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Modifying a Maple Leaf Barrel to Fit a Tokyo Marui GBB Pistol


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I recently bought a TM HK45 Tactical and fancied seeing if there was any significant improvement to be had from a Maple Leaf Crazy Jet barrel and Autobot hop rubber, being impatient, I went for a 97mm barrel figuring that it would be functionally no different from the correct 100mm barrel. Turns out I was wrong and the barrel (designed for the Glock range) didn't fit in the TM hop unit very well at all.


The problem is in the layout of the various locating grooves and flats on the barrels, as you should be able to see, there is a big difference in the size of the flats on the original brass barrel and the new barrel, these flat areas mate with raised areas inside the hop unit, when I first went for a test fit the hop unit wouldn't go back together at all. I've since seen a lot of posts from Mk23 owners who remove the raised area in their units to allow the barrel to seat fully. I figured that wasn't for me for a couple of reasons, TM designed the barrel retention that way and they know more about hop up design than I do, also, a new hop unit is expensive and hard to find, a new Maple Leaf barrel is cheap and easy to find. Decision made, the barrel is getting ground away.


First step is to mark the area and firmly but carefully hold the barrel. Then select a wide radius Dremel grinding stone to help keep the area relatively flat. I wish I owned a milling machine (for probably the fiftieth time this week) which would leave a much nicer and more precise finish. I just have to be careful. You could do this on the kitchen table with a clamp and a file but I have these tools so they are what I'll use.





After grinding the first side it fits well into the opposing side of the hop unit (you can see the raised flat area pretty clearly here).



I tried a test fit and it was a lot better but still not quite closing nicely (notice the small gap between the two halves) so there was a problem on the other side and it is that the groove fits a raised ridge in the hop unit, this should be sorted with a quick buff to widen the Maple Leaf groove.





Once all the grinding I could think of was done it went back together nicely. The Autobot rubber is a wee bit thicker than the TM rubber so it's still a little bit of a squeeze but it went back nicely and the nub is pretty well centred.



Put the whole pistol back together and it shoots straight over ten metres, need a longer test process to set up properly and see what the real accuracy is like.


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