Overbore - but how much?


What do u mean i missed!!
Mar 1, 2002
spent the whole season using a .685 barrel and it has been fine with everything i have put through it, from DXS bronze all the way up to DXS gold and hellfire, the main difference i have noticed is that it is a lot more consistent with the high grade paint, but i would expect that. As others have said use a .685 or .689 and it will cope with pretty much anything you put through it


Active Member
Oct 13, 2011
I've been playing with the freak kit I'm still learning so I'm no expert but I was playing with some polar ice which was extremely small 679 which in my stock etek with a 693 barrel it would not chrono above 245 +- 20 which if fps makes the difference then I'd say that was a big deal. Put my freak kit on with 685 insert which was a slight over bore just to be safe was 280 +- 5 no problems at all I even had to crank the velocity down.

That situation is probably very rare and its a pain to have to keep switching inserts but it definitely makes a difference in my eyes. I always go for a slight under bore as long as the paint is pretty consistent size wise.

My theory well the way I justify the cost of my freak kit is that a ball with even pressure behind it is gonna be much less random flying down the barrel than a ball that is over bored with uneven pressure behind it since you couldn't predict how the air will contact the ball if the gap is bigger. I'd guess a ball that is very over bored is going to be completely random shot on shot and vary in accuracy at long range.

For me overbore is just a way to keep customers from coming back complaining of barrel breaks to manufacturers when they have paint that isnt the average 689 so they play it safe with 693 stock barrels. We need someone with a 10 million dollar camera maybe Greg Hastings can record what happens to a paintball thats over and under bored as it leaves the barrel :p.
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Autococker Tech
Jul 19, 2009
1) Paintballs vary in size. Even balls from the same bag of paint will vary in size. High quality paint reduces this, but does not eliminate it.

2) Overboring is less efficient than underboring. (i.e. other things being equal, underboring will result in higher velocity than overboring)

3) Because of (1) it is impossible to bore match. What you are actually doing is underboring and overboring depending on how big the ball is. Because of (2), this leads to increased inconsistency in velocity.

4) You should either overbore every ball or underbore every ball to eliminate this issue.

5) The only way to be sure is test your paint, then select a barrel which is always either under or over.

6) Underboring does cause ball breaks in certain extreme circumstances, like cold weather or shooting very fragile paint.

Get a barrel a couple of sizes bigger than your stock one and you will be fine. Forget the iFit kit. Just choose your stock one or the bigger boomstick if you have to.

I almost always shoot my 0.693 SL barrel, unless the paint bores out at 0.680 in which case I use my 0.684 Lapco.
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Platinum Member
Jul 16, 2002
Essex, UK
Last time I tried underboring (not a conscious effort I hasten to add, rather I was used to the daft tiny pea-sized paint we've had for ages, only to discover the clear paint at TCUK was the size of beach balls) I ended up smashing half a ton of paint. It might work with a minor underbore on a gentle marker, but try shoving .696 paint down a .690 barrel on an automag with a hardnose bolt and you make rather a large mess.