If the inside length of the hammer is 4.089" and the spring length when cocked is about 3.11", then there must be some kind of spring seat that goes inside the hole in the hammer when cocked about 1".... The solid length of the spring is 37 x 0.072" = 2.66".... With a free length of 6.63", and a compressed length of 3.11", and a spring rate of 8.4 lbs/in. that gives a force of (6.63 - 3.11) = 3.52" x 8.4 = 29.6 lbs.... That is indeed a bear to cock....

We don't know the hammer stroke, so we don't know the force when uncocked, unfortunately.... I did not find a single spring long enough, but I did find what may be a suitable spring if you stack two of them in line.... Century Spring makes one using 0.081" wire, part # 71818....

https://www.centuryspring.com/catalog/compression-regular?page=product&id=71818CSOD = 0.60"

ID = 0.438"

Free length = 4.0"

19.4 coils (ends closed and ground)

Rate = 25 lbs/in

Maximum load = 41 lbs.

Suggest Max. Deflection = 1.6"

Coil Bound Length = 1.57"

If you shorten these to 3.25" long each, for a total length of 6.5", you would get the following:

About 32 coils

Rate = 15.4 lbs/in.

Suggested Deflection ~ 2.6" (more is likely OK)

Coil Bound Length ~ 2.6"

Maximum load = 41 lbs.

If may well be that you could use a shorter LOA, maybe 6".... The spring rate would increase, but the uncocked force would decrease.... This would allow you to play with the average and maximum forces.... You could fit a washer in between the cut ends, or better yet, heat the last coil, push them closed, and grind them flat....

I also found a 3" long spring at Trakar Springs, made from 0.080" wire, part # C1524-203-0762

http://www.trakar.com/products/compression-springs/?part=C1524-203-0762&submitpart=1It has an OD of 0.60", ID of 0.44", length of 3", rate of 29 lbs/in, and a maximum load of 37 lbs at a deflection of 1.78".... Two of them inline would be 6" long, rate of 14.5 lb/in, same maximum load at a deflection of 3.56".... This should fit, and again you could possibly shorten them if this ended up being too much spring.... Since these Trakar springs would not require shortening, you should be able to just drop two of them over the spring guide and try them.... It would increase the maximum cocking force by 25%....

Bob