Bridle/sear screw question

[jpldude]

Greetings all, I am combining 2 locks into one: a Davis 1803 Harper's Ferry lock and a Jim Chambers Deluxe Siler. A lock very similar to this is on a Dickert rifle on page 87 of "Gunsmiths of Lancaster County, Pennsylvania" by James Biser Whisker.

My question is about the screw that goes through the bridle & through the sear and into the lock plate. If I crank down on this screw it bends the bridle just enough to bind the tumbler. As I unscrew the screw, maybe a turn & a half, the bridle unbends, the tumbler unbinds and everything is good. If I unscrew another turn or two, I can see the screw head wobble as I cock the hammer. Which IMO can't be good, so I tighten it back a bit more & life is good again.

Is this bending & binding normal? Does everyone leave this screw just a wee bit loose?  Or should my sear be as thick as the gap between the bridle & the plate so the bridle can't bend?

Any pointers, insites, opinions, etc would be appreciated.


Best rgds,

John

[Acer Saccharum]

Screw ideally should tighten up before pulling the bridle down, Take a little metal off the underside of the screw head, and you should be good to go.

[Dave B]

The screw needs to have a longer unthreaded section so it bottoms out before bending the plate. By using a safe file you could remove the small amount from the thread side of the head of the screw making the unthreaded section longer. Or better yet just counter sink the head of the screw into the bridle the amount it needs to snug down, thickness permitting. Lastly just make a new screw that is the length needed. I have several locks from different makers that are this way and it doesn't affect the performance of the lock so I don't worry about it.

[Dave B]

Tom You are quick on the trigger

[Acer Saccharum]

Ka-Boom! 

[Dave B]

I havnt even had my coffee yet

[Acer Saccharum]

I think the sun comes up 3 hrs earlier over here. 

[Keb]

You could also take some off the outside of the bridle. May be easier than the inside of the screw.
Like Larry, Moe & Curly said; "Gos low".

[mjm46@bellsouth.net]

I usually just tighten up the top screw pretty firm then the one that holds the sear, I only tighten firm enough till it starts to bind then back of about 1/4 to 1/2 turn till it gets loosey-goosey. Works good for me.

I may be wrong but won't removing material on the screw or the bridal actually do nothing, the screw goes all the way through the plate and would just go further through the plate. It's not screwing into a bottoming hole.

[Dave B]

The goal is to run the screw in far enough to have the threads bottom out on the lock plate making the screw more firm of a pivot point. A sloppy sear screw equates to trigger slack

[Acer Saccharum]

I like the sear screw to be firmly bottomed, either on its unthreaded body, or if screw has a slight shoulder, on that. If it's not tight, the shooter will experience different let-off feel at the trigger, because the screw will unscrew over time.

Dang, Dave, you beat me to it! I think I spent too long typing! (or thinking!)

[rich pierce]

I may be wrong but won't removing material on the screw or the bridal actually do nothing, the screw goes all the way through the plate and would just go further through the plate. It's not screwing into a bottoming hole.

The threaded portion is supposed to just be long enough, so that it does bottom out when the end of the threads is reached.  The unthreaded portion of the sear bolt cannot screw into the threaded hole.

[Acer Saccharum]

There is some concern about jamming the non-threaded section into a soft lock plate, this causing a ring of displaced metal to raise up around the screw hole. But that only happen if you're one of those 'screw-jammers', tightening until you ruin the slot, or twisting the screw off. One can also case-harden the plate, and it's then impervious to distortion and wear.

[Jim Kibler]

That raised ring from pulling of the thread near the surface can be an issue when trying to set up very close tolerances.  It's easily solved by countersinking the threaded hole a touch, though.

[chuck-ia]

I do as Micah, allways check the screw after cleaning the lock each time I go to the range, usually take the main spring out for cleaning anyway. However, it would be nice to snug it down. chuck

[mjm46@bellsouth.net]

I may be wrong but won't removing material on the screw or the bridal actually do nothing, the screw goes all the way through the plate and would just go further through the plate. It's not screwing into a bottoming hole.

The threaded portion is supposed to just be long enough, so that it does bottom out when the end of the threads is reached.  The unthreaded portion of the sear bolt cannot screw into the threaded hole.

Thanks Rich, I'm sure that my bridal screws are not far from tight, but I'm going to check them. Sometimes it would be nice if these things came with an instruction sheet. Things that look so obvious to some people may not be so to others. I've been playing with flintlock rifles for 40 years, building for about 6 years and never saw a relationship to the length of the screw threads before, but it makes sense to me. Old dogs can learn new tricks.

[Artificer]

I have to sheepishly admit it took me over 10 years working locks/trigger jobs at the NSSA Spring and Fall Nationals to figure out to cut the inside of the head to get screws to tighten down and not bind parts.  You almost have to do that with the Italian locks, unless you have a lathe and can make your own screws.  Sometimes you can take an extra sear screw and shorten it to make a better fitting bridle screw.   I thought about buying piloted reamers that would cut the bridle deeper and with a flat surface, but never got around to it because frankly I had to spend tool money on other things. 

Brownells sells some unthreaded blank screws that sometimes you can use in black powder locks if you don’t have a lathe.  You can buy them in a kit OR by the size you need.

The sizes in the kit are:

Size 4, shank diameter .115”   , head diameter . .220"
Size 6, shank diameter  .140”  , head diameter  .265"
Size 8, shank diameter .167”   , head diameter  .303”
Size 10, shank diameter .186”   , head diameter .305”

An additional size not in the kit is a Number 12 with a head size of .355”.  I don’t have these, so I can’t measure the shank size, but I’m going to order some. 

http://www.brownells.com/.aspx/pid=376/Product/BLANK-SCREW-KIT

Gus

[David R. Pennington]

Here is another quick fix for the problem of screws withe the threads cut too long that I have used withe success. Put just a little solder on the threads or braze a little brass over them then recut just enough theads back to make them fit right. This may not be the best fix but it is quick, easy and effective.