Hi, I've not ventured into doing anything like this but thought I would share my findings. Clearly I made a mistake with tempering the first time but nailed it with the kiln the second time. Just proper research and taking time as usual...

I used an old flintlock spring for the first piece of metal which worked fine.

Very nice work- a boxlock- 12 gauge? Possibly similar to the first top lever and leaf spring Parker used, later the Hayes re-design (after I think 1906?) with the cam linkage to the bolt and the coil spring in a housing-

Did you do a before and after Hardness test- drawn and hardened 6150 steel for such springs- maybe C scale 48-52-- tempering is crucial- what temperature in the kiln, and for how long, and also the drawn down time??

Looks good for another 100 years of service- I usually do a vice compression-extension test on replacement springs, not foolproof, just a "benchmark"- Thanks for sharing and the good fotos too!!!

Looks like you did a very nice job. JFYI, Brownell's has some top-lever springs for sale. The S-30 will work for a Parker. DGW also sells what they call a Parker spring but it was too short, IMO. If you have the measurements of your old spring, when you call, the tech. guys can measure what they have. I've made some for Lefevers, using spring stock, also from Brownell. I used the flash burn technique for tempering. Seems like the Lefevers are somewhat prone to breaking TL springs. Does that observation match anyone else's experience? I DO love Lefevers.

Trouble is the hardening ,I know I should say this but since you can not get whale oil any more I have never found any thing as good. So I guess the next job is replacing that striker?

By the by is is amazing how many guns an AyA top lever spring can be adapted to fit.

I've using the tempering oil from EJ Blackely here in the UK for the first hot quench...then I use the digital kiln to take the spring to 450 Deg C for one how and let it cool over night.

Then, slowly compress the spring more and more so over an hour...done deal....lovely...erm..so far

OH and FOX sorry didn't reply, it's a Best Grant sidelock not a boxlock.

Jim, you are correct that Lefever top lever springs seem prone to breaking. But the mainsprings and trigger springs seem to hold up well. I have only seen one with a broken hammer spring. I've made a couple top lever springs out of 1075 steel, but I used a tempering temperature of about 700 deg. F rather than the 450 deg. C (842 deg. F) that Ballistix999 used here.