My MB 01 has probably been in pieces more than it's been together! I've been inside a couple of other clones including a JG BASR and no name gas pistols. The one thing they have in common is very similar manufacturing processes and materials, albeit with a significant variation in the quality of the fit, finish and tolerances. Very much a case of you get what you pay for.
Some products are always going to be a better base depending on the result you want to arrive at. Can we agree that a 90° trigger is more effective and efficient than a 45° trigger when using high power springs? Or that an aluminium cylinder is going to be far closer to its failure point with the same spring and you might need a steel aftermarket item?
My point is that whatever base you start from, achieving 3J and enough accuracy for satisfying target practise is a big ask.
I'm certain that your TM is both better made, nicer to use and more accurate out of the box than any Well product, and so it should be, but for a bit of target practise the same money will get you a nice little air rifle that will beat a BB gun hands down.
But this is side tracking the OPs original question.
If you want to put the time, effort and money into building a BB target rifle start with the barrel, hop, bucking and nub. Well barrels are OK but they're not great. Do your research and find out what fits and what doesn't. Get it shooting straight first and then figure out whether you actually need any more power.
Do try and make the best of the parts that the rifle came with. Strip it down and clean and re lubricate with better products. Do the simple mods that improve air seal and consistency, like the dental floss bucking mod. Figure out where the manufacturing tolerances allow movement that can be tuned out. This can be as simple as a couple of wraps of PTFE tape on the threads between mating parts or a few drops of thread lock in the right place. Stabilise the inner barrel to the outer with simple wraps of masking tape to make barrel spacers. The list goes on!
You need to be prepared to experiment and find your own solutions. I've read so many threads where someone had asked, "How should I upgrade xxxx gun? ", and they've received a load of confusing and contradictory answers, or followed advice without understanding how things work and should be installed and the impact it might have on other components.
There are some excellent examples of sniper builds you can look up and mimic, but buying and assembling the parts is only part of it. If you don't put them together carefully with an understanding of why and how you'll likely end up a bit disappointed.
. My goal is to buy a sniper rifle and then upgrade it to at least 3J for target practice only but the problem is that i don't know if some parts are compatible with specifics airsoft rifles. This is what i'm gonna buy( http://www.target-softair.com/cat0_348/fucili-sniper-bolt-action/p612816-sniper-extreme-ops-mod.4410-new-2016.php), does anyone knows what should i upgrade for this and where can i buy it? Thank you 
