Engagement Distance for Snipers

[Sewdhull]

Yeah time to target will be less with a heavier BB. Clearly at first, 15 to 20m if I recall correctly, the lighter BB will arrive first but the amount of time you are looking at is neglible. Only once the distance increases does time difference become a factor and then in favour of the heavier BB.

Range is dictated by the hops ability to spin the BB and this uses energy so if you keep the same spring etc and try to spin a heavier BB you will lose some FPS but not necessarily any range, but you might.

 

[Lozart]

Yeah time to target will be less with a heavier BB. Clearly at first, 15 to 20m if I recall correctly, the lighter BB will arrive first but the amount of time you are looking at is neglible. Only once the distance increases does time difference become a factor and then in favour of the heavier BB.

Range is dictated by the hops ability to spin the BB and this uses energy so if you keep the same spring etc and try to spin a heavier BB you will lose some FPS but not necessarily any range, but you might.

I'm not sure I get this - a heavier BB leaves the barrel at a lower velocity, the energy on impact would be higher because they carry more momentum but I don't see how an object travelling more slowly will get there quicker.

 

[Badgerlicious]

I'm not sure I get this - a heavier BB leaves the barrel at a lower velocity, the energy on impact would be higher because they carry more momentum but I don't see how an object travelling more slowly will get there quicker.

Because lighter BBs slow down significantly faster than heavier ones. It's enough that at about 30m they will impact at about the same time. Past 30m heavier BBs will start to land before lighter ones. I'll link the airsoft trajectory project. Someone using actual maths and simulations to map the ballistics of BBs. In the fifth chart, time of flight vs distance, you see an almost constant ~30% increase in travel time for a 0.2g bb over a 0.3g bb at the end of the range. 

https://mackila.com/airsoft/atp/07-b-07.htm

full list of links https://mackila.com/airsoft/atp/

 

[Sewdhull]

I'm not sure I get this - a heavier BB leaves the barrel at a lower velocity, the energy on impact would be higher because they carry more momentum but I don't see how an object travelling more slowly will get there quicker.

The reason is that the average speed of the bb is higher if it is heavier. With greater mass the bb slows down more slowly and the force due to drag is less because of the reduced speed from the outset.

So you have less deceleration all the time for the same speed (.2 vs .4 is half of the deceleration due to drag of the .2) and more drag for the same energy for the .2, because its going faster and drag is exponentially  increased with speed.

The result is that the .2 has a high force slowing a light bb which reduces it's speed much more than the lower force on a heavier bb. The heavy one overtakes the light one in effect and arrives sooner than the light one.

The graph above from the Airsoft trajectory project  shows the time and mass relationship.

 

[Lozart]

Because lighter BBs slow down significantly faster than heavier ones. It's enough that at about 30m they will impact at about the same time. Past 30m heavier BBs will start to land before lighter ones. I'll link the airsoft trajectory project. Someone using actual maths and simulations to map the ballistics of BBs. In the fifth chart, time of flight vs distance, you see an almost constant ~30% increase in travel time for a 0.2g bb over a 0.3g bb at the end of the range. 

https://mackila.com/airsoft/atp/07-b-07.htm

full list of links https://mackila.com/airsoft/atp/

The reason is that the average speed of the bb is higher if it is heavier. With greater mass the bb slows down more slowly and the force due to drag is less because of the reduced speed from the outset.

So you have less deceleration all the time for the same speed (.2 vs .4 is half of the deceleration due to drag of the .2) and more drag for the same energy for the .2, because its going faster and drag is exponentially  increased with speed.

The result is that the .2 has a high force slowing a light bb which reduces it's speed much more than the lower force on a heavier bb. The heavy one overtakes the light one in effect and arrives sooner than the light one.

The graph above from the Airsoft trajectory project  shows the time and mass relationship.

Ta! Every day is a school day!

 

[Tactical Pith Helmet]

I actually have on my CV:

'C in GCSE Physics

Understanding of BB weight upon exterior ballistic performance of 6mm plastic BB, as presented in posts on AFUK.'

I reckon that's worth a couple of grand extra a year surely?!

 

[Sewdhull]

LOL, it's not weight, it's mass. Then yes, 2k extra for you. Altho the hop works to counter the weight of the BB so i guess either would work...