Best course of action

[sniperslucky]

Right, previously stated that a £3 Ali tube and Ptfe tape my sons M4 was chrono'd at 350 dead on at dog tag, We ended up changing the barrel to a manufactured one re did the Ptfe tape and went back to Dogtag. Gun chrono'd at 411fps (hot gun). So we borrowed a rental until 1st break where i stripped the gun down and took off the Ptfe tape hoping it would lower the Fps so we could use it. Gun then re-chrono'd at 427fps.????

 

Any ideas on how best to get it back to 350fps, the barrel is 560mm long.

 

Don't want to cut barrel down

Can the spring end up to short (if spring is cut down).

Do we change spring to M100 ( as stock spring not known)

 

Thoughts

 

[sp00n]

560mm is a long barrel for an m4 (i may be wrong)

 

easiest to hardest mods to lower the fps

 

shorter barrel or wider bore barrel

swap the spring for a lower powered one, but it may give you pre-engagement issue, if you went too weak

different ported cylinder

short stroking the piston

[Guest PT247]

Wow, 560mm??? The longest I have put in an M4 was a 420mm and that was struggling with getting enough volume from the piston.

Fit a shorter barrel, don't use a tightbore (it IMO is a myth that a TBB will give better accuracy, it'll just increase fps and possible range but not accuracy), a 6.05mm bore is just nice.

 

Set your hop for the weight of BB you are using and then chrono it on that setting as some guns will drop fps as you wind on the hop (some guns add fps when you wind on the hop too) so is important your hop is set right

 

Don't chop the spring unless it is a last resort, as unless you finish it correctly after chopping you will get a very inconsistent gun.

[jcheeseright]

Just buy an M90 spring. Trying to Heath Robinson it will only ever end in an inconsistent gun unless you're a master engineer and or have access to some very sophisticated manufacturing equipment.

[Sitting Duck]

As others have said the barrel is toooooooo loooooooongggggg

 

How much messing about have you done to this M4 ???

What was she like befoe with stock barrel in the very beginning before you tried DIY barrel ??

 

Have you messed with the gearbox/spring before ???

 

What I'm saying is that it is not going to have enough air volume for that length barrel - max 455/469 with a full cylinder

and even then not much over 400mm if you seek to lift heavier bb's - unless you have an extended M4 - SR-25 2.5 gearbox

You won't get the air volume on a std v2 or v3 box past 450mm so the maths n crap say

yes people say they have done this n that but general rules of thumb/consensus is you stay within certain guidelines

 

Is the cylinder a full cylinder or ported one ???

 

I'm going to take a rough stabbing guess that it may have been a 363mm type M4 that was hitting around 350fps

might be full cylinder or a ported one at very back of cylinder

 

You have been trying this n that on barrels - some worked some didn't

 

Now what you have got is joule creep that will often/always take place when using longer barrels

and yes 50fps+ is quite normal even more if you went from say 363mm to 560mm - that is nigh on 200mm

 

As others have said you will need to drop the spring but tbh you will not really have the volume from even a full cylinder on a std v2 box imho

 

I would bet if you grabbed a 363mm barrel the fps will come down quite a bit back to likely what is was

even if a full cylinder is used you would be over voluming a bit but not a massive amount and if using .25 perhaps .30 you will be fine

 

Changing a barrel is going to be a lot easier than opening up the box and changing a spring/cylinder & wotnot

So I would look into running with a barrel the gun's present setup is designed for & within its capacity....

try to seek out a 363 - 400mm barrel and I would be quite sure the fps would then be within the limits of site

and depending on port/cylinder - likely to function correctly with volume n stuff blah blah blah.....

 

you could still leave the gun " looking " like a great big mofo sniper one but maths/physics/volume wise your creep in fps is mostly down to choosing a barrel that is tooooooooooo dammmmmmmmmnnn loooooooonnnnggggg

fit a shorter inner barrel - as long as it don't wobble inside the outer barrel it will be ok - see if the fps drops - should do

but remember - you should not try to emulate an M4 std aeg into something like this:

 

[sniperslucky]

Hi PLEASE SEE ANSWERS IN RED HOPE THIS HELPS.

 

standard M4 with a silencer, barrel is as long to the end of the silencer,

As others have said the barrel is toooooooo loooooooongggggg.

 

How much messing about have you done to this M4 ???

What was she like befoe with stock barrel in the very beginning before you tried DIY barrel ?? 230FPS as stock

 

Have you messed with the gearbox/spring before ???ive shimmied another m4 and have a little experience but the M4 gearbox in question has not been touched

 

What I'm saying is that it is not going to have enough air volume for that length barrel - max 455/469 with a full cylinder

and even then not much over 400mm if you seek to lift heavier bb's - unless you have an extended M4 - SR-25 2.5 gearbox

You won't get the air volume on a std v2 or v3 box past 450mm so the maths n crap say

yes people say they have done this n that but general rules of thumb/consensus is you stay within certain guidelines

 

Is the cylinder a full cylinder or ported one ??????? stock

 

I'm going to take a rough stabbing guess that it may have been a 363mm type M4 that was hitting around 350fps poss but 230fps out of box

might be full cylinder or a ported one at very back of cylinder

 

You have been trying this n that on barrels - some worked some didn't. nope saw a you tube vid on the cheap barrel posted the results on here and was told it was proberly down yo a bad air seal hence the big jump to 350fps spot on!( i was well pleased with the results but son thought a shop brought barrel would increase the accuracy).

 

Now what you have got is joule creep that will often/always take place when using longer barrels

and yes 50fps+ is quite normal even more if you went from say 363mm to 560mm - that is nigh on 200mm even 2hrs between chronoing and taking off the PTFE tape seal!

 

As others have said you will need to drop the spring but tbh you will not really have the volume from even a full cylinder on a std v2 box imho

 

I would bet if you grabbed a 363mm barrel the fps will come down quite a bit back to likely what is was

even if a full cylinder is used you would be over voluming a bit but not a massive amount and if using .25 perhaps .30 you will be fine

 

Changing a barrel is going to be a lot easier than opening up the box and changing a spring/cylinder & wotnot Barrel only this long as M4 has a suppressor on it

So I would look into running with a barrel the gun's present setup is designed for & within its capacity....

try to seek out a 363 - 400mm barrel and I would be quite sure the fps would then be within the limits of site

and depending on port/cylinder - likely to function correctly with volume n stuff blah blah blah.....

 

you could still leave the gun " looking " like a great big mofo sniper one but maths/physics/volume wise your creep in fps is mostly down to choosing a barrel that is tooooooooooo dammmmmmmmmnnn loooooooonnnnggggg

fit a shorter inner barrel - as long as it don't wobble inside the outer barrel it will be ok - see if the fps drops - should do

but remember - you should not try to emulate an M4 std aeg into something like this: Issue is why has the gun jumped so much from 350fps with a DIY shop brought ali barrel to a shop brought barrel both being the same length

 

[Sitting Duck]

Fps shot up from long barrel = creep

 

230fps stock - probable pi$$ poor seal on old stock barrel maybe - you will be amazed how easy you can lose fps on a piss poor hop/bucking air escaping around bucking, torn bucking or if nozzle doesn't seal enough around bucking lips you can easily lose 50-100fps.

 

The increase is from a better seal and deffo creep from longer barrel. Honest you can gain about 30fps from changing barrel to just one that is a few inches longer

[sniperslucky]

Hi Sitting Duck,

 

As you stated the original creep to 350 fps was with the longer ali barrel from diy shop with PTFE to seal, all I've done now is change the barrel to a airsoft ebay barrel so don't see why a better air seal has been gained ,also why would the fps on new barrel go up when chrono'd with PTFE at 411fps then 2hrs later without PTFE tape on it @ 425fps.

Fps shot up from long barrel = creep

230fps stock - probable pi$$ poor seal on old stock barrel maybe - you will be amazed how easy you can lose fps on a piss poor hop/bucking air escaping around bucking, torn bucking or if nozzle doesn't seal enough around bucking lips you can easily lose 50-100fps.

The increase is from a better seal and deffo creep from longer barrel. Honest you can gain about 30fps from changing barrel to just one that is a few inches longer

[Sitting Duck]

If you use a tight or precision barrel you will obtain a further increase in fps

If you use a wide bore or a less precise diy barrel your fps will be lower

 

Your long diy barrel was maybe less precise to put it politely, and so the fps was lower. A decent barrel has basically given the boost just from being more efficient.

 

Or to put it another way - the diy barrel was $hit as we explained a while back

 

The deviation on PTFE and/or removing tape could be down to refitting barrel/hop and better/worse seal.

 

I'm trying to explain the fps shooting up

 

I wonder if you stripped and reassembled the old barrel/hop and reassembled it that the fps would be higher than 220fps maybe ???

 

Yes you could put in a m90 spring if you wish but you really don't need a 560mm barrel in a std m4 is my view

[sniperslucky]

Hi Sitting Duck,

 

We only stuck in the longer barrel as some of the BB's with the stock barrel were hitting the end of the silencer and not coming out. We are getting it re chrono'd at the shop on Thursday to see if its constant increase. If so we will cut barrel back slowly to reduce FPS.

 

Thanks for the info

[Sitting Duck]

It isn't so easy to just hack off and shorten a longer barrel

 

At the end of a barrel is a finish or crowning

 

Yes you can use a cone shaped stone in a dremmel but there is more to stuff than just a bit of pipe and some emery paper...

 

The crown or finish is important - bad crown will produce curvey shots even if everything else is perfect as it can produce turbulence as bb exits the very end of barrel

 

Not saying you can't do it but just pointing out stuff and why we said about getting a good decent barrel and one the correct spec to the gun.

 

As you are starting to realise like myself included, there is a bit more to Airsoft than an electric peashooter

Slight hairline tolerances can make a big difference to how well the gun shoots and the bb's velocity and trajectory

[sniperslucky]

Yes , do you know what sort of drop would be achieved aa I've checked the order and the new barrel is a 6.02mm inner, so would changing to a 6.04mm work?

[Snakeeyes75]

Right, previously stated that a £3 Ali tube and Ptfe tape my sons M4 was chrono'd at 350 dead on at dog tag, We ended up changing the barrel to a manufactured one re did the Ptfe tape and went back to Dogtag. Gun chrono'd at 411fps (hot gun). So we borrowed a rental until 1st break where i stripped the gun down and took off the Ptfe tape hoping it would lower the Fps so we could use it. Gun then re-chrono'd at 427fps.????

 

Any ideas on how best to get it back to 350fps, the barrel is 560mm long.

 

Don't want to cut barrel down

Can the spring end up to short (if spring is cut down).

Do we change spring to M100 ( as stock spring not known)

 

Thoughts

 

If you've put a tight bore in, that will cause an FPS jump. The best thing to so (even if it's not the most easy) is to swap the spring down to a lesser spring. The TBB and PTFE mods are all neccesary to ensure good airseal, it's a common thing though to swap the spring out.