FPS question.

[blackjack21]

I recently did an flat hop and tight bore barrel upgrade on my gun.

Hopup off and .2 gram BBs my gun was shooting an average of 404fps

Hopup on and .3 gram bbs (which is what I actually use in the field) my gun was spot tested and came in at 296.

I was stunned, should going to .3s and putting on hop cost 100 fps or do I have a leak?


Any advice would be appreciated.

(p.s the gun is def more accurate and I think shooting longer than before the mod so I may just keep it as is even though it's low fps is disturbing.)

[Cobrajr122]

going up to a 0.3 should land you around 320 FPS after turning the hop on.

While 296 is fairly close, i think that is a lot of loss that should not be happening.

Numerous things could be causing the issue, I would start with making sure your hopup unit has enough force being applied back onto the mechbox.

[PrIeSt]

As your weight increses your FPS decreses, this is why we say " XXXfps with .20 bb's" as a standard. as you climb in BB weight you drop in FPS.
You dropped a bit to much but this could be due to a tight bore and BB type, which BB's are you slinging?

[lurkingknight]

It's about right, I drop to around 300-320 with .30s and .32s from 400 with .2s

[K3vX]

To put it simply, take your hand and push a light object with some force over your table. Now with the same hand stroke, put a heavier object. The heavier object will land closer to the table.

As other said, you should be around that point, or maybe a little over. But you should NOT be at 400fps with .30

[Hectic]

In theory its only about a 15-20fps loss.
There are alot of other fators but two that are also important are
1.what length of inner did you put in
2. What cylender is in the gun
If for example you have a 4/5 ported cylender and went up to a 510mm inner
The piston would finnish its compression cycle but the bb would still have 50mm to travel through the barrel. Even in this short distance the bb will start to encounter drag because the air is no longer being compressed behind it (creating a cusion around it) causing it to hit or run along the inside of the barrel slowing it down.
You cant go longer then 460mm on a 4/5 ported cylender or the bb will still be in the barrel once the compression cycle is done.
Now another thing that will effect this is the heavier bb.
A heavier round will take longer to leave the barrel. Tho it will to some extent slow down the compression cycle (because it is sort of holding the piston back) it likely wont slow it down enough to match it to the bb exit.
IE maxing out on a 460mm barrel with a 4/5 cylender when using a. 20 will geve maximim use of compression but increasing bb weight too much may have an odd effect.
There are other factors at play but if it fires good on 20's and when ya jump to 30's yer losing that 20ish fps i think you may be finnished compression while the bb is still in the barrel.

[pestobanana]

Keep the hop up set for .3s and chrono with .2s, you should still have the FPS loss. I don't think it's because of air seal, I get that too in my gun set to use .32s. It's because of the high hop setting.

[blackjack21]

To be clear, of course I was expecting an FPS loss going from .2 to .3 but not 106fps! Also having hop up on as opposed to off should reduce fps a bit as well...

[coach]

In an ideal perfect setup, you should be getting 330fps or 1.51 Joules with 0.3's.

[KenTsui]

What's your barrel vs cylinder volume ratio? That could explain the loss in efficiency when moving up bb weight.