FPS drop over distance

[BrightCandle]

Many of us know that the a typical site will use 350fps with no minimum engagement distance but a 420 fps DMR and 500 fps bolt action with a minimum of 30metres. Well today I saw a video that might change that:

 

 

It was mainly about testing what a gopro can stand in terms of impact but he goes on to test a 420 fps rifle at about 30 feet (10metres). The end result was that 420 fps had dropped to more like 305 fps in that short distance with 0.20g BBs.

 

I would like to see some other people attempt this experiment with perhaps some different weight BBs but with the intent of determining in reality what the drop off actually is. Because there is a decent chance that our current MEDs for sites is way above what they need to be in reality to avoid serious injuries.

[Sitting Duck]

hmmmmm......

 

what would of been interesting if he had shot the 320fps aeg into chrono

 

The sniper/dmr was CO2 so this 25% loss at 30ft could have been down to maybe joule creep

well in this case maybe joule loss on lighter bb's

 

My own completely untested unfounded theory is the joule creepy stuff mainly applies to gas/co2 guns on heavier bb's

(still think that aeg and "perhaps" hpa guns do not suffer this as it is air - but gas/co2 reacts exiting muzzle = creep)

 

if he had got a shot on aeg 320fps and it showed 240 (75% power or 25% loss) that would add up

but he didn't so we won't know for sure

 

me thinks hop may not have been great or properly set for .20's either

coz going on that maths another 30ft or 60ft = 90ft total would start to equate to 30m - ish or 30yrds

and if he lost another 25% from 300fps = 225fps at 60ft

and at 90ft dropping 25% off 225 - 56 = about 170fps at the aprox MED 30yrds or 30m

 

that kinda sucks but strengthens why dmr/sniper use much heavier ammo

 

But yeah this is a bit weird looking for dmr stats

[cyrexx]

All this has already been looked at years ago, look at http://mackila.com/airsoft/atp/ for the info.

[BrightCandle]

All this has already been looked at years ago, look at http://mackila.com/airsoft/atp/ for the info.

The ATP is theoretical. The basics of range estimates were tested empiracally but the speed drop off wasn't. Based on the model it would look like the ATP overestimates the speed loss somewhat but still this is the first empircal test I have seen that validates that part of the ATP, the original author of ATP certainly doesn't mention testing that aspect of it.

[cyrexx]

True, he doesn't say anything about testing velocity change vs distance but the theory is sound, considering it's nearly 10 years old and there has not been any real major challenges of it's accuracy it's not bad.

 

There is this one http://www.arniesairsoft.co.uk/articles/fps_dist_time/fps_dist_time.htm which does have higher values for the results.