This is a letter I wrote to Bill Mills, I wanted to know your guys opinions and experiences too:
"Hello Bill Mills,
I have a question for you reguarding control bore length of 2 piece barrels. By control bore length, I mean the length of the first section of the barrel (mostly stainless) where the ball is accelerated before it enters the tip of the barrel where the inner diameter opens up where the ball doesnt even touch the barrel and gas bypasses around the ball rather than propelling it.
I have inquired about this with Tom Kaye of AGD. He wrote an article about barrel efficiency, so I continued on the subject. He went into depth how 2 piece barrel work, because of the sudden change in bore size, it ends acceleration abruptly, by doing this, it results in more tighter velocity grouping.
I inquired further asking him his opinion on what is the ideal control bore length? I used a rolled up piece of paper and pushed it into the barrel until it reached the bore change. Then I marked off the paper giving me the length of the control bore. I measured my DYE Boomstick, it had a 6" control length. My old J&J Full Tilt had a 5.5", while the JT I beleive was even shorter 5.25" I believe.
I noticed the trend in control bore length as new developments come out is that lengths are getting shorter and shorter in the newer barrels. DYE ,being the oldest, has the longest control bore. J&J came out with their barrel next. Now the new JT's have an even shorter bore length.
Tom Kayes response to me was "get what you need, the shorter the control bore length, ideally the more tighter the velocity grouping, but lesser the effieciency." While a longer control bore will give better efficiency, the velocity groupings will be slightly more erratic.
While this seems true, another discussion with online shop techsamd airsmiths explained that it would depend on the valve timing and dynamics of the gun. The longer the dwell period, the need for a longer control bore. Likewise in the reverse condition.
With the dynamics of the Mag valve, there is no dwell due to the fixed volume air chamber. I would be thinking that a shorter control bore would benefit the Mag best. The trend with Mags benefitting from shorter barrels seem to support this theory. While Tom Kayes theory of the control bore length being tied to efficiency/consistency ratio, Maybe in some cases, the control bore can be slightly too long for the designed valve dwell (in the Mag's cases, minimal to none) and may add excessive drag on the ball.
I am seriously thinking of dumping my Boomy and getting a JT instead. I just dont know how the barrel and all this theory will perform on the field. I hardly see any JT's on high end guns. The only JT barrels Ive seen on the field were on Spyders and Piranhas, while the higher end guns here locally almost exclusively use Boomy's.
I just wanted to know your opinion on all this tangled theory, and also yor opinion and experiences with the JT barrel vs other barrels like the Boomy, CP, Freak, etc.
Thanks for your patience and time in reading my email, and am looking very forward to your reply.
Much Mahalos (Thanks in Hawaii) in advance,
Vincent Cecilio aka "HyperSnyper" (AutomagsOnline)"
Let me know all,