Merry Christmas to all. My wife got a FX dynamic compact .177 cal. in the 300 mm barrel today and I am wondering if anybody would know what the barrel twist rate for this it would be. Your help would be greatly appreciated.
barrel twist rate for the FX dynamic 177 cal 300 mm barrel
- Thread starter JR.
- Start date
Just because it is so common for airguns, it is likely to be 1:16". With pellets, twist rate almost does not matter, unless you shoot them over 950 FPS. Then there is potential for spiraling at over 50 yards, if the barrel rifling twist rate is also too fast. The fix is to shoot heavier pellets to bring the velocity down to perhaps 900 FPS. Or retune with available pellets to shoot at 900 FPS; or less.
Twist rate for slugs is more important. Then it is possible that 1:16 is too slow for .177 cal. The solution is to shoot shorter slugs of a reduced weight and increase the velocity to over 900 FPS. Many small cal slugs shoot better closer to 1000 FPS. Although, if barrel twist is a little slow for the slugs you want to shoot, then the problem becomes worse as you approach the speed of sound, with potential instability and yawing of the slug. Then, better to stay near 800 FPS. Or find a shorter lighter slug to shoot near 900 FPS.
Of course, with both pellets and slugs, the consistent quality of manufacture, and matching to the bore and groove diameter of the barrel are more important than the rifling twist rate, unless that is way off for the projectiles you want to shoot.
The length of the barrel does not affect the ideal twist rate, except in terms of achieving the ideal pellet or slug velocity range. Short barrels are less likely to overspeed pellets, but more likely to fall short of ideal slug velocity. But you won't know until you try.
You could determine the twist rate of any barrel by means of a cleaning rod and a snug fitting patch. Mark the rod with two strips of masking tape, with pen lines across the rod length a known distance apart. Add another mark parallel to the rod. Push the rod into the barrel, ensuring that the patch is in the rifling, not just in the shroud or moderator. Measure the distance the rod travels, while observing the number of degrees or fractional turn for the distance travelled. If the rod travels 203 mm for half a revolution, then the barrel has a twist rate of 1:16". And so forth.
Ensure the patch does not slip rotationally in the barrel. Especially at the two ends. So, you may not be able to measure the twist for the full 300 mm length. Nor is that required. Keep the breech open so you do not bang the end of the cleaning rod into the loading probe; and to prove the airgun is in a non-shooting state.
It may be easier to just push the cleaning rod until you observe 1/4 or 1/2 of a full turn. Then measure the travel by means of a pen mark on a piece of tape, that never travels out of sight onto the barrel or shroud. You take the measured distance and multiply by 4, of you used 1/4 turn. Or multiply by 2, if you observed a half a turn.
Repeat the process until you are confident your measurement is repeatable. If the measure does not repeat reasonably, then the patch my not be tight enough in the barrel, or the jag is unscrewing from the cleaning rod.
You need a rod with a free rotating handle, else the job becomes very difficult. Avoid dragging the cleaning rod over the barrel's muzzle crown.
Due to the short barrel on your wife's FX, trying to achieve very high velocities by "pushing it hard" with an aggressive tune is likely to open groups and make it loud, regardless of the barrel twist rate. 10.5 or 13 grain pellets at 20 FPE should still work for Field Target or other longer range competition disciplines. But that is pushing pretty hard, unless you want to shoot slugs.
For 10 meter Olympic target style shooting or short range plinking 8 grain wadcutters at 550 to 700 FPS may be just the ticket. Wadcutter shoot well up to about 20 yards, and cut clean holes in paper targets. They also do a number on small pests at such ranges. Beyond perhaps 25 yards, wadcutters tend to loose their grouping ability. One exception is the 9.3 grain RWS Supermag wadcutter pellet. Those often work well to over 30 yards.
For general use at ranges beyond 20 yards, round nose pellets generally work better. About 800 to 900 FPS is a good velocity range for flat shooting out to 50 meters. If you are seeing too much wind drift at your preferred range, shoot heavier round nose pellets, and retune to restore the velocity to about 800 to 900 FPS.
Twist rate for slugs is more important. Then it is possible that 1:16 is too slow for .177 cal. The solution is to shoot shorter slugs of a reduced weight and increase the velocity to over 900 FPS. Many small cal slugs shoot better closer to 1000 FPS. Although, if barrel twist is a little slow for the slugs you want to shoot, then the problem becomes worse as you approach the speed of sound, with potential instability and yawing of the slug. Then, better to stay near 800 FPS. Or find a shorter lighter slug to shoot near 900 FPS.
Of course, with both pellets and slugs, the consistent quality of manufacture, and matching to the bore and groove diameter of the barrel are more important than the rifling twist rate, unless that is way off for the projectiles you want to shoot.
The length of the barrel does not affect the ideal twist rate, except in terms of achieving the ideal pellet or slug velocity range. Short barrels are less likely to overspeed pellets, but more likely to fall short of ideal slug velocity. But you won't know until you try.
You could determine the twist rate of any barrel by means of a cleaning rod and a snug fitting patch. Mark the rod with two strips of masking tape, with pen lines across the rod length a known distance apart. Add another mark parallel to the rod. Push the rod into the barrel, ensuring that the patch is in the rifling, not just in the shroud or moderator. Measure the distance the rod travels, while observing the number of degrees or fractional turn for the distance travelled. If the rod travels 203 mm for half a revolution, then the barrel has a twist rate of 1:16". And so forth.
Ensure the patch does not slip rotationally in the barrel. Especially at the two ends. So, you may not be able to measure the twist for the full 300 mm length. Nor is that required. Keep the breech open so you do not bang the end of the cleaning rod into the loading probe; and to prove the airgun is in a non-shooting state.
It may be easier to just push the cleaning rod until you observe 1/4 or 1/2 of a full turn. Then measure the travel by means of a pen mark on a piece of tape, that never travels out of sight onto the barrel or shroud. You take the measured distance and multiply by 4, of you used 1/4 turn. Or multiply by 2, if you observed a half a turn.
Repeat the process until you are confident your measurement is repeatable. If the measure does not repeat reasonably, then the patch my not be tight enough in the barrel, or the jag is unscrewing from the cleaning rod.
You need a rod with a free rotating handle, else the job becomes very difficult. Avoid dragging the cleaning rod over the barrel's muzzle crown.
Due to the short barrel on your wife's FX, trying to achieve very high velocities by "pushing it hard" with an aggressive tune is likely to open groups and make it loud, regardless of the barrel twist rate. 10.5 or 13 grain pellets at 20 FPE should still work for Field Target or other longer range competition disciplines. But that is pushing pretty hard, unless you want to shoot slugs.
For 10 meter Olympic target style shooting or short range plinking 8 grain wadcutters at 550 to 700 FPS may be just the ticket. Wadcutter shoot well up to about 20 yards, and cut clean holes in paper targets. They also do a number on small pests at such ranges. Beyond perhaps 25 yards, wadcutters tend to loose their grouping ability. One exception is the 9.3 grain RWS Supermag wadcutter pellet. Those often work well to over 30 yards.
For general use at ranges beyond 20 yards, round nose pellets generally work better. About 800 to 900 FPS is a good velocity range for flat shooting out to 50 meters. If you are seeing too much wind drift at your preferred range, shoot heavier round nose pellets, and retune to restore the velocity to about 800 to 900 FPS.
Last edited:
Upvote 0
Not the identical airgun, but good advice for tuning a short barrel FX:
Same logic applies to your compact:
Same logic applies to your compact:
Last edited:
Upvote 0
Thank you very much for the info. The video was very helpful. So far my wife is doing very well with it she is going to do field and target with it. Just have to get a wheel for the side focus and she will be ready to have some fun.
Upvote 0