[problem] Metal upgrade for marui tactical master

[AlterX]

Hi folks,
I'm italian and new user... :cheers:
I have little problem to upgrade my marui with g&g metal kit.
(I speak english little and bad, so...sorry in advance :grin: )

Original barrel has two lateral gap for fixing precision barrel and little metal group(which has lateral hinges).
The other one (in metal) doesn't have that above and so, precision barrel' hinges
don't match with metal barrel !!
I post here becouse I have seen photos of metal tactical marui with same kit.

Please help me and thanks in advance!!