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Author Topic: R-Hop FPS?  (Read 287 times)

FearNoEvil

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R-Hop FPS?
« on: June 17, 2017, 03:58:19 PM »
So, I went ahead and took the easy route. Had a R-hop install kit ordered. That beig said, my gun is only at 320 fps with .20 BBs. Would this Rhop allow me to shoot heavier BBs at the same FPS? Or would I have to still upgrade my spring to properly use the rhop with heavier BBs? Im looking to use .28s and .30s. I read that the rhop is able to do so without increasing FPS, but I need to be sure. I have a big game coming up.

Thank you.

T6e9a

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Re: R-Hop FPS?
« Reply #1 on: June 17, 2017, 11:52:21 PM »
Pretty sure you got most of your answer on facebook, but just so it is fresh on here as well, and sorta added into archive for future people wondering the same:

In general, FPS changes between bb weights. Heavier the bb, lower the FPS. Lighter the bb, higher FPS. But with a stock gun, the energy output is (or should be) the same, no matter the bb weight. So with a lighter bb traveling with a faster fps than a heavier bb, they both have the same energy behind them, measured in joules. Joules factor in the weight of the bb as well, not just the speed.

A properly done R-hop should be able to be used with any bb weight, no overhopping with the hop turned all the way off. But what you heard is more so what it works best with. R-hops really shine in performance (again, if done well) with heavier (.28+) bbs. Even with lighter bbs, results would/should be much better than the stock configuration.

As for R-hops or any hop modifications changing FPS, depending on the system, there is potential for it to go both ways, up or down. Again: depending on the system. And more specifically the volume ratios behind the bb(cylinder and dead space in the nozzle/cylinder head) and in front (barrel volume).
Basically, for most stock guns(assuming proper voluming), turning the hop up, up, will decrease the FPS, as it is adding friction to the bb to give it the backspin. In a traditional hop up bucking/mound/nub, this is pretty much momentarily. With R-hops, since they have extended contact with the bb, it takes a little longer. Nothing substantial, but still a factor. During that time, the air is passing around the bb as well. So long as the air is still moving before the bb leaves the barrel, it will accelerate the bb.

The ideal volume ratios change with different bb weights, barrel lengths and diameters. So with enough science/calculations, you can tune your gun perfectly to the bb weight you run.

Instances where the FPS would increase with hop up applied, would be when the system is over volume, meaning more air than needed behind the bb. (This plays into joule creep, but that's some science for another day) Over volume systems often don't have the best precision accuracy due to the air is still accelerating when the bb leaves the barrel, thus potentially causing turbulence.

And for FPS to decrease when hop up is applied, would be in a stock or undervolumed setup.

Just understand, FPS and power output are 2 different things, measured differently factoring in different things:
FPS=measured speed
Power output=measured speed FACTORING IN the weight of the item being propelled.

If I missed anything, or am incorrect on something, please let me know. This is all what I have learned over the years and gathered from personal experience as well as research. Always want to make sure I am up to date and not spreading false info.
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luke213

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Re: R-Hop FPS?
« Reply #2 on: June 19, 2017, 10:29:11 AM »
So the only thing to mention which you touched on and I've seen the effects but I don't entirely understand the mechanism well I've got the theory but there are some unknowns.

So the theory is that when applying hopup you're holding the BB in place and either building more pressure behind the BB prior to release, or hitting a point where the pressure builds enough to release. I suspect it's the first but the reason I mention the second is this. If you're running say an irregular pitch spring it releases at a different rate, and then say a full cylinder. If the BB is still in the barrel at a different point in the piston stroke then it typically would have been then you can see different FPS results. IE there are points along that travel where the piston is pushing more air than other points, and as a result you can get a more efficient push basically. So how long and how the BB is held does effect FPS to some degree, and it can be somewhat hard to predict.

Typically with a normal bucking, you need to apply allot of force down on the nub and thus the BB to get enough backspin out of the contact patch. On an rhop it needs allot less force, which makes them a bit more finicky to set and more sensitive. That's also some of the reason behind the Mnub that is recommended, to take a bit of the sensitivity out. But that lower pressure just seems to be more efficient at backspin over a larger area which seems to generally raise FPS slightly because of less resistance.

Another oddity of rhops to note, is that they do seem more prone to ammo pickyness, in the sense that if you've got some BB's that aren't super consistent size wise, they will be more of an issue in an rhop overhopping. Because that slightly larger BB is basically making more contact with the patch, which does allot more than a typical bucking. So good ammo is really even more important in an rhop than a typical mound style bucking.

Also for another note of oddity with hopups that ties into my mention of FPS. Bolt action rifles have an oddity that typically more hopup to a certain point will actually increase FPS rather than decrease it. The theory I've seen mentioned is the way the BB is held causes it. To be completely honest I never worried about it, but it's something to be aware of. Especially important is if you're going to chrono for events it wouldn't be a bad idea for sniper rifles to chrono with the hopup set to the proper setting they will use. Turning it off for chrono may yield a lower FPS than what it will shoot with it on etc. So just another thing to be aware of.

Luke
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FearNoEvil

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Re: R-Hop FPS?
« Reply #3 on: June 19, 2017, 02:19:51 PM »
Thank you all for the intel. Im completely new to the upgrade seen, so the information is greatly appreciated. With all of whats said, on short note I supposr what im getting at...Is will my Rhop be just as effective running 320 fps with .20s Vs running say 350 fps with .30s? I want to be sure if I should leave it as is and run with .20s. Or upgrade spring and run .30s?

luke213

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Re: R-Hop FPS?
« Reply #4 on: June 19, 2017, 03:19:38 PM »
So first things first there is almost zero reason to ever run a BB under 0.25g for almost any circumstances. The velocity will be higher at the chrono but it quickly bleeds that speed while the 0.25g continues carrying more energy over distance than the lighter round. So basically the rule of thumb is heaviest round that makes sense cost wise and velocity wise.

So a quick estimate would be:

150-350FPS 0.25g
350-450FPS 0.28-36g
450+FPS      0.36g+

Generally for myself I run 0.25g from 150-450FPS or so because of the economy of decent ammo at those weights. Going up to 0.28-0.30 can double the cost which is too much in my opinion to account for the extra bit of consistency provided at those ranges possible with that FPS range. Anything above 480 or so I tend to run 0.4g-0.46g and those are long range and significantly more expensive than any of the other weights, IE it costs at least 10 times the cost for those BB's compared to my normal 0.25g ammo.

Also joule creep was mentioned, do read up on that, as well as measuring energy with FPS vs. joules. The reason is while I used FPS in the above example it's not strictly what I mean. It's just because it's a common method of measuring velocity to get energy. So for instance if I chrono something at 1.6J then I convert that number to what it would be in FPS with a .2g projectile and use that number as my measure. That eliminates joule creep from the figure, or rather accounts for it with current rule sets to insure you're complying.

Now that all out of the way, a good rhop should run any ammo doesn't make any difference. If the inside isn't flush then it will overhop lighter weights of ammo. Even a good install is more sensitive as I mentioned in my first reply and because of that it's easier to overhop light ammo even when you don't intend to. But I've run rhops in guns that never get fed anything over a .25g because of velocity etc. So I'd decide what role you want the gun to fill, what MED you want it to have then determine what FPS you'll build for and the ammo weight you'll use.

Take care!

Luke
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