I have an FX Crown MKI .25 that I have been trying to shoot slugs as accurate as I can. Most of what I've read mentions more velocity with slugs for the best accuracy. My tune is maxed out for the most velocity I can get at 145 bar is 850 fps. I'm presently shooting NSA 33.5 grain slugs with a 600 mm Superior liner. I can't get more velocity than that with my rifle now. Would going to a Superior Heavy liner with a twist of 1:18 give me more accuracy than my present 1:24 twist that I have now. Just of note, I have already expermineted with all the lighter NSA slugs, which do give me more velocity, but accuracy is much worse.
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Shooting Slugs for Accuracy Velocity and/or Twist rate.
- Thread starter lamarkeiko
- Start date
The FX Superior Heavy Liner -- the 1:18 twist rate -- is designed for heavier slugs. You will have to test your projectiles at various velocities to determine what speed is most accurate for your rifle.
Contrary to what some believe, higher velocities are not necessarily best for accuracy with slugs. However, slugs do perform better at greater velocities (>900 fps) than diabolo-shaped pellets, generally speaking.
It seems with your FX Crown only producing a maximum velocity of 850 FPS with 33 grain slugs, you are rather restricted in velocity testing.
I'm not an FX Crown owner -- my preference is the Impact -- but I do think there are modifications you can do to your rifle to increase it's power output, i.e.:
FX Crown High Flow Pin Probe
Duel hole transfer port
Tuning hammer spring
Contrary to what some believe, higher velocities are not necessarily best for accuracy with slugs. However, slugs do perform better at greater velocities (>900 fps) than diabolo-shaped pellets, generally speaking.
It seems with your FX Crown only producing a maximum velocity of 850 FPS with 33 grain slugs, you are rather restricted in velocity testing.
I'm not an FX Crown owner -- my preference is the Impact -- but I do think there are modifications you can do to your rifle to increase it's power output, i.e.:
FX Crown High Flow Pin Probe
Duel hole transfer port
Tuning hammer spring
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Addendum: Huma Air sells a regulator for the Crown mk1 that allows for a much higher pressure than the OEM regulator.
Also, have you looked into a 700mm barrel kit for your Crown?
Also, have you looked into a 700mm barrel kit for your Crown?
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If you are running your gun wide open all the time no matter what weight slug you shoot, you are as far away from the best tune for that slug as you can be. If you would get lucky and get some good groups right after you fill the bottle or maybe when the bottle is half full, you will never be able to maintain that accuracy from fill to refill because you are operating on the plateau of the reg setting. You need to do all your slug tuning around the knee of your reg setting. They are much more sensitive than a pellet so you can’t get away with a crappy tune and still have respectable accuracy. If your gun isn’t fast enough when tuned to the knee, you have a couple decisions to make. Bump the reg up and try again, but eventually your hammer spring is going to run out of gas. Shoot a lighter slug. Or buy a longer barrel. If you don’t understand any of the stuff about the plateau and knee, take some time off and hit the books before chasing the slug dragon again.
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I didn't start tuning my Crown at wide open regulator. I started at 130 bar with the various weight slugs including the FX slug and shooting many groups, working up in hammer spring until velocity stopped going up. I worked at 5 bar increments on the regulator up until 150 bar. I don't have enough hammer spring strength to go over 145 bar, because there's no change in velocity at 150 bar. The NSA 33.5 grain slugs proved to be the most accurate at any velocity, and was as accurate as it could be even at 145 bar.
I have a Huma duel hole transfer port installed. After I installed the Huma transfer port, there was no change in velocity. I have since read that Huma sells a high flow pin probe that matches up with their transfer port and should give more velocity. I got on Huma - Airs web site 2 days ago and found they have a heaver hammer spring for the Crown and the high flow pin probe. I ordered them both at that time. I don't know how long it takes to get to the USA from the Neatherlands, but it will be interesting to see how my velocity changes.
I really don't know what to expect in accuracy with slugs. I see lots of reports of people getting consistant 1 moa groups at 100 yds. I have achieved that a couple times with 5 shot groups, but most of the time there closer to 2 inch groups.
I will gladly purchase a Superior heavy liner if it could give me a little better grouping.
As I understand, a 700mm barrel could also give me a little more velocity, but that's a much bigger investment. If I was to do that, I might consider getting a .22 cal.
I have a Huma duel hole transfer port installed. After I installed the Huma transfer port, there was no change in velocity. I have since read that Huma sells a high flow pin probe that matches up with their transfer port and should give more velocity. I got on Huma - Airs web site 2 days ago and found they have a heaver hammer spring for the Crown and the high flow pin probe. I ordered them both at that time. I don't know how long it takes to get to the USA from the Neatherlands, but it will be interesting to see how my velocity changes.
I really don't know what to expect in accuracy with slugs. I see lots of reports of people getting consistant 1 moa groups at 100 yds. I have achieved that a couple times with 5 shot groups, but most of the time there closer to 2 inch groups.
I will gladly purchase a Superior heavy liner if it could give me a little better grouping.
As I understand, a 700mm barrel could also give me a little more velocity, but that's a much bigger investment. If I was to do that, I might consider getting a .22 cal.
Upvote 0
Anything related to regulator tuning. Then once you grasp it then you can read what Mr. Sterne writes with all his graphs. It all comes together nicely if you can get the simple cliff notes version first. Bobs knowledge is a level higher than most and not everything he writes is in layman’s terms. But once you you get it, everything he writes makes perfect sense.
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