Best BB weight for 450 fps gun (with .2's)

[McKee]

The gearbox and all airseal components are only ever capable of delivering a maximum force limited by the spring. All parts other than the spring help determine the efficiency of how that spring power is coverted to air pushing power, but the limiting factor is always the spring. So with a force delivered to a bb, the BB's weight will determine how much momentum is imparted to the bb from the air (momentum = velocity x mass). You increase the mass, the velocity (speed/fps) by law must decrease. Therefore you will always drop FPS with a heavier BB, however a BB with a greater mass can better resist the force of wind and will have different flight characteristics under the same hop up conditions you had with a differently weighted bb. This is why hop up must be adjusted to different bb weight.

Don't get wrapped up in joules or FPS.. joules are a measurement of force through a distance, FPS is speed. Joules will never change regardless of BB weight, again thanks to the law of conservation of momentum. FPS will change depending on bb mass. FPS is actually an inferior measurement for this context since in airsoft, we are worried about energy delivered. Needless to say, a .40g bb at 400FPS is going to do a helluva lot more damage than a .20 at 400FPS. If we measured in joules, you would always be able to determine an accurate safety limit regardless of BB used (as long as you knew which one was used).

To clarify lets say you have a gun that shoots a .20g bb at 400fps. If you put .40g bbs in it, you would shoot 283FPS. Your system always delivers 1.48J if this is your setup.

Also, as for distance traveled... air resistance increases exponentially with speed. A higher FPS bb will meet more air resistance. This is why, with hopup, it is possible to shoot a heavier BB farther than a lighter BB despite a lower FPS. OP: You definitely want to use a heavier BB, unless you can find a physics major to help you out, I would recommend just hitting the range and experimenting with a few different weights of BB to see what you can shoot the farthest (just remember the key to success is your hop up setting). Too bad BB bastard doesn't offer a sampler.

[Fox62]

Originally Posted by McKee

Joules will never change regardless of BB weight

As said before, it will change considerably on a GBB; hence why I've always thought FPS measurements are obsolete and force people to chrono with .20's (giving the wrong energy read for someone gaming a GBB with .40s). Guns should be chronoed in Joules, and with the BB weight they are going to be using in game.


Fox.

[ShelledPants]

Don't forget that if the gun uses a spring loaded magazine (all AEGs) and the spring is insufficiently strong, and you're firing fully automatic, you may encounter jams as the BB is halfway into the hopup chamber when the nozzle comes forward. You will need stiffer magazine springs (Read; better magazines in most cases) to fire heavy weight BB's in full auto.

It's a problem a lot of people never consider.

[ThunderCactus]

Originally Posted by Fox62

As said before, it will change considerably on a GBB; hence why I've always thought FPS measurements are obsolete and force people to chrono with .20's (giving the wrong energy read for someone gaming a GBB with .40s). Guns should be chronoed in Joules, and with the BB weight they are going to be using in game.


Fox.

You are absolutely right sir.
But He was talking about AEG's. Anything spring powered will maintain it's joule rating over any BB weight.
However anything GAS powered will change it's joule rating depending on the weight of ammo used.
And so chronoing with .20s is standard and very accurate for AEGs, but you're correct in saying that GBBRs need to be chrono'd with the BB weight they will be using in game, and a conversion to joules must be done.

Here in Mb, we write out the max FPS for each BB weight. So there's different FPS limits for each BB weight, but they all come out to the same force (1.48j for auto, 2.04j for bolt)

And +1 to everything McKee said. Through field trials I've found that all BB's generally have an optimal relative velocity of 330-360fps.
For example, at 2.04j (470fps on .20s), a .30g BB will have LESS accuracy than it does at 1.7j (430fps on .20s)
This was compared side by side with 2 marui VSR-10s of the same internals, and again on one marui VSR-10 with a 470 then 430fps spring.

[McKee]

I thought this data had been lost but through the power of magnets I found it again..

http://mackila.com/airsoft/atp/

Literally all the physics data you could ever hope for in airsoft. Check out section VII in particular. If you're shooting 450FPS (1.88J) you can see what effect various bb weights would have http://mackila.com/airsoft/atp/07-b-09.htm

Basically to answer your question outright: .30g bbs. They have the flattest trajectory with hop-up and the difference between .36 and .30 is that while .36 goes very slightly farther (like 3 feet), the flatter trajectory of .30s will make for more accurate shots and not to mention they are cheaper!

[CDN_Stalker]

0.30g will get blown off course easier, where the 0.36g will power on through. Add in elevation, your range will increase by a lot, and 0.36g will blast through brush better. I've used every weight and brand (including a few boxes of 0.29g SGM, 500rds at $40 per box), and settled on the Bastard 0.36g as being the best bang for the buck.

[ThunderCactus]

Well physics and math is one thing. What actually happens in the field can sometimes be completely different.
.36g is the way to go