The L.C. Smith Collectors Association

The L.C. Smith Collectors Association
[ The L.C. Smith Collectors Association ]

Main Spring Dimensions

Posted by Michael Tavary on February 11, 2025, 5:10 pm

I bought several new mainsprings from a respected used parts supplier. The dimensions varied in the distance between the leaves and length of the leaves from the apex.
I traced a spring in 5 spaces per inch quad paper for reference.
Dimensions were measured with dial calipers.
Two springs were measured with "a" and "b" labels.

Can these dimensions be verified as proper fit?
This is in reference to a 1928 Ideal 12 ga.
Thanks Mike

Re: Main Spring Dimensions

Posted by John Mistretta on February 11, 2025, 7:33 pm, in reply to "Main Spring Dimensions"

I’m not going to venture a guess as to who the vendor was but if the springs were sold as new reproductions they may not be what you are looking for. The metal is not as robust as it needs to be. Main springs seem to have become hard to find. Contact Lou Rotelli and he can make you exactly what you need.

Re: Main Spring Dimensions

Posted by John Mistretta on February 11, 2025, 7:41 pm, in reply to "Main Spring Dimensions"

Also keep in mind that parts on these old guns, any make, are not plug and play. I’m sure you know this anyway, but you may need to get out a file and do a slight amount of fitting to get them just how you need them to be.

Re: Main Spring Dimensions

Posted by David Williamson on February 12, 2025, 7:07 am, in reply to "Main Spring Dimensions"

I have a mainspring in front of me and the long leaf measures 2.337 long, thickness at tip .058 width .217. Short leaf length 1.686 long, thickness at tip .061. At fold .280. Opened .998

From Brophy's book "Plans and Specifications" it gives dimensions for an FW mainspring, over all length of long tip 2.236, short end 1.695, .055 at both tips. The drawing shows the mainspring compressed.
Dimensions for a Regular frame mainspring: long leaf or tip 2.233, short tip 1.797, .920 fully opened, top thickness .053 both.
Material: Chrome Vanadium steel, Rockwell hardness before machining B 98. After hardening C-46-50
Final drawing Jan. 4-36

Hope this helps, if you can file yours fairly easy then I don't think it is the hardness you want.

Re: Main Spring Dimensions

Posted by Michael Tavary on February 12, 2025, 10:41 am, in reply to "Re: Main Spring Dimensions"

I've got that book.

The book does not state how far the leaves are spread apart in uncompressed state, i.e. if the short leaf is on a flat surface, how far the long leaf is above the surface?
In my sketch, the 1.292a and 1.328b dimensions

Seems to me the spread between the leaves would be critical for force on the hammer and ease of insertion when assembling.
Thank You!

Re: Main Spring Dimensions

Posted by David Williamson on February 12, 2025, 12:34 pm, in reply to "Re: Main Spring Dimensions"

Michael, I think you are looking to far into it.
The dimensions you have shows me that under compression they would be better but how long will they last is uncertain. You say you have Brophy's book. How is anyone going to know what the compression size is at the tip, you don't.
The mainspring that I am looking at the dimension opened is .930-932.

Put it in and try it. If you have never taken a side plate mainspring off, you are in for a surprise. Wear glasses.

Re: Main Spring Dimensions

Posted by Michael Tavary on February 12, 2025, 2:58 pm, in reply to "Re: Main Spring Dimensions"

Thanks David.

These are spares. Just wanted to be ready.

Re: Main Spring Dimensions

Posted by David Williamson on February 12, 2025, 5:13 pm, in reply to "Re: Main Spring Dimensions"

Good. Was that Numrich you bought the parts from? I need two sears and Numrich are out of them.

Re: Main Spring Dimensions

Posted by Tom Garver on February 12, 2025, 9:11 pm, in reply to "Re: Main Spring Dimensions"

David, I have a number of sears. Let me know what you need. 717-887-0545

Re: Main Spring Dimensions

Posted by Louis Rotelli on February 13, 2025, 7:38 am, in reply to "Main Spring Dimensions"

The fact that the legs on your spring are too long is why the opening is much larger than the original. You can shorten the legs as long as you don't over heat the steel. wrap a damp cloth over the leg and grind it shorter. That being said the larger opening will make it more difficult to install but will not hinder the action of the spring. It will however put greater forces on it and it may not last as long as if it were correct

Re: Main Spring Dimensions

Posted by Michael Tavary on February 13, 2025, 11:25 am, in reply to "Re: Main Spring Dimensions"

Yes, Numrich

Several months ago, I saw sears, but they did not have pins.

Re: Main Spring Dimensions

Posted by Michael Tavary on February 13, 2025, 11:39 am, in reply to "Re: Main Spring Dimensions"

Louis, I compressed the springs, per Brophy's book, to 0.321" and measured the legs. Book lengths are 2.236" and 1.695". Mine are 2.210" and 1.719" respectively. So, the longer leg is shorter than drawing, and the shorter leg is longer drawing.
What do you think?

Re: Main Spring Dimensions

Posted by Tom Garver on February 13, 2025, 2:09 pm, in reply to "Re: Main Spring Dimensions"

Michael, please send me the serial number of your gun and I'll look for one close to your serial number. This will give you an original to compare to. Please include your contact info and shipping address. cedarclyffelodge@gmail.com

Re: Main Spring Dimensions

Posted by Michael Tavary on March 1, 2025, 11:19 pm, in reply to "Re: Main Spring Dimensions"

Thanks, Tom,

It is an FWE Ideal 122670. The authentication paper says 1928 mfg.

Re: Main Spring Dimensions

Posted by Michael Tavary on March 1, 2025, 11:22 pm, in reply to "Re: Main Spring Dimensions"

My address:

61 Japonica Ct.
Lake Jackson, TX 77566

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