What is a strain screw?

[Hulkstr8]

Hey guys,

I took my revolver (I'm new to revolvers) out today, SW 19-4, and had light primer strikes. Same ammo I have used before (Fiocchi 38 special) without issue. First time I've show it in the cold, but I have a hard time thinking it was the temps fault.

I was doing some reading online and people keep talking about checking the strain screw. Like I said above, I am new to revolvers. What is a strain screw?

Also, any other advice or tips you have for this issue lemme know. Thanks homies.

[Screwball]

It puts pressure on the mainspring... if you loosen it, can remove the mainspring easily.

Not familiar with your specific revolver, but when you pull the grips, do you see a coil spring running up towards the hammer, or a leaf spring?

If you have the leaf, look for a screw pushing on it. That is the strain screw. My Victory revolver, which is an M&P, has a screw on the front strap. Loosening that reduces pressure on the mainspring.

[srcochran49]

Since the Model 19-4 is an older gun, I am assuming you bought it used. It is very possible that a previous owner turned the strain screw out which will lighten the double action trigger pull. It can also lead to light primer strikes.

[grizzman]

The strain screw is located on the front strap of a 19-4, near the bottom. It should be screwed in all the way against the main spring, which is a leaf.

If the screw is already tight, then either the spring needs to be replaced, or dried lube or misc gunk may be slowing down the hammer.

[Don Quijote]

If the screw is already tight, then either the spring needs to be replaced, or dried lube or misc gunk may be slowing down the hammer.

All true but there's one other possibility: some people grind down the tip of the strain screw a little (the portion that bears on the main spring) to reduce the amount of force it exerts on the spring but still bottoms out so that it won't back out (when the gun is wearing skinny grips) or prevent bigger grips from fitting over the screw's head.

S&W main springs are leaf springs, they don't "wear out". Coil springs don't wear out either unless they're made of shit steel.

Strain screws are cheap. I'd order a few and change out the one in the gun.

[grizzman]

That is a possibility. It should be very easy to find a photo of a 19-4 strain screw for reference....or I can take a photo of one of mine.

Hammer springs don't wear out from use unless they're defective, but there's no guarantee that the spring that's in the revolver is the correct spring.

[jh9]

Strain screws are cheap. I'd order a few and change out the one in the gun.

The blued, square-butt screws aren't. S&W doesn't make them anymore. Which is proably what OP's 19-4 uses unless it's a snub nose. A quick check of midway and brownells shows neither stocks the older (longer) square butt strain screws anymore, even in stainless. Which means he'll have to go to Numrich or find some other NOS source.

https://www.brownells.com/gunsmith-t...r-prod413.aspx

The 150-3 is the correct size bit for the strain screw. 150-4 will be too thick.

If it worked before and doesn't now, it probably backed out because whoever removed it last didn't snug it down. Easiest and cheapest to start there. If OP ****s up the screw with the wrong bit or decides to use a flat head screwdriver getting a replacement isn't as simple as it used to be even a few years ago.

[jsbhike]

Hey guys,

I took my revolver (I'm new to revolvers) out today, SW 19-4, and had light primer strikes. Same ammo I have used before (Fiocchi 38 special) without issue. First time I've show it in the cold, but I have a hard time thinking it was the temps fault.

I was doing some reading online and people keep talking about checking the strain screw. Like I said above, I am new to revolvers. What is a strain screw?

Also, any other advice or tips you have for this issue lemme know. Thanks homies.

So 1 type of ammo only? And how much of a temperature drop versus last time?

Not a recent purchase, but had a case of Fiocchi 9mm JHP that worked fine for the first few hundred rounds, then wouldn't go bang during a GSSF match. The armorer at the match couldn't find any issues with the pistol. When I got home and tried other ammo there were no issues. The remainder of the case of Fiocchi exhibited the same deal of frequently needing more than 1 hit to fire though and in a different pistol also.