An easy way to improve efficiency

[Patron God of Pirates]

I still see quite a few posts complaining about Mag efficiency. This seems funny to me because I thought this was all settled years ago. While RT based Mags will never be able to "shoot to the bottom of the tank" there is a very easy, though not very fashionable, way to improve efficiency:

10" un-ported barrel.

I just picked up a 10" fibur from Deadlywind and requested no porting. First time testing it and on top of being inordinately loud, it chrono'ed at 340fps. Last time I had the marker out it was sporting a Freak with the first porting about 6" down the barrel. Having no porting for the full 10" allowed me to back the velocity adjuster way out to get back down to 280.

Apologizes to the large percentage of this community that already knew this. It's apparent that many people do not. The ball stops accelerating at the first port in a barrel. That means that barrels with porting at 5 and 6 inches need a much higher volume of air to get up to speed. No Porting = Longer Effective Length = Less Air Needed = Higher Efficiency. Of course people that don't like their marker to sound like a hand cannon can achieve the same effect by using barrels that have longer unported sections.

TK recommends 8-10 inches. His original thread discussing this can be found here:

http://www.automags.org/forums/showthread.php?8958-Barrel-Efficiency-Tech-Tip-1

[cockerpunk]

with a healthy underbore, i get an acceptable 1200-1300 out of my mags.

[The Ritual]

with a healthy underbore, i get an acceptable 1200-1300 out of my mags.

"Healthy underbore" meaning a difference of -.004" or greater?

[Justus]

So as far as our guns are concerned, the best efficiency would be had with an 8-10" effective length barrel. Since two piece ported barrels with an effective length of about 5-6" are the rage right now you hear a lot of complaints about gas efficiency. Under some circumstances there is a good reason to use a short effective length barrel. Short barrels cut off the acceleration abruptly by venting and this has the effect of tightening up the shot to shot velocity variation. If you need this at the expense of efficiency then go ahead. Tighter velocity control usually translates into some improvement in accuracy due to better consistency.

So my underbored FLASC kit, which has a 9" control bore followed by 3" to 5" of porting, seems ideal. 9" effective unported length, followed by a section of porting to vent and effectively tighten up the consistency.

Good to know.

[sjrtk]

This is why there has been some tape covering porting on my barrels since i don't remember when. Plus i like them a little louder.

[blackdeath1k]

This is why there has been some tape covering porting on my barrels since i don't remember when. Plus i like them a little louder.

Only issue with the tape is if you break a ball in there. Harder to clean out the ports from paint oozing back in the barrel.

[athomas]

This has been known by a few for quite a while, but its always good to bring it up and be able to add some real user data to go along with it. It shows just how much of a difference the length of the control bore makes.

[sjrtk]

Only issue with the tape is if you break a ball in there. Harder to clean out the ports from paint oozing back in the barrel.

This is true. But for me at least the risk was worth the reward. Plus I always have more tape in the tool box.

[RobAGD]

68 4500 Lapco Big Shot 14 and proper ball Fit 1500 Shots
68 4500 All A 14 ( old style where the backs length change vs the total barrel length ) 1000 shots

2 part barrels are bad on gas in any dump chamber gun. Same goes with just about any insert based barrels.

-R

[Patron God of Pirates]

68 4500 Lapco Big Shot 14 and proper ball Fit 1500 Shots
68 4500 All A 14 ( old style where the backs length change vs the total barrel length ) 1000 shots

A 50% up-tic in efficiency has to be bigger than any of the valve modding or drop ins that people are doing. Plus it does not come at the expense of potential ROF. The 10" fibur I mentioned at the start of this thread is Freak bored, but I still went from 800 shots with AA tipped freak to 1100 with the same 45/45 tank. Lots of other variables to consider but it seems as though the porting is a bigger drain on efficiency than the bore step.

This is also a a pneuMag with lv.10 so I'm very happy to get over 1k off a single fill of a small tank.

[athomas]

A 50% up-tic in efficiency has to be bigger than any of the valve modding or drop ins that people are doing. Plus it does not come at the expense of potential ROF.

this is much easier to implement than valve modding. But, just think what you could accomplish if you achieved an increase in efficiency with the valve and then used the proper length barrel.

You will probably increase your potential rate of fire with the more efficient barrel. The chamber would operate at a lower pressure. Therefore, it would take less time to fill it, meaning the valve would be ready for the next shot sooner.