300mg of meth shot all at once is a massive dose. If you try to chase that then you'll likely end up horrifically addicted and completely wreck your tolerance.
If you want to do extreme stuff like shooting 300mg of meth at once you need to wait for your tolerance to drop before you can expect to get decent effects again.
Please take tolerance breaks.
^^^
What he said.
I would maybe suggest taking DXM to lower your tolerance, but you'll need to also stop using for a while in order for your tolerance to have a chance at dropping. Especially at those high doses, you've got a ways to go. You would need to be basically robotripping all the time to keep your tolerance at bay, but yeah, DXM will reduce the development potential of tolerance to many drugs. But if you want your tolerance to go the other way, you have to take brakes, and/or do small amounts, best to save your stuff/money and do a fair amount of dxm. Also the polistirex form of DXM like that found in Delsym, is a very long lasting version, which works nice as a tolerance buffer when using. But doing DXM is a disassociative hallucinogenic, so i'm just putting a word of caution on the robo tripping. I've found myself mixing meth and dxm ALL the time, and that's another unique experience, but if you continue to use the drug, it makes it hard to lower your tolerance. I've found in my own experience, and what many others have also said, is that it may only take a short tolerance break, while taking a rather small amount of dxm. and after say, a week, you could find yourself with much stronger effects from much less. But yeah, that 300mg IV Dragon is a dangerous beast, i'd find a smaller dragon to ride if you can. Chasing something like that 300mg you did sounds dangerous. Plus you can definitely still enjoy other ROA, especially with a lower tolerance.
But its more of a saying, that once you start to bang it, (shoot up) you cant go back. Not so much that you cant, but you know, it just feels like wasting it.
Honestly i'd look into other substances to help you out in maintaining for a while if you can, that way you can find a nice way to enjoy it for longer if you so desire. Balance is so key.