I would say no longer than 15 minutes
Posted by Ken Pang on December 25, 1999
OBJECTIVE: To determine the effect on a mainspring if airgun is left cocked for an extended period.
Preparation: Airgun was disassembled, thoroughly degreased, examined, lightly lubed with a mixture of Silicone oil & moly, then reassembled.
Procedure: After reassembly, airgun was fired 10 times to eliminate any excess lubricant which would contribute to dieseling.
Muzzle velocity recorded at each period in time was the average of 5 shots.
VO = prior to test;
V1 = gun left cocked for 1 week, 24 hrs per day (168 hrs);
V2 = gun left cocked for 2 weeks, 24 hrs/day (336 hrs);
V4= left cocked for 4 weeks (672 hrs);
V12 = left cocked for 12 weeks (2,016 hrs) and
V24 = 24 weeks (4,032 hrs).
At each period, gun uncocked and left uncocked for 72 hrs to allow the spring to regain as much as possible of its original power (memory effect).
The gun was cocked and uncocked a number of times to get the cylinder walls lubed and then 2 shots fired over a chrono.
The average of these 2 shots were taken.
All pellets have been sized and weighed then batched according to weight. All pellets used in this test were of uniform size and weight. All airguns were .177 cal and all velocity readings are in feet per second.
---------- V0-- V1- V2- V4- V12 V24 % Vel Decrease
HW30----- 655 648 630 592 521 481 26.6
HW50----- 705 682 678 640 565 513 27.2
HW35----- 715 698 689 652 576 533 25.5
R1-------- 975 965 944 891 789 739 24.2
Vulcan3--- 818 808 785 739 640 599 26.8
Hawk----- 655 638 630 589 519 476 27.3
BSA Merc- 695 679 668 630 552 511 26.5
FWB124---795 774 770 728 645 596 25.0
There were 2 spring failures (breakage) suffered by the Webley Hawk on weeks 4 and 12. None other suffered the same fate. I attribute spring failure to the absence of a spring guide in this make and model.
While the percentage reduction in m. velocities varied, reduction was generally around 25% of original m. velocity taken prior to commencement of test.
It should be noted that these percentage decreases are theoretically optimistic as the air gunner would more likely experience reductions in velocity greater than the statistics shown here. Dieseling, weight & size (diameter.) of pellets used, improper lubrication, temperature, conditions of usage etc. can all have an adverse impact on the life and power of a mainspring.
This test does show that leaving a spring airgun cocked, no matter for how long, will adversely affect the life and power of any mainspring.
Custom springs will be more resistant to decrease in power but the process will still occur over a longer period of time. I do not suggest that you change the ways you hunt but I point out, as Tom Gaylord has done very well, that be prepared to pay the price of higher maintenance.
And here's an experience I had:
While one hour doesn't seem too horrible, the figures from 2 hours on are disturbing. It also agrees with an experience I had with a C-1. The gun had been left cocked---on a gunrack in someones pickup truck-- for two weeks. When I tested it afterwards, it was down more than 150 fps with Premiers. Pissed me off ! I wound up buying a new spring from Beeman because of this. RB
This is why don't keep mine cocked for more than 1/2 hour at a time.