Question on Hop-up rubber....angle?

[RacingManiac]

Looking to rebuild the hop-up on my GHK AKM, and am shopping for parts. Looking at whats available out there now(the gun uses AEG barrel and hop-up), I noticed that there are certain brands that sell their hopup with different angle? For example the A+ rubber has 60, 70, 80 degree angle for AEGs. What exactly is that angle of and how does it affect its function? Looking for some enlightenment here...

[RacingManiac]

Actually on second thought, the number might refer to durometer? In which case its the hardness? The HK sites just lists it as "degree"....hmm

[Stealth]

Comparing different offerings from the same company, the "degrees" is just the hardness of the rubber.

To lift heavier rounds at higher FPS, you'll need a less compliant rubber to impart the necessary backspin, thus the stiffer material. 50oo seems to be the rubber of choice for sub-400fps builds.

Although, I have run 50oo on one of my hardball guns to lift .3g BBs in the past and it worked out just fine.

[RacingManiac]

Well the suggestion from the TW sites seems to be to run harder ones for GBBRs, as I think they are less prone to tearing with the propensity of the GBBR having misfeed issue due to the rather more violent bolt/chamber interaction.

[m102404]

The only comparative things I've seen is that some are rated for different velocities...so I had assumed they meant a hardness/durometer-ish rating.

The A+ flat nub is very good from what I've seen...I like 'em a lot.

[Trev140_0]

I would like to add, temperature is a factor.

So yes, the degrees ties in with the rubber compound (hardness) but keep in mind if you are playing in the cold this changs things.

Just like the compound on a summer tire vs winter. The winter is set up to remain more rubbery and keep the grip. An all season gets hard in the cold and looses the grip. Leave a pair of winters on in the summer and they will wear out like an eraser.

The same HAS to apply to a hop up in a gun that is used when it is 44 degrees in the shade (we have played that at the hill) to the now, -3 and on, which we are about to play in.

So my point is, remember you are likley farting around with your gun at ambient temp. May need to get a softer bucking than normal in the colder temps.

Ignore this if you are an indoor guy.

[L473ncy]

Really Racing Maniac??? I would have expected an Engineer to know this already....

That said the Guarder Black rubbers are 70 IIRC while the Guarder Clear are 50.

I personally use a Guarder black in my ~390 FPS rifle with good results. Haven't done comparative/quantitative testing but I like it. I'm assuming that there's some overlap between effectiveness vs FPS so unless you're using a Prommy red in a 270 FPS setup or a prommy purple in a 550 FPS setup I wouldn't worry about it too much. My own personal cutoff is softer rubbers for sub 400 and harder rubbers for over 380 (taking into account the overlap I mentioned) I wouldn't use a hard rubber below 360 FPS or a soft rubber over 430 FPS.

[RacingManiac]

Part of engineering is to expect the language is used properly, all I am judging from is some HK site's listing, so I have no clue what their context is when they say ## degree.....

[RacingManiac]

Secondary consideration here....the standard used to judge what to use seems to be dictated by the gun's designed FPS, which on an AEG is largely depend on the spring rate, which is fixed. How would that apply to a gas gun, when your FPS is driven also by other factors. Kinda hard to quantify the components of FPS just based on the gas output before the hopup...

[ccyg8774]

A somewhat related question... How do you decide if the stock hop-up rubber is bad, and therefore need to be replaced?

[RacingManiac]

Currently mine is just torn, so I am sourcing replacement part....

[MaciekA]

Originally Posted by Trev140_0

I would like to add, temperature is a factor.

The IR-Hop patch is unaffected by temperature so if you can find a bucking that is made of a reasonably similar material that can punt a BB through the bucking lips with no jam, you're basically in business all year long, in theory..

[Kos-Mos]

Originally Posted by MaciekA

The IR-Hop patch is unaffected by temperature so if you can find a bucking that is made of a reasonably similar material that can punt a BB through the bucking lips with no jam, you're basically in business all year long, in theory..

Degree is a bad term... it refers to Durometer Shore A ratings.

However, theses are taken at room temp (20C), and most rubbers/polymers do not have a linear curve or Shore A vs. Temp.

As a reference, Shore A 30 is the average rubber band. Shore A 50 is pure silicone (Guarder clear or bathroom silicone sealant when cured). Car tire are usually between 70 and 110 Shore A.

The rubber/compound used in IR-Hop might have a very flat curve, but most rubbers do not act the same.

You won't find that kind of information from an airsoft manufacturer (if they have it, they won't want to tell you as this is like a fingerprint for composite materials, you could copy them).

But if you want, you could buy everything that is ever made and compare them at different temperatures/FPS for us...

[lurkingknight]

hs5 is pretty tight lipped about what material is used in the r-hop and ir-hop patches... I imagine is pretty common tubing cut down the length to get the patch. IR-hop feels closer to a silicone material than a rubber as it's fairly clear.


as an aside, in my p90 I believe I have a ir-hop and lonex 50 degree vs my g36 with a ir-hop and lonex 70 degree. I haven't really cold weather tested either gun. The coldest I got the p90 was nightfall which I think was low to mid single digits in C mixed with really miserable rain.

[MaciekA]

Originally Posted by Kos-Mos

But if you want, you could buy everything that is ever made and compare them at different temperatures/FPS for us...

I've thought about the systematic testing angle, one idea would just involve sticking a couple barrel + hopup combos into the freezer with buckings on them. I *am* however super lazy... So this testing will just have to happen on the field