What mag brand should I use?

[Sagittarius26]

Hi there Forum,

Not sure if this is exactly the right place to post this but I'll go ahead anyway.

I recently installed a Guarder C8 Carbine upper and lower receiver to my TM M4A1 (Non-blowback). This also included a new mag release button. Prior to the new body kit, I was able to use my King Arms 120 Round Mid Cap mags. No feeding issues and fit flawlessly in the magwell. However, now they don't fit and they seem to too small. Basically the mags don't lock into place.

My question is, what mags should I use now, that will fit perfectly?

Thank you.