SOFT bucking ALWAYS if you want better accuracy and consistency, only downside is that they wear quicker.
For a G36 hop up I think the best rubber/bucking is the madbull blue with a sanded off nub. Amazing results. literally put another 30ft straight trajectory over the stok JG one, with the mod of course.
For an M4 - everyone uses a normal cheap guarder one cause they are just that - cheap and they actually would be close enough to a stock TM rubber which is considered one of the best out there.
For my L96 - DEFINITELY brilliant with any type of gun though - W-hold bucking - I just get great range and accuracy with this. Best bucking ever IMO - I can't wait to get one for my m4.
Then for pistols or VSR's get the nineball or a stock tm is as good
The hold bucking is PDI correct? For some reason I thought it was not for aeg's. I have seen madbull and they seem to be extremely well made but for me to thick to install correctly(will try one eventually. Also when I removed the internal mound on a G&G green bucking and it ripped after a few hundred rounds. By rip I mean it cut the sides of the h-nub being pressed into the barrel (which might have not affected accuracy am unsure). That last statement may be confusing so forgive me if so.
As above I use a dremel and sanding drum to take the main lump off, I then finish off by fitting the rubber (inside out) on to the end of a barrel and hand sand using fine wet and dry (spit as lubricant). Clean using soapy water followed by mitre bond activater spray, sadly not everyone is going to be able to get hold of the last one unless they are or know someone in the building trade.
A blue tipped wrench is a butane torch. I normally use it for unfreezing locked or rusted bolts. Hence the term blue tipped wrench. I though it was a silly question so I decided to mess with you. It's not personal trust me.