Don't reduce the charge too much. A smaller than normal charge of a slow powder can cause a detonation rather than the drawn out push of a normal charge.
reduced by 5% to 10% sounds about right, only fast burning powders should be used for very light loads. Its sort of counter intuitive but its a recognized effect.

I've pulled the bullets from Soviet Steel cased berdan primed 7.62X54R using an inertial bullet puller and then reloaded with a medium charge (forget the exact weight) of Winchester 760 powder and the 150 gr Hornady .312 I use in my .303 loads. These I crimped using the .303 lee loader's crimping feature.

The cobbled together sporting loads gave suprizingly good accuracy in an old and nearly worn out Nagant bore.

When I owned an Iranian Mauser carbine I ran across Canadian manufacture WW2 BESA MG loads which used a boxer primer. Thats probably the best 8mm military load ever made.
I had to anneal the case necks when reloading, but aside from that the brass was extremely durable.

because of the short barrel I looked up low intensity loadings suggested for the G33/40 carbine. they suggested 4198, and 4227 for reduced charges. Power level using 160 grain bullets was pretty close to 30-30 winchester levels are groups at 50-75 yards were very tight. I forget the exact charge weight (30+ grains).

PS
I was given several dozen rounds of South American 7.62 NATO ammo which was loaded with a powder which was manufactured for use in the 7.65 Mauser, and I'm told was exactly like the old Mauser powders, a flat square flake powder.
The powder from these rounds smelled very strongly of ammonia, so I set it aside in a steel powder canister. Some months later on I found the fumes from the powder had eaten away the bottom half of the canister and heavily rusted all the steel objects nearby.

This was a singular case of poor storage of the cartridges in a tropical environment and possibly the powder from only that particular lot was so unstable. The fumes leaking out of the cartridges before I pulled the bullets had already caused the gilding metal to start to peel from the steel jackets. I was not able to save any of the components. even though most of the brass cases showed no obvious corrosion I chose to dump the whole sheebang rather than take a chance on it.

I've heard of no such problem with the Turk Mauser ammo.
It's always a good idea to pull a few bullets from any lot of very old ammo and check the powder for signs of chemical break down. Broken down powders usually smell like cat urine, and pretty strongly.
Most powders have a slight ammonia odor that disapates quickly. If the smell is exceptionally strong, funky, and lingers, the powder is suspect.

I've decided to avoid old surplus ammo altogether as long as new boxer primed cases are available. I do like to use the Soviet steel core 7.62 bullets I pulled years ago in target loads for my two groove Savage .303. They mike at .3125 and shoot very well in the .303 two groove bore. I figure the steel core helps center the slug and the lead sheath between jacket and core is squeezed tight against the core and the hydralic forces of the semi liquid compressed lead extrudes the jacket into the grooves very evenly. I don't plan to use then in my five groove No. 1 bore though.