Test of Hypothesis Regarding Spin in Open/Closed Bolt

[St Elmo's Fire]

A statement I have heard a lot about the difference between open-bolt and closed-bolt markers was that the open-bolt causes the paintball to roll before being hit by the air burst, where as the closed-bolt held it stationary. So I conducted a test to study the matter a while back (it might be on this forum under Law of Loud or some such name).

No gas is needed for the firing, as once the gas is applied, you're disconnected from the bolt, and any difference is already made. Therefore, we only needed to see if the bolt movement itself would cause the ball to roll.

So I took about 5 good paintballs well-sized to the barrel of my Tippmann 98, and drawing along the seams in glow-in-the-dark marker, placed them carefully in the bolt so that the seam was flat. I then proceeded to test firing the bolt forward 4 times, and observed carefully that the paintball still appeared to be at the same flat angle. To check that it hadn't rolled 360 degrees, I stopped the bolt partways with the 5th ball: to find that the ball was still flat upon observation of the results.

Therefore, I conclude that the paintball slides, rather than rolling. Therefore, meaning that there is no spin before the shot, and therefore no difference between a closed-bolt and an open-bolt marker in the creation of spin during a shot.

[ottomobile]

That sounds about right. Roll should only occur for deformed balls or for poor paint to barrel size matching.
My thoughts on open versus closed bolt:

In an open bolt nelson system the bolt and hammer move forward with the same accelleration towards the valve pin/paintball. In this system the air port in the bolt must be long enough so that it seals the valve breech before the hammer strikes the valve and continue to hold the seal until the valve again closes. This just-in-time philisophy means that both the valve and air port holes must be significantly large enough to pass all of the gas while the valve port is open. It also means the bolt is still traveling as gas passes through the air port essentially putting the gas velocity vector in a constant state of flux. This can be beneficial as it compresses the gas at the rear of the air port giving it more energy to move forward and out the barrel. Of course this is probably so small it doesn't make a difference.

In an open bolt blow forward design the bolt is pushed forward from escaping gas. Pressure behind the paintball rises linearly until the power tube is fully open and a spring returns the bolt to its inital position. The advantage of this design is that the entire pressure stored in the valve is not released on the ball all at once. As the bolt pushes the ball forward gas builds up gradually creating a much gentler force making it less likely to break paint in the barrel. On the down side much more valve pressure is needed than in a closed bolt or nelson style system. This is because the gas must expend energy pushing against the bolt and resisting spring. Not a good thing if you are a fan of 'low pressure' markers.

Closed bolt systems have the bolt in place before the firing cycle begins. This is the most efficient design. The bolt is in place creating a tight seal around the valve port and paintball. Most of the ensuing gas is put directly to work moving the paintball. Very little is lost doing other work. The drawback to this design however is energy is needed to close the bolt. Unlike the two above designs there is no inherent mechanism to return the marker to its starting position. To solve this you either need a hand operated pump or an electro/pneumatic system like the autococker. This wastes gas in a complicated mechanism to recock the marker. So while closed bolt designs are efficient in the firing cycle they loose all benefits in the recocking process.

In the end its a matter of personal preference. All performance differences between the three designs are negligible and not worth the cost differnce. Personally I perfer open bolt blow forwards or closed bolt systems. The former is simple and elegant and the latter appeals to the tinker in me.

[athomas]

There are no efficiency or accuracy differences between open and closed bolt markers.

All guns fire when the bolt is forward.

There is a certain amount of energy required to fire a paintball. There is a certain amount of energy to cycle the gun. Ideally all guns would be the same. Design flaws result in inefficiencies more so than whether it is open or closed bolt.