Slow FPS Impact MKII (23gn NSA)

[heavy-impact]

I think I'll try this also. Is that probe dremeled out also? Do you know how long the hole is at its furthest cross point?

The transfer port in the brass barrel inlet should be flared deep at it's entry and elongated forward (egg shaped) where it enters the breach about 13%, with the forward edges smoothed. This tilts the port forward slightly. Do not make the port wider. Blend the flare into the elongated portion Then open the feed hole in the pellet probe a good bit larger than the brass port and knife edge the edges. You should not be able to see the edges of the pellet probe entry when looking through the barrel inlet port. You may be able to thin the probe from the inside to make the wall thickness uniform and provide more airflow. Maintain some taper on the leading edge of the probe so it passes the breach o-ring easily. I use a 1/8" carbide burr in a cordless rotary tool.

 

[shatafire]

Thanks!!!

 

[edosan]

@shatafire so after disassemble and reassemble you got better? IYO it was not assemble good in the first place? (you had to correct 45mm block distance? and loose screws?)

 

[stoti]

My .25 MKII maxes out at 950fps with the 33.95gr. That's with the hammer spring adjuster tight, so the adjustment wheel wont turn and then backing it off just a tad so everything works properly. That's absolute maximum for my stock gun! I then tuned it to about 920-925fps where it shoots like a laser... before running out of MKII JSB's. I think anybody would be hard pressed to get 950fps out of the .30 unless they got an extremely hot gun. Probably not though.

Stoti

 

[shatafire]

Not sure what it was. It has now started shooting slowly again. 750fps max with Nielsen 23gn. I like to tinker, but this really affects my ability to hunt humanely if I can't trust this Mk2 to perform predictably. 

 

[harrymoreland]

I must report that the thought of (possibly) have to "Dremel ports" to get the MK2 shoot slugs satisfactorily, fills me with dread, that kind of precision workmanship, on such a hi end (hi cost) item, surly not.

Thank you shatafire, Thank you Airgun Nation, I Shall be keeping my hard earned in my pocket for now.

 

[shatafire]

Dremeled the port and probe today. Also changed the regulator. Thanks Heavy Impact and Edosan. This worked. Got extra fps from porting. I also had a different regulator pressure when I switched the gauges. I'm pretty sure the reg pressure reading is corrected now allowing me to avoid an overcharged reg pressure that stops the hammer from being ineffective. 



You folks are an amazing resource. 

 

[heavy-impact]

I must report that the thought of (possibly) have to "Dremel ports" to get the MK2 shoot slugs satisfactorily, fills me with dread, that kind of precision workmanship, on such a hi end (hi cost) item, surly not.

Thank you shatafire, Thank you Airgun Nation, I Shall be keeping my hard earned in my pocket for now.

The only parts you touch cost about $35 to replace with new ones from FX so you're not risking much.

 

[edosan]

Imo not a good idea to make mods if your gun is not consistent. An mk2 stock impact should shot a 23gn @ 920-940 fps with 140 bar reg. 750fps is not normal