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Old 05-21-2020, 11:22 AM   #1
Stince   Stince is offline
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approximate fps lost going to a shorter barrel?

I'm currently shooting about 500fps with a 430mm ML stainless 6.01, but I'm planning on switching to a shorter 300mm CJ inner but keeping the same outer to do the Blind Sniper internal suppression mod, how much fps would I lose by going from 430 6.01 to 300 CJ, also does the CJ help me gain or lose fps compared to a 6.01?
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Old 05-21-2020, 11:57 AM   #2
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Crazy jet makes you lose a bit as the last bit of the barrel has a wider diameter.

Fps loss also depends on the weight bb you are using, so it's hard to precisely say. With RAPAX 3+ springs on .48g bbs, supposedly its something like 3.3J on 430mm, and 2.9J on 300mm. Who knows though, but you will need a new spring.

If you are switching to a shorter barrel, I might look into also reducing the volume in your cylinder, as a lot of that gets unused. Easiest way is to use laylax sorbos and stacking them until you lose fps. Then going back one. This should help get it wayyy quieter as you won't have all that extra air running out the end of the gun when the bb has already left. I'm in the process of testing this damper reduction theory with a ton of 2mm thick custom silicone pads, as well as some air-pads. If you don't do this volume reduction thing, the gains you get from the internally suppresed barrel will be minimal because you'll need a stronger spring.
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Old 05-21-2020, 01:01 PM   #3
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Well the whole CJ barrel has a wider diameter. They're 6.03-6.04. It also is obviously shorter. So you'll lose quite a bit at lighter bb weights.

As the bb weight increases the drop will be less pronounced.

I would NOT recommend dropping the cylinder volume. Just use a heavier bb. 300mm is too short to be optimized for .48g alluded to above, but it wont make a dramatic difference in performance. The sound also wont be that bad if you suppress it. Even if you didn't it's unlikely you'll hear the rifle past 30 feet outdoors.
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Old 05-21-2020, 01:10 PM   #4
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@accurate dropping cylinder volume by adding dampers could literally only help. It just quiets down the rifle and thats it. Anyone with a chrono and dampers can easily experiment to find the correct amount of dampening material. Also, what other purpose does all that extra room for piston acceleration serve if it's not to accelerate the bb. Adding the sorbos also slightly short strokes it, so that doesn't hurt.

If the goal is a quieter rifle, none of this can hurt.

Edit: I am NOT suggesting modifying the cylinder. Just suggesting adding sorbos
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Old 05-21-2020, 02:21 PM   #5
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Quote:
Originally Posted by Sodium View Post
Crazy jet makes you lose a bit as the last bit of the barrel has a wider diameter.

Fps loss also depends on the weight bb you are using, so it's hard to precisely say. With RAPAX 3+ springs on .48g bbs, supposedly its something like 3.3J on 430mm, and 2.9J on 300mm. Who knows though, but you will need a new spring.

If you are switching to a shorter barrel, I might look into also reducing the volume in your cylinder, as a lot of that gets unused. Easiest way is to use laylax sorbos and stacking them until you lose fps. Then going back one. This should help get it wayyy quieter as you won't have all that extra air running out the end of the gun when the bb has already left. I'm in the process of testing this damper reduction theory with a ton of 2mm thick custom silicone pads, as well as some air-pads. If you don't do this volume reduction thing, the gains you get from the internally suppresed barrel will be minimal because you'll need a stronger spring.
I'm currently running a ML m135 and I have a spare element m145, also do you think adding spacers (like the laylax ones) on the spring guide will be enough to compensate for the fps drop with .45s?
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Old 05-21-2020, 02:42 PM   #6
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It might be more money you don’t want to spend, but the newer model (I think) EdGi piston is shorter and should give you an fps boost! I’d go that route if you can’t achieve what you want with your desired spring!!
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Old 05-21-2020, 03:04 PM   #7
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Quote:
Originally Posted by Sodium View Post
I am NOT suggesting modifying the cylinder. Just suggesting adding sorbos
He could also port the cylinder. Years and years ago before I figured out that different bb weights needed different barrel lengths, people would port their VSR cylinders to get the most fps with a short barrel. Fps was measured with 0.2gm back then. JC was not even thought of. Everyone thought the if you could get more fps with a 0.2gm bb, then you were onto a winner. Seems dumb now knowing what we know, but that is what everyone believed. Even I used to do it.
The disadvantage is obvious, you can't unport the cylinder once it is done.
The advantage is that the piston will have time to speed up before the port and then once it has passed the port, it will start to push the bb with the piston already at a good speed. With this, if done right, you normally only loose a few fps by switching to the shorter barrel. So currently his rifle is about 500fps (on 0.2gm), and by porting it he will most likely get about 470-480fps (estimate). This will make it quieter with the shorter barrel and easier to get high fps.
The standard ratio for a 0.45gm bb is 3.13:1. I would suggest making the ratio about 3.25:1. Gives you a small amount of leeway. This way you can use all the way up to 0.45gm bb's effectively with the 300mm barrel. This works out to be about 71mm of cylinder length.
Remember that when drilling, not to drill on the exact mark. Drill just before it and then work towards the mark.
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Old 05-21-2020, 03:15 PM   #8
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Quote:
Originally Posted by Sodium View Post
@accurate dropping cylinder volume by adding dampers could literally only help. It just quiets down the rifle and thats it. Anyone with a chrono and dampers can easily experiment to find the correct amount of dampening material. Also, what other purpose does all that extra room for piston acceleration serve if it's not to accelerate the bb. Adding the sorbos also slightly short strokes it, so that doesn't hurt.

If the goal is a quieter rifle, none of this can hurt.

Edit: I am NOT suggesting modifying the cylinder. Just suggesting adding sorbos
I read his main concern to be fps loss and not sound.

Having the gun overvolumed isn't going to affect anything other than the sound, and if he's internally suppressing I didn't see the need to go through the trouble of cylinder volume experimentation.
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Old 05-21-2020, 03:29 PM   #9
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My assumption is that switching to a 300mm barrel while keeping a 430mm outer is to quiet the gun down. Thats why I'm giving short barrel silencing techniques. That, and a ton of dampers inherantly make it quieter.

Adding spacers should not effect fps. The whole point is that with a shorter barrel, the bb leaves the barrel before the piston hits the end of the cylinder. Adding spacer dampers just makes it so that, if done right, the bb hits the dampers just after the bb has left the barrel, eliminating most of the extra piston travel that doesn't push the bb. It just makes it quieter, and the piston hitting a bunch of sorbo makes the thud way quieter as well.
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Old 05-21-2020, 05:12 PM   #10
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I don't disagree with you, I just didn't interpret the OP as wanting to do all that.
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Old 05-22-2020, 01:34 AM   #11
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Quote:
Originally Posted by AccurateDMD View Post
I read his main concern to be fps loss and not sound.

Having the gun overvolumed isn't going to affect anything other than the sound, and if he's internally suppressing I didn't see the need to go through the trouble of cylinder volume experimentation.
switching to a shorter inner for me was mainly to lower sound, and to shorted the gun a little but because right now I have an external suppressor on it, how much of a jump is spring strength would I need?
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Old 05-22-2020, 01:36 AM   #12
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Quote:
Originally Posted by 1tonne View Post
He could also port the cylinder. Years and years ago before I figured out that different bb weights needed different barrel lengths, people would port their VSR cylinders to get the most fps with a short barrel. Fps was measured with 0.2gm back then. JC was not even thought of. Everyone thought the if you could get more fps with a 0.2gm bb, then you were onto a winner. Seems dumb now knowing what we know, but that is what everyone believed. Even I used to do it.
The disadvantage is obvious, you can't unport the cylinder once it is done.
The advantage is that the piston will have time to speed up before the port and then once it has passed the port, it will start to push the bb with the piston already at a good speed. With this, if done right, you normally only loose a few fps by switching to the shorter barrel. So currently his rifle is about 500fps (on 0.2gm), and by porting it he will most likely get about 470-480fps (estimate). This will make it quieter with the shorter barrel and easier to get high fps.
The standard ratio for a 0.45gm bb is 3.13:1. I would suggest making the ratio about 3.25:1. Gives you a small amount of leeway. This way you can use all the way up to 0.45gm bb's effectively with the 300mm barrel. This works out to be about 71mm of cylinder length.
Remember that when drilling, not to drill on the exact mark. Drill just before it and then work towards the mark.
porting the cylinder sounds good and all, but the reason I don't want to do it is because I might switch back to 430 in the future and I want to have the flexibility.
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Old 05-22-2020, 07:54 AM   #13
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I mean what bb weight are you looking to calculate fps loss with? That's the main thing. You're gonna see a bigger drop with .2g, which I assume is what you meant when you said it shoots 500fps, than you will with a heavier bb.

That shorter barrel will be ideal for joule creeping if your site only chronos on .2g, so you'll be able to cram a pretty heavy spring in and weight the piston if you want to maximize joules on, say, a .48g...
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Old 05-22-2020, 01:34 PM   #14
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Originally Posted by AccurateDMD View Post
I mean what bb weight are you looking to calculate fps loss with? That's the main thing. You're gonna see a bigger drop with .2g, which I assume is what you meant when you said it shoots 500fps, than you will with a heavier bb.

That shorter barrel will be ideal for joule creeping if your site only chronos on .2g, so you'll be able to cram a pretty heavy spring in and weight the piston if you want to maximize joules on, say, a .48g...
I run .43/.45s typically and at around 2.3 joules
what should I change to keep that power after shortening the barrel?
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Old 05-22-2020, 01:40 PM   #15
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The spring. That's really it. You can mess around with piston weight as well, but no guarentees there, and it def won't get all your power back.
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