If you are looking for a little more firepower for your MP-10 and have deep pockets, Beta-Mag has finally released their 100 round dual drum mags for AR-10's which includes our MP-10's. I have 2 Beta-Mags, one for my MP-15 and one for my Colt M4 and they are awesome. I am sure that I will be getting one for my MP-10 but going to have to sell some other toys to pay for it.
The Beta Company | BETA MAG C-MAG | 100 Round Maga C-Mag Product Details

Really ?

I just purchased the 50 round X25 from X Products. The thing works like a charm, but when I first thought of buying it, the COOL factor took over my brain and kept me from realizing just how much heavier 50 rounds of .308 would make my rig... I can only imagine what a boat anchor that 100 round drum would make it...

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Corpsman FMF/SW

Like you I too have the X25 mag from X Products and you are right it is a lot of weight added to the MP-10. The advantage to the Beta is the fact that the weight is spread better and more balanced since it sits higher in the rifle and both drums of 50rds. each are moved to each side. I have Betas for my MP-15 and also for my Colt and the extra weight is noticeable but easy to manage. Also I have shot a HK91 with a Beta and it is easy to handle too. The main turn off for me is the price of these dudes.