BARREL INNER DIAMETER
I have read several articles on how to match your paint to your barrel, and vice versa. The authors claim that you must match your barrel inner diameter with that of the paintball's outer diameter.
I'm here to tell you that this is a big load of crap. So long as the paint doesn't roll out the barrel before you fire it and it feeds properly, your barrel inner diameter has nothing to do with the ballistic performance of the paintball.
Some will say that if you put big bore paint in a small bore barrel, the ball will slow down. SO? Adjust your marker's velocity accordingly. Any more questions?
You see, when you fire the ball, it gets compressed and if fits the barrel perfectly. Some airsmiths and barrel manufacturers "step tune" their barrels. Tight at the bore (to stop roll out), wider in the middle (to allow for ball expansion) and tight at the end (for accuracy). I've used step-tuned barrels with varying degrees of success ranging from "absolutely amazing" to "it'll do fine".
What IS important is barrel LENGTH. Any airsmith will tell you that. That is, any airsmith that doesn't make his money by making and selling barrels of different diameters. Here's the scoop.
If you are using CO2 the gas will expand more efficiently the warmer the air temperature is. Therefore you should use a shorter barrel when it's hot and a longer barrel when it's cold. Nothing shorter than nine inches and nothing longer than 12 inches (unless they're vented and you can get away with adding an inch).
With high pressure air, you can have any length (9-12 inches, unvented) because the air temperature doesn't effect the high pressure system as much.
Anybody who tell you otherwise doesn't know what they're talking about. Or they do and they want you to buy their barrels.
BARREL LENGTH
Okay, you saw the magic number I quoted for barrel length. Let's look at them.
Minium Length is NINE Inches. This is to allow complete expansion of the gas. Anything shorter and you're going to waste air. Shorter barrelled stock pistols, like the PGP have excellent accuracy, despite their shorter barrels. This is because the Sheridan valve is a bit more efficient with gas.
Maximum Length is TWELVE Inches. This is because the gas has stopped expanding and there's really no longer a need for the ball to be inside the barrel any more, it's a s fast as it's going to get (at that velocity). The gas just whirls around and causes turbulence.
If you vent the barrel you can add a couple of inches to the maximum length because the holes bleed the extra air away and doesn't allow it to effect ball performance.
While we're talking about vented barrels . . .
VENTED BARRELS
The only good thing a vented barrel is for is if your valve is not properly tuned. The more INefficient your valve is, the more improvement you'll get with a vented barrel. If your valve pushes too much volume of gas then all the extra gas that hasn't expanded properly blasts out with the ball, decreasing accuracy. The venting holes alow the gas to bleed off while the barrel is still holding the ball on it's course.
That's why some players say they see a difference and some players don't. Even if they have the same brand of marker.
The other plus is that it makes the report quieter because it bleeds the gas off gradually, rather than just letting it blast out the muzzle like a non-vented barrel does.
If you think it spins the ball or prevents air pressure from stacking up in front of the ball -- you've been reading too many advertisements.
VENTURI BOLTS
The only reason why you would need to buy a venturi bolt is if your marker is breaking paint at the bolt face. You can tell this is happening buy removing the bolt, if you see shell fragments there an at the part of the barrel closest to the bolt, then the air blasting out is breaking the ball. The venturi bolt helps to prevent this from happening. Otherwise you're not really going to see a difference in performance.
In fact, if your valve is pushing too much air, you're not going to have one swirling column of gas behind the ball, you're going to have SEVERAL.
THE BEST BARREL MATERIAL
You can't go wrong with brass. Most airsmiths agree that it is the best metal for polishing. Amongst all the non-plated/treated metals, brass is the best for smoothness. The problem being that brass is relatively soft and thinner brass barrels can get bent or dented easier than steel or aluminum. Brass is also less expensive.
There are smoother substances. There are slicker surfaces. However, brass just doesn't seem to build up gelatin residue like all the "wonder products".
UNDERSPIN
You have to be impressed when you see one of these underspin bolts, or barrels do their stuff. The ball flies flatter and further. The idea is that the underspin causing increased pressure below the ball and lower on top of the ball, thus causing lift. That's a fact.
What they don't tell you is that this would be perfect -- if the paintball didn't have a seam. When the ball is spinning the seam catches the air and causes the ball to curve. So what you get in increased range you lose in decreased accuracy. They don't tell you that.
Also, unless the barrel is curved, like the Flatline, it's going to slow the spin of the ball. A bolt that causes underspin is great, but the friction of the ball travelling down the barrel slows the spin and defeats the purpose.
Any article I've read on these underspin technology has always complained about the loss of accuracy, what I like to call the "down-range hook".
If you could orient the seam of each paintball the same way every time, the underspin would be perfect. Of course, you'd have to load the balls one at a time by hand.
I've also been on the business end of the underspin technology. Yes, the balls fly further, but not in a concentrated stream, like you'd want.
The true test for me was at Skyball 2000. They had the Tippmann Flatline range set up. The Tippmann guys had a banner set up about half-way down the range at the top of the netting. This was to prevent lobbed shots from hitting the target. So try as they might, the other semis couldn't match the range of the Flatline, because they had to lob the shots in and they didn't hit the target, they hit the banner. It was impressive, that was until I hit the target with one shot with my stockgun. My buddy, who was on a break from reffing was heard saying; "So okay, they've re-invented the pump."
Luckily this underspin technology is applied on semis, so you can just hose until you hit something.
CONCLUSION
I could go on and on, but I've probably pissed off enough people this month.
The bottom line is this: Why use or extol the virtues of this technology when you don't know how it works to begin with?
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