your thumb will break in with use!
it will get easier with time. there are a few things you can do to help it along, but that would probably void the warranty. also, i would rather see a detent be too strong, than too week.
give it a little time, if you use it everyday, you won't notice it before too long.
I didn't know what sarenmu was, so I googled it, and it kinda looks like a sebenza, doesn't it ?
Typically if the ball sticks out a bit too far and consequently falls into the hole in the blade deeper than it maybe could it will hold quite well. I've handled three of the 710 Sanrenmu folders and all three were consistent in build, thickness and the way the ball gripped. I found the Sanrenmu detents that actually work to be refreshing since most knives of this type are made and sold as gravity knives technically speaking for the most part even from so called reputable companies. I say this because I can't count on all my fingers and toes and yours too the amount of liner and frame locks I see here with ineffective detent balls that simply do not meet the legal requirement in most states. Its nice to know someone out there still knows how to do it right but in the event your model is holding a bit too much and could use a tweak what I normally do is take the knife apart and use one of the washers or one from my stock that is just a bit thinner than the height the ball sticks out. Then I surround the ball with that washer and use it as a physical block/spacer to keep from tapping the ball in so deep it no longer works at all. Basically what you will do is you use a flat end punch and a small ball peen hammer like you would use to do copper crafts or something like that. Tap the punch after placing it over the ball and the washer will stop you from taking the ball any further in than that washer thickness. So you end up with the ball bearing in the lock sticking out to the thickness of that washer.
It may help to measure the washer or washers on the ball side of the pivot with a digital caliper so you get an idea of what those are for thickness together or by itself. If you can use one of those great but I'd at least use one to see if that is the distance the ball sticks out now or not. If say two washers together on one side was how high the ball was out there then I'd drop that down just a bit more. For example if the two washers together are .020 thickness then find a .015 washer from another knife and tap the ball in .005 more for depth and it should help a lot in how much it grabs but not knock it in there so deep that it really changes a lot. Some of the Sanrenmu folders do have two washers on one side based on the pictures I've seen of them taken apart. Also, it appears that the detent ball in the three I've are 2mm size balls. I'm just guessing but I tell you this because in the event you tweak one too deep and need it to come back out it is possible to pop that ball out of the lock by coming in from the outside with an upside down drill bit placed in your chuck and simply pressing it out of there using your drill press but of course not turned on. Just be careful to place the lock ball side down in a spot where the ball can fall into a shallow hole so you can retrieve it. A small block of wood with a small hole should be all you need to catch that ball once you pop it out of there. Hope that makes sense. I spit things out fast sometimes and have been accused of losing people in the translation. I try though.
STR
I just recieved a new sanrenmu 710. The knife is very high quality, but I have a problem with the detent ball. It is so strong, it hurts my thumb to open it. Will this get better after use?
Also, no "hating on the sebbie clone" comments please