Slide Travel Measurement

[niemi24s]

Does anybody know of a reasonably safe way to measure how far back the slide travels after firing (short of high-speed photography)?

The gizmo I cobbled together to make this measurement is kind of dangerous. Get a real bad case cold sweaty palms and heart pumping when using it!

Thanks in advance for any input.

[Hawkmoon]

Sure. Remove the recoil spring, set up the pistol with the slide and barrel in battery and set whatever you use as a reference point, then push the slide all the way to the rear and take the measurement.

[niemi24s]

Pardon my poorly worded question. I should have said " . . . measure how far back the slide the slide travels after firing (. . .) - even if the travel is less than the maximum (at slide/recoil spring guide contact)."

I suppose this sounds like a goofy idea, but the goal in setting up my bullseye target gun has been to use a recoil spring that is:

A. Strong enough to prevent the slide from contacting the recoil spring guide's flange, yet

B. Weak enough to allow the slide to lock open after the last round.

Measuring the last one's easy - the slide stop will do it.

Measuring the first one's not so easy. I've done it, but the method is pretty scary (to me, at least). Just looking for a safer way.

[Hawkmoon]

I suppose this sounds like a goofy idea, but the goal in setting up my bullseye target gun has been to use a recoil spring that is:

A. Strong enough to prevent the slide from contacting the recoil spring guide's flange, yet

B. Weak enough to allow the slide to lock open after the last round.
Ain't gonna happen.

[1911Tuner]

Just curious...Why do you want to prevent slide to frame contact? It can be done, I suppose...but would prove to be problematical in getting the gun to function reliably...and to what end? If you're concerned over impact shock stresses...shock buffers are cheap.

[John]

I assume that he is trying to reduce the felt recoil, by eliminating the impact.

May I suggest that instead of trying such untested paths, you replace your firing pin stop with a square bottomed one and use the proper recoil spring for your loads? A shock buff is a good way to see if your gun has the proper spring and the square-bottom firing pin stop will give you enough recoil reduction to be happy with your gun.

[gbw]

Can you make (get) ammunition to provide recoil that consistent? It's a very small window to hit.

Interesting question, though.

Some sort of marker attached to the slide that scribes on paper taped to the frame? Sort of like the old circular recorders they used to use in process control rooms. How to attach the marker would be the question.

[Canuck-IL]

Strong enough to prevent the slide from contacting the recoil spring guide's flange, yet
I must be missing something that everyone else that responded has seen...where do you want to measure? Do you suspect that the recoil plug is travelling all the way back to the spring guide, without coil bind?

If you want to see the impact on the guide rod, you could cut a couple of circles from a styrofoam coffee cup and mount them on the guide rid where a buffer usually goes - evalute the extent to which 2 are chewed up in one shot. They're unlikely to last more than 1 round before leaving shards in the gun.

A common metric for a Bullseye gun is a spring that yields 100% feeding and locks the empty gun open 19 out of 20 times.
/Bryan

[John]

Bryan, what niemi24s wants to achieve, is to have a spring which would allow his slide to move back enough for the pistol to work OK, but not enough to hit the guide rod flange. I assume he wants that to avoid adding the impact of the slide so that the perceived recoil and muzzle jump are minimized. It sounds more like splitting hair to me, but I wish him luck.

[robot1911]

I understand what he's trying to do, but it ain't going to happen. What he wants to do is stop the slide's rearward motion just before contact is made with the recoil spring guide. I'm dismissing contact with the vertical impact surface here because (1) it needs to be contacted by the barrel lugs and (2) recoil felt by such contact would be minimal relative to that felt by the recoiling slide.
Tuning a 1911 to stop the rearward slide motion at a pre-determined position short of the mechanical stop is an exercise in futility...far too many variables are involved in pushing that slide in recoil...bullet weight, powder weight, powder effeciency, case length, crimp type, crimp dimension, etc... just to name a few.
So, get the EGW firing pin stop, install the proper recoil spring and a C-P recoil buff, and rest assured you've done the optimum to achieve what you're seeking.

Bob

[niemi24s]

Hi Hawkmoon: Keep in mind, this is a bullseye target gun, and the handloads used chronograph at only 621fps with a standard deviation of 6.4fps. I have made it happen with proper recoil spring selection - based on measurements made with the gizmo in the pix below. Problem is rechecking slide travel after tinkering with the gun. I probably tinker with it too much, and get real nervous checking slide travel with it.

Hi Tuner: Guess I want to prevent slide to frame contact just because it can be done and I've got too much spare time on my hands. Don't have any reliability problems with this old gun with the mild stuff I shoot in it. Had considered shock buffers but with a proper recoil spring they'd do nothing for the gun - IMO. Impact's probably not all that much anyway.

Hi John: Want to eliminate the impact shock just because it adds nothing to the functioning or reliability of the gun. The path is not untested. The gun does have an EGW firing pin stop with very small radius. Selection of the proper recoil spring is what this measurement is all about. Perceived recoil was never an issue with the powder puff ammo used.

Hi GBW: The owner of the chronograph used to test my handloads said the 6.4fps standard deviation at 621fps was very good. Don't know what's good or bad for that figure, but maybe it's good enough for consistent recoil. And thanks for input on how to make the measurement.

Hi Canuck-IL: Don't want to detect the impact on the guide rod. I want to measure how close the slide gets to the guide rod.

Thanks for all the inputs. Should have taken these pix first and posted them, but maybe they'll help explain how I take this measurement and why I get nervous using it.

First pix shows the gizmo on the gun, with the grip removed for clarity. The brown stuff is a thin phenolic material that's the holder for the scribe (the little brass arm just above the trigger). A removable lifter is used to raise the scribe which is rotated forward to allow a trace of liquid sight blackening fluid to be put on the slide. The scribe is then turned back up to its vertical position against a stop and the lifter removed, dropping the scribe's small dimple onto the sight black. All these steps are done with a live round chambered. Even with the thumb safety engaged, I get jittery. Bullseye shooters don't normally use the thumb safety for much else but to pin the grip safety to the frame!

http://i129.photobucket.com/albums/p232/niemi24s/P2050008a.jpg

The second pix shows the gun and gizmo as they'd be after firing, with the sight black removed by the dimple on the scribe arm.

http://i129.photobucket.com/albums/p232/niemi24s/P2050014a.jpg

After lifting, the scribe is rotated forward to expose the entire length of its mark in the sight black, as shown below. The lenth and width of the mark are measured and slide travel found by subtracting the width from the length.

http://i129.photobucket.com/albums/p232/niemi24s/P2050015a.jpg

This entire process is repeated for each individual measurement. The gizmo does work and allows slide travel to be measured with an uncertainty of about 0.02 inch. But, it's a slow, tedious and (to me) scary process. Just looking for ideas to improve it - or a whole new better way. Regards.

[gbw]

I'd say that's very clever. As long as the gun is pointed downrange, and the safety is used, and no one gets in front it seems safe enough. It also looks like all steps except the final re-set of the scribe could be done with the slide locked back?

The sd you quote is very good indeed - Bullseye powder? Whether it's good enough to hit the small window of movement variability you're looking for, well, that's why we test stuff.

Another factor would be the difference in friction on the slide from the magazine / cartridges. It seems it would vary depending on how many are in the mag - the more shells, the higher the cof.

[niemi24s]

Hi GBW: Thanks for the quick reply. Not sure how clever it really is, probably just the product of an old retired guy with too much time on his hands who may have been a metrologist in a previous life.

The powder is Bullseye, 3.5 gns as thrown from my 40 year old Lyman 55 powder measure. Bullets are H&G 130's cast from wheel weights, sorted only to remove gross visual defects (not individually weighed). Bullets seated, then crimped in a separate operation with a Lee Factory Crimp Die. Nothing special about the brass or primers.

Appreciate the tip on its use and your comment about its safety. Maybe I'm just a "nervous Nellie" who's not used to having a loaded 1911 on the shooting bench unless it's firmly gripped, waiting to be raised to fire. Regards.

[Canuck-IL]

That's a neat gizmo! Clever idea.

Beyond all the variable that Bob mentioned previously, I'm afraid your efforts are further bedeviled by the inherent variability in spring rates, even when brand new. I assume your tolerance is fairly tight and even a half-dozen brand new Wolff springs will show enough variability to cause an issue...then, presumably, they won't all take a set at the same rate or to the same degree.

/Bryan

[niemi24s]

Hi Canuck-IL: Selecting a recoil spring that'll arrest the slide's motion somewhere in the last 0.2" or so of it's possible 2 3/16" of travel does, I guess, make the tolerance kind of tight. I somehow managed to do it last year using this contraption, but have tinkered with the gun (new EGW firing pin stop) since then. When the weather permits I'll try using it again to select a spring from my Wolff assortment. Can also monitor for changes in the selected spring with a tester that'll measure them within about 1 or 2 ounces, at best (testing long, limber compression springs is a real ordeal!). Thanx for the input. Regards.

P.S. BTW, I've heard of cryogenically treating rifle barrels to impart some beneficial property. Anybody heard anything about cryogenic treatment of springs?