fps vs barrel size

[sniperslucky]

Hi All,

I've searched a little on the following but can't seem to find the answer so here goes:

At said length which will produce less fps 6.01mm or 6.04mm barrel as when i searched the 6.01mm gave lower fps but was shorter in length than the bigger barrel and  i thought it would of been the other way around due to there being more losable pressure around the BB in a 6.04mm barrel. Any equations for length vs size + FPS

 

[PT247]

if they were the same length then the 6.01 would have higher fps, but if the 6.04 was longer the BB would have the air pushing it for longer allowing it to accelerate to a higher velocity. At some point the length increase would allow for a higher fps than the tightbore.

 

[proffrink]

Tighter bore and longer length should give better muzzle energy up to a point (both independently of one another, so a short 6.01 will be outperformed by a longer 6.05, for example). I believe with most AEGs that point is just under 400fps on a .2. However, the difference is pretty small and some AEGs do struggle to put out the air to make significantly longer barrels give an effective boost. HPA and spring tend to benefit a lot more from bore size and barrel length.

Again though, 6.01 will give you higher muzzle energy but don't expect more than a single digit difference. The biggest thing to fix is having a good bucking with a decent airseal on your nozzle and sometimes a better hop unit can yield small increases too. Replacing and Teflon taping your bucking (or just taping your existing bucking) can net a few fps for a fraction of the price, so I'd always check that on a custom build/second hander/older production date gun. Newer stuff tends to be very good out of the box in terms of air seal.

In the UK though this isn't really a problem as hitting 335 or 350fps is really easy on the vast majority of AEGs. On springers there tends to be opportunities to increase muzzle energy just through swapping out the piston and making sure everything is properly lubed. Remember that the finish on the barrel will affect accuracy too, so sometimes a cheap 6.01 is much less useful than an expensive 6.05 if in something like a sniper rifle or DMR as it'll mess with the hop.

 

[sniperslucky]

Tighter bore and longer length should give better muzzle energy up to a point (both independently of one another, so a short 6.01 will be outperformed by a longer 6.05, for example). I believe with most AEGs that point is just under 400fps on a .2. However, the difference is pretty small and some AEGs do struggle to put out the air to make significantly longer barrels give an effective boost. HPA and spring tend to benefit a lot more from bore size and barrel length.

Again though, 6.01 will give you higher muzzle energy but don't expect more than a single digit difference. The biggest thing to fix is having a good bucking with a decent airseal on your nozzle and sometimes a better hop unit can yield small increases too. Replacing and Teflon taping your bucking (or just taping your existing bucking) can net a few fps for a fraction of the price, so I'd always check that on a custom build/second hander/older production date gun. Newer stuff tends to be very good out of the box in terms of air seal.

In the UK though this isn't really a problem as hitting 335 or 350fps is really easy on the vast majority of AEGs. On springers there tends to be opportunities to increase muzzle energy just through swapping out the piston and making sure everything is properly lubed. Remember that the finish on the barrel will affect accuracy too, so sometimes a cheap 6.01 is much less useful than an expensive 6.05 if in something like a sniper rifle or DMR as it'll mess with the hop.

All,

Thanks for the insight, i was looking to decrease the fps of a 2nd barrel as the DMR is @ 390fps (barrel no1) changed it to a 6.04mm same length and still got 390fps:

So either barrel no1 (stock) was 6.04mm or due to being same length fps stayed the same, it it likely if i cut around 200mm off the barrel this will reduce fps by 40fps to used the gun in a different scenario on full auto?

 

[Sitting Duck]

if i cut around 200mm off the barrel this will reduce fps by 40fps to used the gun in a different scenario on full auto?

DON'T CUT THE BARREL - well not if it is a good one

Good decent barrels are not just hacked up bits of pipe

(I know you have attempted to make your own)

But apart from anything else they have a crown or taper at the ends

and if this crown is crap the results will be too

Yeah I guess at push you could say WTF if chucking together a CQB 30 to 40 footer gun

But I'd resist the urge to hack a half decent barrel if I'm honest....

As for barrel length & fps crap....

Most springs are "supposed" to give out their rating on a 300 to 363mm M4 carbine barrel

If you shorten the barrel the fps drops

and if you use a similar but longer barrel the fps will increase

How much is a bit of guess work but I'll take a rough stab:

altering the barrel length by 100mm will drop the fps by about 33fps

or by the previous spring rating by SAME make.

EG m100 & say 229mm barrel = a m90 or 32.8fps drop expectation

(other makes like Guarder SP100 springs = M110 or there abouts)

A full size 455mm AK pushing 350fps will probably have a m95

A 110/140mm MP5k may only hit just over 300fps with a M110 or M115 in there

Obviously spring ratings/makes will vary

Spring final compression & final stroke will vary if spacers bearing spring guide AoE corrected etc...

Std or tbb used will effect fps - blah blah blah....

But a very rough guide is expect the fps or spring rating to vary a M10 notch or 32.8fps each 100mm

Not being funny but you can drop the fps say 15fps if you lose a bearing spring guide & a std spring guide

or bearing/spacer inside the piston - use a M3 penny washer & M3 nylon locking nut or M3 bolt

(depending how the piston head is fitted to piston)

And/Or Shortstroke a tooth or two if your piston has more than just one metal tooth to release on

(providing your barrel isn't too long as full AK's need a full piston stroke)

you could lose a tooth on a 400m barrel, 2 teeth on a 350mm & 3 on a 300mm barrel OK

This will bring down fps - but you need a piston with 3 or 7 or full metal tooth rack to SS

Cut or change spring - change spring would be best but sometimes you can get different results

If the spring is not quite the expected rating or mis-labelled

A SHS M100 "should" get you near 340fps depending on barrel

Element M105 should work for a 250mm barrel gun

But there is so many variables like bearing/spacers in piston that can alter fps by about 30fps

Then short long barrels can alter this again and that is if the spring is exactly what it says on tin

So if you have a slightly high fps but consistent and you can lose some spring compression

(bearing/spacer correct AoE if you haven't done so already)

Or buy a shorter barrel to save opening her up again - but resist the urge to hack one up

More than one way to skin a cat but hacking barrels up requires a decent finish or crown or it will shoot like $hit

best of luck

 

[sniperslucky]

DON'T CUT THE BARREL - well not if it is a good one

Good decent barrels are not just hacked up bits of pipe

(I know you have attempted to make your own)

But apart from anything else they have a crown or taper at the ends

and if this crown is crap the results will be too

Yeah I guess at push you could say WTF if chucking together a CQB 30 to 40 footer gun

But I'd resist the urge to hack a half decent barrel if I'm honest....

As for barrel length & fps crap....

Most springs are "supposed" to give out their rating on a 300 to 363mm M4 carbine barrel

If you shorten the barrel the fps drops

and if you use a similar but longer barrel the fps will increase

How much is a bit of guess work but I'll take a rough stab:

altering the barrel length by 100mm will drop the fps by about 33fps

or by the previous spring rating by SAME make.

EG m100 & say 229mm barrel = a m90 or 32.8fps drop expectation

(other makes like Guarder SP100 springs = M110 or there abouts)

A full size 455mm AK pushing 350fps will probably have a m95

A 110/140mm MP5k may only hit just over 300fps with a M110 or M115 in there

Obviously spring ratings/makes will vary

Spring final compression & final stroke will vary if spacers bearing spring guide AoE corrected etc...

Std or tbb used will effect fps - blah blah blah....

But a very rough guide is expect the fps or spring rating to vary a M10 notch or 32.8fps each 100mm

Not being funny but you can drop the fps say 15fps if you lose a bearing spring guide & a std spring guide

or bearing/spacer inside the piston - use a M3 penny washer & M3 nylon locking nut or M3 bolt

(depending how the piston head is fitted to piston)

And/Or Shortstroke a tooth or two if your piston has more than just one metal tooth to release on

(providing your barrel isn't too long as full AK's need a full piston stroke)

you could lose a tooth on a 400m barrel, 2 teeth on a 350mm & 3 on a 300mm barrel OK

This will bring down fps - but you need a piston with 3 or 7 or full metal tooth rack to SS

Cut or change spring - change spring would be best but sometimes you can get different results

If the spring is not quite the expected rating or mis-labelled

A SHS M100 "should" get you near 340fps depending on barrel

Element M105 should work for a 250mm barrel gun

But there is so many variables like bearing/spacers in piston that can alter fps by about 30fps

Then short long barrels can alter this again and that is if the spring is exactly what it says on tin

So if you have a slightly high fps but consistent and you can lose some spring compression

(bearing/spacer correct AoE if you haven't done so already)

Or buy a shorter barrel to save opening her up again - but resist the urge to hack one up

More than one way to skin a cat but hacking barrels up requires a decent finish or crown or it will shoot like $hit

best of luck

Hi Sitting Duck,

Thanks for the info, i've cut down a barrel before and machined the cut end and with a little persistence i've managed to get a straight enough shot. This is more a quick change barrel set up from DMR to full auto m4 based on scenario's. I will cut the barrel down by 150mm and hope the fps drops to around the 450fps so my son can vary the role he wants to play.

Again thanks for the insight and if i could manage it i will upload the results for all to see.if not it will be plain text lol. 

 

[proffrink]

If you're using a DMR then surely the surface finish is far more of a concern that the length or bore size anyway? Especially what with the new laws meaning there's only 350fps to play with, getting in the way of a consistent hop is a real negative.

Honestly I'd just get a short barrel with a good finish and then only swap the external barrel.

 

[sniperslucky]

If you're using a DMR then surely the surface finish is far more of a concern that the length or bore size anyway? Especially what with the new laws meaning there's only 350fps to play with, getting in the way of a consistent hop is a real negative.

Honestly I'd just get a short barrel with a good finish and then only swap the external barrel.

Not sure if i've confused all, we had a great DMR set up we are trying to get to a <350 fps set up by changing the barrel as the M4 is a quick release upper and this could be changed at lunch time to run the full auto  set up depending on type of game being played. As you stated if cutting down the barrel works with the fps then i'll just buy a new shorter barrel. Thanks for your input.

 

[Lozart]

Not sure if i've confused all, we had a great DMR set up we are trying to get to a <350 fps set up by changing the barrel as the M4 is a quick release upper and this could be changed at lunch time to run the full auto  set up depending on type of game being played. As you stated if cutting down the barrel works with the fps then i'll just buy a new shorter barrel. Thanks for your input.

Changing out ONLY the barrel won't drop enough FPS (assuming you have it set up to 400+FPS to use as a DMR).

The only way I can see this working is if the gun in question is an ICS with the split gearbox and you change out the entire upper box or something like a Katana with the different powered cylinders.

Additionally, a "proper" DMR running a high FPS would need to have the fire selector locked to semi which would mean that you wouldn't be able to easily switch to full auto after changing the upper anyway. Sorry.

 

[proffrink]

Like Lozart says, barrels are negligible. Most loss in FPS on an AEG comes from problems in the gearbox (specifically the piston and piston head) and the hop unit and its seal with the barrel or the bucking and nozzle), but for the sake of consistency these aren't things you'd want to sabotage yourself on purpose.

I'm also worried about consistency if you're really going for a 'DMR' - disturbing the hop unit that often is just going to create inconsistencies in the medium term. Frankly I'd just pick one or the other and roll with it for the reasons Lozart specifies. I feel best case scenario you end up with a meh DMR and a good rifle. Worst case it's a huge pain in the arse. I could certainly be wrong though.

 

[Hangtight]

Not sure if i've confused all, we had a great DMR set up we are trying to get to a <350 fps set up by changing the barrel as the M4 is a quick release upper and this could be changed at lunch time to run the full auto  set up depending on type of game being played. As you stated if cutting down the barrel works with the fps then i'll just buy a new shorter barrel. Thanks for your input.

That one ain't gonna fly...

 

[Sitting Duck]

Thanks for the insight, i was looking to decrease the fps of a 2nd barrel as the DMR is @ 390fps (barrel no1) changed it to a 6.04mm same length and still got 390fps:

So either barrel no1 (stock) was 6.04mm or due to being same length fps stayed the same, it it likely if i cut around 200mm off the barrel this will reduce fps by 40fps to used the gun in a different scenario on full auto?

OK well I originally saw figure of 390fps & OP wants to reduce fps by 40fps....

Barrel length does effect the final fps how much we shall have to see with the final results...

Can he lose 40fps by lopping off the barrel 150mm - yes I think so

Can it be used as a DMR - hmmm this all depends if you have a full complete cylinder

But this assumes that the original barrel is say 363mm with full cylinder @ 390fps

then creep it up with a longer 400-455mm tbb to max 425/450 but gun needs to be locked to semi blah blah blah DMR

Can fps be dropped in a shorter barrel - yes I believe it can

By my own findings and other instances like the MK23 pistol with the barrel extension taking the fps well over the 350fps

Or other guns with a barrel extension making the final fps vary like this one....

http://www.evike.com/products/45599/

Still don't agree with hacking barrels even with crowning diy but to each their own

Plus you are using a stronger spring than needed & losing fps to arrive at 350fps

(so its not very efficient pulling a stronger than required spring)

If you are talking of losing 40fps - yes imho/findings a shorter barrel will do this

if you are considering creeping it back up for DMR work - needs to be locked to semi

PLUS - needs to be re-chrono'd and marshals notified - you can't just switch around stuff mid game

The semi only requirement is not a guide for DMR's it is a std ruling afaik

So there are some serious regulations and integrity to adhere to if peeps start messing about with stuff

Not saying you would switch stuff around or cheat chrono etc...

But everybody - including others reading this thread need to be aware of this changing of barrels does alter stuff

If anybody attempts this mid game they are cheating the chrono - no excuses and deserve to be banned

So to use as DMR it fails if not locked to semi

To continue to use with longer barrel & higher fps is cheating chrono & a ban would/should be enforced

Try a shorter barrel to lower fps if you must but be fully aware of consequences if considering switching barrels again mid game

No offense to anybody - not accusing OP of considering this but just strongly pointing the semi DMR & cheating chrono issues

 

[Sacarathe]

That one ain't gonna fly...

Could get an autolocking mosfet...

 

[Sitting Duck]

Could get an autolocking mosfet...

True - even a Kong burst wizard or maybe Avacado plug in burst thingymajig

But truth of the matter is if you want DMR get/make/build a DMR semi only

Them bursty plug in ones never really quite work 101% well not in the HC05

I mean yeah it kinda worked but a PITA to configure & due to crazy speed it varied depending on battery juice

If ya want a DMR - get/build a DMR

if you want a general AEG get a decent mid 300mm barrel gun

if you want something for cqb - learn to use your gun,

or buy a folding stock G36c, a stubby M4 or pistol

Yes you can go with a split gearbox/receiver ICS thingy

but tbh think I'd just get another gun - that way you got a backup/spare if ya main gun busts

(split guns/receiver means jack if the gears/bevel gear goes crunch)

I mean yeah many do this, it works well for them & to each their own etc....

I'd just get another gun - but then I would say that I guess with my OCD/Autism & all my other issues

 

[Samurai]

Barrel length and cylinder volume should be balanced. If you put a way too short barrel in to reduce fps, the BB will exit the barrel way before the piston impacts. Normally the BB with air behind it acts as a cushion to soften this impact. If your gun is that overvolumed, the full power impacts will break the v2 gearbox. Only CNC aluminium gearboxes can handle that stress.

 

[Sitting Duck]

True - I avoided this bit as my replies were long enough

SNIP - got carried away once again

 

[sniperslucky]

OK well I originally saw figure of 390fps & OP wants to reduce fps by 40fps....

Barrel length does effect the final fps how much we shall have to see with the final results...

Can he lose 40fps by lopping off the barrel 150mm - yes I think so

Can it be used as a DMR - hmmm this all depends if you have a full complete cylinder

But this assumes that the original barrel is say 363mm with full cylinder @ 390fps

then creep it up with a longer 400-455mm tbb to max 425/450 but gun needs to be locked to semi blah blah blah DMR

Can fps be dropped in a shorter barrel - yes I believe it can

By my own findings and other instances like the MK23 pistol with the barrel extension taking the fps well over the 350fps

Or other guns with a barrel extension making the final fps vary like this one....

http://www.evike.com/products/45599/

Still don't agree with hacking barrels even with crowning diy but to each their own

Plus you are using a stronger spring than needed & losing fps to arrive at 350fps

(so its not very efficient pulling a stronger than required spring)

If you are talking of losing 40fps - yes imho/findings a shorter barrel will do this

if you are considering creeping it back up for DMR work - needs to be locked to semi

PLUS - needs to be re-chrono'd and marshals notified - you can't just switch around stuff mid game

The semi only requirement is not a guide for DMR's it is a std ruling afaik

So there are some serious regulations and integrity to adhere to if peeps start messing about with stuff

Not saying you would switch stuff around or cheat chrono etc...

But everybody - including others reading this thread need to be aware of this changing of barrels does alter stuff

If anybody attempts this mid game they are cheating the chrono - no excuses and deserve to be banned

So to use as DMR it fails if not locked to semi

To continue to use with longer barrel & higher fps is cheating chrono & a ban would/should be enforced

Try a shorter barrel to lower fps if you must but be fully aware of consequences if considering switching barrels again mid game

No offense to anybody - not accusing OP of considering this but just strongly pointing the semi DMR & cheating chrono issues

No offence taken just appreciate the comments.

1st The gun is locked into semi when played as a DMR (def no chrono cheating here 390FPS),

2nd i was just looking into being able to change the fps (with re chrono)  with a shorter barrel as some times the game role my son wishes to play he wants  a 350fps aeg to run around with.

3rd We did try this with another barrel and it got chrono'd at 191fps due to being rushed to strip the hop down and insert new barrel hence now we have a complete barrel & hop up to change over. He didn't like that 

The idear was that if we could achieve 390FPS DMR with 1complete barrel setup and then reduce FPS to 340ish with another complete barrel setup then this would beat buying another gun for this purpose.

He is awaiting the Kriss vector to be released and before anyone screams " i have a UKARA to purchase free of charge gift to my son ".

I'm hoping this will clear any.

We both take our hits and play fair there is no point in cheating whether it comes from players or guns. Just a parent trying to satisfy a sons need to play different styles all within the site rules and fair play.As he is the future like most others of our sport.

 

[Hangtight]

You would be better off having the different guns for different roles. There's always the danger when messing around with your gun in the break that it doesn't go together properly and that can spoil your afternoon. And unfortunately with trying to build compromises you often end up with the worst of both worlds rather than the best.

Besides, you can never have too many guns....

 

[Sitting Duck]

Besides, you can never have too many guns....

 

[sniperslucky]

Welcome back all,

It's done ! "LOCKED TO SEMI "DMR shooting 380-390fps (site limits 400fps) then quick change of barrels and 335 -340fps .

Loooking to get a short vid sorted for your thoughts.