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BB weight and range: WHAT is the truth?

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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BB weight and range: WHAT is the truth?

Unread postAuthor: lozz08 » Fri Oct 09, 2009 6:38 am

It seems to me that all over the internet we have people saying that lighter bbs go further than heavier ones, because they will go faster, and therefore travel further before gravity has caused them to hit the ground.

But there is another bunch of people that say the greater density of heavier bbs causes them to lose less kinetic energy as time goes on, and therefore keep their speed for longer and go further.

What is the truth? (Assume we are using a perfectly dialled hopup)
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 09, 2009 7:41 am

If you fire them at the same speed, the heavier BB will travel farther because of its greater sectional density, it will slow down at a slower rate.

However, a heavier BB will leave the the muzzle at a lower velocity than a lighter BB from the same launcher, so in some ways, both are correct.

In a nutshell, heavier BBs are ideal, but only if your launcher can fire them fast enough.

Here's a comparison with my burst disk 6mm launcher,0.12 grams vs 0.25 gramsfired at a steel lighter fluid tin:

As you can see, the 0.25g retained enough kinetic energy after penetrating the first side to go through the other, while the 0.12g did not.
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Unread postAuthor: Moonbogg » Fri Oct 09, 2009 7:47 am

So if fired from the same gun, does that mean heavier stuff goes farther despite the lesser velocity?
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 09, 2009 8:20 am

Moonbogg wrote:So if fired from the same gun, does that mean heavier stuff goes farther despite the lesser velocity?


It's subjective, there's always an ideal weight.

Let's take a 0.177" HW97 springer air rifle as an example, there's some detailed testing with different pellet weights here.

For the purposes of this discussion we'll ignore pellet shape as a factor, the important thing here is that they all have the same frontal area and therefore sectional density varies with weight.

Note also how it's not a straight line for velocity increase with decreasing pellet weight. There are other factors involved, like barrel friction for example, and a lighter pellet will tend to start moving quickly and not allow enough pressure to build up behind it to extract the rifle's full potential.

Take a look at the data, in general though if you want range, you want the heaviest possible projectile with the smallest possible frontal area, taking that to the extreme means you usually end up with a long thin dart made up of a dense metal.

Ergo, vis a vis, concordently:

Image

;)
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Unread postAuthor: inonickname » Fri Oct 09, 2009 8:21 am

Within reason, usually. You can't fire a neutron star and expect it to go far.
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Re: BB weight and range: WHAT is the truth?

Unread postAuthor: Ragnarok » Fri Oct 09, 2009 9:05 am

lozz08 wrote:What is the truth? (Assume we are using a perfectly dialled hopup)

That very much depends on "perfectly dialled hop-up", for that is subjective.

As lift is a function of velocity, it falls off as the projectile slows down. If lift is precisely equal to projectile weight at the muzzle (thus causing no fall at all), then as drag hits home, it will start to fall.

So really, you want lift to be MORE than projectile weight at the muzzle, causing it to rise slightly at the muzzle, then be equal to projectile weight some distance from the muzzle - thus, in the end, giving a "flatter trajectory".

Of course, the distance from the line of sight that the player considers acceptable varies. Some people consider a 4" diameter hit zone fine. In other words the projectile rises 2" above the LOS, then they define their "point-blank range" (in the proper ballistics sense, not the "almost no distance" sense) as when the BB falls 2" below the LOS.
Some would accept 6" diameter, and that would give them a longer point blank range, because they can use a more arced trajectory.

However, for the settings I was messing with when simulating this a while ago, I recall that launched from a 1 Joule airsoft gun, a 0.25g BB takes less time to get to 20 metres (at least, I think it was 20 metres) than a 0.12 gram BB does, despite only having 70% of the initial velocity.

I'm no airsofter, but my guess is that you're inside 20 metres, I doubt the tiny advantages the velocity of lighter pellets might give you would be notable, and beyond 20 metres, by using a heavier pellet you've got less drop, and less time to target.

There's a range at which each pellet weight (to an upper limit, of course) becomes more ideal than its predecessor - but after that distance, it is almost certainly dramatically more advantageous than the other pellet was before that point.

My personal recommendation based solely on the numbers (and limited knowledge of airsoft) is more use of 0.25g pellets - but it does depend on the player and field.
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Unread postAuthor: Davidvaini » Fri Oct 09, 2009 2:45 pm

I am a seasoned Airsoft player and I play every week.

Typically Airsoft BB's come in a variety of weights.

These are the most common:

.12g (BB's that are typically not recommended for any midrange airsoft gun or higher)
.20g (Standard Weight for Chronographing for Airsoft Field Use)
Most fields require 400fps or lower with .20g BB for outdoor use. There are rules that allow you to have a gun shooting higher, but it is classified as a DMR or a Sniper Rifle.
.23g (**Personally recommended for any gun shooting 330fps to 360fps)
.25g(**Personally recommended for 350fps-390fps)
.28g(**Personally recommended for 370fps-430fps)

** figures depend on the quality of the hopup and all fps measurements are done with .20g BBs. For example:
If your gun is shooting 350fps with .20g, chances are you could probably use .23g or .25g. Again it depends on the hopup.

There are also .26g .30g, .36g, .40g, .43 but are less common and/or used for Sniper Rifles or DMR's.


Now the heavier the BB the less it will get effected by wind resistance and will be more accurate and loose less speed at further ranges. I have learned from experience that an airsoft gun shooting 400fps with .20g BB will shoot quite a bit further if you put in .25g BBs(which drops the velocity down quite a bit). You have less intial velocity, but you hold that velocity for a lot longer and therefore the distance it can travel is further and is more accurate. However I have noticed people using too heavy of BBs which increases their accuracy, but their distance will be slightly less than if they were to find the "perfect weight BB."

In my AKM airsoft gun, When I would use .25s I would hit 180 feet effectively(9 inch groupings). When I used .28s, I could not get out 180 feet.. my max effective range was 160 feet with 5 inch groupings. When I used .25's my groupings at 160 feet were 8 inches.

So it really is just about testing different ammo to see which ones your gun shoots the best. I can help with a general estimate via the velocity of your gun, but it also depends on how good your hopup is. (hopup in airsoft is the number 1 contributer to good rang*1)

*1 - A 300fps gun with a decent hopup will outrange a 400fps gun with a crappy hopup. I have even seen 200fps guns(my glock) with a much shorter barrel that has an awesome hopup outrange a 400fps gun that had a bad hopup.(almost no backspin.)
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Unread postAuthor: lozz08 » Fri Oct 09, 2009 10:21 pm

My problem is I can only get either .12g bbs or steel bbs that probably weigh like .5g. I'm expecting an energy from my rifle of 3-4J.

Is it safe to use such a heavy penetrating bb in skirmishes if we're wearing proper safety gear?

Also, will a steel bb damage my aluminium inner barrel? (6.035mm)

(I'm making my own hopup from pen grip rubber and a screw- that old trick)
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Unread postAuthor: Davidvaini » Fri Oct 09, 2009 11:38 pm

3-4j? you would get almost no accuracy with .12s.. its way too much velocity for that weight BB..

1.48 joules is the typical limit of most fields(400fps with .20).. most fields have a sniper limit of 550fps with .20g(2.8 joules) but then they have a minimum engagement distance of 50-75 feet(sometimes further).

Also most fields have strict rules against metal BBs of any weight, especially ones heavier than .43g.

It would be against 99% of the fields out there.

As far as them damaging the inner barrel, I have no idea really as I have not tested it.

I will not inform someone of something I have not tested, studied a lot of, or have seen. So I can't tell you if it will damage your barrel.
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Unread postAuthor: jackssmirkingrevenge » Sat Oct 10, 2009 1:37 am

In order to fire a steel BB at a velocity high enough for a trajectory that doesn't look like one from a mortar, you're going to endow it with significant kinetic energy, more than I would consider safe.

steel bbs that probably weigh like .5g


More like 0.89 grams, ouch. British special forces during the Malayan Emergency trained for jungle warfare using lead rounds in ordinary air rifles with only fencing masks for protection, but that would be only for the more masochistic.

Did you plan on sniping or CQB?
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Unread postAuthor: lozz08 » Sat Oct 10, 2009 3:08 am

Im not doing anything official as I'm from Australia, just with friends, thats why I'm making these guns. So the only limit for me is where it would start to get dangerous getting hit. I don't know where I'm going to find some proper .3g bbs but it looks like its my only option for this sniper.
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Unread postAuthor: jackssmirkingrevenge » Sat Oct 10, 2009 4:01 am

lozz08 wrote:I don't know where I'm going to find some proper .3g bbs but it looks like its my only option for this sniper.


For good long range shooting you need significant velocity, and high speed steel BBs are not the sort of things you should be directing at your friends. If you're stuck with light BBs, try and make the most powerful launcher possible but then keep a minimum engagement distance to avoid injury, as linked to about even a light BB with punch through steel at close range if it's travelling fast enough.
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Unread postAuthor: lozz08 » Sat Oct 10, 2009 7:18 am

Hmmm, maybe someone around here should do an energy vs. Ideal bb weight graph. I'm totally surprised something like that hasn't been done.
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Unread postAuthor: jackssmirkingrevenge » Sat Oct 10, 2009 8:02 am

lozz08 wrote:Hmmm, maybe someone around here should do an energy vs. Ideal bb weight graph. I'm totally surprised something like that hasn't been done.


Eat your heart out ;)
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Unread postAuthor: lozz08 » Sat Oct 10, 2009 9:07 am

Yeah but that just calculates muzzle energy, not the effective range for different pellet weights at the same energy level doesn't it?
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