Ported or non ported.

[ShelledPants]

Originally Posted by The Saint

You pick your sleeve type based on actual fps of the BB, rather than the spring.

Is that correct?

I'm only questioning because;

If I have a barrel which is 100mm and a spring which is gives 400fps, and my actual fps with 0.2 is 320 you're saying I would need a hopup rubber set for ~350fps.

But if I have the same setup, only with a 300mm barrel, and my actual fps with .2 becomes 400, will need a hopup rubber for ~400fps even though the initial friction and force from the bb passing the hopup rubber is exactly the same.

Why?

EDIT: My actual question, is: Why would you decrease the rubber's hardness with the lower fps setup when the spring is able to get 400fps with a longer barrel? Wouldn't the soft rubber wear much faster than the hard type rubber?

[CDN_Stalker]

Originally Posted by m102404

Stalker, I get what you're saying and would tend to agree...but a question or two spring to mind.

Isn't the traveling speed of the piston a direct factor in resulting FPS as well?

Don't the ports serve more purpose other than to break the airseal and fill the cylinder with "fresh air" quickly on the piston head's return stroke?

When the spring is fully compressed, the piston is at it's most rearward position. In a full cylinder, it's still in the compression zone (i.e. if it moves forward, it'll start forcing air and start building up pressure behind the bb). In a ported cylinder (port mid-way, 3/4 back etc...) the piston isn't in the compression zone yet and has some distance (maybe half the cylinder, maybe less...) to travel before it starts moving air.

I'm not a big physics guy...like you I'm more of a learn with hands/eyeballs type...so I'm probably going to butcher this explanation...

If a piston is at rest and starts to move forward, the pressure builds behind the bb and eventually reaches a point where it starts to move the bb past the hopup nub. As it continues to move forward, the piston speed will increase to hit a max speed largely based, I'd figure, on the expansion/compression characteristics of the spring/coils/material/temper. Perhaps the acceleration curve is steep...maybe more linear.

Now, if it's a full cylinder, the piston will start the bb moving before the piston has reached full speed...and in a very short barrel the bb could very well exit the barrel before gaining the full compression benifits that the spring could provide...resulting in a lower than optimal velocity.

In a ported cylinder...the piston has time to reach a higher speed before starting to compress the air in the compression zone. So the pressure behind the bb is higher than that of the same setup but with a full cylinder...resulting in a relatively higher FPS.

Taken to an extreme...where the port is very much forward...so that the piston is traveling as fast as it can...but the compressible air volume is tiny...you'd end up with a very low FPS because the volume of air in the compression zone may not exceed the volume within the inner barrel.

I hope I explained things right...I probably didn't.

I'd appreciate your opinion,

Tys

Yes, but I was just saying what is the determining factor on ported or full cylinder.

Mad Max wrote a great thread at one point explaining why ported and why not. Is the air volume yes, but also the length of the barrel. Shorter barrels need the BB hit full blast early in order to make the BB travel at the speed it should, aka the full power stroke instantly. Longer barrels will have the BB inside for a longer period of time so can get away with the more gradual full piston stroke. And using a ported cylinder in a long barreled gun will create what we all know and love, barrel suck/suckback or whatever we call it. Isn't so much the retracting piston sucking the BB back reducing the velocity, is the vacuum created behind the moving BB (it can happen in a bolt action rifle also, nullifying the retreating piston arguement). If you have a ported cylinder that has an internal volume of say "7", and a long inner barrel with an internal volume of "10", then the BB will get to the "7" mark and start to slow down due to no more air being pressed into the barrel, hence a slight vacuum being generated.

[m102404]

Stalker, I get you...thanks! I've haven't owned nor worked on an AEG with such a short barrel length for a while now...so I'm going on not-recently reinforced thinking. Maybe I'll chop up a barrel this winter to run some tests...bitch is that my FAL's not as easy to take apart as a split body m4... Maybe one of the guys will loan me a rifle for a bit.

Tom's got a good point with the FPS/Spring/hopup rubber question...personally I just swap them out whenever I feel like it, which is probably more frequent than needed. Durability's never been an issue in my own rifles...but they're shooting 380-400 with M100 or M110 springs. Guarder black in one and guarder clear in the other (the softer clear one is actually in the "harder" shooting rifle...the accuracy/range is just better with it).

[The Saint]

Originally Posted by ShelledPants

Is that correct?

I'm only questioning because;

If I have a barrel which is 100mm and a spring which is gives 400fps, and my actual fps with 0.2 is 320 you're saying I would need a hopup rubber set for ~350fps.

But if I have the same setup, only with a 300mm barrel, and my actual fps with .2 becomes 400, will need a hopup rubber for ~400fps even though the initial friction and force from the bb passing the hopup rubber is exactly the same.

Why?

Beats me. If the issue is initial friction, I wonder what the real difference between a 350fps and a 400fps gun is when hopup rubber is concerned.

EDIT: My actual question, is: Why would you decrease the rubber's hardness with the lower fps setup when the spring is able to get 400fps with a longer barrel? Wouldn't the soft rubber wear much faster than the hard type rubber?

Because he isn't using a longer barrel? I've found that softer hopup allows for better adjustment. Since the issue is a given hopup effect applied to a given fps, it's about what gives you better control over the amount of hopup effect at the actual fps you're firing at. What he can potentially be shooting at is not a factor unless he actually shoots at it.

I really don't know if hopup rubber wear is a significant factor.

[CDN_Stalker]

I used the Guarder clear rubbers for a few years and love them............ even used them in my 500fps M24, although I'd have to replace the rubber twice per year mind you due to eventual tearing. Currently I have an RH65 in there (rated for up to 400fps, but it's been going for two years now and is still good). Have to get new rubber for both my MP5s, one 330fps and one just under 400fps, and am stuck. Have a bunch of the blue Madbull rubbers but always have a sealing issue with them, massive airleaks with upwards of a 100fps drop, so likely I'd go back to the clears. My only issue with the clear is it's made of silicon and regular maintainance (drop or two of oil in the laoding tube to ensure proper feeding), the rubber ends up absorbing it, and after a year swells then tears. Hehe, last year both my guns had hop up set totally off, yet was at the point I could get 0.28g BBs past 200ft easily............ in my previously set 360fps MP5.

Softer rubber gives you a more supple nub in the barrel, it allows the BB to pass by easier without upsetting it too much. But is more suseptable to damage in higher fps guns.

[m102404]

I've monkey'd around with a soft nub (i.e. Guarder clear) with a harder (i.e. reg Guarder black) rubber sleeve....and vice versa...couldn't tell the difference, but I didn't really have the chance to shoot at distance.

My thoughts on the "which rubber to use" are:
- go with what gives the best results for accuracy at distance
- rubbers are cheap, buy different ones and try them out (a pain in an MP5)
- replace them regularly...they're cheap

I do find those clear ones really sweet and easy to get the longest/straightest shot with my current field gun...must be it's "stickyness" and give.

I must confess to not oiling hopup rubbers at all...ever. But then, maybe replacing them at least twice a season, perhaps more frequently, a season negates the need to do that?

[CDN_Stalker]

The breech part of it needs to be oiled somewhat regularly, depending on dust, etc. otherwise plugging will occur, BB will refuse to be shoved through by the nozzle. I don't kno whow many guns I've fixed on the field that were plugging because of a jammed BB, drop of oil and cycle, back up and running asap. Does suck that you can't control where the oil goes, but such is life in airsoft.

Oh ya, I've always washed my sniper ammo to get rid of the slightly oiled finish on them, let me set my hop up a bit lower due the increased friction on the hop up rubber. Too bad it won't work to great on an AEG though.

[m102404]

I'm far from "clean" with my stuff...my FAL still has some swamp on it...and not a problem yet. Never had an issue with any of my other AEGs either. Lucky I guess.

Although, I have seen plenty of repairs come through where the rubber is melded to the brass barrel (and had to be peeled off like a sticker), worn/cut, mashed up (usually by a "cleaning rod") or else swimming in so much oil that they were almost dripping with the stuff...

I'll certainly keep that in mind though, thanks!

Tys

[plastikpyro]

I have a systema silicon soft bucking which I'll install tonight. Would I see any increase in FPS by upgrading the barrel to a tight bore of equal length(208mm)?

[plastikpyro]

So I put in a systema silicon soft bucking and the FPS dropped from 350 to 330. Then I installed a Guarder 70% and it went back to 350. I went ahead and took the 120 spring out and replaced it with a systema irregular 130 and the gun is shooting 380. Is there any way to get the gun to shoot over 400 without using a heavier spring or a longer barrel? The compression is pretty good as it can sustain pressure holding the piston at half cylinder length when I cover the nozzle. I assume a bore up kit would be pointless on a 208mm barrel? Would tight bore do the trick? What I don't get is my KWA M16 with a G&P stubby killer front conversion shoots 380 with the stock spring and the barrel is only 5"?

[The Saint]

A bore up kit would be extremely useless on a 208mm barrel.

You're basically stuck. If your compression is already good and there's no air loss between the nozzle and hopup chamber, you're not going to get 20+fps short of changing the spring or a longer barrel. A tightbore might give some more fps, but I highly it'll push 380 over 400.

You might want to settle for 380fps? I can only assume you're in the States. Running the fps arms race with a short barrel gun is a significant handicap. Though.... You could try Systema's new Revolution mechbox. That might let you safely get above 400fps, if that's what you're really keen on doing.

[plastikpyro]

yes I'm here in the States, California to be exact. My goal was to use a CQBR armalite platform for mobility that can safely hit 400fps with good range for outdoor skirmish. Basically a step up from a stubby killer but a step down from a full length M4. It appears that I'm handicaped by the barrel length. I may look into a tight bore as my last option. Thanks for your help Saint. BTW I find the members on this forum alot more mature and very knowledgeable by comparison to other forums that I frequent.

[zone 69]

Originally Posted by plastikpyro

So I put in a systema silicon soft bucking and the FPS dropped from 350 to 330. Then I installed a Guarder 70% and it went back to 350. I went ahead and took the 120 spring out and replaced it with a systema irregular 130 and the gun is shooting 380. Is there any way to get the gun to shoot over 400 without using a heavier spring or a longer barrel? The compression is pretty good as it can sustain pressure holding the piston at half cylinder length when I cover the nozzle. I assume a bore up kit would be pointless on a 208mm barrel? Would tight bore do the trick? What I don't get is my KWA M16 with a G&P stubby killer front conversion shoots 380 with the stock spring and the barrel is only 5"?

Once you match your Cylinder to your barrel length so a 208mm barrel = 3/4 Hole Cylinder. Then it's airseal time, here's things that will help in having less airleaks. Tightbore barrel, good hopup rubber, one peace hopup, airseal nozzle, and good fitment of thess parts, less airleaks or less wasted air = better efficiency.
Useing a systema irregular 130 main power spring is getting to the eage of what a mechbox can handle with out high quality Reinforced parts.

[ILLusion]

Trying to push a short barreled gun like that to such high velocities will give you a minimal return with exponentially increasing costs...

[plastikpyro]

here's an quick update. I installed a Modify M4 (ported) bore up kit over the weekend and the chrono dialed the gun in at 430fps.

Stock King Arms M7A1 with stock 208mm 6.05mm barrel @ 300fps
+
Systema m130 irregular spring
+
Modify M4 Bore up kit
=
430fps