TM Mk23 hop-up arm steel modding guide

[Amoki]

The problem: TM Mk23 GNBB pistol has one achilles heel: the weak brass hop-up arm. It lacks enough "base" for a firm resistance when force it exerted against it (e.g. when you push a hop-up rubber, when you apply hop to a BB via it, etc) - so either you'll eventually lose hop on your .25 g and above BBs, or your hop is ineffective especially when using aftermarket hop rubber that is fairly thck e.g. Nineball.

There were a few posts here about how people actually wanted to do the mod but never posted a complete guide. So here's one:



What you'll need to solve the problem:
1) Prog4/Illusion Kinetic Steel hop up arm:
http://www.prog4.com/db/product-show.asp?refno=AR1891

2) Dremel + Diamond Cutter Wheel
http://www.dx.com/p/20mm-diamond-cut...ce-pack-136790

3) Vice

4) PPE - glasses primarily

Do NOT follow the indent on the hop-up arm. See the last pic.


Standard arm


Standard TM 1911/hi-capa/g17 steel arm too "fat":


After modification. Original arm left, "standard" TM arm middle, modded piece right.
Notice how thin the "wing" that hooks to the hop up wheel on the original piece is and how much you need to cut off


+ buffing and grinding for the arm to sit flush. You may need to twist the arm slightly so that your hop is set straight.


I made the mistake of cutting by following the indentation mark - easy mistake to make when you can't line up both hop-up arms in 2D. This is what happens:



Now, as far as I can tell from shooting the beebs from a 30m distance (my backyard), I did not experience any inconsistent hop characteristics and the "back" of the arm + some parts in front appears to be sitting flush with the outer chamber. Still, it *may* be a problem, so I recommend cutting about 1-2mm before the indent rather than directly to it.