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Discussion Starter · #1 · (Edited)
Hello VSR tinkerers :)

I just started working on what will be my first sniper rifle: A scout rifle.

Targets:
VSR based.
Light compact and nimble (g-spec sized without suppressor).
Aiming for just below 3J, which is the limit in my country.
.45g bbs (or the heavyest biodegradable bb I can get)
light bolt pull...
as quiet as I can make it.

I already got all parts for my build, if it's relevant I'll post the list. Mostly recommendations from this forum.

What my problem is now: how do I get a light bolt pull (and make it quiet).
Since the inner barrel is g-spec length (~300mm), the stock cylinder is really oversized. So low efficiency, and high noise.

I'm pretty sure porting the cylinder is the best way to improve both aspects, and I'm willing to do it.

So the question: does anybody know where to port, so I get the best energy from a spring? Does anybody have experience values with cylinder poring?
I thought about starting lengthening the slit in the cylinder, a few mm at a time, and measuring the output energy for the same spring.
And stop when the improvement stops. But I don't have enough time to do this experiment. :(

Also - how much would the results be piston or spring dependent?
What If I get a lighter piston? Would I get more energy from the ported cylinder? Or from a heavier one?
What if I get a new spring? If RAPAX springs live up to their claims, they are exactly what I want! Would that spring have a different "FPS vs port placement graph" compared to the element m145 that's been waiting in my parts box for 4 years? :)

Any other tips on how to get the most energy from the lightest bolt pull on a 300mm barrel would be welcome. :)

Already done:
Polished the cylinder a bit, AirsoftPro steel cylinder.
Got an AirsoftPro cylinder head with larger diameter hole in it's nozzle.
(piston is a 40g AirsoftPro unit, so compatible.)

PS: I have read the posts and guides about matching volume to the barrel length, but they all talk about varying barrel length, or reducing cylinder volume from the front with spacers or short stroking.
I think porting will be at least a bit different because in case of porting, the piston will already have a lot of speed and inertia when starting compressing the air, in comparison to a non-ported cylinder. Thats why I am asking explicitly about experience with porting...

Br, Gru.
 

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Porting your cylinder is a bad idea, I suggest a 380mm barrel and a Rapax 2J spring instead.
You will never be as quiet as a Wolverine BOLT, but probably around the point of a MK23
 

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You can try to reduce the cylindervolume by adding airbrake and thicker Cylinderdamper. Otherselse drill hole into cylinder
 

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Discussion Starter · #4 ·
Hi.

Thanks for the opinions, but I'm already set on this build.
I got all the parts, including a 310mm ML CJ barrel. So I really don't want to buy a longer barrel, and then also a suppressor to cover it up... would have gone full length if I didn't want the short rifle, then I would not have had this problem in the first place.

The question with drilling the hole into the cylinder is "where?" :)

Also, you mentioned a Rapax 2J spring - what energy can you get normally out of that?
Rapax rate their 2J spring like this: "Results : 2+ spring gives between 2.2J (G-Spec) to 2.6J for longest SRS barrels. "
Can you get more than 2.6J in a VSR?

PS: Quiet is not really my top priority. I hope to do more team game-play, where the longer range and accuracy will come in handy from time to time to the team, more than the "lone wolf" type of sniper, where I would need the extra stealth.
Efficiency is my top priority, up there with the "light compact and nimble" part. So I can keep up with the speedy game-play of my AEG wielding teammates.

Br, Gru.
 

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Discussion Starter · #5 · (Edited)
Went to search again for the volume matching guides, and found this:
So I found a first data point, also some practical advice :). However, there's no mention of BB weight.

Did the maths:
ASP cylinder (22mm inner diameter), 90mm practical length -> about 4:1 volume ratio. (my current setup)
BAR10 cylinder ported at 54mm -> 45mm practical length -> about 2.1:1 volume ratio (quite a bit lower than 1tonnes recommendation of 3.13:1 for .45g BBs)

Any other experience values with heavy BBs ?

Br, Gru.
 

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Extend your port another 17mm. I would not do more than that as you risk losing energy. (Play it safe)
 

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Discussion Starter · #7 ·
Thank you 1tonne for the recommendation. That would give me 3.26:1 volume ratio. In line with your guide :).
 

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Discussion Starter · #8 ·
Still far from the cylinder porting part, unfortunately.

I assembled my VSR build for the first time, and did a compression test. What I heard was a loud crack of unpleasant surprise (piston vs cylinder head ) followed by a hiss of disappointment (escaping air from the hop up chamber).
Since the cylinder itself passed the seal test, and I have an AA hop up chamber and ML bucking that fit in perfectly this was quite unexpected. I mean the seal was so bad that the piston slammed loudly against the cylinder head.
I think I have 2 problems:
1) late seal of O-ring in cylinder (otherwise I would expect at least some attenuation of the piston "crack" against the cylinder head by the pressurized air)
2) the obvious bad seal of the hop up chamber.

for 2) i have some suspicions:
a) the airsoftpro cylinder head has a too thin nozzle. Thinking of thickening it with heatshrink / nail polish
b) the hop up chamber leaves some room (1-2 mm) for the barrel and bucking to travel forward under pressure from the nozzle. Thinking of adding some teflon tape, or a spacer.
Any other ideas?

And... how do you deal weath a late seal problem? I have an automotive 22mm oring that fits in extremely snug in the cylinder, to the point the piston can barely move without lubrication inside. I would have expected the seal to be excellent, which it is towards the end.

By the way, the 3 grub screws of the AA hop up chamber.... I tightened them, but they come loose easily. I don't want to overdo it, not to damage the barrel or grub screws.
has anybody used threadlocker on these? Any other ideas?

PS: Am I allowed to off-topic my thread? :D

Br, Gru.
 

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You should put a thin strip of electrical tape under the metal clip on your bucking, to squeeze it inwards.

For the long screws in the AA chamber, you can wrap a layer of Teflon tape on them, or use wax or something, and for the little one, don't do anything.
I torque mine down with the long end of an Allen wrench and my thumb and finger, about as tight as I can get with those 2 fingers as the Allen wrench starts to slip.
I have never had those screws come loose, and neither have I stripped them, but use a healthy amount of torque like mentioned.

It's your thread, do what you please
 

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Discussion Starter · #10 ·
Hi
about as tight as I can get with those 2 fingers as the Allen wrench starts to slip.
Whoa - that's quite a bit more than I put on. The second time they did not come loose, but I only shot a few times, maybe 10-20, as compression test, trying to figure out what's going on.

Thanks for the info, I'll tighten it up a bit more next time, let's see!

Regarding airseal:
I got the thing apart, and the nozzle seems to fit perfectly and tightly in the bucking, as does the bucking on the barrel. Can't imagine where the air is escaping, really.
But this seems a very good ideea, definitely worth a try:
You should put a thin strip of electrical tape under the metal clip on your bucking
Thanks!

Br, Gru.
 

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I think I didn't word that correctly, I mean the Allen wrench starts to slip out of your fingers or starts to hurt, not slipping out of the hex slot lol.

For the barrel and bucking stuff, maybe wrap some Teflon tape on the last 1/3 of the bucking on the muzzle end, or about 1mm away from the contact patch.
That doesn't really give any other possibilities besides the bucking entrance, which seems to sound good.
 

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Discussion Starter · #12 ·
Hi SiliconeSword,

For the barrel and bucking stuff, maybe wrap some Teflon tape on the last 1/3 of the bucking on the muzzle end, or about 1mm away from the contact patch.
That doesn't really give any other possibilities besides the bucking entrance, which seems to sound good.
Thanks a lot! It turns out you were right.
Nozzle in bucking -> good seal.
Bucking around barrel -> bad seal.
Wound 4 layers of teflon tape around the bucking => I now have the epic perfect seal I was aiming for.

Next problem: chronoed my VSR 3 days ago, and it shoots waaaay too hot. 122 m/s wiht .45. That's 3.35J !!! (legal limit is 3J where I live).
And that with a 310mm ML CJ barrel (so 295 effective length). And a Element m145 spring.
Either something about my build is making it crazy efficient, or the spring is actually stronger. (it's not easy to pull, so probably just a bad spring).

I hoped to get something like 2.3J (m145 spring on a 300mm barrel, seemed plausible) and slowly increase it by porting the cylinder until I got as close as I could to 3. and surprise surprise. 1 full Joule more than expected, and well over the upper limit in my country...

Either cutting this spring, or getting a Rapax...

Anyway, it's still some time away from its first game. :(

Br, Gru
 

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Don't cut the spring. Just wrap some solder around it and then hold it on with a layer of electrical tape. This should bring it back to about 3 Joules. Then when the spring wears in and slows down, you can take the weight off and it should increase the energy again.
 

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Badass, glad it worked lol.

I suggest that in the future you upgrade to a 6.01X430mm inner barrel and a weaker spring in the future so you have a more efficient and quiet gun, but that's not really urgent.

Otherwise, don't cut that spring, weight the piston like 1Tonne said, that way you can remove weight as the spring weakens.
That being said, weakening takes a long time, so I'd just replace it with a Laylax or Rapax something or other spring, as they are quieter and have a nicer pull due to being in different weights and better quality.
 

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He doesn’t want a long barrel though, he wants short with decent power and light pull. It’s a good thing it’s hot because he can get a weaker spring, add weight to piston or an air brake to help with less sound. I think light pull g specs can be tricky depending on what you consider a “light pull”. If the pull is heavier than you want I’d aim for the shortest and lightest as possible for the piston specs. That can help boost numbers if you run a really light spring.
 

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Discussion Starter · #18 ·
Hi,
He doesn’t want a long barrel though, he wants short with decent power and light pull.
Precisely, that's what I'm looking for. Light maneuverable thingy.

The piston is a ~40g super old and worn AirsoftPro aluminium/steel one, with an 22mm od automotive o-ring.
Weighing it down is an interesting idea... The problem here: I am planing to port the cylinder for maximum energy out of the easiest pull (as the thread title states). A heavier cylinder might actually not work that well for a ported cylinder, or even have the opposite effect (as far as I have read around here and on an AEG specific forum). Or is this a myth?

The Spring I have is a 7mm inner 11mm outer diameter spring, and both the piston and the spring guide (via sleeve) accept a 9-13 mm spring. So the twang is loud.
What's the max J i could get from a 2J Rapax? or should I go for a 3J and cut it down if I'm hot again?

My wild dream (and unlikely given the chronic lack of free time i have): I'd like to progressively port the cylinder and test with 2 cylinder weights and 2 - 3 bb weights, and plot some graphs.
Realistically I'll just get it down under 3J and call it a day :D

Thanks for all the input.
 

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Honestly, given all of the variables and possibilities; weigh the piston down and go from there. See what the output/sound/performance look like after adding weight before you do anything extensive
 
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