.25 Crown MKII….600 mm slug liner with barrel swapped to slug port. Hammer spring max… 170 bar regulator… it’ll BARELY push 26gr hybrid 850fps… I started with 36gr NSA and it was 780-805fps… I see people shooting mid 900’s. What am I missing?
.25 FX crown FPS problems
- Thread starter Chris-Kratos.25
- Start date
I’m at 150 bar and can shoot 60 foot pounds plus with 34 JSB’s In .25 cal. I’m assuming your HS is not high enough to match 170 bar.
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The screw is just lose enough at setting 23 to wiggle the knob…. That’s maxed at correct? Any tighter and the knob won’t turn at all
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Chris;
I've got the same gun. As delivered the regulator was set at about 145 Bar. When I raised the regulator pressure, to increase velocity, the velocity actually decreased. My experimentation found that I achieved maximum velocity with the regulator at 135 Bar. I deduce that as delivered, the Crown MKII's don't have enough hammer energy to adequately open the valve at higher pressures. I've added the power slug kit. I haven't finished sorting it out and don't know if it is "the answer". I have noticed higher standard deviations on my shot strings. If I can't find a consistent tune I may remove the power slug kit and just shoot pellets.
I also think FX has a design / assembly problem. I have had repeated problems with various screw working loose. When the hammer adjuster and / or transfer port work loose it will mess up your tune. For me it resulted in lost velocity. Vibra-Tite is the solution I found for the fastener problem. Do not use Loctite. On smaller screws it may be permanent!
Good luck.
George
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I have the same setup I get 963 fps, wheel set at 24 and 155 bar, changed out the prob and spring to the HUMA
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As others have said, the hammer doesn’t have enough momentum to open the valve all the way with your regulator pressure at it’s current setting. Get a heavier spring, tungsten hammer, and pick up a high flow pellet probe while you’re getting the parts. That should make a big difference.
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I'm talking about the internal hammer spring. You will have to take the stock off to adjust that. Its right in front of the power wheel.
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Yup, I’ve come to a similar conclusion that the original hammer weights on these guns aren’t designed for high power slug pushing. The slug power it will improve your speed significantly. If still not enough, you may need to experiment with heavier hammer weights that some have custom made for their applications.
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Here is a pic of my FX Crown MKII .25cal 600mm barrel set at 150 bar on HS #23 max. I added a Huma pin probe and Huma Hammer spring. Same Hammer weight as stock version and a Dual transfer port. IHS is about 2 turns away from max
The top number if a FX Hybrid 26 grain at 986fps and 984 fps
The next 2 are NSA 34.9 grains at 902 and 912 fps. That's almost 64.5 foot pounds
The button number is a JSB 25.39 at 1018 fps
Hope this helps.
The top number if a FX Hybrid 26 grain at 986fps and 984 fps
The next 2 are NSA 34.9 grains at 902 and 912 fps. That's almost 64.5 foot pounds
The button number is a JSB 25.39 at 1018 fps
Hope this helps.
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Thank you for your input. I did a quick test at 135 bar. 2 shots were 967 & 964 fps. I’ll test tomorrow when I have time. Thank you! Also, let me know when you finish sorting it out. I’ll test NSA slugs 33.5 & 34.9gr at this bar aswell
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I shoot my .25 600mm crown mk2 with a reg at 160, tfp H, power wheel at 23, throw 29 gr Neilson slugs at 953fps to 960fps. 44 shots. No other mods. Works great on ground squirrels!
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i just got a new crown 2 days ago its a 177 the reg was set to 100 i cranked it up to 110 shot it for a bit decided to crank it up a little more so that i could get 920 fps which is about where i wanted shot about 200 pellets this morning and then it started shooting at about 720 fps what the so i brought it inside scrubbed the barrel it was filthy ( gonna polish it when my stuff comes in ) then the fps went up to 820 any suggestions the reg gauge says 120 and i still have about 150 on the tank
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Is there a puff of air coming from the breech area? It may be an O-Ring inside the 'barrel' that has expired or ripped. If so, you'll need to remove the barrel assembly in order to get better access for replacement.
mike
mike
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Make sure the transfer port wheel isn’t partially turned and between settings. I’ve had this happen, and been stumped for a bit until I figured it out.
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I talked to someone in the club and they think i am over airing and causing the opposite affect so since then i took the bottle off and dumped all air set the reg to 105 it seemed when i went past 110 is when all hell broke loose, he seemed to think that since it is a 177 cal that the hammer may not weigh enough to depress the valve with the higher pressure and that could be the reason why the opposite affect i am going to shoot it tomorrow and see if it helps then I am going to take the stock off and tweak the hammer to get some more power/speed
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