slide guns.  Was not there but I'd bet the 2680 record was shot with a heavy slide gun like this..