judgment_arms wrote:Ragnarok, I thought porting worked best when it went entirely around the barrel’s circumference?
Yes, for two reasons.
In theory porting just the base could result in an unbalanced force that would create a slight muzzle rise, but at low pressures, that wouldn't be too big a problem. Of course, it wouldn't be vaguely suitable for a high power spudgun - there you'd need porting on all sides to create a net force of zero.
Also, if you had more porting holes, you could vent the gas faster... which would bleed off more gas, and thus lessen muzzle blast further.
However, it comes down to what you think would be best.
Ragnarok brought it to my attention that 1-in-102 was far to slow if a twist rate to stabilize the paintball properly so my new barrel will have the much more appropriate ROT of 1-in-14.
Joannaardway, a few others, and myself discussed rifled paintballs and came to the conclusion that if you got it up to speed slowly it would give it time to properly distribute the weight, and that the longer it remained in the barrel the better distributed the weight would be.
I have full faith that my barrel will work, provided I can accelerate a paintball to 300fps slowly enough.
Paintballs are far from ballistically perfect. They've got low density, and are spheres, which gives them a disappointing ballistic co-efficent, equivalent to about 0.02 G<sub>1</sub>. However, low ballistic coefficient doesn't make something intrinsically inaccurate, it just limits effective range.
Wind and air density changes will affect range, but with a little application of common sense, that's not hard to compensate for.
Now, their liquid core does also create some inertia problems - if they're accelerated too fast.
Now, I'm sure you all know the old trick to tell the difference between a boiled egg and a raw one - spin them both, then touch them with your finger just long enough to stop them spinning, then let go again.
The raw one will start spinning again after your finger has been removed, as it's core has inertia and keeps spinning.
Now, there are important differences between an egg and a paintball. Where as egg white is fairly runny, (although much more viscous than water), paintballs are filled with a deliberately thick and sticky fluid (Polyethylene glycol), so it sticks to people better.
Also, when made, the process causes the paint inside to be under slight pressure from the skin which contracts on cooling - which is what makes paintballs firm, and helps to maintain their round shape.
Last, but not least, a paintball is smaller than an egg, which means that the spinning torque is effected on the core more effectively.
This means that when a paintball is spun, the core is much more wont to follow the skin than with an egg. That's why if you try the same egg trick as I talk about above but with a paintball, it won't start spinning again.
Especially if spun up over several feet, and thus over more time than a short barrelled paintball gun, there shouldn't be any concern about it.
Of course, you don't need my complex explanation to reach this conclusion. Just ask yourself, if you couldn't successfully spin a paintball, why would paintball guns deliberately try to achieve back spin?
If it had no effect, then the companies wouldn't waste resources on it.
Now, having thought that idea through, it does create another interesting thought... could a projectile filled with a low viscosity liquid, be used accurately?
If the core itself was next to immune to spinning effects (a major cause of inaccuracy), then the minimal mass of the projectile's surface wouldn't be able to generate significant Magnus forces to affect trajectory, and would quite quickly be slowed down by friction with the air.
I suspect it might not be completely effective, and producing a projectile that would properly benefit from it would be a little difficult. Still, unless it's tried...
Also, another reason for the long barrel, I shoot Creedmoor style and I’m nearly 6 foot tall.
Hmm. I'm 6' 2", and although I have used spudguns with barrels that long, my current preference is for barrels a little under 4' (120 cm to be precise) in length.
Longer than that, and it doesn't feel quite as "real", because it's too cumbersome and large. (HEAL's current overall length is 144 cm, a hair less than the full length Barrett M82, at 144.8cm)
With the scope and bipod, it does look like a quite convincing AMR (although my original plan was to look more like a shotgun, but hey, who cares) - which is part of the cool really.
Although I know it's not really one, there is that real sense of: "Hey, I'm firing a high power rifle" when I'm using it, with looks, firm recoil and all that building into a neat effect.
I just can't get that from a launcher that doesn't have some kind of "authenticity" to it.
So I can understand why you're looking to build a replica long rifle. It's not going to be fully practical, but heck, if it gives that feeling of cool, who gives a damn?
