6-48 Screw Shear Strength

[Dennis The B]

Does anyone know the shear strength of a 6-48 screw?

I have a 1911 Colt pistol with a rib atop it, and mounted with (2) 6-48 screws holding it. Right now 185gr target loads will stovepipe with a 13lb recoil spring. I'd like to up the poundage of the recoil spring to 16, and shoot hardball loads instead.

The question is, would the recoil generated from a 230gr hardball round cause the screw to shear?

 

[toasted]

Shear Strength

This is a link to Screw Shear Strength Data:

http://www.cactus.org/~tbodine/Alarms/ScrewShear.htm

The strength is shown for 6-40 and is given in lbs/in so I would convert that to 168.79 lbs/ft.

If you would prefer psi here is a useful document from Fastenal.View attachment FastenalTechnicalReferenceGuide.pdf

 

[scooter123]

Your problem is a lot more complex than a simple shear strength situation. You need to know the mass of that rail, the acceleration rates of the slide, the coefficient of friction between the slide and the rail, and the clamp force exerted by each screw. Once you know all that then you can then enter the data into a Dynamic Modeling program and come up with an answer that probably won't mean spit in the real world. Because about the only factor you can accurately measure is the weight.

To put it simply, you are going to have to try it and see what happens.

 

[Dennis The B]

That's what I feared.

The pistol is a John Giles custom, built for bullseye shooting. I came upon it at a LGS, and it's a temperamental piece of hardware. Giles made his own ribs, and attached them, fore and aft, with 6-48 screws to the slide. No silver soldering. To get the recoil and firing pin springs down to the appropriate weights, he evidently cut coils from standard springs. The recoil spring was 5.5 inches. However, it has a superb trigger, and balance of the work was great. Of course, Mr. Giles is no longer alive (died 2007), and neither is the gentleman from whom I purchased the gun.

I replaced the extractor and firing pin with Wilson's; then put in a Wolff 13lb spring kit, including recoil and firing pin springs.

When I went to the range today, Federal 185gr JSWC ammo, would still fail to eject. I've taken that to mean that the 13lb recoil spring is still too heavy (maybe an 11lb is needed), or that I switch to 230gr hardball and install a 16lb recoil spring.

Hence, the question about whether the 6-48 screws had the shear strength to withstand the additional stress generated by the heavier round.

I just ordered a recoil spring test kit from Wolff. This may turn into a Galahad-type quest. I love a mystery!

 

[tomcatt51]

I'd be more worried about the screws coming loose than shearing. Blue Loctite is in order. If the rib is a good fit on the slide I'd apply Loctite to the rib/slide contact areas too.

Your 13 lb spring is probably too heavy for 185 gr target loads. 'Specially with the added weight of the rib. A 10lb spring is the traditional bullseye "softball" spring and with the rib you may need still lighter.

I really don't think you'll like shooting bullseye with hardball ammo.