In my relatively short, but immersed experiences with DMT... it takes work for vaporization breakthroughs! My first efforts were all across the board--I tried the machine, vaporgenie, aluminum foil, weed pipe and bong wasting copious amounts of DMT to edgy, half-trippy states of being that were quite uncomfortable (for me at least).
First thing I want you to know is the problem of "breaking through" is not unique to you, so rest easy and take the load of all those stressful thoughts off your shoulders
Secondly, I as well did not weigh my doses at first thinking I had a good idea of the mass I was putting into the vaping apparatuses.. Well I definitely didn't I realized when I bought my scale. Every body requires a different amount to break through seemingly determinate upon countless factors including diet, previous drug history, and metabolism. Heck even someones mind can prevent them from fully allowing the drug to take over. The point is even if your friends are breaking through with X amount it's not gonna guarantee it for the next person, pretty obvious I know but it has to be said
Also, everyone's breakthroughs are unique to themselves as well, the content of the experience that is. This is something I had to come to terms with--the fact that some people will have conversations with God every time while I just keep getting harassed by elves for my lifestyle hehe. Don't expect to see what you want to see when you do finally breakthrough. If you are really serious about the experience then I recommend getting something to weigh the doses, 25 bucks will get you a sensitive enough scale!
Thirdly, If the ash bed sandwich method is not working for you, change it up! You are right about the fact that it's not the best method and while it can work it is hit or miss for beginners it takes a lot of technique. Torch lighters are a great investment for your future journeys the bursts of heat are incredibly useful for controlling the vaping. The only way I was ever able to breakthrough vaping was in a water bong using a layer of herb, then DMT, then some more herb. I would light the top layer of herb to a rolling cherry and this would vaporize the large amounts (75-100mg) of DMT. Because it was in a bong I could clear the whole bowl in one hit filling up the chamber with the herb/DMT smoke/vapors. The large chamber then acted as a storage device for me to catch my breath quickly and breathe it all in in one large breath without wasting lung capacity to pulling the smoke through.
Again, this is just MY personal way of breaking through.. many other people I have talked to have entirely different methods, you have to find the right one for you
Lastly, as for your question about 100mg being dangerous... You will always come back no matter what my friend--recently I have had some very strong experiences where the concept of "I" did not exist and there were no thoughts of coming back to reality. Alas, I did come back just like the rest of us!! The last resort for attaining breakthrough with vaping is to add more of a dose. Again my personal experience has shown me I need more than most people to really lose touch with physical reality, perhaps you are like this as well or perhaps your method needs to be better--I'm certain no one has an exact answer for you unfortunately.
In closing I should also note the addition of harmalas from natural plant sources or in their pure forms will greatly increase both the effect and length of your dose. Harmalas will also orally activate DMT creating a several hour long experience in which you can navigate your consciousness with much more ease. This type of administration has many different nicknames all ending with the -huasca suffix: ayahuasca mimohuasca pharmahuasca etc. Since experiencing orally active DMT I neither have the urge nor the motivation to vaporize it anymore... Vape sessions with DMT are too intense and fleeting for this guy
The forums here on the nexus have a wealth of information regarding all methods of administration as well as health and safety and dosing. Everything I've told you so far has already been said somewhere else in the forums but that's ok cause we are here to help
I do highly recommend browsing the forums extensively before setting out for your next journey.
Welcome to the Entheogenic University from iomega, and just remember DMT is an unbiased, unrelenting teacher that deserves A LOT of respect... patience and dedication my friend
Hope I've helped in at least some small way!