.25+New Hammer=WooHoo
Yel01zo6 was nice enough to send me a bronze hammer to play with. My .25 with the Walt from Hawaii barrel has been doing great! But she likes using a LOT of air!
I have found that this particular bbl. really likes the new JSB King .25 pellets. Even more so that the .25 Kodiaks. Especially at 80 and futher yards. At 100 yards it is still putting them in there at minute of tree-rat angle. 1 1/2″ consistently, with many groups well under an inch!
The problem has been, they don” seem to like the fps much over 1000 fps. Once they drop below 1000, they are tack drivers. It doesn’t seem to matter much one way or the other with the Kodiaks, BUT—the Kodiaks are great out to 60 or so yards, but they cant’ hold a candle to the JSB’s at longer range in my gun. Teh Kod’s will group at around 2″ at 100 yards, with may groups going 2 1/2″. AT shouter ranges, they do just fine.
When trying to get lower velocity with the factory hammer, the shot string would start at say 1020 and consitently drop from there. Very even though. Only a few fps lost with each shot. But never a bell curve. 20-25 shots, and back to the house for a fill.
Now this is fine for hunting, but there is a lot to shoot at around here in Texas. All kinds of tempiting targets. So I like to hunt, and plink at the same time. Leaving me out of air most of the time.
The new hammer is changing this a bit. So far, it is not quite as consistant, (I’m still learning where to set the tune). But it is comming along well.
I am having to set the gun up a little bet differently. Before the top hat was set at .080, and the power wheel at 8 to 9 to really work well.
this was with teh factory hammer and the extra Condor weight. I figgured the two piece hammer woue cause a little bit of bounce, and wanted to try a solid hammer. The new one is 90 grams. I don’t know what the factory parts come out to.
to get the FPS I was looking for, I had to eventually turn the Top Hat down to .050. Which worries me a bit. I don’t want to damage toe valve!
and supriseingly, the power wheel had to be turned down to 4/10 to get it to the power I was looking for.
What I got in return, was somthing I have never had with teh .25. A nice power curve starting with a very good bell curve. But the curve is climbing rapidly. So more test are required.
Along with finally having a Bell Curve, The .25 really picked up in the shot count. It went from a 20-max of 25 shot count before to 35-40!!! 😯 😀 and doing it with LESS AIR! 1000 psi before, 700-800 with the new hammer. Now thats an improvement that I can live with! WooHoo!!! + even after 40 shots, there are still another crap load of usefull shots if I am willing to use the mil-dots’ to adjust for less velocity. Before, it just dropped like a rock. 🙁
Here are the #’s As always, any advice is more than appreciated!
Mike
2800 fill-.25 Jsb Kings
End pressusre 2100 psi
Top hat .050 wheel at 4/10
21.5 bbl. standard LW twist.
1. 918
928
942
958
967
978
986
994
1000
10. 996
1008
1006
1013
1012
1011
1008
1000
996
991
20. 985
977
974
975
960
959
949
949
950
940
30. 943
930
928
935
920
917
914
906
899
894
40. 887
This is the first full string. I was having trouble getting the max fps under 1025. So far, so good.
Mike
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Also, I used to run my tophat at .90 and use a .61 flat rubber washer behind it. I used to get nice consistent power with that, and no chance of tophat slapping the valve housing. This was in .22 caliber using JSBs, always got right around 975fps.
The power dropped off using that setup in .25 with Kodiaks, around 880’s so I quit using the rubber washer and set the tophat to .70 and thats where it is today.
With the lighter JSB, the rubber washer thingy might be a good option.
Would a lighter or heavier weight pellet influence valve duration?
Just so you know Mike, my standard Condor hammer and weight totaled 68 grams. 49 for the hammer and 19 for the extra weight.
Also, I used to run my tophat at .90 and use a .61 flat rubber washer behind it. I used to get nice consistent power with that, and no chance of tophat slapping the valve housing. This was in .22 caliber using JSBs, always got right around 975fps.
The power dropped off using that setup in .25 with Kodiaks, around 880’s so I quit using the rubber washer and set the tophat to .70 and thats where it is today.
With the lighter JSB, the rubber washer thingy might be a good option.
Thanks Jerry and Voltar.
That is making a lot of sense. I have a lighter hammer on the way shortly. The factory hammer is 48+ 20 for the Condor weight if I remember correctly. BUT!!! The two piece system seems to introduce it’s own problems. Bounce between the two on impact being one of them.
I have a 90 gram hammer in it at moment. Trek is doing me up a 70 gram hammer to test. We’ll see what that does when it comes in. 😉
Thanks for the help Guy’s! 😀
Mike
“Self regulating seems to need a stem that can be driven deeper as pressure falls which results in a compensation for the lower pressure with increased flow.”
Exactly. If the valve is stopping artificially shallow when the pressure drops off in the bottle, the velocity will drop off unless somehow the valve holds near max open duration long enough to compensate for reduced travel. That seems unlikely if the TH is bouncing off the valve body. (and transfering the momentum of the hammer into impact energy delivered to the valve and bottle threads and the metal surfaces, and the valve seal retaining threads…)
the tophat adjustment will limit flow at the end of a fill and reduce power
At the start of a fill the hammer should not be able to open the valve fully
can be confirmed with a wrap of solder.
Self regulating seems to need a stem that can be driven deeper as pressure falls which results in a compensation for the lower pressure with increased flow.
Pretty challenging to get all teh bits pulling together for sure.
would be good to really understand what Rob did to achieve his incredible curve.
its all good eh?
Hmmm… this advice is strating to form a pattern. 😀 You might want to see what your other hammer weighs. I’d guess you’d be good with maybe a 60 or so and just enough preload to get consistency.
I don’t really like the idea of the TH being set so low either. There’s more than a bit that I don’t know about the dynamics of these guns but it seems as though setting the TH that low is regulating the air by means of having the valve come to a hard stop during the firing cycle. That could affect accuracy but it also seems to introduce wear and tear on all the bits aft of the breech. I’d rather see the curve established through a pure interaction of hammer momentum vs. bottle pressure and resulting flow.
Inconsistency at very low preload might be an indicator that the hammer is not sliding smoothly. You might have a little “sticktion” going on, to borrow a term. It might be worthwhile to look at the hammer bearing surfaces, ensure they are smooth and lubricate with graphite.
Here you go. I’m commenting.
Begin comment:
Very nice.
End comment.
You’re welcome!
Yep, I can see how that could help!
Thanks Pab.
Mike
I reckon you must be striking the tp on the valve towards the end of that string being its so low set. If you want to avoid that you gotta bring it out again. Which will give you too much fps, so you gotta drop the fill pressure, lighten the hammer and less preload. This should put you back in the ballpark of that string, save the tp and valve(not actually sure the tp striking the valve does any harm anyway??) give you an easier fill on a hills, or more fills from a scuba, easier to cock and a smoother firing cycle.
Works for me anyhoo…. 😀
Thanks Pab’s! That would be SWEET! I was just wondering mostly abut the first few shots on the low end. They seem to climb in fairly big jumps. Other than that, I’m just worried about damaging the top hat and valve. Everything else is WOOHOO good!
Mike
Mike, what more do you want from this? The only improvement you could have is a little bigger plateau before it drops away again… You’re not getting much above a 1000fps which is good, nice predictable movements in fps. I would say you have 30 good shots there.17.5 psi per shot is outstanding, I can only manage 20 psi per shot.
I have achieved pretty much the same string as you, except I can do it from a 2500 fill. That does away with that big hammer and large preload, which in turn makes it easier to shoot.
All in all, I would be happy with that string mate. Shame you can’t turn the tophat out easy after shot 30 to keep in the powerband.( I do this with my Blodvalve to squeeze out another 10 good shots)
I need to find some of those little suckers!
i have thath o ring behind my top hat aswell works great.
Does any one here run their top hat at a small gap? I was thinking about using a small “O” ring behind the top hat to cushion the smack and at the same time lessen the hammer slap. Seems someone here tried it a few years back.
Mike
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Without a doubt, maybe. I think it comes down to gun design and the magnitude of the pellet (slug) differences. In big bores shooting slugs that sometimes differ by a couple hundred grains, there are significant differences apparent in valve duration, energy transfer and air usage.
I doubt the difference between a JSB at 25+ gr and a Kodiak at 30+gr is going to be obvious as afr as valve duration but I would not rule it out. Now, if you go from a JSB 25.6gr pellet to a 87gr 9 ring slug, you’re going to notice differences.