Tight Bore Barrels - Airsoft 201

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Guges Mk3
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Tight Bore Barrels - Airsoft 201

Post by Guges Mk3 » Tue Jul 06, 2010 11:40 am

Airsoft 201 – The right diameter Tight Bore Barrel.

I have been repeating this a lot lately. I am putting these concepts forward and if someone using Physics come up with a valid reason that it does not work like this and explain why that is. This will be left as written for posterity.

Why and Ideal Tight Bore barrel in Airsoft is ~6.03/6.04mm. Even PDI of Japan says anything tighter then 6.03mm is not good for accuracy and fps in Airsoft.

Okay…as some of you know. Airsoft guns are Blow Guns, not firearms. So stop using firearm physics in trying to make your Airsoft gun shoot more accurately or further.

There is a level of diminishing returns for a TBB. A stock TM barrel is 6.08mm and in the old days, BB’s were also true 6mm. This leaves a .08mm gap and there is a reason for this.

An airsoft gun barrel needs the gap. This will allow air to move around the bb as it travels down the barrel. If the bb is too big and the barrel is too tight, the bb in the barrel starts acting like a plunger. The bb has to push the air out of the barrel as it moves through the barrel. It also has to draw air in behind the bb as it travels down the barrel. In these instances, the bb is being slowed by the air in front and by drawing the air in back. Increase the gap around the bb then the bb moves down the barrel with less resistance from the front and the back.

For those of you that are experienced enough, notice how moving from a 6.08mm bore barrel to a 6.04mm barrel nets a noticeable increase in FPS for s stock TM, the average of ~12fps increase.

However, if you bump it up to .01mm more the FPS only goes up to ~15fps and going down to a 6.01mm barrel the FPS gain goes down to an average of ~10fps (Tests were with 363mm length barrel, type 2 cylinder and ~5.98mm bb’s).

With the effect of pushing and pulling air as a bb travelling down a barrel that is too tight, the additional effect that the bb is subjected to is turbulence within the barrel. This turbulence will make the bb less accurate and slow the bb down even more. This is caused by air trying to move around a bb from the front and from vortices from the rear as air moves in from behind.

And if you notice, the good bb’s now days are roughly 5.95mm…see the magic number? The good bb’s with the ideal TBB barrels around ~6.03mm is roughly .08mm.

TM got it right in the beginning didn’t they?

Now throw in additional factors with undersized cylinders and barrels that are to long. FPS and accuracy will drop even further.

So, can anyone state in physical terms why this would not be true?
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Re: Tight Bore Barrels - Airsoft 201

Post by vanossster » Sun Jul 11, 2010 10:45 pm

This makes alot of sense. Thanks for the info. :D

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Re: Tight Bore Barrels - Airsoft 201

Post by NullTheWorm » Tue Aug 10, 2010 9:51 am

Yes good info, this seems vital in respect to accuracy and distance.
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Re: Tight Bore Barrels - Airsoft 201

Post by Moose » Sat Aug 14, 2010 7:40 am

Guges MK3,
Your explanation of these valid physical concepts is again much appreciated. The addition of this workable and precise data is of immense value to the entire community. Thanks for the knowlege and learning never ending.
With respect,
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