I am going to get a lot of feed back for saying this but the SP50 and SP51 are made of 5160 and in my opinion 5160 is not meant for a true survival knife.
5160 is traditionally a sword steel and for a reason. It is meant to distort before breaking as where a survival knife made of 1095 will chop right through something before distorting like 5160 will. The reason you see a lot of small chips on the edge of some 5160 steel survival knives is because the heat treat is to much for a softer steel so it is now brittle. 5160 in my opinion is not suppose to be at 56 to 58 RC like 1095 is. They do harden it to 58 to 63 RC for springs but not a cutting edge.
Will 5160 work? Yes if you are not being too rough with it but saw down a couple of trees and start de-branching trees with a knife made of 5160 steel and notice how before your shelter is finished the steel is sometimes distorted. Not something I want in a real survival knife.
If I was in a jungle with soft limbs to chop I may be ok with 5160 but not in the woods of North America.
One of the reasons I like the SP10 a little better than the BK9 is because if I am in a survival situation and I am sawing down trees and de-branching them with my chopper knife I feel that after 2 weeks of shelter building my SP10 will still be going while the BK9 has hit its stress limit and while chopping a branch it will break with a loud chinggg. I want a knife for the long haul and not for a few days.
5160 is a tougher steel than 1095, which is why it is commonly used on larger knives and swords. This helps it deform and not break when subjected to large impacts or forces.
Running a steel softer makes it tougher, and more malleable, not more brittle. Brittleness comes from (among many other things) being very hard. Knives that are too hard (and used hard) will "chip" rather than "dent". Chips being where metal broke off, and there are pieces missing, and dents are where the steel gave, that you just need to push back into alignment. That said, I have no idea why Ontario runs their 5160 so soft (52-54 iirc), which to me is contributing to the "distortion" that you are talking about, which will for sure effect the edge holding.
The upside is that something that soft should be nice and easy to sharpen (like most machetes, which are run soft for the same reason, because they're frequently hitting rocks, chainlink fence, etc)

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Also... Did you have a bad experience with the BK9? I know you prefer the SP10, but I just wonder what makes you say you feel like the BK9 will "break with a loud chinggg". I certainly don't know everything about knives, or about everything that have happened to them. But since I've been on Bladeforums, I've only heard of
one BK9 breaking. And... it broke in the middle of the blade (just forward of the thumb ramp) due to a bad HT and probably part of the old roll stamping process. I'm sure there are more out there, but I personally would not be afraid of it just snapping outright (other than the chance for bad heat treat/ quality control that is inherent in any production blade).
I have no problem with the BK9 not being your favorite knife (or anyone elses for that matter), but I feel confident in saying that it won't just snap on you any more than any other knife would (because of material flaws). And I feel like saying it would is a bit over the top is all.
Doesn't the BK 9 have a skeletonized handle/tang like the other Beckers? Not an engineer but I don't get this at all in a large chopper. Weight savings at the expense of strength in a knife that most people are going to beat the hell out of.
For what its worth, the Beckers don't have skeletonized tangs for weight savings, its actually to get the balance point how Ethan likes it. He likes each blade to have a forward balance, and that helps him achieve that goal.
*crom, this is not entirely directed at you, I've just seen this one a few times recently, so I'm just venting
.*
<rant>
Also, this topic has come up a lot lately, and I'm honestly really confused by it. I see no reason why a
properly designed skeletonized tang should be feared. There have been failures on them yes, but like before, I've heard of exactly one of those (not saying there are not more out there, just saying its not frequent at all), and that one was... also by a bad HT. And I know I keep saying that, but there is a statistical percentage chance that a product misses its quality control checks and makes it out into the wild defective. Its a chance that is taken by everyone everyday in some way or another (be it cars, computers, knives, appliances, etc), that something will have either a manufacturers defect, or a materials defect. This is why warranties exist, to cover those types of things. With the number of Becker knives out there in the wild, and only hearing of a few, the percentage that actually break has got to be extremely low.
I think the point I'm trying to make is that while a solid tang might be
stronger, a well done skeletonized tang is more than
strong enough for the type of use it was designed for.
TLDR:
When I hear people say that the skeletonized tang worries them, It sounds like someone saying "I'm worried about how I-Beams are missing whole chunks of the sides, its probably not strong enough to build with".
</rant>
Anyway, to each his own. I'm no expert, and am willing to be corrected on any of the above, but as of right now I feel like I've got the main parts sorted out

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