Sorry in advance for the rambling, lol. All this is just my trial and error. Though she did musk a lot, I never saw any other stress behaviors from her (throat puffing, regurgitation, meal refusal, etc.)
I let her settle in for a few weeks; QT for me means paper towels so after meal 1 she got 1 pick up/relocate handle so I could change the towels from poop/pee weekly (more if she pooped or peed more of course). Did that for most of QT and she wasn't super musk-y then, almost entirely rattle and flee, but I only had hands on her 20 seconds or so at a time.
By the end of that, she was probably 30 grams? So I tried 2x weekly handling for a few minutes at a time; that's where she really started in earnest due to opportunity; I'm sure she would have musked more during QT if I had handled for more than the time to move her around. She was so squirmy I didn't want to freak her out and I had others that I could handle for my "fix" of snakes.
Continue like that till she wa 50-60g which is when my corn had started to really calm down, so I had hoped she would too; it seemed like enough added size to at least begin calming. That's when I came across the frequent, very brief sessions that you aim to end positively (all directions said snake must be calm to end, but that was not gonna happen for her in < 5 minutes, so I adjusted to "calmer than the start").
It worked... ok? She did calm a little bit, but pretty much musked for the full 5 mins with 10 seconds burst of freeze/no musk "calm"... not really a positive as it was definitely a fear state. I gave it the good old college try and didn't give up right away in case the changed process was her issue rather than the handling at all, so I did it for 4 or 5 weeks, I think.
By then, especially since she started "projectile musking" the first session after a meal and being super dramatic about it, more than she was before, I decided it was not a good method for her (even if people online found success with it on other snakes). Also, I was sick of cleaning musk off of not only my hands, but my shirt, pants, the floor, her tub, her hides, her water bowl... etc. It was not very localized once she was long enough to swing her tail around and get it everywhere.
From there I kind of decided she was not likely to be a handling snake. I considered seeing if there were any breeders looking for a female with a year of feeding down that wouldn't care if she hated handling, but ultimately decided that I was committed to her. Even with her "awful" personality, I was too attached.
Instead I thought I would do a combo approach for 2 different things. Unlike most kings people talk about, when I had her in a display-type cage, she was NEVER out, and if she was would be extremely frightened if anyone entered the room. So I have her in an opaque tub; she is maybe 2.5 feet now and in a 3ft long tub. If/when she gets over 3-3.5 feet, I'll look for a bigger tub for her. Even if I need to make it opaque myself with spray paint, lol.
2nd I stopped handling her if at all possible. In the tub, she mostly pooped away from her preferred hide, so if I was quiet I could sneak it out of the substrate without disturbing her; I could also manage the water the same way. So I had probably 3 months where she was handled twice to do a full cage clean and nothing else. Then I moved to this every other week lift her out when spot cleaning, and keep her out about 2 minutes longer. I also tried for a bit leaving dirty socks or scrap fabric I had carried all day in her tub to hide in and smell me, but it didn't make a noticeable difference.
In a few months I may work up to weekly holding past the cleaning or just 5-10 minute sessions every 2 weeks, but we will see if her improvements hold.
She is probably 1 year old now, I got her early March of last year as a probably 1-2 month old. (And I do NOT touch her in shed.. she's so skittish and defensive that it isn't worth it at all for her; as soon as I notice, I avoid even lifting hides to look in on her until I spot shed in the tub and only spot-clean the open area outside the hides; tub gets fully cleaned when she is shed out usually)
I'm convinced that her calmness has nothing to do with being handled. I think it is almost purely her increasing size and her comfort and security in her tub. Even now, if I open the tub and wake her up without immediately scooping her up, she rattles like mad and if I hesitate I can almost guarantee it will cause her to musk me. She also rears up rattlesnake style and will chase me out of the tub trying to bite. Needless to say, I don't hesitate and if I do by accident somehow, I just close the tub and try another day.
I have done the "you can't scare me, I will handle anyway" routine, but she never calms if I do that and usually the next few sessions are bad for us both (I stopped doing that "handle anyway" during the low handling time about 2 or 3 months ago; I doubt her improvement is related, but she hasn't regressed after brief improvements like she had been doing consistently before); as long as I get her out promptly before she fully wakes up to be fearful, she doesn't seem to have the association that she "scared" me off before nor is she as afraid of being out..
What works for me may not work for you, and I don't know how temperamentally similar a MBK is to a chain king, but you can try any of the methods to see what helps you. Just don't make changes constantly to your process. Pick a few things and do them for 1-2 months minimum once yours has had a few more weeks to settle in (like boger said).
For example, 1) keep lots of clutter & low traffic, 2) handle only for spot cleaning + or - a few extra minutes, 3) don't wait for the snake to wake up fully and get into full fear mode by seeing you (I gently touch the side if lifting the hide got no reaction, then smoothly lift from the middle body onto a flat palm; enough to say "hey I'm here" before just scooping a fully asleep snake;if the hide lift results in movement, I just scoop up cuz that means she isn't asleep).
Or do it reverse on #2 & 3, handle often and briefly and ensure the snake knows you are there well before attempting to handle... success has come from both directions that I've heard.
I don't get pics of her often since she is a handful, but here is an older feeding shot.
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