Discussion: Airsoft ammo ballistics vs. aerodynamics vs. conditions

[CDN_Stalker]

Anyone interested in learning/discussing the ballistics and aerodynamics (screw the math, let's go for the real shit) that affects a BB's flight path? I figure I'm the best and the most experienced one to bring the topic up, namely due to my observations of various weights of BBs in various guns (0.43g BBs in a GBB anyone?), as well as my experience in my career in aerospace research for the government (turst me, even though I'm only an Instumentation Technician, I get overwhelmed with areodynamics knowledge because of projects around my hanger).

This is the kinda thing I've been mulling over in my head for well over a year, and largely it's geared towards airsoft snipers understanding what happens once they launch their round and what might happen, and why (I'd like for Sha Do to read and contribute, I'd appreciate his input and it could very well add a very important set of info to his Sniper Clinics. When I host my own Sniper Certification Clinics in the Ottawa area, I'll use ALL info as well as safety and fieldcraft in the clinic/course).

While I've largely understood what hop up is and how it works, I've been tweaking my CA M24 a lot and watching where the BBs go, and trying to figure out why they do what they do, and how to better predict where to aim to use the conditions to my advantage to "hook" a round into a target in a cross wind that makes the BB over-hop and yaw, etc..

This is going to be useful info for beginner and vet alike, and I think it'll be a benefit to the community, is why I'm releasing it (has been authorized last year for posting to Sniper_Chic on the WolfPack forum where it seemed welcome) but I think it's time to bring it to the national level, a discussion and a learning experience for all.

To preface it, I'm going to post some info I posted on the Warmonger forum's "Sniper's Range". I wrote it over a year ago (some of the info might be worng, I haven't looked at the content for a long time, but I'll be adding more later if anyone pays attention to it), and have added bits a while back as well, but I haven't even touched on the aerodynamics of a BB's flight yet; drag caused by turbulence (suction), stagnation point, laminar airflow, how side wind affects the yaw (and lift generating ability of the hop up), etc.

Anyways, here's my basic start because I'm lazy right now (used a couple pages of paper and pencil drawing out my understanding of the airflow between no hop up and hop up) and it's late. I'd like to see interest before I start babbling on about nothing interesting and waste server space.

Originally Posted by Stalker

Ok, here I'm going to attempt to outline airsoft ballistics (as it applies to sniper rifles) as I have experienced it and as I understand it. It seems that the general concensus is that it's all in the fps, which isn't completely true. Well, paritally it is, but it's not a "Be all, end all" solution. I'm going to break it down into the three basic areas: Velocity, hop up, and BB type and choice. And I am placing it in this section because it's more important for a sniper rifle since you aren't dumping a lot of plastic downrange.

Velocity

Ok, this IS an issue and will help dictate the range the BB will travel. Consider it to be 2/3 of the entire determination of range & accuracy. A BB will go straight out to a certain point that it'll get to the ratio of speed vs. BB weight vs. hop up backspin.

The velocity determines how far the BB will go before that ratio is acheived. The higher the velocity, the farther the BB will go before it goes up or down (or in the case of side wind, how far it goes before it blows off course.)

Keep in mind though, that velocity doesn't play such a huge role that one can't get long range unless the gun is really hot. Remember I hit a guy 200ft away at Op: Cold Wind? My M24 at the time was shooting around 400fps. Last I chronied at the LZ, it shot a .36g BB at 315fps with full hop up.

Hop up

Here this is, we all know how it works. It takes over the rest of the distance after the velocity gets to that magic point and carries the BB farther.

BB choice

This is the tough one as it's based completely upon the gun and hop up. You adjust the hop up based upon the weight. (NOTE: The APS2-SV has a fixed hop up set for Maruzen .29g SGM. Means that .36g will be too haevy, therefore .30g is best overall use. Unless you are shooting really high, upwards of 500fps with .2g BBs, then you might find even the .36g BBs are over hopped, in which case you shift over to .43g BBs and live happily ever after.)

Seems that the higher the fps, the more erratic the hop up and accuracy is. When my M24 was shooting around 500fps (when I first got it), I could barely get a .36g BB accurately out past 150ft. Yet with full hop up and shooting 400fps, I could easily get it past 200ft.

The higher the velocity, the harder it hits the hop up, the faster the back spin on that BB (we'll say RPM for the fun of it, since that's essentially what it is), which means that aerodynamically, it will be much more unstable and therefore inconsistant. Remember that there are various uncontrollable air currents at every point between you and the target. Any irregularity in the air will send the BB with a fast backspin off course, where a slower spin will be more stable through those air currents.

The weight is obvious to us all as well. The higher the fps, the faster a heavier BB will go, etc. Heavier is needed to punch through leaves and crap, as well as making it less suseptable to wind and air movement. Added bonus is that it hits a lot harder than a lighter BB, and if you shoot a guy with a single BB, you want to make sure he feels it to call himself out (really sucks to get an obvious hit on a guy only to see him react then decide to ignore it and keep playing.) So we need as heavy as we can get to work well with the gun. Lighter BBs out of my M24 aren't that shit hot, .36g seems to be the best, .43g seem too heavy for the level of hop up I can get out of my M24. Same as .36g BBs are too heavy to use in the M700 (not enough hop up to get them past 150ft, even with propane). I recommend .30g BBs for the M700, adjust hop up to suit.

BB brand choice is another issue all together. Believe it or not, the Straight graphite .36g BBs are considered in the airsoft sniper circles to be very inconsistant and basically crap (but the WHITE .36g are considered better). Surface irregularities (as well as the inside of them, yet the .43g BBs are considered to be better due to the denser composition inside) cause them to fly when you don't want them at times. Out of a mag of 10, you might have one or two that go screwy, maybe 3 to 4. Maybe none! No way to tell. Also the issue is within the BB. Most BBs have an airbubble inside from manufacturing. The better brands have this pretty close to center, the cheaper ones don't, which makes them fly like a paintball which the paint has settled on one side. Best for airsoft are the Airsoft Elites, but not so good for sniper rifles due to the light wieght. Best for sniper rifles are the Maruzen Super Grandmaster .29g BBs (obviously, $15USD for a box of 500).

Hope this helps you guys understand the issues to consider when it comes ot sniper rifles. Higher velocity isn't always a good thing, and very hot guns will burn us for limits, yet might not nearly be as consistant or accurate as a lower fps will. I know guys in the states that can get a .29g SGM BB (guns shooting 500-550fps with .2g) out to 300ft and 6-7 times out of 10 hit a reasonably sized tree. But that's only in low wind conditions. If I was able to hit a 12" tree at 230ft away with .36g BBs flying at 315fps.................

Oh, last to write. The higher you make your gun shoot, in the case of bolt actions, the faster it'll wear out, in my case not cutting down my 300% spring will make the bolt pull much harder, high chance of ripping my bolt handle off, and the heavier the trigger pull will be.

EDIT:

Posting new stuff.

Temperature:

Temperature affects real steel bullets, especially at longer ranges, and it'll affect airsoft just as much, if not more. Colder air is more dense than warmer air, so in colder weather the hop up effect will be more exagerated (hop up creates lift, lift is dictated by the density of the air under the BB) and in warmer weather the same setting will have a lesser effect. Make sure to adjust your hop up before every single game, it's not just about setting for different BB weights, it's also to compensate for temperature. Side Note: Denser air also affects your velocity, it'll slow your BB down, which ALSO has an effect on your hop up setting. Keep that in mind! Might be a minor point, like 1ft difference at 200ft, but since Mother Nature decides in the end whether we get the hit or not (remember, being an airsoft sniper isn't "one shot, one kill", it's literally "one shot, one hit" that is the best we can go for. We can't count on the guy either feeling it or being honest enough to call his hit to give it as a kill to us. I count every solid confirmed hit as a kill. If it takes me three hits to make the guy call hit, that's three kills for me. I did my job of getting my rounds on target, so............. :wink:

Wind:

We all know wind is a pain in the ass as far as airsoft goes, especially with our lightweight BBs. Having yoru hop up set for say, 0.25g BBs in still conditions, once you intoduce wind with the same setting you'll find your hop up gets more exagerated. Wind is a higher density of moving air. See above about lift vs. air density. The main difference between wind and temperature, is temp remains pretty constant around any areas you will be playing, but wind will be completely variable, as well as wind having direction. Shoot with the wind, hop up effect won't change very much. Shoot into the wind, you will easily overhop. Add in shooting perpendicular to the wind, same effect as into the wind, but your BB will carry more to one side or the other. Best case for actually playing is to set your hop up a touch under flat & level setting. It's FAR easier to raise your crosshairs a slight bit to get your BB on target, than it is to lower your crosshairs because your gun is overhopping and try to hit your target.

Elevation:

An odd one that most of us tend not to experience, but is worth mentioning. Shooting downhill at an angle your BBs will overhop by roughly a foot or so due to gravity not being perfectly perpendicular to your shot. Opposite effect for shooting uphill. Keep that in mind if you are ever looking down at someone from a hill and planning to send them to re-spawn.

Difference being in all the above, an aimed chest shot could very well nail your target in the mouth or face. Happened to me once when I tried using 0.25g BBs in my M24, aimed at Shaddy's chest about 80ft away (my M24 was shooting about 380fps at that point in time) and the wind was at his back, he was walking towards me. I shot, something on the ground made him look down, my BB went severely upward about 6ft away from him, slammed into his lower lip. It bled and swelled pretty bad. He was cool about it then and even now, but I learned a lesson about shooting into the wind. ops:

[tony123]

Very good work Stalker! As i'm just starting sniping too I found allot of this usfull. I'm still trying to get my g-spec work good stock but i'm finding out that ain't to easy

[CDN_Stalker]

Originally Posted by tony123

Very good work Stalker! As i'm just starting sniping too I found allot of this usfull. I'm still trying to get my g-spec work good stock but i'm finding out that ain't to easy

Thanks. Read it quite a few times, it should help (it's NOT easy, it's actually fucking hard to get "One shot, one kill" in airsoft, literally it's as easy as getting a "hole in one in golf' past 200ft with a 6mm golf ball) but a lot of the other stuff I have to figure out how to add (the aerodynamics parts and drawings........... I'm a computer dummy, will probably hand draw and take a pic to post) will really add to this. I've never seen this sort of thing posted except for little tidbits on why heavier BBs are always better for range and accuracy, but this should bring it all to the front for everyone.

BTW, I posted it in the Upgrades section because it applies to the players as much as it does to the guns. Lt. Poncho has always made a point of saying "Upgrade the player, not the gun!" Well, here is my addition to upgrading the player! Lol

[Firas]

Very informative post. Thanks

[Donster]

where do you find your high weight BB's that are not graphite coated and not aluminum coated?

[WarChild7]

A guy named Nathan Allen has done a fantastic study on airsoft BB physics called the "Airsoft Trajectory Project." His calculations, tables and formulas are very thorough, and cover the following principles:

-BB characteristics, volume, density and terminal velocity
-air density
-kinetic energy
-drag force
-magnus force
-spin decay
-drag coefficient
-lift coefficent
-gravity
-effects of hop-up
-effective and maximum range determinations with all weights of BB's, 6mm and 8mm
-effect of wind on trajectory
-headwind/tailwind component
-crosswind component
-effect of altitude on trajectory
-effect of temperature on trajectory
-determining muzzle energy
-safe impact energy
-recommended minimum engagement distances
-velocity comparisons of BB's using equal masses
-mass comparisons of projectiles fired at equal energies

i have never found any better info ever on the physics of airsoft. i encourage you to check out his information.

his study can be found here: http://cybersloth.org/airsoft/trajectory/index.htm

[CDN_Stalker]

Thanks very much Warchild, I'll print it off and scan over it over the next couple days. I recall something along the lines of this being posted before somewhere, I was less than impressed, but your link I've delve into (checked out a few items in there, is the same as I found before. While it outlines a lot of scientific stuff that 90% of people don't give a crap about, my approach is literally the dummy version with airflow drawings (when I get them done), hence my saying "Screw the math, let's get into simple stuff. Is one thing I've always been pissed about at school, I want to learn how things work and interact with each other, but math was always the thing that fucked that concept badly. Who cares how much kinetic energy an electron hits the plate of a certain value capacitor............ yes, was a question asked by my college physics teacher, and a 100% reply by the students!!!) Airsoft ballistics should be simple and very easy to understand, not a bunch of scientific crap only 5% of the airsoft population can understand. I want everyone to learn, is why I posted this up, knowing there was lots of mathematical models out there that mean nothing. I want to talk basic. "Airsoft abllistics and aerodynamics for dummies, leave your calulator at home" kinda thing.

BTW, glad you got things sorted out over the weekend, Friday night was somewhat "stressed" as far as fun went.

[CDN_Stalker]

Originally Posted by DONSTER 125

where do you find your high weight BB's that are not graphite coated and not aluminum coated?

None are aluminum coated, except solid aluminum BBs (they are listed as 0.29g BBs).

The other ones you mentioned are graphite coated, but only Straight makes anything over 0.30g (have heard of 0.33g but haven't found). As far as getting non-graphite coated, it's really up to the retailer in what they give you. But you can (and are best to) wash the coating off. Leaving it on is almost the same as soaking every BB you shoot in oil. It reduces the friction on the hop up rubber, reducing the hop up effect, causing you to dial in more hop up, larger intrusion into the inner barrel, making the BB more unstable and also reducing the velocity of it.

[rambopfc]

Awesome post Stalker, as with all your info posts i will read it as if it were gospel great comparisons from the things you talk about, to the experience with your own gun, it really helps to put things in perspective.
keep the great info coming!

Joe

[HaZarD SFD]

I will concur with all of this. It is good to dial down hopup in windy/cold days
as if you have it set perfectly in non windy situations that in a windy situation it will overhop like its on acid.

[CDN_Stalker]

Originally Posted by HaZarD SFD

I will concur with all of this. It is good to dial down hopup in windy/cold days
as if you have it set perfectly in non windy situations that in a windy situation it will overhop like its on acid.

Yes, that was one of my observations and have been telling the boys about it recently. I'll get into more details at a later date, but as pointed out the lift created by a BB's backspin is sensitive to the air density/pressure. We all know that even little gusts are a bit higher pressure/desity of air molecules, so once your BBs get out past the point yourengery wears off and the BB is really in just 'loft mode', it'll lift and possibly veer off course. So set your hop up as best yo can then tweak it down a slight bit. You'll lose a bit of range, but it's a lot easier to raise your muzzle a bit to get that extra range, but if your BB hits any little gusts or denser air pockets, it'll hop a bit more making it fly straighter. And of course, it's MUCH easier to deal with a BB that consistantly drops at X distance than it is to try to lower the muzzle to deal with overhopping.

[Donster]

now i found Straight BB's in the .43, and they say matte silver on them. Does this mean that it is just their color, or should i expect them to be graphite coated?

On WGC Shop, the product #: STG-BB-043

BTW, this was a great and informative post, but i am still confused as to why some BB's despite their weight are better then others? First you said the heavier the better, but later on you said that sometimes certain weights (even if they are lighter) are a better choice then the heavier bbs. that being said, should i go with the .43 as you seggest, or something lighter like .36s or .3s for my eventual TM M14?

[CDN_Stalker]

I've seen Straight 0.43g BBs come in both the dark graphite coating (which rubs off easy, your hands will turn grey from handling them) to the ones I currently have that have a lighter colour coating that doesn't rub off. The construction of the 0.43g is a dark graphite grey plastic compound BTW. Straights are only good because of their weight, but there was a guy in the US that measured various BB types and found the Straights to have the worst consistancy out of them all.

Regarding your M14, don't bother going higher than 0.30g BBs. Last year I upgraded an already upgraded G&P SPR to close to 500fps, and found that it wasn't very good at flinging non-graphite (aka. white) 0.36g BBs. We were limited to a range of about 100ft, but I didn't like the performance.

I might have mis-spoke or you might have mis-understood, but heavier isn't better when you get over 0.30g weights. 0.25g are much better to use over 0.20g, and about the same performance gap, 0.28g are better to use than 0.25g. But you get to a certain point that heavier isn't better. Sure, if one has a 550fps or 600fps gun, then 0.43g BBs will be best to use, but for all practical purposes in average/upgraded AEGs or even upgraded bolt actions, it's best to stay around 0.36g. I have and use all weights of BBs in my CA M24 (it currently shoots around 470fps with 0.20g), but the best for my preference is 0.30g. I'd have to reset my rifle to use 0.36g BBs, but due to my preference for 0.30g and the amount of time to do so, it's not practical for me.

[Donster]

oh ok, thanks a lot! thats very helpful and a relief in may regards cause i dont have to set my sights on getting straight BB's, but rather the KSC perfect which i have heard are very consistent in shape. Its too bad the Straights are so inconsistent. Thanks for the help stalker!

[CDN_Stalker]

That's my intent Donster, to help people understand things better.