smaller always better? , .684 vs. .688

[djinnform]

I've always used .688 Titanium Dye back with Evil, but noticed at lot of guys using .684 bore size for the same Evil paint at our field.

So I bought a .684 Dye digi cam, and used it all day, and never broke one ball.

But, I don't feel like the .684 is more accurate, in fact, it seems less accurate than my Titanium .688 Dye back.

Could this be?

[Patron God of Pirates]

The bore size will effect your consistency and efficiency, not your accuracy. Granted, greater consistency makes it easier to predict the flight path of your paint.

[OPBN]

The bore size will effect your consistency and efficiency, not your accuracy. Granted, greater consistency makes it easier to predict the flight path of your paint.

Yep. I use a Freak or J&J kit depending on the marker I am playing with and use the best bore to barrel match I can. I know there is the great debate on underboring, but I don't get into that much honestly.

[athomas]

Ideally, you want the bore size that causes the balls to lightly touch the barrel in two spots on opposite sides of the ball, usually at the seam. This will give you maximum consistency. Ultimately, consistency depends on having paintballs that are consistent. A larger bore is more forgiving than a smaller bore when it comes to paint that is not perfectly round. A larger bore also prevents barrel breaks due to weak seamed paintballs. The guys that are underboring for their paintball size, are depending on having good quality, consistent paintballs.

[Hook]

I exclusively underbore if I am playing pump with quality paint, such as Marbs. Usually works great efficiency-wise

[cockerpunk]

Ideally, you want the bore size that causes the balls to lightly touch the barrel in two spots on opposite sides of the ball, usually at the seam. This will give you maximum consistency. Ultimately, consistency depends on having paintballs that are consistent. A larger bore is more forgiving than a smaller bore when it comes to paint that is not perfectly round. A larger bore also prevents barrel breaks due to weak seamed paintballs. The guys that are underboring for their paintball size, are depending on having good quality, consistent paintballs.

that is actually the worst for consistency. and its because of inconsistently sized paintballs. we underbore exactly because paint is not consistent.

you see, at paint to barrel match, the barrel is a fixed size. meanwhile, every paintball is a different size (even good paint). so each ball is at a different place on the over to undebrore scale ... which means the drag to seal ratio is different for each ball, which means each one will come out a different speed. meanwhile, at a large overbore, every ball will not touch, so the drag to seal ratio will be very close on the balls. conversely, at a reasonable underbore, every ball will seal tight, so the drag/seal will be consistent, providing consistent velocity.

a large over or underbore will give you good consistency, with underboring .003-.005 being a bit more consistent. underboring is also much more efficient (up to 30 fps). paint to barrel match will be the worst consistency.

the answer to your question though OP is another one "what size is your paint" without knowing what size paint you are shooting, its impossible to tell you what bore size to use. my general rule of thumb is to aim for .003" to .005" underbore. i select this by blow testing the paint, and then when i find a match, use teh barrel 3 to 5 under it. we have not found underboring, even with extremely brittle paint, to break more paint until .007" - 009" underbore. so smaller is not always better, the reason underboring caught that bug was because before it was popular, getting barrels in the sizes to make a .003 to .005 underbore to work was nearly impossible due to shrinking paint. so we all cheered when the return of .679 and smaller barrels came out, as paint is consistently below .683 here.

using high speed videos from jack wood, and simon, and our own work, we have determined most "barrel breaks" are really minor damage to the ball during the loading cycle which later fail completely when subjected to the power pulse. a true "barrel break" where a perfectly normal, undamaged ball, breaks int he barrel is extremely rare, and has a distinctly different symptom to most "barrel breaks"

[athomas]

that is actually the worst for consistency. and its because of inconsistently sized paintballs. we underbore exactly because paint is not consistent.

No, I mentioned that the best consistency is if the ball touches on both sides of the ball but it depends on consistent paint. That is paramount. It takes much less energy to pop that cork as well, which makes it very efficient.

If you are talking inconsistent paint, then that is where we either underbore or overbore for increased consistency. I think we are talking the same language but you are interpreting my writing a bit differently. I suspect we are interpreting the amount of touch differently. What I interpret as the right amount of ball touching, you might be interpreting as a couple of thousands of underbore, in which case we are on the same page.

I remember back in 1990 when we were using PMI premium and were shooting barrels that were 0.690". The paint was popping like a cork and flying all over the place with no predicability. I was one of the only ones that had a barrel with known id sizes, and changed to a near perfect match at 0.6925". The balls flew perfect and consistent every shot. We checked the paint and found it to be consistent from ball to ball, so underboring by even 0.0025" was not working for us at that time.

As a personal preference, I like to overbore because I have less barrel breaks. This is even when I have sized the barrel for my paint. It is the one or two odd shaped balls in a bag of 500, that could cause a problem. I prefer not to take a chance when in a tournament environment and goo in my barrel could be the difference between winning and losing due to a missed shot.

[Dark Side]

The bore size will effect your consistency and efficiency, not your accuracy.

How could you possibly believe this? Efficiency and consistency is directly tied to accuracy. Muzzle speed helps to dictate accuracy and you can even go so far to show that if improperly sized the paint will wobble in the barrel further decreasing accuracy.

[cockerpunk]

How could you possibly believe this? Efficiency and consistency is directly tied to accuracy. Muzzle speed helps to dictate accuracy and you can even go so far to show that if improperly sized the paint will wobble in the barrel further decreasing accuracy.

up to about a 15 fps spread, consistency does not effect accuracy.

[Patron God of Pirates]

How could you possibly believe this? Efficiency and consistency is directly tied to accuracy. Muzzle speed helps to dictate accuracy and you can even go so far to show that if improperly sized the paint will wobble in the barrel further decreasing accuracy.

Lol. Way to quote only the part of my statement that supported this. You missed "Granted, greater consistency makes it easier to predict the flight path of your paint."

Question for those who do underbore? Do you use digital calipers? The only time I tried underboring the first ball only made it past the detent, The next ball engaged my LV.10 so I was fully jammed up. I've always used the paint to barrel matching technique outlined above by athomas and had (empirically) good results.

[cockerpunk]

Lol. Way to quote only the part of my statement that supported this. You missed "Granted, greater consistency makes it easier to predict the flight path of your paint."

Question for those who do underbore? Do you use digital calipers? The only time I tried underboring the first ball only made it past the detent, The next ball engaged my LV.10 so I was fully jammed up. I've always used the paint to barrel matching technique outlined above by athomas and had (empirically) good results.

i undebrore on my cocker threaded mags, but i also don't tune my level 10 that hot. i already explained how i select my bore size.

works great, i can squeeze 1350 out of a 68/45 on a soft fill with a nice underbore. thats almost reasonable efficiency!

[athomas]

Question for those who do underbore? Do you use digital calipers? The only time I tried underboring the first ball only made it past the detent, The next ball engaged my LV.10 so I was fully jammed up. I've always used the paint to barrel matching technique outlined above by athomas and had (empirically) good results.

Once the bolt gets past its level 10 small stem part, it will smash a ball into the breach regardless of if it wants to go or not, and then fire the contents of the ball out the front. If the ball only made it past the first detent, it is more likely a result of the level 10 bolt spring being too strong for your velocity setting than it is that the extra friction from the underboring is halting things. It is possible that the level 10 bump is just enough to push the ball forward and allow the next one to drop into the breach.

[Patron God of Pirates]

Once the bolt gets past its level 10 small stem part, it will smash a ball into the breach regardless of if it wants to go or not, and then fire the contents of the ball out the front. If the ball only made it past the first detent, it is more likely a result of the level 10 bolt spring being too strong for your velocity setting than it is that the extra friction from the underboring is halting things. It is possible that the level 10 bump is just enough to push the ball forward and allow the next one to drop into the breach.

That all makes perfect sense, but when I swapped out the freak insert for a larger (big enough to drop the paint through) one the problem went away. I came to the conclusion that the air blast escaped via the powerfeed tube.

[nak81783]

What I'm struggling with is one underbores to remedy inconsistencies in paint, but one must use that same inconsistent paint to determine which bore size to use. This can be applied to overboring as well.

If the blow-by is inconsistent if attempting to overbore, and the drag is inconsistent when attempting to underbore, does it truly make a difference?

What about coefficient of friction between a constant barrel and inconsistent paint? What about the ball deforming when the air blast hits it? Would that increase the seal of an inconsistent paintball within the barrel similar to an oring deforming into a seal when pressure is applied? Should we therefore aim for a -.001" underbore to +.001 overbore to get maximum seal, but minimum drag?

So many variables (especially when measuring to thousandths of an inch on gel capsules), but the only constant is the inconsistent paint.

Given all these and many other variables, get the paint to barrel match relatively close, and continue on the premise that paintball continues to be an accuracy by volume game.

Only exception would be for closed bolts, where the barrel is your detent, but that's a design influence not really relevant to the question at hand.

-Nathan