OP, the load you mention is one of the most common loads for several powders in the burning range you mention such as H335. It would be a safe load for that powder and bullet weight.
I have never used ZombieMax ammo but your mentioned velocity isn't difficult to achieve with several different ball powders, including BLC2, H335 to name a few.
HS-6 is way to fast and is intended as a PISTOL/SHOTGUN/Cast Bullet powder.
I'm just about willing to bet your cartridge was loaded with a commercial double base BALL POWDER that isn't normally available to hand loaders. Not all BALL powder is spherical because some of it has been rolled to slightly flatten it for whatever reason.
Let me give you an example. A few years ago there was a lot of Chinese Ball ammo released onto the surplus market in 223rem(5.56Nato). I pulled 50 bullets from the cases so that I could measure the powder charges, bullet weight, case weight and check case capacities with water. Other than a few off center primer flash holes they were extremely consistent. Less than .20 grains of powder weight variation for an average of 24.5 grains of powder. The bullets were even closer in weight. The cases were as consistent as any commercial brass. The velocities over my chrony were around 3200FPS. That velocity could easily be duplicated with that weight of H335 or another "surplus" powder being sold by Higginson's at the time.
Check your burn rate charts and go onto the internet to look at the descriptions of powder types. The Lyman manuals has a pretty good description of shape and lists those shapes in the powders section of their manual.
I so often see folks here that instantly shut down when it comes to making decisions as to powders. Mostly it's because they DON'T DO ANY DUE DILIGENCE. It isn't that difficult. Most of the information is there to extrapolate what you're looking for.
You made a good start but now you are asking us to make a decision for you. OK I can understand that you might be asking for some guidance. Fine.
Don't make an assumption on physical appearance. The reasons are self explanatory when you read the manuals and understand how burn rates happen and why they are fairly consistent. Just understand that consistency varies from lot to lot. Sometimes by quite a bit. That's why I don't buy powder by the pound or part containers of opened powder. Also If I have to purchase several one pound cans of the same powder and the lot numbers on the cans are different I pour them all together and mix them into ONE large lot. That way I can be sure my powder charge will be fairly consistent in performance, rather than get a sudden change from a different lot. This works very well when you have to replenish your stock. If you have gotten down to around a third of what you like to have on hand, say ten or twelve pounds, pick up another keg and mix it with what's left of the last batch. It will still be SAFE to use your already established load as a starting point and very likely won't require any tweaking.
Now if any of what I've mentioned makes you UNCOMFORTABLE, err on the side of CAUTION and don't do it. I've salvaged a lot of powder by blending powder with the same designation, made by the same manufacturer. It isn't often that two lots of powder will be identical. Sometimes powder with the same description on the can will be made in a different country or factory than the next lot. Still they will be similar enough to be safe, unless your loads are at maximum or over.
Litigation is what keeps manufacturers in line. I don't blame them one bit for being excessively cautious. Delving into hand loads without doing any due diligence is a recipe for disaster.
You can't tell what any powder is just by looking at it because the same manufacturing processes are used to give it the shape it has. It's the coatings on the outside that determine burn rate for the most part. By having a velocity, combined with a bullet weight tells you a lot and allows you to go to a MANUAL for comparisons to deduce similarities with other powders for that cartridge component combination.
