valky - great job!!. You get research further than I did.

I can guarantee that these caches are still available after the quest end. Maybe during the quest two others are created so you can get total of 4 caches there. Something to check...;)

Still in Hephaistos there is also an Asteroid labelled "Asteroid fragment" in the center of that same ring that you can smash, it will give you the following : fusil, lycanthrope, gunsliger (tier4), mortar, shield prototype (pretty nice at this stage of the game), m-115 yataghan.
I found it trying to find the second wreck that drop the trident, but it seem i dont have that second wreck in my game :s seem i havent triggered the quest yet for that wreck

does it mean Fort Russ has a cache? I did not find one.

found a stash in Pegasus,

4 grids north and 4 grids east of the Southwest corner. A Wyrn Mk 2 for me;
1 grids east and 5 grids north of the Southwest corner. A Trident for me;

and
first Grid northwest corner, already been mentioned, 2 Gunslingers for me.


found a stash in Tarrot
4 grids northa and 6 grids east of the Southwest Corner. A Wyrn Mk 2 and some guns.

The Destroyed Patrol Station in XK 41 is also a stash

Fort Russ: Garbage Patrol Station (?)

I can't help you if you did not see a "BIG" (..debris) Patrol station *eg* - it's the one below the northern most portal, just blow it up

I've got some more specific directions:

9 squares from the left
4 down

on the line between 13 and 14 from the left
on the line between 2 and 3 from the top (blow up the ship)

*SPOILER*
a good tip to permanantly tank aliens in Precursor system is to use the following setup on your Astarte :
kali * 2 (+3000 shield hp and +10 hp regen/s each)
tungsten *1 (+20 armor hp regen/s)
helios * 3
system firmware mk 3 (for the 250% armor/shield regen boost)

You can get those modules at normal cost in Charon at the Styx station, if no access to FTU warehouse or dont wanna pay for smugglers fee. Make the money for them in XB-19 and get the firmware easily.

With the IA pilot you regen 50 shield and 50 armor per second, you are generally at 90-100% armor because of aliens missile and shield generally drop at 10-20% when they are all on you at same time, but by the time a wave is destroyed, shield is back to 50-80% enough to protect from next wave. If you want to use your fighters the trick is to redock them all when there are 4-5 aliens left on the field before next wave pop so they dont get hurt by missiles and let the Astarte fnish them (had a triden with a phoenix repair system, but wasnt enough to prevent damage from missiles over time)

The tungsten is mandatory because even if they (almost) never get past throu your shield with their guns, their missiles blast in a green cloud that harm your armor over time preventing you to stay there indefinitly. This way you can leave the game running without watching at your ship.

I even left the game running for 1h in 4x time mode without getting killed, with fighters docked. Made a few thousands stat points ^^ well that's a bit of a cheating i admit, that was purelly for testing purpose, i reversed my save after obsiously ;)

Beside this fit, i'm using all the time a similar fit using 2 kalis and an emerald on the astarte with system firmware mk3, this setup tank almost every huge ennemy pack fleets at this stage of the game (managed to beat all ships in InoCo system multiple times before the precursor mission and cleaned Beta Larethia with the mothership as tank when entering system). Only non laser user weapon are a real threat to this setup (like kinetics on gunslinger ships, they melt this fit but you can tank 30 tiers 4-5 laser user fighters easily). No need of Smog unit with such fit.
*SPOILER*

Precursor sector secret
 

*spoiler* That tip with starhammer memorial was amazing. Since I had a good mothership I managed to easily and continuosly kill waves of aliens that were spawning and gained 2000 exp points for each of the characters. But the memorial is not the only secret in the system. Right in the middle of the sector at the border of dust field there is a ship hull that will drop an artifact. It doesnt have a value or any use but if you want to see what message did game creators leave on it in a form of poem you might wanna check it out since you will have to go to the middle of the sector at some point any ways.:-) *spoiler*

I found that artifact too, its the only one Aliens dont take back when you leave Precursor sector.

I'm really wondering if the op of this thread was very lucky or not but i never got any artifacts (gun or anything) from the Star Hammer memorial or from the Artifact contener close to it.

Any confirmation of drop? i reloaded over 50 times an old save there to check for that precursor gun but no luck at all (i guess there are more guns later in the game from precursor since Joseph has the skill for them)

Just unlucky, you might have to reload before you enter the system.

I found something very interesting, apparently the patrol station in Argon occasoinally offers missions for you to kill some pirates for 10,000 credits. This mission is apparently repeatable, since I am now doing it my second time (been going to the Argon station to offload pirate pods).