I recently purchased a .25 pup for the wife and have been working to sight it in for her. Long and short of it, I can group under 1" at 60 yards and my grouping goes to 3.5+ at 75 yards. Because I don't have a chronograph I've made incremental power adjustments, gauging velocity by grouping size. This is how I landed on the current power setting (very good at 60 yards and single hole for a clip at 20-30 yards). That said, I cannot seem to get any consistency at 75 yards, even adjusting power from what I believed to be near optimal due to performance at shorter yardage. Based on what I've read and watched, this rifle is very capable at 75+ yards. Does anyone have an idea of something I'm missing... Is there any possibility it's my scope? For perspective, I can group my Hercules Bully .357 tighter at 75 yards than my wife's FlashPup .25. This doesn't make sense to me given the barrel design and caliber differences between the two rifles. I'm still very new to this hobby and very much appreciate any thoughts!!
Hatsan FlashPup .25 accuracy issues at 75 yds.
- Thread starter chadray73
- Start date
A chrono would tell you what the gun is doing. If you don’t want to guess, a chrony is an inexpensive investment. Without actual numbers it’s difficult at best to try and diagnose what the issues may be. So many variables, pellets, different pellet weights, actual velocities, etc. without a chrono it’s all guessing. Good luck.
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I suspected that would have to be my next step... was just hoping I had missed something more simple.
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I can’t wrap my mind around how the grouping can deteriorate that much at 75 if it’s under an inch at 60. The only explanation would be spiraling and that could be a result of the velocity being too high and destabilizing as the velocity decays much faster than the spin rate.
Lacking a chronograph, you could try reducing the velocity an arbitrary amount and see if it will remain stable at a greater distance. If your gun has a power wheel or transfer port restrictor screw, that would be the easiest and least invasive way. Simply backing off the hammer spring tension would be another way but that will affect your usable bell curve if it’s an unregulated PCP or increase the extreme spread if it’s regulated. Still could be an informative experiment, just pointing out that such an adjustment may not produce a desirable state of tune for permanent use.
Definitely need a chronograph to do a proper job. If you don’t want to spend much and can stand to wait for it to arrive, get one of these little muzzle-mounted versions for $30. https://m.aliexpress.com/item/4000569862057.html. I have a full-sized one but I find myself using this little one often, particularly when I need to test at night and don’t feel like setting everything up. This type has its own built-in infrared light source. Only displays in meters per second though.
Lacking a chronograph, you could try reducing the velocity an arbitrary amount and see if it will remain stable at a greater distance. If your gun has a power wheel or transfer port restrictor screw, that would be the easiest and least invasive way. Simply backing off the hammer spring tension would be another way but that will affect your usable bell curve if it’s an unregulated PCP or increase the extreme spread if it’s regulated. Still could be an informative experiment, just pointing out that such an adjustment may not produce a desirable state of tune for permanent use.
Definitely need a chronograph to do a proper job. If you don’t want to spend much and can stand to wait for it to arrive, get one of these little muzzle-mounted versions for $30. https://m.aliexpress.com/item/4000569862057.html. I have a full-sized one but I find myself using this little one often, particularly when I need to test at night and don’t feel like setting everything up. This type has its own built-in infrared light source. Only displays in meters per second though.
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@Nervoustrigger,
I like & appreciate you Jason so don’t take this wrong. I simply don’t understand & am asking.
If my .25 original Smooth Twist can group any pellet at 75 with a much much slower twist, his must be going too fast for the twist rate?
Are you saying a pellet could be spun too fast, that twist is too fast, or it’s simply going too fast for that specific twist? I’d like to know the pellets used & twist rate.
If that’s the case, I’d try lightweight slugs that need a faster twist. The new RBT Griffins are available in very light weight options due to hollow Delrin spheres inside that displace 5-7 grains of lead 4-4.5mm & weigh 0.9 grains. Dave Corbin creation. They literally explode the slug when they hit anything with resistance by acting as a piston.
Maybe OP doesn’t want to use, try slugs. I fully understand. I’d gladly send you some free Griffin RBT .25’s because they like faster twist.
It’ll tell you if it’s twist related if they’re driving tacks at 25,50,75,100, however far you can shoot. Just shoot them as fast as you can.
To OP: I have owned chronographs and needed it, especially when I wasn’t an Alkin dealer with access to unlimited air. Now, I don’t want a internal reg in any high power Ag that can shoot slugs. I shoot tethered with a step down in-line reg.
I set my guns up with scope optically centered & fully adjustable rings. I get that done/level at 12 yards. Then with StrelokPro & Chairgun Pro, I just work with near/far zero. The Apex/zenith, & use whatever ammo is most accurate.
A chronograph is helpful but if you have a ballistics program and a level bench, level near & far zero targets you can be within 25 to 50fps or less of set speed. Helping know exact BC & tuning efficiency, that’s where a Chronograph is super helpful.
Just don’t do what I did and end up shooting it trying to get a BC reading at 3’ & 100 yards.
I like & appreciate you Jason so don’t take this wrong. I simply don’t understand & am asking.
If my .25 original Smooth Twist can group any pellet at 75 with a much much slower twist, his must be going too fast for the twist rate?
Are you saying a pellet could be spun too fast, that twist is too fast, or it’s simply going too fast for that specific twist? I’d like to know the pellets used & twist rate.
If that’s the case, I’d try lightweight slugs that need a faster twist. The new RBT Griffins are available in very light weight options due to hollow Delrin spheres inside that displace 5-7 grains of lead 4-4.5mm & weigh 0.9 grains. Dave Corbin creation. They literally explode the slug when they hit anything with resistance by acting as a piston.
Maybe OP doesn’t want to use, try slugs. I fully understand. I’d gladly send you some free Griffin RBT .25’s because they like faster twist.
It’ll tell you if it’s twist related if they’re driving tacks at 25,50,75,100, however far you can shoot. Just shoot them as fast as you can.
To OP: I have owned chronographs and needed it, especially when I wasn’t an Alkin dealer with access to unlimited air. Now, I don’t want a internal reg in any high power Ag that can shoot slugs. I shoot tethered with a step down in-line reg.
I set my guns up with scope optically centered & fully adjustable rings. I get that done/level at 12 yards. Then with StrelokPro & Chairgun Pro, I just work with near/far zero. The Apex/zenith, & use whatever ammo is most accurate.
A chronograph is helpful but if you have a ballistics program and a level bench, level near & far zero targets you can be within 25 to 50fps or less of set speed. Helping know exact BC & tuning efficiency, that’s where a Chronograph is super helpful.
Just don’t do what I did and end up shooting it trying to get a BC reading at 3’ & 100 yards.
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James, that's right. Obviously I'm speculating a bit because we have so little information but Hatsan uses fairly typical twist rates so if, for example, his gun is running hot and zipping them out at 1000fps, a 1:16 twist rate is spinning the pellet at a blustery 45,000rpm. A diabolo pellet sheds velocity like mad (disproportionately) at such high initial velocity, whereas downrange it is still carrying a large portion of its starting RPMs, making it what's called overstabilized. That term is kind of an oxymoron...such a condition diminishes its dynamic stability and can lead to spiraling.
The very slow effective twist rate of the original Smooth Twist barrels is thought to be a key reason why spiraling is virtually unheard of, but also why they would seldom work well with anything but JSB.
The very slow effective twist rate of the original Smooth Twist barrels is thought to be a key reason why spiraling is virtually unheard of, but also why they would seldom work well with anything but JSB.
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I would just try a heavier or lighter pellet until your chrono arrives. See if the gun exhibits the same behavior of opening up drastically.
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this topic goes good with my strong cup of coffee,thank you.Vetmx has a simple idea,diifferent wt.pellets...with some research you may be able to achieve results without spending money,good luck.
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I get best longer range accuracy with heavier pellets in my FP. But not all. I have seen the same effect you mention with some like the JSB 25.39gr Monster Diabolos. One hole at 35yds and 3 to 4 inches with owrse flyers at 75 yds. The overpriced JSB 25.39gr Ultra Shocks do one hole at 35 yds and most at about a MOA at 75yds. I'm shooting them about 900 to 940 ish through a string.
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Gents,
Thank you much for the feedback. It would seem I’m headed down the right path based on your cumulative feedback... velocity must be determined. I must have gotten lucky with my .357 and will need to know the numbers for this .25 flashpup. I may burn through a few pellets at, shooting every 10 yards to determine shot geometry and plug velocity into the ChairGun app until I have a curve that matches. Different pellets and a chrony will have to be ordered. Thanks agin, I very much appreciate the responses!
Thank you much for the feedback. It would seem I’m headed down the right path based on your cumulative feedback... velocity must be determined. I must have gotten lucky with my .357 and will need to know the numbers for this .25 flashpup. I may burn through a few pellets at, shooting every 10 yards to determine shot geometry and plug velocity into the ChairGun app until I have a curve that matches. Different pellets and a chrony will have to be ordered. Thanks agin, I very much appreciate the responses!
Upvote 0