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I am planning to build an pneumatic Airsoft long range sniper rifle for my next cannon. But I have some questions to ask...
1) What barrel is best for 6MM BBs (length, ID, OD)?
Does using just a hose handle for the triggering system like in the link allow fast air flow?
3) What should I do to make it a non-muzzle loader or a muzzle loader that doesn't allow BBs to fall out by aiming down?
4) Is there other things I can do to increase the FPS of this gun? I am aiming for 400FPS+.
Airflow through the hose handle is just as fast as allmost anything else, just not much volume. You can build a breach loader barrel, but for keeping the BB in, well, thats a tough one. For more FPS, a longer barrel, more power/air presure, good fitting ammo????? More experanced gunners can help you with the last 2 questions better then i can!!!
If you got ten thousand hours to look and read up on it, you can probly find the answers here somewhere.
When life gives you lemons...throw them back they suck!
I don't know if it's the best fitting barrel, but people typicaly use 1/4" brakeline for their airsoft barrels.
They don't really care about accuracy, as they are shooting cans with BBMGs operating at a couple thousand of rounds per minute, so the fact that they use it isn't any indication of it's quality.
Personaly, I wouldn't go with a hose handle. Mcmaster.com sells some QEVs which would be quite usefull for this application, if a bit more expensive - they don't require large, quick momvents to use (accuracy concerns) and will generate higher (and more consistent) velocities than a slow-opening manual valve.
This is a more complex problem. Rubber washer type arangments tend to give the projecitle a random spin, which makes it veer off randomly.
Perhaps you could get a relitivly soft plastic, like polyethelene, and drill a slightly undersized (5.5mm?) hole in it. You could then simply push a bb onto this hole, and it'd stay.
Good valve - opening time especialy. QEVs would work well.
Fuzzy dice. (not really)
Are 6mm BB's a requirement you need? I also hope you dont intend on using my suggestion and f*cking someone up in a airsoft game with this.
Get your self some metal BB's <a href="http://www.classifiedbuyers.com/ItemDetail.asp?AdID=96021&BuySell=2&id=">6MM</a> or the regular .177 kind that can be bought anywhere. Either order tubing from McMaster, buy brakeline, or salvage a old barrel. I would have normally said us a o-ring to stop the projectile, but after further pondering I remember the good ole' magnet. This can either be attached to the pipe or the head of the bolt. Now I dont know how serious your taking this design, but ive been designing a bolt action pneumatic sniper for some time.
Onto the power issue. Basically as BLB said you want a fast opening valve. Since using anything to interfere with the BB in a essence to increase pressure will lead into a accuracy problem. So to exert the most "power" you want a fast opening time, tight fitting barrel, and a long barrel so the air pressure has a longer time to act upon it. Again I dont know how all out your going, but you could also use CO2.
Among my babbling im not completely sure if I answered all your questions, but hopefully I did.
Thanks for all the suggestions. I think I'll use that polyethelene idea. But I don't really want to buy a QEV as they tend to be high priced...Should I use a supah-valve? Maybe a piston or diaphragm...Is it really neccessary to have a fast opening valve when you have a LONG barrel? I'll find a barrel for hit one way or another. I'm thinking about a 60" so it will allow plenty of time for air flow.
If you use metal bb's,to keep them from falling out of the barrel,epoxy(or somthing) a strong magnet to the bottom of the outside of the barrel,right where you put the bb's in
Supah valves are 100$ and will take months to arrive. (Joel is rather behind)
A properly sized QEV from mcmaster will cost 12$ or so, and will ship the next day. Check part number 6646K34 or 6646K11. Shipping is relitivly inexpensive, and you can buy your polyethelene there too.
Wow, a 60" barrel?
Anyway, modling in with the GGDT...
Using a QEV instead of a manual valve seems to increase muzzle energy 2-4 times - it was predicting a muzzle velocity of nearly 800 fps with a .25g projectile using a QEV and a 4 cubic inch chamber @ 100 psi.
A manual valve is sufficient if you only need 400.
Why don't you buy an airsoft rifle?It is cheap not less acurate then what you are planing and it is brech loading.My apinion is that bbs are bad for snipers.They have bad air resistense/mass ratio.A strafer won't be less acurate then the sniper rifle you are planing.
1/4" brake line is for .177 bbs, 5/16" is the only brakeline I found to fit airsoft bbs. <unimportant>The funny thing is, the 20" I used of it on m bbmg was far less accurate than 2 pens taped together.</unimportant> Anyways, 1/4" ID pipe should work as a barrel, seeing a 6mm is just a hair below that. I am not sure on how to get eh bb to stay though, maybe a ball detent like on paintball guns?
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