Engagement Distance for Snipers

[Rogerborg]

Great to hear that it went well.  Are you minded to push the power up towards 2.3J?  Once you start doing that, you may find yourself chasing the White Rabbit of robustness and performance mods, which can get expensive, fast.

 

The other option is to cut a coil off the spring[*] and drop it below 1.14J, so your son can use it without a MED.  This is a viable play-style if you enjoy it.

 

[*] With it being that close, I reckon I'd just heat and flatten a coil instead, then chrono it.

[Reef]

5 hours ago, Rogerborg said:

 Are you minded to push the power up towards 2.3J?

Not at the moment, my son said he had a great time so that’s all that matters for now. The distance rule didn’t worry him yesterday but let’s see what happens after a few games. I’d be interested to see the difference in performance v BB weights first before changing springs, etc. No rush….
I spent a few years modding Subaru’s so understand the cost in chasing a performance figure 😂.

 

Thanks for the input.

 

 

[mrfoxhound]

17 hours ago, Reef said:

Not at the moment, my son said he had a great time so that’s all that matters for now. The distance rule didn’t worry him yesterday but let’s see what happens after a few games. I’d be interested to see the difference in performance v BB weights first before changing springs, etc. No rush….
I spent a few years modding Subaru’s so understand the cost in chasing a performance figure 😂.

 

Thanks for the input.

 

 

the heaver you go up , on a stock vsr you will start to lose range  and gain travel time , .28 is probably the sweet spot .30 might be the maximum you could probably use before you start to see longer travel times and less magnus effect  

[Rogerborg]

13 minutes ago, mrfoxhound said:

the heaver you go up , on a stock vsr you will start to lose range  and gain travel time

 

Why would that be?  Starting with the same energy at the muzzle, and assuming that the hop can impart enough spin[*], a heavier BBs will always retain more energy than a lighter one and go further.

 

It'll take longer to reach a closer target, but that's hardly an issue for a sniper with a 30m MED - which is about the point where it will overtake a lighter BB.

 

[*] If your gun can't fully hop it that's a different issue, but it's an issue with the hop unit or bucking and nub, not the BB.

[mrfoxhound]

On 08/04/2024 at 11:45, Rogerborg said:

 

Why would that be?  Starting with the same energy at the muzzle, and assuming that the hop can impart enough spin[*], a heavier BBs will always retain more energy than a lighter one and go further.

 

It'll take longer to reach a closer target, but that's hardly an issue for a sniper with a 30m MED - which is about the point where it will overtake a lighter BB.

 

[*] If your gun can't fully hop it that's a different issue, but it's an issue with the hop unit or bucking and nub, not the BB.

try it, use heavy bbs and watch them drop faster , i think they run out of magnus effect faster  is why it happens , tho i have only seen it sporadically  with .30s with certain shooters .i see it consistently  with .40 and up 

[StoveCap]

13 hours ago, mrfoxhound said:

try it, use heavy bbs and watch them drop faster , i think they run out of magnus effect faster  is why it happens , tho i have only seen it sporadically  with .30s with certain shooters .i see it consistently  with .40 and up 

I'm certain that has nothing to do with the BB weight, sounds more like hop problems.

Sure, on lower power builds the performance increase of using heavier BBs is less noticeable than on higher power builds. Because the Heavy BBs have less initial velocity to conserve better than their lighter counterpart.

But no matter what, if you have a hop that imparts the same relative spin on both the light and the heavy BB, the heavy BB goes farther. It wont run out of magnus effect sooner. It is heavier, heavy things conserve energy better, and as such will spin longer, prolonging the magnus effect, and conserving the muzzle energy for longer making them faster than lighter BBs at any range farther than ~10-20 metres.

[mrfoxhound]

12 hours ago, StoveCap said:

I'm certain that has nothing to do with the BB weight, sounds more like hop problems.

Sure, on lower power builds the performance increase of using heavier BBs is less noticeable than on higher power builds. Because the Heavy BBs have less initial velocity to conserve better than their lighter counterpart.

But no matter what, if you have a hop that imparts the same relative spin on both the light and the heavy BB, the heavy BB goes farther. It wont run out of magnus effect sooner. It is heavier, heavy things conserve energy better, and as such will spin longer, prolonging the magnus effect, and conserving the muzzle energy for longer making them faster than lighter BBs at any range farther than ~10-20 metres.

he is talking about stock vsr 

[Rogerborg]

2 hours ago, mrfoxhound said:

he is talking about stock vsr 

 

There is an argument to be made that if you're not going to do anything to a stock boltie then you might be unable to fully hop a heavier BB, or you have to apply so much hop pressure that you drop the muzzle energy to the point where a lighter BB would end up going further.

 

Which is why I was careful to say "starting with the same energy at the muzzle, and assuming that the hop can impart enough spin".

 

The thing is, a stock Tokyo Marui VSR is likely to be shooting at something comically low like 0.72J (280fps with a 0.2g). I'm not sure if OP is rocking a VSR10 clone, or if it's pre-meddled, or if it Joule crept upwards rapidly with heavier BBs.  Either way, there's only really two sensible ways to go with it: tune it down to under 1.4J, or up to 2.3J shooting the heaviest BBs that it will hop at that muzzle energy.

[Reef]

Thanks for the reply's guys. I didn't realise this thread was still going

 

It is a brand new stock TM VSR we have. My son (12) is happy with the range using .28's at the moment, I'm sure we will be upgrading the internals at some point though. My worry with heavier springs is his ability to cock the gun. 

 

When/if I get to have a go with the gun in the field I will get a better idea of what needs to be done.

 

Thanks again for all the info, its a learning curve for me.

[Rogerborg]

Huh, then that's surprisingly high power for a stock VSR-10.  I'm guessing that it Joule-crept up to there on the 0.28g and might have come out under 1.14J on 0.25g.

 

If your son is enjoying using it, I'd be minded to leave it as stock, other than dropping the power very slightly so that it's just under 1.14J with the heaviest BBs that it can lift (I'd hope 0.32g wouldn't be an issue).  You'll keep the light pull, not stress the components, and lose the MED.  Just dropping in 0.25g might bring it under the MED limit.

[Reef]

Thanks Rogerborg, I’m sure the Marshal said 1.17 but will check next time we crono.

 

I need to understand this ‘joule creep’ and ‘hop up’ terminology. Still don’t really get it. 😂

[mrfoxhound]

4 hours ago, Reef said:

Thanks Rogerborg, I’m sure the Marshal said 1.17 but will check next time we crono.

 

I need to understand this ‘joule creep’ and ‘hop up’ terminology. Still don’t really get it. 😂

 

[Sewdhull]

A heavier BB will go further and quicker than a lighter one if it has the same forwards energy.

The issue comes when you add hop to impart more of the springs energy to the BB to make it spin in a similar way to a lighter BB which leaves less energy to make it go forward, so it's slower out of the barrel not only because it's heavier, but also because some of the pushing energy got used up getting it to spin.

Normally we would adjust the spring to add some FPS to compensate for the hop rubbing more.

 

Joule creep happens because a heavier BB takes longer to speed up and exit the barrel than a lighter BB so the force acting on the BB can do so for a longer time (potentially the pressure will be higher too). This only works if the lighter BB wouldn't have used all the energy.

 

Edited April 18 by Sewdhull

[Lozart]

4 hours ago, Sewdhull said:

A heavier BB will go further and quicker slower than a lighter one if it has the same forwards energy.

The issue comes when you add hop to impart more of the springs energy to the BB to make it spin in a similar way to a lighter BB which leaves less energy to make it go forward, so it's slower out of the barrel not only because it's heavier, but also because some of the pushing energy got used up getting it to spin.

Normally we would adjust the spring to add some FPS to compensate for the hop rubbing more.

 

Joule creep happens because a heavier BB takes longer to speed up and exit the barrel than a lighter BB so the force acting on the BB can do so for a longer time (potentially the pressure will be higher too). This only works if the lighter BB wouldn't have used all the energy.

 

FTFY

[Impulse]

I think he meant that at range it will (generally) hit a target quicker because it decelerates slower than a lighter projectile. I don't have the exact numbers, but it's typically at longer ranges. Up close, the lighter BB will hit first because of the initial speed and less time for it to decelerate.

 

But yes, they leave the barrel slower with the same energy. 2.32J with a .2 is 500fps and with a .48 is something like 322fps

[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]

54 minutes ago, Sewdhull said:

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]

1 hour ago, Lozart said:

 

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/

Edited April 18 by Badgerlicious

[Sewdhull]

1 hour ago, Lozart said:

 

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.

Edited April 18 by Sewdhull

[Lozart]

30 minutes ago, Badgerlicious said:

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/

 

28 minutes ago, Sewdhull said:

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...