Impact C3 bumper as a tuning aid?

Jump to latest Follow Reply
bucketboy

bucketboy

Member
Apr 5, 2019
1,190
661
Lincolnshire, United Kingdom
Here is a question for you fx tuning gurus, instead of fitting a weaker spring to reduce power, could I use a thicker c3 bumper? A thicker bumper would reduce the time the hammer has to attain speed so reduces power. I could then fit a stronger shorter spring to decrease lock time.

The reason, I have a sub 12fpe impact, compared to my other guns, the action noise and vibration is horrible, it shoots nice enough but does not feel like a $2000 gun, I think this could be due to the hammer and spring guide wobbling about after the shot as is pushes back against a weak spring . This is not just something I can feel and hear, when I take a shot I can see the target image blur momentarily, 

I may need to modify the hammer slightly but I was thinking 5-10mm thick delrin bush attached the nose of the hammer in addition to the rubber c3 bumper. I would also fit a better hammer spring guide made from a less noisy material.



while I am at it, what is the minimum I need to disassemble to remove the hammer and spring?



Thank for your time



Bb
 
Hi, I ignore the sub12 setup, but in a normal impact, you can not do that, 5mm bumper will be too thick and the rod will not seal in the back for the impact block.

if you need less power you can use a lighter hammer (quite easy to make with a lathe). Also you can use a oring c3 duro 70, more cushion = less power (original is duro 90), but need to check for consistency and durability. Also you might want to try to remove the spring guide and test how it goes.

Or you can change the VS from 5.5 to 5.0mm
 
Upvote 0
Hi, I ignore the sub12 setup, but in a normal impact, you can not do that, 5mm bumper will be too thick and the rod will not seal in the back for the impact block.

if you need less power you can use a lighter hammer (quite easy to make with a lathe). Also you can use a oring c3 duro 70, more cushion = less power (original is duro 90), but need to check for consistency and durability. Also you might want to try to remove the spring guide and test how it goes.

Or you can change the VS from 5.5 to 5.0mm
Click to expand...

The hammer is already lighter as it is uk spec MK2, what I want to do is reduce the travel length of the hammer. Currently from the point from which the cocking lever starts to move the hammer to the point where the trigger sear engages with the hammer is 22.5mm, Compared this to my rapids that are only 7mm. It is my belief that the combination of short strong spring and short hammer travel, decreases lock time and reduces vibration.

If I can’t modify the hammer would it be possible to make a hammer stop that was 10mm longer and screwed 10mm further onto the valve stem and reduce the length of the floating spring guide by 10mm?

I don’t want to alter the VS, making it smaller makes it even easier for the hammer to open so I would need an even weaker spring which is completely opposite to what I would like to achieve.

I really like the impact but there are a few things at the moment that stop me loving it, action noise and vibration being one of the biggest niggles. Again compared to my rapids, the impact block is 96.8dB while my rapids are around 80bB and that it a big difference.

The other niggles, the 1/2unf liner tension nut does not align concentric to the bore of the liner meaning the moderator needs a larger exits hole to stop clipping issues, Head position is slightly compromised inducing parallax issues at loser ranges and I really need to sort out a bag rider, it is so awkward supporting the butt of the gun.



Bb


 
Upvote 0
You may be on to something there. However, wouldn't the stronger spring also add to the vibrations you are trying to eliminate? Changing just the C-3 bumper and adding a spacer is easy enough to do by degassing the rifle and removing the valve stop adjuster. Getting the hammer weight out requires a disassembly of the whole too rail so the cocking block pin can be lifted off the hammer weight (so it will slide out the front).
 
Upvote 0
You may be on to something there. However, wouldn't the stronger spring also add to the vibrations you are trying to eliminate? Changing just the C-3 bumper and adding a spacer is easy enough to do by degassing the rifle and removing the valve stop adjuster. Getting the hammer weight out requires a disassembly of the whole too rail so the cocking block pin can be lifted off the hammer weight (so it will slide out the front).

Click to expand...

Thanks for the disassembly sequence.

I can only relate to the guns I know best, but from experience, my rapids definitely feel and shoot better with a shorter stronger spring moving a lighter hammer for less distance. I have no idea if this is true for the impact but I will find out.



Today I let one of my friends who is a total novice with an airgun ( he shoots shotguns) have a go with my impact and one of my rapid. Without any prompting he said the rapid was smoother. Although he shot the rapid very slightly more accurately, he was extremely impressed by both.

Personally, I think the impact has some serious potential but FX have concentrated on the US market and not bothered to find the ideal tune for the sub 12fpe uk, instead they just fitted a weaker spring and reduce reg pressure. Given time, I am sure I can get mine better.



Thanks 

If the barrel tension nut isn't concentric and causes clipping issues, it may be a warrantied part and easily replaced with a phone call to FX.
Click to expand...

No, it is not clipping, its my attention to detail that is the problem, I make my own shrouds and moderators, normally I would expect to have the hole in the endcap no more than 1mm larger than pellet Dia without any clipping issues, the hole in the fx shroud is 3mm bigger than pellet. With a piece of tape over the endcap, the exit hole of the pellet is not central to the bore. When I get the chance, I will turn up a better barrel location fitment that will be 100% concentric to the liner bore.



Bb




 
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu