FX FX .25 Impact MkII to M3 upgrade

[cgun]

Hi all, I don't post a lot on here, but I have been a member for some time. My question is pretty simple. I have a .25 FX MkII Impact, tuned with the slug power mod and set up to push a custom swaged (Corbin) BT 45 grain slug to around 920fps for about 84 ft-lbs. I am considering going up to an M3, but I am not totally sure it if I will be gaining that much. Any opinions on this are welcomed. I am also considering the pathera, because its longer magazine would allow me to make a 52 grain slug of the same design and hopefully, push that to around the same speed.

I use this gun mostly for night time predator hunting and pest control around my farm.

Thanks!

 

[bigHUN]

I have the Impact MK2 and I did a lot of machinings on parts to upgrade to the most performance. And somewhere earlier this year I bought parts (the power block upgrade kit) to upgrade to next level. I am saying waste of money... mine diy upgrade was performing better. If I can advise - leave the MK2 as is and spend the money somewhere else.

 

[cgun]

I have the Impact MK2 and I did a lot of machinings on parts to upgrade to the most performance. And somewhere earlier this year I bought parts (the power block upgrade kit) to upgrade to next level. I am saying waste of money... mine diy upgrade was performing better. If I can advise - leave the MK2 as is and spend the money somewhere else.

What exactly did you machine on the FX to get the most power? How much were you able to get out of it? I have a feeling like the MkII could probably be pushed to almost 100 ft-lbs in .25 with a few tweaks... Mine is currently on Power setting 3 with the reg at 148bar. I could bump the reg up to 170 and push to power setting 5 with a 47 grain slug (50 grains if I swage it into a SWC and still fit in the mag). I still feel like, even with those tweaks I would only be up around 89-90 ft-lbs and my hammer spring would be maxed out. I would also only get about 18-20 shots on the reg, then it would drop off.

 

[bigHUN]

I have a same .25x700 MK2 originally the PP.
I have unrestricted the airpath in the Rear Block and Valve House, slug HUMA port and adjustable pin probe, heavier HS and 8 gram brass HW, lighter VS, still about 1mm on HS tension and never got to the end. That mod gave me 1050 fps with ZAN 44gn or 1080fps ZAN 41gn with Reg at below 150. I never shoot above 150 bars, tried it ones about 170 but from the wibration I got a feel that I over stress it.
With replaced bigger Plenum and Power Block and stock HW, 143 bars on Reg it is set currently on 980 with ZAN 41.
So, that kit have a better potencial with .30 or .35 heavier slugs, maybe.
The key for a higher power is in airpath through the Block and Valve House. I think a stock is 6.5mm and I open it to 7.2mm. With the old VH cannot make it bigger because the larger peek Valve poppet won't fit. I think the new VH is a same dimensionally only you can swap the Valve Seat, and FX rearranged the orings.

 

[qball]

My MK2 is basically a M3 without the front reg, micro adjuster and cocking block. Zero difference in power and anything else really.

 

[cgun]

I have a same .25x700 MK2 originally the PP.
I have unrestricted the airpath in the Rear Block and Valve House, slug HUMA port and adjustable pin probe, heavier HS and 8 gram brass HW, lighter VS, still about 1mm on HS tension and never got to the end. That mod gave me 1050 fps with ZAN 44gn or 1080fps ZAN 41gn with Reg at below 150. I never shoot above 150 bars, tried it ones about 170 but from the wibration I got a feel that I over stress it.
With replaced bigger Plenum and Power Block and stock HW, 143 bars on Reg it is set currently on 980 with ZAN 41.
So, that kit have a better potencial with .30 or .35 heavier slugs, maybe.
The key for a higher power is in airpath through the Block and Valve House. I think a stock is 6.5mm and I open it to 7.2mm. With the old VH cannot make it bigger because the larger peek Valve poppet won't fit. I think the new VH is a same dimensionally only you can swap the Valve Seat, and FX rearranged the orings.

Wow! Thats impressive for an MkII!. I have the pin probe, heavier hammer spring, lighter valve spring and slug barrel port. I will have to look into modifying the power block.

I took a 35 lb bobcat that had already killed a few of my laying hens. She was at about 45 yards one night and I was running 34gn Nielsens at around 950. While it did the job, I would have preferred a little more power. Hence, I designed my slug swage dies with Dave Corbin (capable of making slugs up to 60 grains) with a blunt round nose (no HP, so that they penetrate) and a boat tail for High BC. They look like teardrops and are accurate to boot! I would love to be able to push the 47 grainers to 975 at a reasonable reg pressure for coyote and bobcat bodyshots. On groundhog, those slugs pass through and through from almost any angle in a nice straight line to ensure the vital organ I aimed at was perforated. Without a hollow point that opens up and stopped short of its objective. I'd rather have a little less damage along the wound path, but surety that they round passed through the vitals. A pencil-holed heart is better than a completely destroyed shoulder blade in my book.

But I need power to accomplish that on predators, hence the desire for more power.