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Ursu13

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Discussion starter · #1 · (Edited)
Just like the title says, it's something I thought about before getting asleep. Maybe it was talked before, but I couldn't find it on the forum.
I attached a diagram so you can better understand what I'm trying to say:

So, if you have a gun with a longer barrel, let's say an SVD, and you don't need the 650 mm inner barrel and you replace it with a 510 mm, won't the X difference from 650 to 510 reflect in the diameter of the outer barrel and act like a widebore barrel in continuation of the tightbore barrel, thus influencing the air output, cylinder:barrel ratio, accuracy, m/s and so on?
The same question applies to silencers too when an inner barrel ends inside them, since their diameters are even bigger than the outer barrel's.
 
#2 ·
Not really, since the diameter is so big, there's no real compression anymore, so it won't accelerate (or decellerate) the bb anymore once it's out of the inner barrel.
 
#3 ·
An open space beyond the inner barrel exit will not accelerate the BB, but it can have a distinct impact on accuracy.

I have been working with discreet joule creeping HPA DMR's, crown angle, airsoft suppressor design and stabilization. What I have come to find is post inner barrel air handling, even in volume matched systems, significantly affects shot repeatability in long range (250ft+) airsoft systems. Adding open space between the inner barrel exit and outer barrel exit with no provision for the turbulence it creates doesn't do the system accuracy any favors.
 
#4 · (Edited)
You are right about that, Corriander. It would depend on the ability of the new barrel diameter to disperse the pressured gas away from the BB to minimise the effect on the travelling BB. I kind of used the same train of thought when I built my M16. Slow the rate of fire down, give a slight chance for things to stabilise between shots. Of course on semi auto, no big deal, but on full auto it did make a notable difference in accuracy.

Oh, and good to know I'm not the only one who lies awake thinking about stuff like this. hahaha
 
#5 ·
I've wondered about that extensively, it's the reason I originally got a 650mm inner barrel when I got my SVD.
 
#6 ·
I wonder if it would make a difference if the remainder of the outer barrel was uneven. For example if there's holes in it or something. Wouldn't the pressure wherever the whole was be lower, resulting in potential movement of the bb towards the side where the whole was?
 
Discussion starter · #7 ·
From what you guys wrote, I think it would be better to match the inner barrel's length to the outer barrel's. There are some guns, for example like my AUG, in which the inner barrel fits perfectly inside the outer one and then it really comes into play that air expansion.
So, thank you for your answers.
 
#8 ·
philbegas said:
I wonder if it would make a difference if the remainder of the outer barrel was uneven. For example if there's holes in it or something. Wouldn't the pressure wherever the whole was be lower, resulting in potential movement of the bb towards the side where the whole was?
Click to expand...
I've coupled high dwell HPA systems (0.45g or 0.50g builds) up with engineered/machined inserts to control pressure dissipation while being used with lower weight BBs (0.32g). The results have been to tighten up the cone of fire significantly while using the lower weight bbs.

Another build, a HPA MP7, incorporated a similar design machined directly in to the outer barrel plus the addition of inset o-ring stabilizers for the inner barrel. It used a P* Jack which, by design, requires a dwell higher than the efficiency point for the inner barrel length of a TM MP7. While the inner barrel was extended, the addition of the monolith serves to make the MP7 both quiet (<45dB) and effectively manages the excess air allowing for a stable shot with on-field accuracy exceeding 200ft. This particular build has yet to be tested on a tape, so exact precision is unknown.

Image

Image

Image
 
#9 ·
Boy, that's some nice handiwork!

Because we stay up night thinking about this stuff, I started to remember wave labs from a previous life and how wake was observed to increase the stability of the hull, not the bow wave..because the surface up front was undisturbed (in the lab). So, if the BB is the boat, everything ahead of it is undisturbed and what we're concerned about is the pressure wake propelling it forward. Things that screw up the spin and trajectory. Now, because the 'water' is pushing the BB out the barrel, and not the BB exerting pressure on the water behind it (like a prop), this more like surfing than boating. So, we need to study how the load (BB) is affected by a force from the rear and what happens when it is suddenly or irregularly altered.

Corriander's doo dad (scientific term) works so well because it essentially returns the back pressure to atmosphere where the BB is now flying once it leaves the inner barrel. Partial differential in pressure could have a negative result on the BB whereas complete absence would also affect trajectory. So, the trick would be to gently and accurately reduce back pressure much like a wave collapses slowly behind the surfer...I know, good luck with that!

But, we shall continue to ponder late into the night. It pays off. I just tested the latest revision of my SCAR L yesterday and it could be a bolt gun! hahahaha. Based largely upon what we're discussing right here, it has far exceeded expectation.
 
#11 ·
Absolutely...merely an approximate comparison as liquid doesn't compress or disperse like a gas. That said, you'd actually get a more pronounced effect than you would with liquid based on mass and the compression factor.
 
#12 ·
Corriander, do you have any further info or somewhere where I could read more about that? I'm very interested.

I'm currently in the process of redesigning the suppressor part of the VSR-R which does something very similar to the muzzle piece you put on your MP7, however my philosophy has just been to reduce the barrel pressure as much as possible, which leads to some sort of cage construction inside the outer barrel from the end of the inner barrel all the way to the end cap of the outer, through which the bb travels. Do you think this will have a negative effect on accuracy?

Will post some pictures later...
 
#13 ·
I'm doing similar for my stubby Striker project, as well as another DMR, using 33mm matte carbon fiber tube for the outer barrel with aluminum for the monolith and stabilization sections.

Research monocore/monolith suppressor designs. Those will get you started. I experimented with 3D printed inserts to get the basic proportions at first but generally found they didn't matter much at the air pressures we are dealing with.
 
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Corriander
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