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The Joule and the Impact of the hit with heavier BBs

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Old July 9th, 2007, 21:51   #1
XerxesYoung
 
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The Joule and the Impact of the hit with heavier BBs

Okay, so I've been wondering about this for a while now.

When people use Higher weight BBs, they are usually for better accuracy.

But some people use it to make the opponent notice that they actually got hit(Because they think that heavier BBs = More impact)

But then again, if the velocity of the gun is... say 330FPS with 0.2g. That's 1Joule of Impact.

So if you use a 0.25g BB and the velocity goes down(lets say 280FPS), that's still 1 Joule of impact.

So if you use a heavier BB, and say that someone would feel the BB hit them harder, it's theoretically speaking, wrong isn't it?

I mean, it's the same impact power.
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Old July 9th, 2007, 22:11   #2
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Conservation of Momentum/Conservation of Energy would dictate so.
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Old July 9th, 2007, 22:34   #3
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Yes, heavier BBs hit harder but travel less distance. There is a finite degree of velocity an AEG can impart which is really a function of the spring power, volume of air in the cylinder, degree of seal around the BB the barrel has, and the length of the barrel. Add to that the influence of the hopup.

Another finite factor I've found is BB weight + hopup. Depending on the velocity of the BB passing through the hopup limits the time the hopup has to have an effect, and the heavier BB takes 'more hopup' to spin the BB than a lower weight BB. The net result is I've found most stock guns top out somewhere between .28 and .36 grams where the hopup becomes ineffective - ie: dialed all the way up and the BB still drops.

So, the only way to really test it, is get different weighted BBs and line yourself up and do the Coke vs. Pepsi test and let us know the results!

I tend to accept the anecdotal evidence from people who've been shot by .20, .25 and .28 when they say the .25 and .28's hurt more than their lower weight counterparts.
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Last edited by Scarecrow; July 9th, 2007 at 22:37..
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Old July 9th, 2007, 23:29   #4
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Quote:
Originally Posted by XerxesYoung View Post

But then again, if the velocity of the gun is... say 330FPS with 0.2g. That's 1Joule of Impact.

So if you use a 0.25g BB and the velocity goes down(lets say 280FPS), that's still 1 Joule of impact.

So if you use a heavier BB, and say that someone would feel the BB hit them harder, it's theoretically speaking, wrong isn't it?

I mean, it's the same impact power.
You are correct. The energy generated by a particular gun is constant; lighter BB's travel faster, heavier BB's travel slower. Impact force in joules is the same.

Quote:
Originally Posted by Scarecrow View Post
Yes, heavier BBs hit harder but travel less distance.
This is incorrect. Heavier BB's actually travel slightly farther. For example, mathematically, a 400 FPS gun will fire a 0.2g BB with hop-up a distance of 187 feet. Switching to 0.25g BB's will increase the flight distance to 198 feet.
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Old July 9th, 2007, 23:41   #5
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Quote:
Originally Posted by Scarecrow View Post
I tend to accept the anecdotal evidence from people who've been shot by .20, .25 and .28 when they say the .25 and .28's hurt more than their lower weight counterparts.
As I said. I think you also have to count in wind resistance and distance to target. You're not firing in a vaccum.

Additionally if you do the math, a gun shooting at 400 fps with a .20gr BB imparts 1.49 joules, where as that same gun at 400fps at .25gr BB imparts 1.86 joules. Let say you shoot that out of the same gun and the FPS drops with the .25gr's to 360fps, the joules is still 1.51. Of course all of these calculations presume you're shooting in a vaccum with no ballistic arc or gravity effect which would influence it further.
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Old July 9th, 2007, 23:46   #6
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Quote:
Originally Posted by WarChild7 View Post
This is incorrect. Heavier BB's actually travel slightly farther. For example, mathematically, a 400 FPS gun will fire a 0.2g BB with hop-up a distance of 187 feet. Switching to 0.25g BB's will increase the flight distance to 198 feet.
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Old July 9th, 2007, 23:55   #7
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Okay, example, my M4 (Matilda) shoots .20's at 407, and .25's at 386.

.20 / 407 = 1.54j
.25 / 386 = 1.73j

Now of course there is a difference between muzzle velocity and at target velocity. Getting hit a 10 feet versus getting hit at 50 feet will of course have less impact as the BB loses velocity.
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Old July 10th, 2007, 00:16   #8
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Quote:
Originally Posted by WarChild7 View Post
This is incorrect. Heavier BB's actually travel slightly farther. For example, mathematically, a 400 FPS gun will fire a 0.2g BB with hop-up a distance of 187 feet. Switching to 0.25g BB's will increase the flight distance to 198 feet.
really? isn't this just the hop-up's fault? i mean we readjust the hop-up when we use different weight BBs.
because realistically, Using the same angle of trajectory and the same amount of force, i throw a 1 pound stone first and then a 5 pound rock later, now whats going to travel farther?
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Old July 10th, 2007, 00:18   #9
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Gun output is not always a constant. I have several gas guns where a change in BB weight did not change the velocity any real amount. Case in point: KSC USP Compact. I chrono'd the thing with 0.20, 0.25 and 0.36g BBs and the velocity stayed at about 300 fps +/- about 5 fps no matter what weight was used. Another case in point: KJW M700. I chrono'd that thing with .25 and .36g BBs, also with no large difference in output, at least not what you'd expect to see if you used a base energy output from the first test shots. Both weights were good for about 475 fps at 5 degrees C with green gas.

I have not gone to this level for an AEG, especially not a stock Marui or anything like that. But I do know from years ago that running .20 in a Marui would have netted an expect 290 fps vs. 0.25 at around 265 fps, but nothing more detailed than that.
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Old July 10th, 2007, 00:41   #10
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Quote:
Originally Posted by BBS View Post
really? isn't this just the hop-up's fault? i mean we readjust the hop-up when we use different weight BBs.
because realistically, Using the same angle of trajectory and the same amount of force, i throw a 1 pound stone first and then a 5 pound rock later, now whats going to travel farther?
That's not a very good analogy. The force used to launch those rocks is relatively small compared the their mass and the speed you could throw them at would make air resistance a non-factor.

A somewhat more extreme example would be launching one of those rocks with a catapult, then doing the same thing with a paper ball of the same size. Which will fly farther and why?

From a sniper's point of view, heavier weight bb's have an advantage over the lighter ones in that they are less affected by air resistance and air currents at long range. A lighter bb will fire farther, but a heavier one will have a flatter trajectory to target. It's of little use to fire a bb farther if it won't travel in a straight line to a distant target. That makes it very hard to properly fire an aimed shot long distance.
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Old July 10th, 2007, 00:44   #11
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Old July 10th, 2007, 00:59   #12
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Heavier BBs maintian their inertia better, they hit harder and at longer ranges, and are more accurate at longer ranges too. One thing I've separated when explaining to people about maximum range, is this: Are you referring to the maximum distance you can hit something, or the maximum range where the BB lands? Due to air, a lighter BB will travel farther before it comes ot rest than a heavier one, but a heavier one will travel farther more accurately.

And to rehash, heavier BBs DO hit harder. Try a 0.20g fired out of a GBB at 100ft, and a 0.43g BB out of the same gun, next shot at 100ft. You WILL feel the hit (and leave a lump if it hits you on the top of the head, right Chef/Jackals?) a lot more with the heavier BB. If you don't feel like having or being a human target, shoot at something hard yet hollow about 100-140ft away, like a plywood wall of a shed. A lighter BB will give you a tick sound, a heavier one will give you a loud THWACK!!!
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Old July 10th, 2007, 01:46   #13
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But then doesn't that contradicts the law of physics?

Because a gun that shoots 1 Joule, will shoot 1 Joule with any weight of bullets, so the impact is all the same.

And that is what the law of physics suggests.

So I guess it's a debate?
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Old July 10th, 2007, 01:51   #14
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Who says the gun shoots 1 Joule? It's the BB that has 1 Joule of muzzle energy. The gun may be more or less efficient with differing BB weights, hence the changes in energy with different BB weights. That BB merely "accepted" 1 Joule of energy. The gun amy in fact be capable and producing more output potential energy than what the actual kinetic energy of the BB is. The hop-up will eat up some energy in friction, air loss around the BB will eat up some, air seal losses in the hop-up may change due to different weights as well.

There's alot that goes on inside an airsoft gun, lots of areas for losses.
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Old July 10th, 2007, 03:49   #15
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There is a confusion in this conversation that requires clarity, not just for the original poster, but for some of the replies.

Xerxesyoung:

You are 100% correct. AT THE MUZZLE, a gun shooting 328fps with 0.20g BBs will shoot 1 Joule, and if you use 0.25g BBs, it will STILL output 1 Joule, albeit at 298fps.

The clarification: Velocity measurements are typically done AT THE MUZZLE.
CDN_Stalker hit the nail on the head. 100 feet away, a heavier BB will carry more energy through its trajectory. This is why heavier BBs are more stable in longer flight, especially in the wind. It carries more forward energy than a lighter BB. This is typically what is meant and understood when people say "I want to use a heavier BB so my opponent can feel my hits." At range, the target WILL take more energy from the BB than a lighter BB - only because the lighter BB has lost much of its energy in flight.

So why are there replies in this thread that contradict each other, including the above statement I just made about muzzle energies being the same?

There are two fairly different systems being discussed here:
1) "Constant" systems such as electric and spring powered guns
2) "Variable" systems such as gas powered guns.

The stipulation: The above theory ONLY applies under the rule of "constant" systems such as electric guns (that use electricity to crank a spring powered piston) and spring powered single-cocking guns (such as bolt action guns or cheaper springer guns.)
No matter how heavy the BB is, the spring will only compress so far, and the spring will always release at the same rate. The force of air leaving the nozzle, and the volume will ALWAYS be the same, regardless of BB weight. This is why AEGs and spring powered guns can have BB velocities calculated, as long as you know the muzzle energy.


So let's explain the contradicting posts:

The other system at discussion here, are "variable" systems, ie gas powered guns.

Gas, in itself, is not consistent. It expands at different rates, given different conditions and variables. At warmer temperatures, gas expands faster, colder temperatures, gas expands slower. That's pretty common knowledge.

However, there's more to it than that. Why are there users (such as mcguyver) who claim similar velocities, despite differing BB weights? Exactly as he stated when he started off his post: "Gun output is not always a constant." At least not with gas guns, they aren't, especially if different weight BBs are used. A major variable that affects the amount of gas outputted is the weight of the projectile being thrown.

Heavier projectiles accelerate slower. They require more energy to accelerate as fast as lighter projectiles. Due to this fact, heavier BBs stay in the barrel of a gun for a longer period of time than a lighter BB will, and because the BB has more time in the system, it has been subjected to more gas expansion time. By the time it leaves the muzzle, the gas would have had more expansion time than a lighter BB would. Not only does the gas have more expansion time, but the longer amount of time the BB is in the system has allowed the gas valve to stay open longer, and as a result, a GREATER volume of gas is expelled when using heavier BBs. It must be understood that almost all modern self-chambering gas guns these days do NOT shut off the gas valve until the BB has left the barrel! Greater expansion time + greater volume = greater energy expelled.

This knowledge, I believe, is important to know and understand. Players who are familiar with constant systems typically don't understand the variance in gas systems. To them, 1 Joule is one Joule, regardless of what gun you use. It's not true. Gas guns, WILL output more muzzle energy if you use a heavier BB! In this thread alone, mcguyver cites velocities that back this claim, as does CDN_Stalker, and I can as well if needed. I have 6 gas powered guns here that I have taken readings off of to back this claim, as have many other players in the past. I also have several different constant system guns (mostly AEGs and some springers) that back the theory that their energy is always constant.

For game safety reasons, players and game organizers SHOULD understand this knowledge that muzzle energies will differ at the muzzle, especially with gas guns. Otherwise, they could chronograph a gun with 0.20g BBs and be well within safe gaming limits, but the moment they drop in heavier BBs, they could potentially have a gun that could cause unnecessary hurt. I still think that imparting energy limits, rather than velocity limits is a more consistent and safer method of keeping players in check. Otherwise, players who know this difference can (and will) use this loophole to their advantage: test with light BB, use super heavy BB to shoot harder and cause more hurt.



SO

To sum up, and answer the original question: Although heavier BBs have the same energy at the muzzle in some guns, there are other guns that have higher muzzle energies when using heavier BBs!
But despite that fact, no matter what kind of gun is used, YES, heavier BBs DO hit harder at range!

Last edited by ILLusion; July 10th, 2007 at 03:58..
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