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The Optimum BG

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The Optimum BG by GKU

First of all the below is, IMO! It is what I found to be, and works for me.
Each individual has an optimum length/caliber. It doesn't matter what shooting technic one uses as long as he or she is consistent within the one chosen. One will be limited by the amount of air your lungs can put out unless you are still growing. Yes, and it can become very confusing for the beginner blow gunner. It depends on one's physical abilities and if the optimum BG needs to be found by BGner the below will help you to find it.

Easy or not you decide but I don't think it's hard at all. You'll just need to find some common household items. I'm not suggesting that you should cut your CS blow gun down to this Optimum size or length. But to help understand where you (we) are to better understand what is going on. Like fatigue from over exerting, I notice after shooting my 5 foot pro after about 30 minutes my shot(s) start to go bad most of which start to go lower. Trying harder to compensate for this ill effect only made my shooting worst for me. After using my Optimum Bg this negative effect of fatigue has diminish greatly.

I have a friend at work that has a small lung capacity with a very strong peak output burst power and he shoots his 4 foot faster than his 5 foot. Witch I think he is very close in combination with me needing a 4.5 footer or so, but not willing to cut down my CS 5 foot pro yet. Also have another friend that has a very large lung capacity and very weak output burst power, this make for one of the saddest combination. The saddest would be small lung capacity with weak output burst. But, they can still BG they just need to be fitted with a small caliber with a shot length BG (.4" Cal x 24-36" maybe). And another that has a force to be reckoned with large lung and a very hi powered output burst, he now shoots a 7 footer! I think the length controls lung volume and ones peck power burst can be adjusted by caliber size with it occurring somewhere within the middle of the pipe. Well my reason is that it's not that one has a stronger lung then the other. But an earlier occurring peak burst then the others that have it occurring a little later. This is the timing at which the peak occurs and the magnitude of the burst is another thing again. It's related to the weight of the dart one selects and uses that makes the trajectory cure flatter. The higher the magnitude one can creates the heavier the dart they can employ. This peak power burst of yours happens between the beginnings to middle of the pipe, you may need to use a larger caliber or lighter dart. If it occurs at the middle to end of the pipe, you may need to use a smaller one or a heavy dart.

I have found MY OPTIMUM size BGs to be a .625" bore size and 50.5" in length. This setup will give me the flattest trajectory curve with darts ranging in weight between 2.2 - 3.1 grams. And a .6" bore size and 55" in length will give the flattest trajectory curve with darts ranging in weight between 2.1 - 3 grams.

Vital Capacity

Method 1)
We tried to use a balloon to measure this but it has a tendency to elongate and has to be push down a little to measure the circumference. If that is what you choose to use you should take three measurements and take the average. Take some deep breaths and inhale deeply blow into the balloon and empty your breath into it. Compress the height of the balloon to make it the same in diameter as close as possible. Use a string to go around the circumference and measure it with a ruler in inches, repeat three times to get a good average.

Here is the formula I simplified it using some algebra: Where V is the vital capacity and C is the circumference of the balloon in inches.

V=C ³/59.2176

Method 2)
Find a gallon jug that is somewhat clear enough to see water level through it or a rectangular container with tall side about 5"x5"x12". Fill a 5 gallon bucket up with water and submerge container and fill it with the water with the opening on the bottom use a drinking straw that has the ripple joint bend on it. Slip the end under the opening and perform the above, again three times for an average.

V=L" x W" x H" , for a rectangular container.
V= 22/7 x r² x H" , for a cylindrical container.

To only check the results from above not as accurate, but a good approximation:

GKU defining the Optimum BG = a custom BG that is made to fit the person shooting it and will give him the best advantage for maximum accuracy, not speed or distance but accuracy. I have a funny feeling I'm going to be editing this also.

There is also a chance that you maybe already using one. Mine turn out to be within 2.5" short of the 4 foot pro and a couple friends were even closer. I all way wondered why I seem to like it better than the 5 footers I have and catching myself always grabbing it over the longer one. I always thought it was the weight but it turn out to be less fatiguing to shoot long term. It's better to be on the money and not fall to short or long from this measurement. I don't know the terms if any so I will call the too long to be choking and the too short to be overdriving. Both of which cause ill effect on accuracy, to short causes fliers and spiraling to long causes shots to drop and or have to physically over compensate to correct.

In the above link I posted are some take home messages. If the vital lung capacity goes down with age in time I may need to hack off about 3/8 " off of my .625" Optimum BG a year. If one starts without knowing his Optimum BG length is and using one that is 8 " to short in about 21 years later it's possible he or she will be using the Optimum BG without knowing. So in 6.5 years from now my 4 foot pro will become my Optimum BG also, but in the mean time I cut down my CS 5 foot pro to the optimum length of 50.6" long.

AGAIN, I wouldn't cut down your BG just yet. If you would like to experiment with this I would recommend a cheap steel conduit instead for await anyway.

About 5 months ago we used 11 as the divider to calculate the Optimum BG and after two months of trials we settled on 12 for 3 months now. The way I found this value is kind of a reverse engineering feat using a Crony and some Mathematics. But, to keep it as simple as I can for everyone I'll omit this from this posting.

Okay, Vc = your vital capacity, write this down and keep this value for future reference and redo the measurement every 3-5 years or so. Only time will tell if Blow gunning aids in this beneficially, I believe it does !

The Optimum BG length in inches = ( Vc x 7 ) / (66 x caliber ²)

If you are interested in the maximum speed and distance only than multiply your Optimum BG length by about 1.2. Finding the dart weight is your challenge.

Now where were we, ah yes the Optimum Dart to use in your Optimum BG. If you already have calculated your Vc and made one out of a electrical conduit or if your present BG length is within ± 1.5" or so you should be getting good results @ 10 meters with darts weighing in at an average of 3 grams or so. If you are about 8" too short or too long from your Optimum BG length and have a average group size of 2-3". This set up will improve it to about a 1-2" group size. But this formula will give you the Optimum dart weight (Ow) in grams to use. This is the weight of the dart in which when used together with your Optimum BG that will give the greatest accuracy with a proper cone ratio to shoot at 10 meters.

Ow in grams=.06974 x (Your cal in inches) x √ [21.55 x (Your Vc in cubic inches)]

After calculating this dart weight you need to find the right cone ratio to use with it to make the peck of its trajectory curve at 10 meters. I would just start shooting with this dart weight and look and watch to see where it is. It's not that hard I done it at 42 feet. If the peck occurs to soon I would try using a longer cone and a shorter one for the opposite case. Once this cone length is found make a set and it should perform very well for you. I did post somewhere the way that I tune my cone/darts to create a match set, I need to repost.
If you are having trouble calculating any of the above or just hate math, please feel free to PM me for help. I will need to know your Vc and caliber size to the second or third decimal place.

Yes, note that if it's okay and one doesn't mind viewers to know their age it would be okay to post ones Vc or being a serious professional BG competitor to gain an edge on.


Long distance shooting is very interesting, you can learn a lot by studding what goes on after the peck. This IMHO is where BGing problem at closer ranges can find solution to accuracy issues. If you have been following my old post I often said, "strange things can happen on the other side of this rainbow", hence the different colors used in the graph. Now you know what I've been working on.


You can experiment with this Optimum weight (Ow) dart by shooting darts ranging in weight between about ±1 gram from this weight in ½ gram increments. If you don't have a precession scale I used a CS Mini broad head dart, its shaft is pretty linear or 1"/1 gram. For every inch you remove (measuring from the head down, shaft only) you are removing a gram. I used only one same cone for all the shafts seen to get a fair comparison.

Keeping your point of aim (POA) the same for all dart weight used you will find that this Ow dart will impact (print) in the middle of your target, the lightest one the highest and the heaviest the lowest. This may be hard to see or achieve at 10 meters, I went as far as 120 feet using a 4' x 8' sheet of plywood standing up 8'. At 10 meters the dart start out high with the lightest and point of impact (POI) drops as you increase the weight of. At longer ranges this effect will have hidden information that you can't see at 10 meters. Again keeping your point of aim (POA) the same for all dart weight used, starting with the lightest dart it will have a low POI and increases as the dart reaches Ow and then starts to drop again. In my test the 2 g dart had the same POI as the 3.5 g dart and the 3 g the highest.

The Ow dart will achieve maximum range with your Optimum BG and thus producing the greatest accuracy after the peck. Because of this Ow dart used together with the Optimum BG, the trajectory curve is the flattest and together will keeping any error(s) to a minimum. You could get a greater range by multiplying your Optimum BG length by 1.2 this will produce a farther POI and even flatter curve, but your grouping will be much larger than.
Using this Optimum weight dart (Ow) with a cone ratio between 1/3-1/4 gave me much longer ranges. You don't want to be using this long of a cone to do this test at 10 meters you will not see that much of a difference at longer distances a longer cone will require a longer shooting range and unless you have the range distance and like walking it should work also.

I know very well that experience blow gunner already knew all the above and more but I can't assume or image that everyone does. I hope this post has brought insight to the Bging community and this intriguing sport/hobby. In hopes of posting newer things that I have been doing in the future.

My wife side that calculating this Vc is better done with water displacement other than a Spirometer (for about $35). There are many factors like race, respiratory diseases, what abuse one does during their life time, diet and exercise as well. I too once was a smoker and believe this was a contributing factor in my Vc being a bit low. I met my wife and I decided to quit. It's not good to be married to a Surgical Oncologist and be a smoker, being unsure which one will kill me first scares the pants off of me !

Food for thought:
Months ago in the beginning before the Optimum BG became my goal in finding. When I try shooting with a 2 footer and a 10 footer electrical conduit pipe. The results were obvious the short one was being over driven and the long under driven (choking) both of which grouped poorly at 10 meters. I said to myself, what made the popular .625" calibers in the 4' and 5' length ideal for every adult ?

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Thanks for the post. Very good info here.
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WOW , you really broke it down that's a lot of info . When I get the time i would like to find my perfect fit. For now I settle for the 5 foot CS. With the standard darts. Thanks for putting that out there
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