Tuning Springs and things: Share your experience!

[Michigander]

This may be old hat to many of you, but it is new to me and I thought worth posting. There are two ways to store spring energy in an airgun, a low rate spring with a lot of preload, or a higher rate spring with less preload. I just happened to have a pair of spring setups for my short stroke TX200HC that store close to the same energy, and here is the comparison in numbers.





The OEM spring is stiffer but with less preload, so there is more of a difference in initial and final loads. The Vortek spring is less stiff but with more preload, and has less of a difference in initial and final loads. I prefer the more uniform cocking force of the Vortek spring. It is just easier and more pleasant to cock and stores the same energy as the OEM spring. The Vortek spring is also lighter, and the kit uses a plastic top hat, which seems to reduce recoil somewhat. And for whatever reason, the Vortek spring proved more efficient in transferring energy to the pellet. All improvements in my book over the OEM setup. Although to be fair the OEM configuration was intended to provide maximum power using a long stroke piston.

 

[JayJay]

Very interesting. I recently put a Vortek PG3 kit into an HW95. 

There may be an advantage to a higher initial load and lower final load. The piston would accelerate faster at the beginning. There would be less force at the end of the stroke which might lessen the slamming. Just a thought.

How did you measure the loads?

 

[Michigander]

I didn't measure the loads, just the amount of spring compression at preload and cocked. The loads came from an online spring calculator.

https://www.thespringstore.com/spring-calculator.html

You need to measure the spring dimensions, the amount of preload compression, and know the stroke for the gun being considered. The rest comes out of the calculator. The only trick is making sure you get the number of active coils right. If the spring has closed ends the number of active coils is two less than the total number of coils. The PG3 uses a spring with open ends, so the number of active coils equals the total coils. The stored energy is just the average load times the stroke in feet.

I was hoping to get some feedback from some of the more experienced tuners here. What I found online was that greater force at the end of the firing stroke (what I called Initial Load) might help reduce piston bounce, so I went that direction.

The terms initial and final might be confusing. In any case, the lower number is the load at the beginning of cocking and the end of firing. The higher number is the load at the end of cocking and the beginning of firing.

 

[CharlieNC]

What is the comparison of velocity SD and accuracy?

 

[Michigander]

All for 20 shots

With JSB 8.44/4.53

OEM: ES 12.7 SD 2.9 KE 10.3

Vortek: ES 12.0 SD 4.3 KE 10.6

With AA 8.4/44.52

Vortek: ES 10.2 SD 2.6 KE 10.8

With AA 7.87/4.52

Vortek: ES 13.3 SD 4.4 KE 10.8

I will be playing with the Vortek setup and Air Arms 8.44/4.52 going forward. I am getting better consistency with both the AA 8.44s and 7.87s than I ever got from the equivalent JSBs. As for accuracy, boy that is tough to evaluate in a springer unless there are big differences in pellet performance. Too much depends on the shooter, and how well you are doing that day. I track average group size and accuracy over time to try and determine differences. Average of 5 consecutive groups for me (NRA protocol) ranges from 1.5 to 2.0 MOA using the TX. I will be hoping to see a lot of averages close to the 1.5 MOA mark with the AA pellets.