BB weights...

[gavinkempsell]

Can someone in the 'know' explain to me the benefits & adaptions required to a rif depending on bb weight please?

 

I can understand a heavier bb flying straighter & possibly further especially on windy days or even cutting through a bit of shrubbery but when I tried .3's on one game day it put my fps over the site limit but .2's were fine.

 

I've read several forum members talking about adjusting their hop for different bb weights, is this common as I thought the hop was to add or reduce spin to improve flight.

 

Thanks in advance.

[MrTea]

Apparently I read the thread wrong. Ignore my stupidity. I would have expected a heavier BB to decrease FPS, not increase it. I can't say i've ever seen this personally.

Edited August 11, 2023 by MrTea

[Duff Beer]

Heavier BB’s can increase the dwell time of the BB in the barrel and make the RIF more efficient and capable of developing more power.

 

For example, if I gave you a ping-pong ball and asked you to throw it as far as you can, and then gave you a tennis ball and asked you to do the same the tennis ball would go further even though your strength hasn’t changed.

 

This is why good sites chrono based on joules of the ammo you’re using, not 0.2’s for FPS.

Edited August 11, 2023 by Duff Beer
Clarity

[gavinkempsell]

6 minutes ago, Duff Beer said:

Heavier BB’s can increase the dwell time of the BB in the barrel and make the RIF more efficient and capable of developing more power.

 

For example, if I gave you a ping-pong ball and asked you to throw it as far as you can, and then gave you a tennis ball and asked you to do the same the tennis ball would go further even though your strength hasn’t changed.

 

This is why good sites chrono based on joules of the ammo you’re using, not 0.2’s for FPS.

That makes sense, however you haven't seen my girly throw.

[Krisz]

10 hours ago, gavinkempsell said:

Can someone in the 'know' explain to me the benefits & adaptions required to a rif depending on bb weight please?

 

I can understand a heavier bb flying straighter & possibly further especially on windy days or even cutting through a bit of shrubbery but when I tried .3's on one game day it put my fps over the site limit but .2's were fine.

 

I've read several forum members talking about adjusting their hop for different bb weights, is this common as I thought the hop was to add or reduce spin to improve flight.

 

Thanks in advance.

Joule creep. It's more prevalent when you've got a longer inner barrel.

 

That's correct hop's sole purpose to get the most out of your BB regarding distance and to have a "straight" fly path.

 

I think you can decrease your FPS with no hop but no sane marshall is gonna accept that chrono reading. 

Edited August 12, 2023 by Krisz

[Madhouse]

11 hours ago, gavinkempsell said:

I've read several forum members talking about adjusting their hop for different bb weights, is this common as I thought the hop was to add or reduce spin to improve flight.

This is correct, a heavier BB may need a bit more hop to counteract gravity and keep in flight for longer. It’s not to bring their pew within chrono limits.

 

Sounds like you experienced Joule creep, there’s tons of info on that here.

[Impulse]

Going to be a bit of a wall (such a glorious wall that I'm scared the FBI is going to raid my house and throw me in jail), so I will add a TL:DR at the end with some key points for those who don't want/need to understand the physics and mathematics behind our hobby.

 

Ok, so I've done a LOT of research into BB weight and ballistics due to my interest in long distance shooting in airsoft. Also, please bear in mind that this is, at the end of the day, a layman's explanation of this. I'm operating on A-level mathematics and GCSE physics here, and I haven't done them in about a decade. It's also really hard to explain this without a whiteboard or sheet of paper to draw diagrams and stuff, so bear with me I'll do my best to keep it accessible!

 

So, the maths behind our hobby! Kinetic energy is calculated by 1/2 x mass x (velocity x velocity), using brackets as order of operations means we do the squaring before the multiplication but it's easier to show this way exactly what I'm doing. However we can't just translate that to airsoft measurements of fractions of a gram and feet per second, as joules are calculated using mass in kg so really really small numbers in our context and velocity in metres per second, not feet per second. So a 0.2g BB shot at 328fps, which is 100m/s would calculate as:
 

Energy = 1/2 x 0.0002 x (100 x 100)

Energy =  0.0001 x 10000

Energy = 1J

 

Only reason I used 328fps instead of 350fps is to avoid plaguing you with weird numbers and make the example easier to follow. Really, feet per second is annoying and we should be using metres per second since it's easier to work with in terms of energy calculations. It's why springs are m100, m120 etc, as they're designed in m/s rather than ft/s. What we can take away from this is that mass and velocity work in tandem to calculate joules (I know, I'm big smart for drawing such a conclusion). However we need to briefly consider momentum to understand ballistics; my physics teacher always described momentum as "how much something will hurt when it hits you" and is a lot simpler than kinetic energy. Momentum = mass x velocity. Easy. I'm not going to bore you with the calculations I'm doing for this example now, but I'm looking at 1.14J on a .2 and on a .48 as a comparison. That's 350fps on a .2 and 226.1fps (1 decimal place) on a .48. We can already see that momentum is going to be very different, but for argument's sake...

 

momentum = 350 x .2 = 70 gram feet per second

momentum = 226.1 x .48 = 108.5 gram feet per second (1 decimal place)

 

So a heavy BB fired with the same kinetic energy as a lighter BB has more momentum (just over 50% more!). This is why when someone point blanks you with a .48 from a 1J pistol and says "stop crying, it's only 1J" is talking bollocks. Do I think we should be operating on momentum-based rules for airsoft? Hell no, that would be cancerous, but it's a consideration that I feel comes under the golden rule of "don't be a dick". However, this also goes a LONG way to explaining why heavy BBs tend to go further than lighter BBs; they simply have more momentum pushing forwards due to how physics works (the old example was if I throw a balloon vs if I throw a cricket ball with the same kinetic energy, which goes further). However, there's one last thing to consider when it comes to range and that's deceleration, as the BB is being affected by a number of things trying to slow it down and drop it to the ground, namely air resistance and gravity respectively. Hop up creates a backspin to give the BB an upwards lift to combat gravity, but combating air resistance isn't happening. I won't go into the mathematics on this as deceleration past GCSE level is really maths intensive (I would probably have to break out calculus and trigonometric functions to explain my point), but essentially an object moving at a higher velocity has more air resistance acting on it, so that BB travelling faster actually has more pushback from Mother Nature than a slower BB. Furthermore, that air resistance is going to have more effect on a lighter weight projectile as lower mass makes it easier to push back, so a combination of higher air resistance and more impactful air resistance means that a lightweight BB fired at the same energy is going to slow down and lose that energy a hell of a lot faster than a heavy projectile.

 

Anyway, I hope you're all still awake after that (I find it fascinating, but I know not everyone does), but now I'll move into airsoft specific phenomena like joule creep and cylinder to barrel ratio.

 

With AEGs, it's rare that power goes up with weight but it is possible. I couldn't explain to you in detail how the maths works out, but essentially there's a sweet spot for ammo weight with most guns and it varies dependant on inner barrel length and cylinder size. What tends to happen is that shorter barreled AEGs are more efficient with heavier ammo, but longer barreled AEGs tend to drop in power with heavier BBs due to voluming issues; the cylinder doesn't have enough air to fill the barrel so the BB starts to decelerate while it's still in the barrel, meaning that a heavier BB that comes out slower originally will start to have forces working against it (friction with the barrel and air resistance) sooner by fractions of a second, but it all affects it. It all depends on if there's enough air in the cylinder to fill the barrel. Look up cylinder to barrel ratio for a better explanation than I can give; I don't use AEGs much and they're the only guns I don't tech myself because I'm useless with gearboxes. Also, as has been said, heavier ammo typically needs more hop pressure to be applied which can also drop your power (as at the end of the day you're adding some resistance to the BB's flight path.

 

Assuming you have enough air volume in an AEG, or if you're using another platform like a GBB, then heavy ammo will typically cause your power to go up due to joule creep as long as you're not having to apply incredible amounts of hop to lift them. The BB will accelerate while it's in the barrel as long as there's something to push it, which for a gas gun is the gas expanding when it leaves the magazine, so a longer barreled gas rifle will have a higher power than a shorter barreled gas rifle as it has more space to accelerate before leaving the barrel; it's the same as real-steel firearms, a long barreled AR-15 will shoot better at longer range than a short barreled AR-15 assuming the same ammo due to acceleration in the barrel.

 

So why am I saying any of this? Well, it's the considerations part of your question. With AEGs you need to consider cylinder to barrel ratio and with gas guns you need to consider barrel length. In both you need to consider the hop setup and how much you need to apply to lift the BB and the barrel diameter also impacts power; wider = less power, tightbore = more, as there's less space for air to escape past the BB in a tightbore so it has to push the BB out to escape the inner barrel, which at the end of the day is what the gun is trying to do with all that air and is why air seal is so important for consistency, as the air will seek to escape from wherever it can.

 

Now in terms of the benefits, a heavier BB will tend to have a more stable trajectory, has a bit more punch to get through foliage and will retain its kinetic energy for longer, though we're talking about fractions here. Will a .32 be all that different to a .28? Not really, but will a .48 perform differently to a .2? It most certainly will but I think often times people over-estimate the difference in BB performance. Wind will still carry a .48 off to Narnia and a leaf will still deflect a .48; trust me, speaking from experience there as a bolt action enjoyer who has watched many shots through my scope go their own way because of wind or leaves in the way. Really, punching through foliage requires volume of fire as opposed to weight of BB and I think "go heavy to punch through foliage" is a false economy. Even my .48s fired at 2.3J have issues punching through foliage and I usually try to post the shots through empty spaces in the bushes rather than going through any leaves; precision over power.

 

Anyway, I feel like I've gone on enough about this. Thank you for coming to my TED talk on BB weight and the physics behind our hobby. In short:

• Heavier BBs fired at the same kinetic energy as lighter BBs have more momentum, which is why it hurts more getting shot by heavy BBs, even at 1J
• Faster projectiles have more air resistance acting on them
• Lighter projectiles are more affected by air resistance
• Therefore lighter BBs travelling faster both have more air resistance acting on them and are more affected by said air resistance
• This means that heavy BBs will travel further as they have more momentum, less air resistance acting on them and are less affected by that air resistance (assuming your hop can lift them)
• Joule creep will cause power to go up in gas guns with longer barrels as the BB has more room to accelerate
• Cylinder to barrel ratio affects power (and consistency) in AEGs. Heavier BBs can up the power in short barreled AEGs, but tend to drop the power in long barreled ones
• If you want the absolute maximum performance of your gun you generally want to be as close to the power limit as possible with the heaviest BB that your hop will lift
• I will still call you a dick if you run .48s in a pistol, especially if you're shooting up close 

[gavinkempsell]

Holy shit Impulse, great reply.

 

I can't help think a more fitting 'thank you' is required but I have crap communication skills so...

 

Cool.

 

[Esoterick]

12 hours ago, Krisz said:

I think you can decrease your FPS with no hop but no sane marshall is gonna accept that chrono reading. 

 

Reducing the amount of hop applied will increase FPS, not lower it. 

 

First time I chronoed an upgraded VSR it was firing at around 510 FPS on 0.2g. Realised the hop was on the lowest setting so dialled it in and it went down to around 490 fps.

 

It would make most guns unusable past around 20-30 metres anyway.

[Adolf Hamster]

35 minutes ago, Esoterick said:

Reducing the amount of hop applied will increase FPS, not lower it. 

 

Not in all cases, some setups can have a dramatic drop in power when the hop is almost/completely off, so dramatic the bb can struggle to even make it down the barrel.

 

I've never quite figured exactly how that works but i've seen it often enough that i got into the habit of setting hops at least mid-way when bench testing.

 

Hence why it bugs me when sites do the whole "chrono with the hop off" thing because its basically asking for false readings.

[Rogerborg]

1 hour ago, Esoterick said:

VSR [...] 0.2g

 

My TAC-41 has never had a BB under 0.43g run through it. Not once.  I couldn't even tell you what "fps" it's slinging them at, only that it yeets properly hopped 0.43g-0.46g at 2.2 - 2.3J.  It's CURRENT_YEAR, after all, not the Before Time, in the Long-Long Ago.

[Dan Robinson]

12 hours ago, Adolf Hamster said:

I've never quite figured exactly how that works but i've seen it often enough that i got into the habit of setting hops at least mid-way when bench testing

Is it because the magnus effect helps stabilise the bb's flight in the barrel.  Without it, the bb literally rattles it's way down losing all it's energy? 

[RostokMcSpoons]

24 minutes ago, Dan Robinson said:

Is it because the magnus effect helps stabilise the bb's flight in the barrel.  Without it, the bb literally rattles it's way down losing all it's energy? 

 

I remember an explanation of barrel bores from YouTube that said the BB rattles down a standard bore, floats down a wide bore, and runs along the top of a tight bore barrel.

I have no idea if that's actually true but as in two cases the BB is supposedly contacting the walls of the barrel, I think it means energy loss would be negligible.

 

My thought is that the hop holds the BB in place long enough for back-pressure to build up before the BB starts traveling.  But that's just an intuitive guess, with no evidence either way.

 

It would be great to know for sure ?

Edited August 13, 2023 by RostokMcSpoons

[Adolf Hamster]

37 minutes ago, Dan Robinson said:

Is it because the magnus effect helps stabilise the bb's flight in the barrel.  Without it, the bb literally rattles it's way down losing all it's energy? 

 

I did suspect basically this:

23 minutes ago, RostokMcSpoons said:

My thought is that the hop holds the BB in place long enough for back-pressure to build up before the BB starts traveling.  But that's just an intuitive guess, with no evidence either way.

 

Although i've never really dug into it enough to find out conclusively.

 

16 minutes ago, RostokMcSpoons said:

remember an explanation of barrel bores from YouTube that said the BB rattles down a standard bore, floats down a wide bore, and runs along the top of a tight bore barrel.

 

The issue i have with that as an explanation is that whilst the bb is in the barrel, the airflow past it will be inverted so the magnus effect would be pulling it down against the bottom of the bore, and that additional airflow around the bb would magnify this effect, ie that it would rattle in a tightbore and run along the bottom of a widebore.

 

I did for a while contemplate the idea of an intentionally curved barrel, putting a slight radius along its length to force the bb to roll along the top surface which would help add a little more spin (although likely still need a hop for adjustability) but more importantly mean that the bb would consistently be riding along one surface.

 

Ultimately though in practical terms the trick is getting a pew consistent enough to even be able to notice these sorts of minutia, and that generally the main boost from a better quality barrel is not in its nominal diameter but in how consistent that diameter is along its length, how straight it is and how good the internal surface finish is.

[Rogerborg]

29 minutes ago, RostokMcSpoons said:

the BB rattles down a standard bore, floats down a wide bore, and runs along the top of a tight bore barrel

 

To my simple mind, a BB that so much as touches the barrel once it's been through the hop would emerge with no, or random, backspin.  I'd wonder on what evidentiary basis these claims are being made.

 

What I have observed is that adding some hop can increase muzzle energy, so I fully agree with half-hop while bench testing, or ideally with the hop dialled in for the BB weight.

[RostokMcSpoons]

34 minutes ago, Rogerborg said:

To my simple mind, a BB that so much as touches the barrel once it's been through the hop would emerge with no, or random, backspin.  I'd wonder on what evidentiary basis these claims are being made.

 

Given that a hop rubber with a bit of silicon lube on it loses its ability to impart backspin, I'd say the effect of a BB touching the sides of a clean polished barrel will be fairly negligible.  But as you say it's really all guesswork with no evidence. 

 

The makers of wide bore barrels claim great things, but I've watched a video where testing showed they tended to be less accurate. 

Too many variables in play, and not enough science, so far.

 

(I daydreamed of a glass barrel so someone could actually film the BB traveling along, but I suspect in reality even that would effectively be impossible due to the realities of manufacturing difficulties and  costs, refraction affecting observation etc)

[Tommikka]

1 hour ago, RostokMcSpoons said:

 

I remember an explanation of barrel bores from YouTube that said the BB rattles down a standard bore, floats down a wide bore, and runs along the top of a tight bore barrel.

I have no idea if that's actually true but as in two cases the BB is supposedly contacting the walls of the barrel, I think it means energy loss would be negligible.

 

 

 

1 hour ago, Adolf Hamster said:

 

 

The issue i have with that as an explanation is that whilst the bb is in the barrel, the airflow past it will be inverted so the magnus effect would be pulling it down against the bottom of the bore, and that additional airflow around the bb would magnify this effect, ie that it would rattle in a tightbore and run along the bottom of a widebore.

 

I did for a while contemplate the idea of an intentionally curved barrel, putting a slight radius along its length to force the bb to roll along the top surface which would help add a little more spin (although likely still need a hop for adjustability) but more importantly mean that the bb would consistently be riding along one surface.

 

Ultimately though in practical terms the trick is getting a pew consistent enough to even be able to notice these sorts of minutia, and that generally the main boost from a better quality barrel is not in its nominal diameter but in how consistent that diameter is along its length, how straight it is and how good the internal surface finish is.

My science knowledge is misty as it goes back many decades - and also my barrel / projectile experience is with paintballs, which have the added effect of distortion under pressure whilst inside the barrel

 

All the theories mentioned ring true with my recollection & experience, particularly the bent barrel which seems very wrong at first but effective when right (this was the Tippmann flatline) it does exactly as per the theory - drag in the curve causes backspin

 

 

Next we had the Apex tip which is pretty much the same thing as an airsoft hop

 

 

An adjustable rubber element gives backspin, but the tip can also be rotated to change the angle of the backspin

 

(spoiler in the following video but he rated it as ‘it sucks’ - it does give backspin and additional range, but can impact on consistency - I have a team mate who puts in all the practice, he was an apex ninja and as a result could place a ball where he wanted it to go - though this was courtesy of numerous factors with the Apex as just one of them to adjust the spin)

https://youtu.be/Vfgi_AwdTR8

 

Flatlines and Apexes have had their day, some will still use them, but most will go for bore matching a barrel / insert with the ball - and everyone has a different preference that they swear by of bore match, overbore or under bore 

 

Still to add are the consistency of the gun itself to reliably send the ball out of the chamber, and the length of the barrel which must be long enough to allow the ball to accelerate but not so long that any drag/bounce along the barrel is so much that it  loses the energy that was gained in acceleration

Consistency and practice are key - consistency gives you a reliable benchmark and practice let’s you first understand the combined effects  and fine tune each in turn

 

[Adolf Hamster]

I did think paintball might be more suited to the curved barrel thing, intuitively it would seem less strenuous on the round and i'd have assumed an airsoft style hop might results in bursting rounds if its set too tight.

 

Plus curved barrel would only suit one particular weight/energy combination which wouldn't be popular in airsoft given people want to make dmr's out of basically everything, change hop weights on a whim etc.

[Leo Greer]

Curved barrels, or LRBs (Long Range Barrels) were a thing before hop up existed. Enthusiastic players would bend the last third of the barrel a few degrees in order to impart some kind of backspin.

 

People have been debating where the BB flies in the barrel for years at this point. Over on the American forums, we actually have members working on a glass barrel project.

 

On examination of the fluid dynamics, it seems that no proper quality airsoft BBs contact the top of the barrel or rattle around, but instead float through the barrel, closer to the top but not touching. Bore size is practically irrelevant. The people who say the BB rattles around in some bores and skids or floats in others are completely ignorant of how little the difference actually is between these barrel bores we care so much about.

 

I will also cite that BBs rattling or skidding down a barrel produces a very distinct, noticeable sound that is lacking when you shoot your airsoft gun, even upside down.

 

Naturally, air will push and flow around the BB due to its spherical shape. The proponents of the skid theory, where the BB rides along the top, propose that the Magnus effect forces the BB to “hop” off the hop patch and cling to the top of the barrel.

 

However, this does not make any sense, as the Magnus effect does not become stronger than the forward velocity of the BB until long after it has left the barrel (overhop), even using extremely short barrels, which should theoretically prove this.

 

I am not a physicist either, but having spent time both talking to people smarter than I, and researching fluid dynamics, I believe the most logical explanation is that the BB does ride closer to the top of the barrel, because of a negative pressure cushion created by the backspin (Magnus effect), but does not touch, because of air naturally flowing between the BB and the barrel and causing an opposing cushion.

 

For some excellent practical evidence, Google Tanio Koba Twist barrels. They were airsoft barrels with rifling, tuned for 1J, that spin the air around the BB. Because they have cut grooves along the top, yet shoot normally, they prove that the BB does not ride along the top or rattle around,