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[Fridge Gnome]

I just recently got one of Noobies TDCs in the mail, and I was wondering what was trending in hopup arm shape was.

I had an arm with an SCS glued on.  Is a concave shape still the way to go?  Or have any new designs come up.

[xbeeongx]

In my experience, the standard internal nub shape is perfectly fine for pretty much every application.

It has the best chance to center the bb each time with maximum consistency of the bucking shape. "Fanged" shapes like those used in the firefly style buckings are too flimsy and don't return to their original position as consistently after prolonged shooting.

It is better to look at your hop up systems' rigidity and spacer-placement for fine tuning rather than your internal bucking nub shape.

[Fridge Gnome]

Oops, I meant the hopup arm shape, not the bucking nub.

[xbeeongx]

Oops, I meant the hopup arm shape, not the bucking nub.

Well in that case, I use a set of standard PDI hop up arms in a PDI L96 hop up chamber, but instead of the clear spacer, I used an SCS. Just dropped in, and held in place with a dab of modeling clay.

This mod gave me a 2.25 inch grouping using bioval .27 bbs at 110 feet with my current weapon system.

[lulukchoo23]

I do the same, using modeling clay, except with an H nub. I feel that stiffness and rigidity are the most important factors, because they rob less fps from your bb and apply the most consistent hop.

Personally, I like H nubs better than SCS's. I like to explain with the use of bowling balls. When bowling balls are returned to you after you roll them down the lane, they are shot back at you on these 2 long rails that guide the ball all the way back. The ball rolls smoothly and straight, whereas when you throw it in the gutter, it rolls to the left and right and it's not quite smooth.

2 points of contact provide the bowling ball with the smoothest roll, and they provide the bb with the most consistent hop. However, a concave shape like a gutter has too much leeway.


As for the nub shape in the bucking, it really doesn't matter all that much. It just has to be stiff. 2 points of contact would be preferable, like in the PDI bucking, but other than that, a thick rubber bump like in most buckings would be fine too. No nub in the bucking also works as well too.

[SVT Cobra]

^^^ Im not too sure if I would agree with the bowling ball analogy. It makes sense, however the SCS has a radius of 6mm and matches the profile of the bb. There really shouldnt be any "leeway". Additionally the bb will be centered by the H-nub/SCS as it gets chambered, so the analogy of the bowling ball rolling down the rail/gutter doesn't apply to a bb being chambered and shot. If the spacers are used with "nubbed" buckings, then their actual shape wont have too much of an effect of how the bucking nub actually guides the bb since the shape of the spacer wont be pronounced through the nub. All it really does is to give the nub in the bucking a concavity which allows it to apply equal pressure over the surface of the bb (as opposed to a flat bar applying the most pressure directly over the center of the bb). Either spacer will accomplish this.

The shape of the spacers may have different effects from each other in "nubless" buckings since the shape of the spacer will be more easily pronounced through the thinner material.

I cant vouch as to whether one spacer is better than the other since I have not tested the H-Nub. However I wanted to offer my opinion on the matter

[lulukchoo23]

Actually, what you said does make sense. I kinda felt like someone was going to say somethig about that. But I mean, I still feel kinda iffy on the consistency of the SCS, mainly because reality is always a little different than the theory.

My concern is, when using the SCS, the shape of the actual surface that makes contact with the bb is different than the shape of the SCS. I doubt that the SCS can make a perfect shape with the bb (right now, we're talking about a bucking with no bump or nub inside), since there's a good amount of variables, like the thickness of the bucking and the amount of hop applied. The thicker the bucking is, and the more hop applied, the bucking becomes less concave and more of a flat shape. However, an H nub pushes down on the bucking in a more direct way with all of the hop focused on two points, so the bucking is more likely to retain a shape with two points of contact, regardless of thickness or hop amount.

Then again, this argument is all just as theoretical as the argument for SCS's over H nubs. Maybe in reality, the two are equally consistent and effective! It's something that would be really hard to discern, since I doubt that the difference is really significant at all.

[SVT Cobra]

Actually, I think you make a good point there lulukchoo23. I feel that the SCS works better in AEGs since the buckings are so much thinner. I can see the SCS give the nub in an AEG bucking some concavity. I also recall seeing the bucking nub relatively flat when I tried out an SCS in my VSR. I never had much luck w/ SCS in my VSR. They work great in my AEGs however!

...and like you said, the shape would be more pronounced without a nub ...i've never gone that far though.

[Fridge Gnome]

Maybe I should try making a concave arm that's larger than the bb to compensate for the extra rubber.

[The Crimson Falcon]

I think the SCS nub is generally probably better.  The only important factor is consistency in where it applies pressure.  The closer your hopup gets to applying consistent pressure in the SAME spot every time, and the closer that spot is to perfectly vertical on the BB, the better your shot-to-shot consistency will be.  And at the end of the day, that's the be-all and end-all.

[Fridge Gnome]

I have 3/16th rod coming in tomorrow for the arm, but I found some scrap rod and tried to cut an SCS shape with my dremel and it went pretty horribly.

Is there any better way to cut a perfect concave shape like that?

[gunfighters]

buy it?
short of a lathe chucking it in a drill will be your best bet