[JoshOwnsAll]

Alright... I joined this forum because you guys know better than any other forum I've checked about long range know-how, and I need some opinions and answers. I'm fairly knowledgeable when it comes to DMRing an AEG, but there are some things that I'm still trying to figure out. (I'm definitely overthinking some things, like my obsession with trying to make an equation to optimize bb acceleration varying the barrel length, bore and bb weight, to find how to make the most stable, perfect flight possible)

I have a Snow Wolf Barrett M82, which I'm upgrading, and I'm one of those blokes that doesn't settle for second best. Money isn't much of an issue, so PDI parts are on my must get list. The goal is getting close to 300 feet, while being able to consistently hit the torso of a man sized target. So far I have a prowin hop up unit, a prommy hard bucking with the nub removed, and a flat nub. I'll work on the gearbox parts later. The main question is: is it really necessary to have a 650mm inner barrel in it? I'd get a PDI 6.05 barrel, and with a bore up kit I'd get a cylinder/barrel ratio of barely over 1.5. I plan on using .40g bbs, then I'd try different springs to see which gets me to the results I want, assuming near perfect compression.
The barrett has a pretty wide outer barrel, and I already have spacers. Should I run a shorter 6.05 barrel to get to a ratio of at least 2 (which is considered ideal, I believe), or is the 1.5 ratio ok? PDI 6.05 is non negotiable, only the barrel length. Would the bb's flight be altered too much because it's exiting the inner barrel, and there's still about 50cm of outer barrel left?
Also, would you recommend the Retro Arms gearbox body? I've heard that it can run a m150 spring pretty much forever, and I really want to maximize my baby's durability.

Yes, it's heavy, clunky, dumb, uncomfortable, silly, etc... But we all have this dream gun that we have to get sometime, and upgrade it to godly levels no matter the cost. The barrett is mine. No, I'm not a COD fan, and I'm not a little kid, contrary to airsoft barrett owner demographics. Just roll with it and help this idiot with his impractical gun, please? I'm from Chile, so I'd have to import pretty much everything. Quality parts are very scarce, and extremely expensive here, so I have to be certain of what I'm getting before I buy... Taxes and shipping can almost double the cost.

 

[Reliku]

650mm is WAY too long, especially for an AEG cylinder with .4g bb's. 1.5:1 is way too low, haha.

1.5 is what you'd want for .12g bb's perhaps. For .4g I'd look closer to 2.6:1-3:1.

Get a shorter barrel. A much shorter barrel. A wide outer barrel won't really be a problem, the biggest issue I can see is noise, but accuracy wise you shouldn't really suffer.

You WILL suffer accuracy if you go with a 650mm barrel though, because that is way too long. Your .4g bb's will decellerate while still inside the barrel because the pressure just completely drops. This leads to inconsistency and massive efficiency loss. You'll also get negative joule creep.

 

[JoshOwnsAll]

650mm is WAY too long, especially for an AEG cylinder with .4g bb's. 1.5:1 is way too low, haha.

1.5 is what you'd want for .12g bb's perhaps. For .4g I'd look closer to 2.6:1-3:1.

Get a shorter barrel. A much shorter barrel. A wide outer barrel won't really be a problem, the biggest issue I can see is noise, but accuracy wise you shouldn't really suffer.

You WILL suffer accuracy if you go with a 650mm barrel though, because that is way too long. Your .4g bb's will decellerate while still inside the barrel because the pressure just completely drops. This leads to inconsistency and massive efficiency loss. You'll also get negative joule creep.

Thanks a lot!
If I use a shorter barrel, there would be a lot more spare outer barrel. I've thought about cutting it for performances sake, but if you say that it's not important, I'll leave the intimidating 1.5m rifle just the way I like it.

 

[JoshOwnsAll]

650mm is WAY too long, especially for an AEG cylinder with .4g bb's. 1.5:1 is way too low, haha.

1.5 is what you'd want for .12g bb's perhaps. For .4g I'd look closer to 2.6:1-3:1.

Get a shorter barrel. A much shorter barrel. A wide outer barrel won't really be a problem, the biggest issue I can see is noise, but accuracy wise you shouldn't really suffer.

You WILL suffer accuracy if you go with a 650mm barrel though, because that is way too long. Your .4g bb's will decellerate while still inside the barrel because the pressure just completely drops. This leads to inconsistency and massive efficiency loss. You'll also get negative joule creep.

I ran the numbers, and the PDI barrel that gets me closest to a 3:1 ratio is a 347mm inner barrel. This should get me the acuraccy and range I want, assuming near perfect gearbox seal, that would leave me with just changing the spring to modify the initial energy... what spring would you recommend?
I believe the "moral limit" is 500fps with .20g bbs, but it isn't regulated in my country.

 

[3413]

Bear in mind with the massive outer barrel you may have a problem with the BB clipping the muzzle brake on the way out. Planning a CQB Barrett build myself and trying to figure out would be the best length barrel would be.

 

[Jlay]

You mentioned that you were using some barrel spacers within the massive M82 outer barrel to stabilize the inner, did you make these yourself or is there an aftermarket option? I'm building an HPA M82 in the near future and the unstable inner barrel set up was a concern for me.

 

[ghost ghillie]

im at the moment working on a post (whit links to others) around energy transfer and joule creep.
have a look and it will give you some answers to barrel length and such. link.

other than that, hpa can be a good option here (use co2 if you want it all contained in the rifle). as your not restricted in the terms of air volum.

 

[Linski]

Why don't you try cutting down a sacrificial stock brass barrel until you find your optimum barrel length. Then you will know exactly what barrel length to order. Seems like the way to go given how expensive it is to import parts.

Also you would find out if the outer barrel length will be an issue.

I'm in the same boat as you as I have a RS SVD that has a stock 690mm inner barrel and I want to shoot .43's. Luckily I have a Prometheus 409mm EG barrel lying around that I intend to try.