Tuning FX Impact MKII velocity loss

[Corvid_hunter]

I had my MKII .25cal tuned fairly good yesterday and today I took the scope off and I had the cheek rest off and put on a K&L sling plate (with the supplied longer screws). I decided to go check my zero tonight hand I had a velocity loss of about 100fps and then it would come up 20-30fps and stay there for a few shots and then dip again and continue the cycle. Did I mess something up on the back end of the gun (pellet probe seems tight) or is this possibly the C1 issue that crops up from time to time?

 

[dannya1a]

sounds like the C1 or the HST screw backed out on you. that is a quite common area to back out if it doesn't have to sort of vibratite to help it keep position.

 

[Vetmx]

I just dealt with this two days ago. Wounded a raccoon, checked my zero and the gun was off and not grouping as nice. Went to the chronograph and I was -20fps. I thought man I hope I don’t have to tear into the gun. Checked my HS setting. It’s supposed to be 16.62mm but was 17.56mm. Put it back to where it’s supposed to be and everything is back to where it’s supposed to be. My gun wasn’t doing what yours is doing so maybe you do have a C1 issue.

 

[Corvid_hunter]

Thanks for the help gentlemen. I checked the hammer spring setting and it was over 19mm. I used purple lock tight last time and won't be making that mistake again. I put blue lock tight on and reset it to 17.5mm and will let it sit for 24 hours and check it out on the chronograph tomorrow. The power wheel had moved on its own from MIN up to the second notch so I'm guessing that's where the fluctuation came from. It's a learning curve, but I'm definitely enjoying this rifle. Has anyone ever tried the blue lock tight that more like a paste? I've seen a guy using it in a knife reassembly video and it looks a lot less messy. 

 

[dannya1a]

I just use VC-3 vibra-tite on the common grub screws that loosen up on my impact. seems to work well for holding. except the probe grub screw still loosens up regularly.

 

[Vetmx]

I just put blue lock-tite on a toothpick and dabbed it on the threads. Used purple the first time and obviously didn’t use enough. I’m just paranoid because that is a tiny hex screw and don’t want it to get too difficult to turn. I used my girlfriends fingernail polish on my first Impact and it held. It also helped me recognize the gun when it went up for sale 4 years later. If your wheel is spinning on its own, it’s time to shorten the screw to around 10mm I think. Aren’t these $2,000 guns great!!!

 

[Corvid_hunter]

I just put blue lock-tite on a toothpick and dabbed it on the threads. Used purple the first time and obviously didn’t use enough. I’m just paranoid because that is a tiny hex screw and don’t want it to get too difficult to turn. I used my girlfriends fingernail polish on my first Impact and it held. It also helped me recognize the gun when it went up for sale 4 years later. If your wheel is spinning on its own, it’s time to shorten the screw to around 10mm I think. Aren’t these $2,000 guns great!!!

I'm using the Monster Wheel so maybe that is why it is not staying on MIN without a lot of hammer spring tension. I went out today and it did it again. It didn't do it when I had the hammer spring close to maxed out. I think I'm going to reset the gun back to the factory tune and start over. I measured everything when I first got the rifle and wrote it down in the manual. I might even go back to the factory transfer port and probe. Not sure about that though. I could probably lower the reg to 90 bar and still have similar velocity to the factory setting at 100 bar. 90 bar is doable on the factory reg?

 

[Glem.Chally]

I just put blue lock-tite on a toothpick and dabbed it on the threads. Used purple the first time and obviously didn’t use enough. I’m just paranoid because that is a tiny hex screw and don’t want it to get too difficult to turn. I used my girlfriends fingernail polish on my first Impact and it held. It also helped me recognize the gun when it went up for sale 4 years later. If your wheel is spinning on its own, it’s time to shorten the screw to around 10mm I think. Aren’t these $2,000 guns great!!!

I'm using the Monster Wheel so maybe that is why it is not staying on MIN without a lot of hammer spring tension. I went out today and it did it again. It didn't do it when I had the hammer spring close to maxed out. I think I'm going to reset the gun back to the factory tune and start over. I measured everything when I first got the rifle and wrote it down in the manual. I might even go back to the factory transfer port and probe. Not sure about that though. I could probably lower the reg to 90 bar and still have similar velocity to the factory setting at 100 bar. 90 bar is doable on the factory reg?

Yes 80-85 is about as low as I'd go.

 

[Corvid_hunter]

I just put blue lock-tite on a toothpick and dabbed it on the threads. Used purple the first time and obviously didn’t use enough. I’m just paranoid because that is a tiny hex screw and don’t want it to get too difficult to turn. I used my girlfriends fingernail polish on my first Impact and it held. It also helped me recognize the gun when it went up for sale 4 years later. If your wheel is spinning on its own, it’s time to shorten the screw to around 10mm I think. Aren’t these $2,000 guns great!!!

I'm using the Monster Wheel so maybe that is why it is not staying on MIN without a lot of hammer spring tension. I went out today and it did it again. It didn't do it when I had the hammer spring close to maxed out. I think I'm going to reset the gun back to the factory tune and start over. I measured everything when I first got the rifle and wrote it down in the manual. I might even go back to the factory transfer port and probe. Not sure about that though. I could probably lower the reg to 90 bar and still have similar velocity to the factory setting at 100 bar. 90 bar is doable on the factory reg?

Yes 80-85 is about as low as I'd go.

I set the reg so the needle is just touching the 90bar line in my cool basement. I find the reg will move after I get outdoors and it's hotter out, I'll see if I need to adjust it a bit. The valve is at 3 lines and I turned out my hammer spring to the absolute minimum where I can just feel the adjustment move when I turn the dial up from MIN. 20.30mm if I remember right. This should be the tamest I am able to shoot the rifle and I'm interested to see what it's like.

 

[Corvid_hunter]

Went out today with the rifle and tested it to see that the max velocity was with 25gr pellets at approx 89 bar. 977fps was the max before increasing the hammer spring didn't make a difference. If I turn the valve adjuster from the 4th line to just under the 3rd line it makes a noticeable difference in loudness, but the Power Wheel will only change the velocity about 20fps between MIN and MAX which is not right. I will reset the hammer spring to 20.30mm (around 900fps on MAX and 700fps on MIN), increase the hammer spring tension to give me about 930fps and then use the valve to bring it back down to around 900fps. Hopefully it will be a little more quiet and efficient than just leaving the hammer spring at 20.30mm and the valve wide open.