Increasing hammer spring tension on the Crown

Forums PCP Airguns Increasing hammer spring tension on the Crown

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    As I understand it the reason velocity goeas down when having to much hammer spring tension, is because there is a spring behind the valvepin which throws it back, making it close faster than if you had some less tension.  Almost like a squash ball bouncing back quicker the harder you slams it against a wall.



         Thank you everyone for all of your help. I was really hung up on the cause and effect of the whole thing and why one pellet weight would increase in velocity while the other stayed the same, why the group size was all over the place and most intriguingly, why the deviation rose to 47 fps. with the 33.95gr pellets but was like 7-8 with the 25.4gr pellets. The whole reason I messed with the settings in the first place, even though the 25.4gr pellets were shooting one ragged hole, ten shot groups from 50yds is because I also wanted accuracy and more velocity with the 33.95gr pellets. 

         I took the advise of the people who had done this before and backed down the regulator pressure from 140 to 125 and also backed off the hammer spring tension about half way. I went out back with a shooting mat, my tools, a note pad, my gun and pellets. I removed the stock and just left it off for testing which made the whole process a lot easier and faster. It took me most of yesterday and about an hour after work today to get it totally dialed in to my liking, both velocity and accuracy.  I started with the reg. pressure at 125 and increased it about 3-4bar and then increase the spring tension about 3/4 turn, if the accuracy was good and the velocity kept increasing, I would just repeat the process. I did this quite a few times and ended up with my reg. pressure back at 140bar which is where I started. I had to fine tune the spring tension quite a bit and it was a lot lighter than it was after I messed with it in the first place. I can only guess but I would say the spring tension was 3-4 full turns lighter than when I began this process. After I got to a point where the velocity quit increasing, (never decreased) I focused on adjusting the spring tension for accuracy. I would shoot a 3 shot group, decrease the spring tension about 1/4 turn and then try again. After doing this just two-three times, I ended up increasing it a little bit and called it good. 

         I ended up with the gun shooting the 25.4gr JSB's though one ragged hole at 40yds and averaging 955fps. The 33.95 JSB's are also shooting super tight groups at 50yds with a velocity of 850fps. I need to test the 33.95 pellets more at distances past 50yds. but haven't had enough time, maybe tomorrow after work. The way they're shooting out to 50yds. I have no concerns about accuracy! I couldn't be happier with the accuracy, the gun is shooting as good as it was when I got it and the velocity has increased 15fps with the 25.4's and about the same with the 33.95's. These increases are over the settings I have been using since about a week after getting the gun when I turned the reg. pressure up from 125bar to 140bar. 

         I have read over and over that the Crown will not shoot accurately with the 25.4 JSB's at velocities over 940fps and the sweet spot is from 900-920fps. I can't speak for other people or even guess what their gun is doing.  I can tell you that my gun is an absolute tack driver with both of the pellets that I've been testing and I'm getting velocities above what I had originally hoped for. I can't wait to test the 33.95 JSB's more and try out the Mk II's too. I've heard they shoot great out of most Crowns. My point is, if I would have left my gun alone, as it was when it arrived, it would still be set with a reg. pressure of 125bar, a spring tension way lighter than it is right now, shooting at around 915fps. Of course it was super accurate but it was shooting with a lot less velocity and  wasn't anywhere near it's potential for accuracy and velocity. I made some adjustments, screwed it up a bit which really had me worried, but then came on Airgun Nation and got some advice.  Viola, problem solved and the gun is shooting as good as ever…with a lot more velocity!!! 

         Again, thank you for all of your thoughts, suggestions, ideas and comments. It's really nice to hear varying opinions and ideas when it comes to tuning or adjusting these airguns. As with most things in life, there are often many ways to reach the end goal. I really do enjoy this site and appreciate all of you that are willing to help when a problem arises. Airgun Nation is are a wealth of information and also just a fun site just to be a part of. Thank you. Stoti


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