Load data for 8x57mm Mauser with 170gr hornady sst bullet

This isn't even a firearm! It is a grass seeder - an agricultural implement you tow behind a tractor.

Start with a couple good loading manuals. The bullet and powder manufacturer web site all usually have loading
data. I like to start with the bullet mfg. Using data
from any " Keyboard Commando " Handloader without
proper research, comparison &. testing is a very dangerous thing

More than likely several different powders & several different loading, depends on what "Your " firearm likes.
First place to start would be a couple different loading manuals, compare published loads, start low & work up always looking for sign of high pressure.
aIt is a very bad & very dangerous thing asking for load advice on the internet. Never, Never, Never take as gospel any load from the internet. Do your research, check your manuals, if it seems viable, well your on your own..
Best of luck, Take care & be safe..

Try Hornady with the VLD bullet.

This depends on the rifle and the ammo combination. I'd try Hornady with VLD or ELD bullets.

I think you are asking for an EXPLANATION of why, when you put a bullet in a CHAMBER with your fingers the bolt won't close but when you put the bullet in the magazine, it goes in the chamber and the bolt locks DOWN fine. Is THAT a safety system?

ANSWER: No, it is not a safety system. I am assuming that you are speaking of a standard BOLT ACTION rifle in a centerfire caliber configuration. The extractor, located near the bolt face is why it won't close. When you put the bullet into the chamber and then try to shut the bolt, the extractor has to jump over the rim of the shell casing. When you place the bullet in the magazine and then shut the bolt, the bolt face pushes the bullet up out of the magazine allowing the rim of the case to slide between the bolt face and the extractor claw and feed into the chamber. After firing or if you simply just want to remove the bullet from the chamber, pulling the bolt rearward, the extractor claw hangs onto the rim until the case hits an extractor bar causing the shell to fly out of the rifle.
A good question.
I would suggest a firearms training session. Check with the NRA or a local gun club for help.

1:7 would be ideal,but your rifle may shoot this ammo very well.you will just have to try it out.bullet placement is critical with a small caliber,but,300 yards should be ok,if you put where it needs to be

What exact bullet? Hornady makes a lot of .270 boat tailed bullets, many 145 grains weight.

Could need a new spring in the magazine tube.
Ebay has complete inner magazine tubes.
search for Marlin Model 60 .22 Inner Magazine Tube

Can't say without knowing the weight of the bullet.
You can see data for many calibers listed at the Hodgdon web site.
Go to http://www.hodgdonreloading.com/