Can someone tell me what's a good hammer weight for an impact .25 cal at 150-160 bar? My stock hammer with max hammer spring tension is not getting anymore fps once it hit 150 bar. I tune to 160 bar and its getting same fps as 150 bar. I tune to 170 bar and still getting same fps as 150 bar. I guess stock hammer isn't strong enough to fully open the valve. But idk which hammer weigh to go with. Someone with more knowledge of the impact tell me a good hammer weight to use. Thanks.
What's good hammer weight for the impact?
- Thread starter 2fast2furious
- Start date
It sounds like you do need a bit more hammer weight. I have a 5.35 gram brass weight added to my .30 caliber with a 6.5mm valve seat hole and it seems to be good through 170+ bar. There's about 1.5mm of pretension added to the spring with this as well. I'm thinking of adding more weight to see what it does, without making any other changes of course. Right now it is a bit jumpy with all that reg pressure dialed in and I'd like to see if the difference in hammer weight changes that one way or the other.
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@2fast2furious 7grams is what im using with 7.1mm VS.
@Airgun-hobbyist What kind of power are you making?
@Airgun-hobbyist What kind of power are you making?
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@cfs916 With 50.15 JSB's it runs 975-980@170+- bar. I just turned it down a bit to do some grouping experiments with the new slug liner and those JSB's, as well as with a couple NSA slugs in 50 and 55 grains.
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Valve is 6.5mm, pressure will be 150-160. Is there such a thing is too much hammer weight? I dont want to damage to rod or wasted air. 6gr brass enough for my need?
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For what it's worth, I did one per the specs in the FX Impact Mods for More FPS/FPE thread and it came out at 5.6 grams (turned from brass rod stock). Seems like a good design similar to what E. Rowe had been producing.
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That
The idea of adding a hammer weight is to open the valve fully in order to achieve the desire fps. Increasing reg pressure make more force on the valvepin seal, making harder and harder to open it fully over 150b (on stock impact), as the VS bore increases, the the limit decreases, meaning for example (not exactly just an example) in a 6mm bore VS you need weight in 140b+ and 6.5mm VS on 130bar+ to get more speed
No much weight for that, 4 grams is probably fine
You are right, That is exactly the symptom telling you the valve is not getting open fully and you need more weight on the hammer.
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@Aigun-hobbyist Nice, btw the NSA 55 shoots good off the 700mm STX pellet liner. Didn’t notice much difference with Slug liner.
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The NSA 50 grain hollow points through the STX pellet liner had a really big group. With the longer 55 grain dimple nose slug I can imagine it will stabilise better. The liner twist rates are very different from each other too. The STX had 1:41" and the Slug Liner A has double that twist rate.
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@Airgun-hobbyist I shot the 55gr HP FB. Got the typical slug group. Not one ragged hole but small groups at 20yards. I haven’t shot passed that since my range is my backyard. Pellet liner vs Slug liner (.30cal) was no difference for me. The pellet liner actually gave it more FPS (maybe due to the choke). But they’re pushing 905@155bar 700mm STX pellet liner. Also my crown in 600mm STX pellet liner doing good with 47gr HP NSA as well.
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