Reply To: Increasing hammer spring tension on the Crown

Forums PCP Airguns Increasing hammer spring tension on the Crown Reply To: Increasing hammer spring tension on the Crown




So check this out… I read the thread at the beginning and have been contemplating the adjustment of my hammer spring tension too, so I did it. There are some very strange results I'm hoping someone can make sense of.

MY Crown's regulator is set at 140bar, power wheel .25-.30, and the hammer spring adjustment set on high. The velocities before adjusting the hammer spring tension were verified by many, many shot strings and averaged as follows: 

JSB 25.4gr. – 940fps.  

JSB 33.95gr – 835fps.

After tightening the hammer spring tension about half way, these are the velocities I got:

JSB 25.4gr. – 948fps (average of a 10 shot string) deviation was 11fps and the velocity average went up about 8fps.

Here's where it gets totally whacky…

JSB 33.95gr. – 800fps (average of 11 shot string) the maximum deviation was 47fps. The shot string looked like this: 793fps, 812fps, 812fps, 773fps, 820fps, 785fps, 815fps, 796fps, 790fps, 802fps, 778fps. 

After getting these numbers, I am absolutely stunned and baffled. I don't know how these numbers are even possible or what could cause this kind of shot sting. The velocities decreased over all of the previous shot string averages by 35fps and the velocities are totally up and down with the deviation average of 47fps. SAY WHAT???

I got some good advice from what of the most knowledgeable members of this board who told me to tighten the hammer spring tension all the way and lower the regulator pressure to around 120 and work my way back up. The gun is still super accurate with the 25.4gr. pellets and surprisingly accurate with the 33.95gr pellets too. The inaccuracy with the heavier pellets can totally be attributed to the velocity deviation.

I would really like to hear anybody's  thoughts on my situation  and hopefully get a dialogue started as to what could be causing one pellet to increase in velocity, have a small average deviation and remain accurate while the other pellet has a decrease in  average velocity, and an average deviation of 47fps. 

Please help!!! I'd really love to hear what you master tuners and long time PCP shooters/tinkerers have to say about this. It doesn't even seem possible to have the same exact settings and have one velocity increase while the other decreases???

Thank you in advance for your help! Stoti



Looks like you went too far, hence the erratic numbers.

The way to do it properly, is to set your reg. pressure as desired, 140 bar in your case. 

Back out the set screw of the hst sliding block (anti clockwise)

Set hst adjuster to "max"

Work your speed up by turning the set screw in (small increments, clockwise diirection.)

Make sure to use a chrony (kind of mandatory for this job) and look for the peak where the speed will not increase anymore. 

Turning in any further will actually lower the speed, and make the gun inconsistent. (This is the case with all FX airguns.)