@SkyNex0 Ah another swede, welcome to the club / addiction ! ( funny Nybro of all places, my father is from there ). Regarding the nub, yes, try first 0.28 with the standard nub and you can always mod it by filling the rubber ring with something solid ( piece of metal rod or similar ). Second, GBBRs run a bit differently from the little fortune of replicas you already have. The MWS is weather dependent like ajumma says and you might have to chrono and check how yours run in the different seasons. For reference, mine more or less stock was able to go CQBR during the colder seasons of the year ( yes, Sweden ).
I'd highly suggest you to take the time and scan through this 160 page document as it contains a lot of useful information. I think there is also a google doc which sums up the "essentials" ( which should be pinned ), it appeared not too long ago. But I'd recommend the long tour to see how the discussion has varied and to also get some inspiration. There are some pretty interesting builds along the way.
As for buying parts, these stores have the biggest assortment for the MWS:
Hong kong:
RedWolf ( Slightly cheaper, price match, best shipment costs but mostly sold out / few items in stock )
Rainbow8 ( Overall good price, o.k shipment and good stock )
J.K Army ( Slightly more expensive, nisch items that others don't have, annoyingly high shipment costs and customer service which leaves much to be wished for )
Europe:
Firesupport
Emperion