Nub/window relief

[Crashtest33]

Hi all. 

Bit technical this one, sorry. 

When flat hopping, how much smaller than the window do you cut the nub?

I'm running a Promy .03 EG barrel with a 5.00mm long window.

(Firefly bucking, soft black)

 

[Hangtight]

I've always made mine the same length as the window in the barrel, same width as the cutout in the hop and 3mm thick. Check the position of the window against the cutout in the hop as they often don't match so you know where to position the nub on the arm. Easiest way is put the barrel and bucking in the hop, place the nub in the right place on top of the bucking, tiny drop of superglue on top of the nub and then press the arm down on top of it.

 

[ImTriggerHappy]

Thats not flat hopping that just using a flat nub with a firefly which is correct.

Make it so its about .3mm smaller all round for best results. If you make it too tight then there is no room for the bucking to stretch down so the tension pushes back, its only slight but its enough that it can cause inconsistencies and slightly lessen performance.

 

[Hangtight]

Been a while since I did a flat hop. 5*4*3mm is what I use for my R hops. Just been back and checked what worked best with flat hops. Same size but I put a slight chamfer around the face that contacts the bucking. Same sort of effect as making it a little smaller all round but easier to get the little bugger in the right place when glue is involved.

 

[Hangtight]

Blimey, I used to actually make notes about this stuff. Apparently I only found it makes a noticeable difference once you have a properly rigid hop arm set up. This was on my L96 before I put an AA hop in it, and I went to the trouble of making a properly fitting aluminium hop arm rather than the plastic thing. I dug it out to take a look and I used to put a chamfer on the front and the back of the nub.

 

[Crashtest33]

Thanks for the help peeps. 

I'm running a TM recoil with a 407mm Promy 6.03mm, Firefly soft bucking and a firefly normal flat nub. I'm also using the metal pin in the nub. 

I've gone for 4.5mm to allow a 0.5mm gap for the bucking to squeeze into the window. 

I'll let you know how she fires asap.