Nielsen 33.5gr .25 cal best fps range.?

[Powerbroker]

My 25cal fx impact x (with upgrade kit to mkII) can propel ns 33.5 at max 880fps (all dialed to max including valve lines). To fine tune at 860fps, it might not have enough speed designed for the slug and barrel’s accuracy. I intend to go back to pellets.

 

[Bob_O]

What reg pressure did you max out at?

Also, did you set the D5 screw for maximum hammer spring compression?

 

[Powerbroker]

What reg pressure did you max out at?

Also, did you set the D5 screw for maximum hammer spring compression?

Hi Bob. Thank you for the quick reply. Dialed at 145bar reg presure, Max on the power wheel plus max spring adjuster (hammer spring) with 1/4 turn to have a little slack. The valve control is between 3 and 4 line (the control is now hitting/touching the fix shroud (sound is a bit louder like metal drop).

 

[Bob_O]

Try 155bar and see if you get an increase.

 

[ImpactX]

You gonna need a 6g hammer weight and change c3 o ring to delrin and enlarge transfer port. I got max 950 with the 33.5gr nsa using 600mm slug liner. Reg is set to 160 bar. This is with mk1 impact. 

 

[Powerbroker]

Try 155bar and see if you get an increase.

I will bob. Thank you. I did some shooting today using your process and i did a 1/2 inch group at 75 meters BUT at 850fps only. I will update after a week. Need to fly out.

 

[Powerbroker]

You gonna need a 6g hammer weight and change c3 o ring to delrin and enlarge transfer port. I got max 950 with the 33.5gr nsa using 600mm slug liner. Reg is set to 160 bar. This is with mk1 impact.

Hi! Mine is an impact x with MKII upgrade kit. 600mm slug liner too. In this part of the world, any modifications other than "plug and play" is not a cup of coffee. It's either i change the weight of the slug or keep it below 900 fps and make the best tuning to get a tight group. At least, i can shoot the pellet and the slug 1/2 inch group at 100 meters. I may be able to duplicate it at 150 meters  

Bob and you are suggesting beyond the 150 bar limit. Are we not in the red zone? 

Best regards from the Philippine Island with the unlimited beach front hotels all year round.

 

[Bob_O]

The tune I settled on and that I used the most was 155bar.

 

[biohazardman]

I tuned my gen2 Impact and shot the 33.5 NSA's at sub MOA. A week or two later I sent some through the chrony it said 740fps. So they shot fine out past 100 yards but they started to keyhole at about 150. I re-tuned for about 920fps after I found the low fps and got equally good groups and I shot spray paint cans at 200 yards. Best BC is in the low 900's

 

[Powerbroker]

I tuned my gen2 Impact and shot the 33.5 NSA's at sub MOA. A week or two later I sent some through the chrony it said 740fps. So they shot fine out past 100 yards but they started to keyhole at about 150. I re-tuned for about 920fps after I found the low fps and got equally good groups and I shot spray paint cans at 200 yards. Best BC is in the low 900's

This cleared and verified what i noticed a few days ago. Looks like it is a must to go 900 to 950 fps to hit the desired 200meters. 

 

[Powerbroker]

The tune I settled on and that I used the most was 155bar.

Bob, i will go 155 until that reg screw levels. Another 100 slugs needs to fly in the next tuning session. Thanks. 

 

[Powerbroker]

Late post and update (for beginners guide).

After experimenting with all the suggestions, i have concluded that the stock fx impact x regulator can only be dialed to a maximum of 150 bar because the hammer spring (spring adjuster has no slack and power wheel adjuster is dialed to max) and the weight of the hammer Is too light to open the valve if the valve tube has more than 155 bar pressure. The result is the fps will start to go down from 155 bar. The maximum speed i can get for the 34.5 gr nielsen 25 cal with the slug liner 600mm is 872fps with no modification. The mk2 upgrade kit (new valve with bigger tube) will not help because the hammer spring and weight of the hammer is not enough to open the valve with too much pressure or above 155bar regulated pressure. i need to upgrade to a heavier hammer to get into the 920-960 fps or wait for the new slug from fx. 

For now, using the slug liner, the jsb diabolo 24.7 gr has a sweet spot at 885-890 fps. The Nielsen 34.5 gr slug has a sweet spot at 850-860. All at 100meters. 


Thank you everyone. 

 

[Powerbroker]

The next project is to find the most accurate fps given the limitations stated above.

 

[Powerbroker]

After days and hundred of slugs flying over a 75meters target, i have finally realized the fx impact x, 600 mm slug liner, 25 cal with 160 bar reg pressure at max hammer spring tension is not enough to reach 920 fps required to stabilize (when compared to pellet jsb 25.4gr) the 33.5 gr nielsen slug designed for fx slug liner. I have a thousand more slugs but intend to keep it for future modifications. For now, back to pellets.

Accidentally, like most inventions, i have discovered that the jsb 25.4 gr cal 25 is perfect for the slug liner at high reg pressure and lower hammer spring tension on the wheel to get the 920 fps. Similar with other comments, 880 to 920 fps is the sweet spot. Hole in hole is repeatable at 50 meters (max distance on the nearest firing range). Happy days. Happy plinking (hunting is illegal here. No exemptions).