Tuning Crown MkII .22 tuning questions

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dgeesaman

dgeesaman

Member
Nov 14, 2019
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Hershey, PA
Hello,

I'm dipping my toes in tuning my Crown. It's currently outfitted with the .22 700mm standard barrel, and I'm tuning for long range accuracy (15-110y) of 25.4 JSB R/D's.

Beyond factory, I have the reg set at 145 and I adjusted the hammer adjust grub screw so that there is minimal play when the hammer knob is at 24. Now it's shooting those 25.4's at 985 and occasionally shows signs of brilliant accuracy (first time I've put three consecutive shots in one hole at 80y with an airgun!). With the hammer at 21 I'm getting almost the same average velocity as at 24, so I'm hoping it's not wasting much air.

I plan on polishing the hammer components and doing a more carefully optimized tune after I settle on the baseline setup.

So here are my remaining questions about this setup, if I could draw the opinions of experienced Crown tuners.
Q1) Is the current power level excessive for factory hammer components?
Q2) I have a Huma high power spring, an FX power slug kit, and a Huma high flow probe. Would it make sense to install any of those, considering the power levels I'm at now?
Q3) I'm getting 45 shots from 235 bar fill before velocity falls off/hits the reg. Not sure how good that is but it seems reasonable considering the power level.
 
Sounds like you’re having great luck. My only advice would be to turn the hammer down until velocity starts to drop. Then you’ve reached the “knee” of that reg pressure, and it’ll be the most efficient. Otherwise, you’re wasting air for no extra velocity. Also, those mrd’s did well in my crown at 960. The extreme Differences in pellet weights and Sizes of those mrd’s made it hard for them to group fir me, but they do lIke speed. You could try lowering the hammer even more to 960 and see if they still group well for you. You’d get more shots per fill too
 
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What madeintheUK said. Back the hammer off until you lose some speed. Right now you are blasting air out the barrel after the projectile exits. Not only is this wasting air but may also be washing the back of the pellet and causing some destabilization which will affect accuracy.
I would back the hammer down until I was around 965-970 and see how it does.
 
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Hi Guys,
Just thought I would add my two cents. Each click on the Power Wheel (say from 23 to 22) is a 0.2mm change in the spring compression. One complete turn of the Internal Hammer adjustment screw is 0.5mm change in spring compression (exactly the same as on the Mavericks, Impacts and Wildcats). So the Crown is setup to make gross adjustments with the IHS and fine adjustments with the Power Wheel. That is the opposite of the Maverick/Wildcat where the Power Wheel is a 0.5 mm adjustment for each click.
All that being said the advice from the previous posters is correct for the Crown. Just keep adjusting the power wheel down until the velocity starts to drop. If you don't like shooting at a PW setting of 15 instead of 20, just open up the rifle, turn the IHS out 2 complete turns (2 x .5mm/rev on IHS = 5 x .2mm/click on PW) set the PW to 20 and you have almost exactly the same hammer spring compression.
Cheers,
Greg
 
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madeintheuk said:
Sounds like you’re having great luck. My only advice would be to turn the hammer down until velocity starts to drop. Then you’ve reached the “knee” of that reg pressure, and it’ll be the most efficient. Otherwise, you’re wasting air for no extra velocity. Also, those mrd’s did well in my crown at 960. The extreme Differences in pellet weights and Sizes of those mrd’s made it hard for them to group fir me, but they do lIke speed. You could try lowering the hammer even more to 960 and see if they still group well for you. You’d get more shots per fill too
Click to expand...
Hey madeintheuk,
About the JSB MRD's. I have done a fairly large experiment on the 25.4 gr JSB's (about 150 rounds) where I measured head size, weight, then when I shot them recording the muzzle velocity and POI (elevation and traverse). The JSB MRD's head size on average was just over 5.52, with about 50% at 5.52 and 30% at 5.51 and 16% at 5.53. The weights ranged from a low of 24.8 gr to a high of 26.2 gr with 36% right around 25.4, 20% lower and 40% higher. Interestingly enough, I did the same experiment with the FX versions of the MRD (FX 25.4). Over 75% of the pellets had a head size of 5.54mm with the remain pellets evenly split between 5.53m m and 5.55mm. The weight distribution was almost exactly the same as the JSB MRD's. As for accuracy I saw some differences between the two groups. I think the 700mm Superior STX liner in my Maverick liked the 5.54 head size better at the average 915 fps I was shooting.
The purpose of my experiment was not to compare the two groups, but to see if there is an obvious difference in accuracy depending on weight and head size in any one group of pellets (e.g., should you sort pellets). So far I can't see any. I plan to do some more testing with different pellets before making all the results available.
Cheers,
Greg
 
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NAProf said:
Hey madeintheuk,
About the JSB MRD's. I have done a fairly large experiment on the 25.4 gr JSB's (about 150 rounds) where I measured head size, weight, then when I shot them recording the muzzle velocity and POI (elevation and traverse). The JSB MRD's head size on average was just over 5.52, with about 50% at 5.52 and 30% at 5.51 and 16% at 5.53. The weights ranged from a low of 24.8 gr to a high of 26.2 gr with 36% right around 25.4, 20% lower and 40% higher. Interestingly enough, I did the same experiment with the FX versions of the MRD (FX 25.4). Over 75% of the pellets had a head size of 5.54mm with the remain pellets evenly split between 5.53m m and 5.55mm. The weight distribution was almost exactly the same as the JSB MRD's. As for accuracy I saw some differences between the two groups. I think the 700mm Superior STX liner in my Maverick liked the 5.54 head size better at the average 915 fps I was shooting.
The purpose of my experiment was not to compare the two groups, but to see if there is an obvious difference in accuracy depending on weight and head size in any one group of pellets (e.g., should you sort pellets). So far I can't see any. I plan to do some more testing with different pellets before making all the results available.
Cheers,
Greg
Click to expand...
I was just talking to a friend about retrying the mrd pellets in my crown. It’s been a while since I have, so maybe their discrepancy woes have been improved. Thanks for the info.
 
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jps2486 said:
For some strange reason, velocity in my Crown increases as I change the hammer wheel from Max to 1. It's totally a$$ backwards. Can someone explain?
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The valve works like an air spring, a source of potential energy. The hammer of course is a kinetic energy source. The hammer strikes the valve and uses that kinetic energy to release air from the valve.

They need to balance each other out so that the hammer releases the valve fully, in just one clean release. That’s optimal, or ‘in harmony’.

Where you are right now does not open the valve cleanly. Winding up the hammer more is moving them further out of balance.
 
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Raider03 said:
From what I have read, 970fps is the sweet spot for accuracy with JSB 25.39gr pellets.
Click to expand...
Good luck. Ive been all over the fps place trying to find accuracy at 100yds. Id put three in one hole then crazy erratic accuracy. 920-930 seemed better for me but still had issues. I’ve abandoned.22 in the crown and went to .30 as im just shooting benchrest and was tired of fighting accuracy. Tried a bunch of things and couldnt get it sorted enough for its intended use. Those that have found the setup wont share it. So screw it, .30!!
 
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Mcleod said:
I am pushing the 22g FX hybrid slugs at 935 FPS with a REG. setting of 140, PW of 13, medium setting. accuracy 25 - 100 yds is good.
24.1g FX pellets are running at 930 FPS with a REG setting of 140 and PW of 18, and medium setting - accuracy 25 to 75 yds has been outstanding.
Click to expand...
Mcleod, what was/is your reg pressure for that post? And were you using the slug or pellet port on the barrel?
Thanks in advance.
 
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