Purpose of extended firing pins?

[BCRider]

A buddy and I have been working on tuning his JM 625. We've got it firing rounds consistently but only with a higher trigger pull than we think it should have. We're currently using the stock mainspring ground SLIGHTLY narrower (not thinner) and this is working with the 14lb rebound spring from a Wolff kit.

He's got an extended firing pin and we're wondering if it would help with allowing the tension on the mainspring to be set to a little lower value which would also then allow the use of the 13lb rebound spring.

Note- the mainspring tension screw on this gun is a longish set screw with the frame drilled and tapped for a locking setscrew. So mainspring tension is intended to be adjustable. Not sure if this is a stock setup for the JB625 or if it was done by the previous owner. It's NICELY done though.

The pin that is in place does in fact extend out to what seems like a decent amount. Haven't measured it to be fair but the Mk I eyeball suggests that it should be OK. But it does require pushing on the pin's anvil fairly far into the frame.

Thoughts? Experience with extended pins? Folklore on why one would want an extended pin?

 

[ontarget]

The set screw on your main spring is not intended to be an adjustment. It should be bottomed out.

 

[fxvr5]

The set screw on your main spring is not intended to be an adjustment. It should be bottomed out.

I think you misunderstand. I think they're describing:

https://i.imgur.com/Bm4fuoz.jpg

 

[fxvr5]

Note- the mainspring tension screw on this gun is a longish set screw with the frame drilled and tapped for a locking setscrew. So mainspring tension is intended to be adjustable. Not sure if this is a stock setup for the JB625 or if it was done by the previous owner. It's NICELY done though.

I think TK Custom did some of those, too.
https://tkcustom.com/services/adjustable-main-spring-system

 

[ontarget]

OK. Looks like the gun has been modified?

 

[fxvr5]

OK. Looks like the gun has been modified?

Yes. S&W might have done it, but custom gunsmiths have done this as well. It allows users to fine tune their strain screw adjustment in a fairly easy manner.

 

[Jim Watson]

That is a gunsmith job, never saw a factory Smith like that but there are several brands of add on screws.
Teddy Jacobson has a simpler method that does not call for an extra screw and hole. He grinds the end of a long 8-32 set screw into a pyramid shape, which "clicks" from flat to flat in the groove of a Wolff Power Rib spring.
The strain screw was designed to be turned down tight, but everybody and his brother has twiddled with it to reduce mainspring load.

A longer firing pin will not allow a softer rebound spring, that is determined by the strength of the mainspring and how quick you want the trigger to return. Jerry Miculek uses a bent and thinned mainspring, twiddles the strain screw to the minimum, but he likes a strong rebound spring to keep up with his fast firing.

 

[AzShooter1]

Yes, a longer firing spring can help if you are shooting a lighter than normal action. I've been doing it for about 30 years. I use an 11 pound rebound spring and my mainspring is bent but the screw is set in all the way against the frame so it doesn't come loose.

The set screw is an excellent idea. It will let you adjust your trigger and balance the springs. You need too have the hammer reset completely when using a lightened mainspring.

 

[243winxb]

Your extending lock time & reducing pin velocity. Tuning for 1 lot of primers will result in misfires when the new primer lot has a harder cup.

View attachment 1012647

 

[PWC]

He's got an extended firing pin and we're wondering if it would help with allowing the tension on the mainspring to be set to a little lower value which would also then allow the use of the 13lb rebound spring.

Change the pin and try; easiest way to find which way to go. Measure the new before install, and measure the original. You may have to shorten/reconture the new pin. Don't go shorter than original.

 

[BCRider]

The tensioning screw setup is the TK Custom one. Or someone copied it. Either way that is what is on this particular gun. Long adjustment screw with no head on it and the locking set screw up from below.

My own thoughts where that the extended pin should not make any difference in terms of allowing a lighter mainspring setting. And which in turn would allow a lighter rebound spring. But he's got one and is wondering. And I'm still learning the gun smithing and tuning side of things as a side line hobby to go with the actual shooting hobby so that's why I'm asking.

 

[RugRev]

There are limits as to how far one should extend the firing pin past the recoil shield. An APG gunsmith I talked to said that optimal would be 0.055". Two other factors to also consider in lightening would be endshake amount and headspace as these can influence how much spring tension will be necessary. An aftermarket firing pin may need to be modified to get to the optimal length.

I have had an N frame whereupon I used the Teddy Jacobson screw and it worked well. I have also had a L frame 686-5 Mtn. Gun that I used the separate locking screw on. This was with an extended firing pin that was adjusted to 0.055" protrusion. I had the guns dimensions optimized for 0.006" forcing cone clearance, minimal endshake and 0.061" headspace. This allow a 6.75 lb DA trigger pull and would fire factory and my reloads with WW magnum primers. One could go much lower on an N frame if they wanted to use Federal primers only and some of Randy Lee's parts (Apex). I believe the extended firing pin set to max protrusion would allow about a 1/2 pound lighter double action than otherwise would be needed.