distance between barrel/tophat
i know its been discussed before, but in no great depth, that i can find. i was checking out leupys spot a while back, and noticed that he makes a longer tophat/valve stem and states that it reduces the “dead space” in the breech, allowing for less dilution of the air between valve and pellet. i myself have made a removable tophat extension that also contains an o ring groove in it as a secondary seal. made it from an old damaged stem/tophat when i was bored. i am still waiting to afford my 25 barrel, and tony says the HPA tank he sent me will certainly dump with a 177 barrel, so i have no way to test the potential benefits this affords. i am also aware that a similar effect can be had by moving the barrel bushings forward a bit. has anyone tested the potential benefits or drawbacks of this type of modification, maybe even with numbers to show your results?
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I dunno but he likes when you pull on it 😆
Last shot string I chronied was
Hi – 910
Lo – 881
Avg – 898
ES – 29
SD – 8
30 shots with JSB.25 Kings
😆 😆 😆
Use something smaller like you penis 😛
Sounds like the voice of experience. So how does that feel when the breech slams shut? Did it feel like it did when you pierced your clit?
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LOL 😯 too funny wok…sorry riffraff couldnt help myself BTW wok were you refurring to the .25 or the fat thunb remark?? 🙂 me thinks maybe your avator may have witnessed just that very process..hehehe..be careful wok you know people take your advice on this fourm 😉
Use something smaller like you penis 😛
I have my 25cal barrel moved .25″ toward the tophat. Makes loading pellets a bit tougher with my fat thumb.
I didn’t really see a big increase in velocity, but as I said elsewhere I DID see a big improvement in FPS consistency.
The smaller the airspace to fill, the more consistent the time is before the pellet starts moving. This equates to more consistent velocity at the muzzle.
In turn, I got a more accurate rifle out of the process.
well, wok, i was already saving for a barrel, its the last piece of a .25 conversion. as for the tophat extension, i made it just to salvage an old damaged stem/tophat. i recognize the benefit is likely to be minimal, but the cost to me is nil, and at least i will be able to confirm that for the rest of my TAG brothers 😉
Sometimes after a lot of money and time is spent on an upgrade you realize while cool it totally does not justify the slight gain it might provide. 😀
ill do my damndest. now lets start a collection plate for my new barrel! 😀
BB, with the breech closed & a pellet in the end of the barrel, picture moving the barrel towards the TOP HAT 1/8 inch. You will have reduced the breech air space by the volume of the barrel diameter x 1/8 inch. Of course the effective air volume between the o-rings isn’t much except the now shortened gap between the pellet & on down the valve pin to the valve seat.
I think this is a big difference because it is already the small space that is instantly hit with the full volume of PSI in the tank when the valve opens. The pellet will get hit sooner at effectively a larger compression ratio.
Will it make a measurable difference? I don’t know. Maybe Moneyshot will be the first to discover and measured it.
You’re talking about the space between the end of the TH and the beginning of the barrel? The breech orings seal that space. If the orings aren’t doing their job then yeah the air would dilute but otherwise? It’s still the same length and very close to the same ID. If your breech is leaking you need new orings prob. Also make sure they are lubed with some silicone. Or could be misalignment. I have read a few posts about the alignment of th to barrel being off causing a leak.
thats what i was thinking. when i get my barrel and some pellets, ill post some “with and without the extension” shot strings to show exactly how signifigant/insignifigant the effects are. by the way, what are some long pellets in .25, i will use them to gauge my minimum distance. no good if you cant load the gun…
Moneyshot, I believe someone mentioned they did get some improvement by shortening the gap. I had wondered if a shimed E-Tac would make much difference since the gap would increase by the thickness of the shims. I haven’t tried it but it seems to me a smaller gap would increase velocity like increasing a compression ratio.
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i think it helps someone above explaned it prity well. but all i did was move the barle back i made a spacer that went inbetween the bushings so i could put the set screws in easly. and sence the space in the breach is small moving the barle back to the point u can barrley fit a .22 21 grain kodiak. im no super math guy but the end where pellet goes is 0.048 thick and the breach hole is 0.310.5 in diamiter so it then gose to 0.266 smaller. thats a big difference when numbers are that small. so dose it really make a difference hell yeah i think . can someone find the volume change . im pritty buzzed so yeah peace out all