S&W fixed sight K-frame 38 special

User avatar
mtngun
Site Admin
Posts: 1537
Joined: Fri Feb 01, 2008 5:45 pm
Location: Where the Salmon joins the Snake

S&W fixed sight K-frame 38 special

Post by mtngun » Sat Nov 09, 2019 2:45 pm

Recently I inherited a fixed sight, 4" barrel S&W 10-5 (3 screw, pinned barrel) 38 special. YAWN. :roll: I would never have purchased this gun for myself -- I have no interest in the cartridge, and I have no interest in another fixed sight revolver. But ... as long as it's here, let's take a look at it.

This particular gun was used by security guards in the 1960's, so like a typical security guard gun, it was carried often, and has some holster wear, but rarely fired. Mechanically, it's like new. I did not bother to measure the trigger pull but it is quite decent as it came from the factory, 3 - 4 pounds single action, typical for Smiths of that era.

Throats measured with a tri-mic ranged from 0.3578 to 0.3583" -- not bad.

A 0.357+ pin gage could be push through the throats, but a 0.358- pin gage would not quite go all the way through. That's a good example of how pin gage measurements tend to err on the small side, nonetheless, pin gages are a quick and easy way to measure as long as you keep in mind that the actual diameter will be slightly larger than a pin that fits.

By measuring how deeply a 0.361" pin gage could enter the cylinder, I deduced that for reliable chambering, I should use a front band no longer than 0.080".

The cylinder is long enough to chamber a round that is 1.595" long, about right for a 357 mag, but excessive for 38 special..

I have no easy way to measure the forcing cone but it looks to be the typical oversize S&W forcing cone -- not good, but it's a necessary evil to allow for the inevitable barrel-to-cylinder misalignment on mass produced revolvers.

With those dimensions in mind, I conjured up a bullet design similar to what has worked well in my N-frame 357 mag, but with a slightly longer nose to take advantage of the K-frame's excessive cylinder length. However, it was not practical to make the nose long enough to fill up the entire cylinder. Here's the bullet. I went with an 80% meplat, which has shot well at 100 yards in my 357, but no guarantee that such a blunt bullet will stabilize well at 38 special velocities.

The bullet has a long, oversize bore riding section to engrave the rifling yet allow effortless chambering.

At 38 special velocities, the powder coating is overkill, but my experience with coating is that it sometimes helps and never hurts. Ditto for the lube on the coated bullet. Alloy was air-cooled wheelweight which should be 8 - 11 BHN though I did not bother measuring. After coating and lubing, the bullets were sized 0.358" to match the cylinder throats.
Image

Even with a bullet design tailored for this gun, the bullet still has to jump roughly 0.28" before it starts to engrave the rifling, owing to the generous forcing cone and the excessive cylinder length. It's not practical to lengthen the bullet nose because there isn't a great deal of bullet inside the case as it is.
Image

As my readers are aware, I like to experiment and tinker with guns and loads, but I resisted the temptation to do much tinkering with this gun, because no matter how much you tinker with it, it's still going to be a fixed sight 38 special. YAWN. :roll: The only suitable powder I had on the shelf was Unique, so that's what I used, and after walking the powder charge up I settled on 5.9 gr. Unique ignited by a CCI500 primer. Quickload predicted 945 fps at 19,700 psi (slightly in excess of the 18,500 psi SAAMI spec because I like 'em hot :twisted: ). Actual chrono velocity at 15 feet averaged 946 fps.

After putting a few shots on paper to observe the point of impact, I shot standing at a swinging steel target from 25 years, and the K-frame had no problem staying on target as long as I used the appropriate Kentucky windage, which was substantial as shown. Therein lies the problem with fixed sight revolvers, and my lack of enthusiasm for this gun. Even for home defense and plinking -- which is all a 38 special is good for -- you need to be able to hit what you're aiming at.
Image

So .... I don't foresee myself using this gun. I may eventually trade it for something more useful. Unless of course, Santa Claus brings a set of Crimson Trace laser grips that can be adjusted for POI. I've never used the Crimson Trace grips before so I don't know whether they would be a satisfactory solution to the fixed sight problem? :|