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Glock 18 with slide mounted optic... reliability question

2K views 35 replies 13 participants last post by  MWJOHNSON 
#1 ·
hello, I am a new member. A question to those members familiar with the 18... any opinions/experience on the reliability or otherwise of a slide mounted optic, under full auto conditions... thankyou in advance.
 
#3 ·
Welcome to the forum kiwishooter. Please head over to the Introductions thread and introduce yourself.
Same question as DK, Do you own a G18? If so, how about some pics of it.
 
#19 ·
Jim Beam, thankyou for your perspicacious response...
You must be from outside the US. Haven't encountered 'perspicacity' since the 70's; we use shorter, more dumbed-down words now so the semi-illiterate herd feel better about themselves. :D
 
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#20 ·
Will it work? Sure. For how long? My guess is not long with continual use. The life of a slide ride on a semi-auto is mixed. Some get several years and thousands of rounds. Others are failing far short of that. The abuse a G18 would put on a dot is staggering. I wonder how well it hold zero?
 
#27 · (Edited)
... any opinions/experience on the reliability or otherwise of a slide mounted optic, under full auto conditions...
My guess is that the stresses of "full auto" are only marginally different than that of semi-automatic operation.

Stresses are generated by acceleration, deceleration, and jerk (changes of acceleration or deceleration).

So, what slide speeds change from semi-automatic to automatic operation?

The following picture is graphs of the slide recoil speeds of a G19, screen-grabbed from...

9mm Luger Glock 19 firing slow motion


Rectangle Slope Line Plot Parallel


The graphs read from right to left.

When a round is fired, the slide speed starts 0 fps (black arrow), ramps up to about 25 fps (until the RSA starts to slow the speed of the slide assembly), stabilizes at about 14 fps, then stops very abruptly as the slide strikes the slide stop of the frame (red arrow).

What isn't shown is the return phase of the slide cycle.

However, given that the G18 cycle rate is about 1300 rounds/minute, then the total slide cycle time is about 46 milliseconds.

And, given that the average slide speed during the recoil phase is 14 fps and the slide cycles 2 inches, then the recoil time is about 12 milliseconds.

Therefore, the slide return time is about 34 milliseconds and the slide speed is about 5 fps (shown below under the black arrow)... one-third the speed of the recoil phase (red arrow below).

View attachment 171489

The stresses effected by the slide speeds described above are the 'semi-automatic' stresses.

So, what's different during "full auto"?

Not much.

Assuming that the slide assembly is 'almost' in battery when the chambered round fires in automatic mode, the slide speed at the 'reversal' point may effectively increase about 1 fps... to about 6 fps... a marginal increase in speed... and still significantly less than the stresses incurred at the end of the recoil phase.

Accordingly, comparing the semi-automatic and automatic modes of operation, I fail to see any significant differences in the stresses per slide cycle.

That said, given that mechanical devices subjected to stress will eventually fail, let's consider the following...

Bill has an XYZ optic mounted on his G17. He shoots 100 rounds a week and the optic was designed to survive 50,000 cycles. Bill can expect his optic to be useful for about 10 years. Cool! :cool:

Fred has the same optic on his G18. But, because he LOVES his "automatic", Fred shoots over 1000 rounds a week. Consequently, Fred's optic may fail in less than a year. Not so cool! :mad:

In my opinion, the perception that an optic will fail faster when mounted on an automatic pistol has much less to do with the actual stresses involved and much more to do with the unconscious realization that the cumulative consequences of those stresses will occur at a much faster rate.

In other words, the amount of trigger time required to over-stress the optic is much less with an automatic pistol than with a semiautomatic pistol... as the same trigger time sends many more rounds down range with an automatic vs a semiautomatic. That is, a given trigger time stresses the optic on an automatic much more than the same trigger time on a semiautomatic.

To me, it's perception, trigger time, and slide cycles... because, for all practical purposes, the stresses appear to be the same.

Just my thoughts... :D

Best regards,

Bob
 
#28 ·
My guess is that the stresses of "full auto" are only marginally different than that of semi-automatic operation.

Stresses are generated by acceleration, deceleration, and jerk (changes of acceleration or deceleration).

So, what slide speeds change from semi-automatic to automatic operation.

The following picture is graphs of the slide recoil speeds of a G19, screen-grabbed from...

9mm Luger Glock 19 firing slow motion


View attachment 171469

The graph reads from right to left.

When a round is fired, the slide speed starts 0 fps (black arrow), ramps up to about 25 fps (until the RSA starts to slow the speed of the slide assembly), stabilizes at about 14 fps, then stops very abruptly as the slide strikes the slide stop of the frame (red arrow).

What isn't shown is the return phase of the slide.

However, given that the G18 cycle rate is about 1300 rounds/minute, then the total slide cycle time is about 46 milliseconds.

And, given that the average slide speed during the recoil phase is 14 fps and the slide cycles 2 inches, then the recoil time is about 12 milliseconds.

Therefore, the slide return time is about 34 milliseconds and the slide speed is about 5 fps (shown below under the black arrow)... one-third the speed of the recoil phase (red arrow below).

View attachment 171489

The stresses effected by the slide speeds described above are 'semi-automatic' stresses.

So, what's different during "full auto"?

Not much.

Assuming that the slide assembly is 'almost' in battery when the chambered round fires in automatic mode, the slide speed at the 'reversal' point may effectively increase about 1 fps... to about 6 fps... a marginal increase in speed... and still significantly less than the stresses incurred at the end of the recoil phase.

Accordingly, between the semi-automatic and automatic modes of operation, I fail to see any significant differences in the stresses per slide cycle.

That said, given that mechanical devices subjected to stress will eventually fail, let's consider the following...

Bill has an XYZ optic mounted on his G17. He shoots 100 rounds a week and the optic was designed to survive 50,000 cycles. Bill can expect his optic to be useful for about 10 years. Cool! :cool:

Fred has the same optic on his G18. But, because he LOVES his "automatic", Fred shoots over 1000 rounds a week. Consequently, Fred's optic may fail in less than a year. Not so cool! :mad:

In my opinion, the perception that an optic will fail faster when mounted on an automatic pistol has much less to do with the actual stresses involved and much more to do with the unconscious realization that the cumulative consequences of those stresses will occur at a much faster rate.

In other words, the amount of trigger time required to over-stress the optic is much less with an automatic pistol than with a semiautomatic pistol... as the same trigger time sends many more rounds down range with an automatic vs a semiautomatic. That is, a given trigger time stresses the optic on an automatic more as compared to the same trigger time on a semiautomatic.

To me, it's perception, trigger time, and slide cycles... because, for all practical purposes, the stresses appear to be the same.

Just my thoughts... :D

Best regards,

Bob
Thanks Bob! :)
 
#29 ·
I have 'access' to a few G18s. One has a Doctor red dot sight on it. It seems to hold zero. Its kind of a moot point as the the full-auto shooting technique involves spraying like a garden hose rather than sighting. The red dot works in semi though.... These guns are at least 15 years old and probably get roughly 750 rds per year through them. Several years went by when we didn't bother to put a coin cell into the sight.. When we did, it was still roughly sighted in.
 
#34 ·
There were optics on the four 18Cs we got. They seemed to go through batteries so the guys took the optics off of three of the four and put on standard rear sights.

You line up the sights and then watch the impacts on the target and adjust. If you are holding very firmly, you can keep them on a single target or multiple targets close together. The red dots are vey quick to align, since they are designed to let you put your focus out there on the target.

I am not very good or experienced with these so I find the actual red dot is pretty darn hard to track after the first shots. If you looked at the video of me shooting ("Testing a Glock 18C" above) - actually the first time in years - I started out very relaxed (WRONG) - standing upright, actually leaning back a bit - and quickly realized that that was not going to work. So I tensed up and leaned into it. The guys with more experience with these clamp down hard, take a low, knees bent, weight forward posture, and let 'er rip. (e.g. the fella in black in the G18 Demo video above.)
 
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