You're probably noticing decreases stats (firearms, stamina, electronics) with the full set of lone star vs your mixed bag gear because the mixed gear probably has stat bonuses that are better than the lone star pieces. This is something that you can fix by recalibrating the lone star gear so you get the same kind of bonuses as the mixed gear.
What do I mean by this? Say you have a random chestpiece that has +500 firearms and you swap it out for a lone star chestpiece that has +475 electronics. When you look at your character, changing your gear results in a drop of 500 in firearms and a boost of 475 in electronics. This can be compounded when you're swapping all 6 gear pieces and even further when you consider the set bonuses and what skill bonuses each of the individual pieces have.
If, as you mentioned above, you want a firearms/stamina build, you can benefit from using multiple pieces of a set, be it lone star, some other set, or combos of sets. What you need to do is recalibrate any of your pieces that done have the stat bonuses you want. In this case, if you have any pieces that have electronics as the main bonus, you want to switch that to firearms or electronics. Recalibrating like this should help you out.
That being said, remember you can only recalibrate one thing on each piece of individual gear: i.e. the stat bonus or a skill bonus or buff. Start by recalibrating stat bonuses that you don't want to bonuses that fit your build. Then, with the pieces you have left start changing skill bonuses or buffs that you don't like to ones that you'll use. If you have a piece that gives bonuses to turrets and you don't use turrets, that's something you might change in hopes of getting a bonus to pulse, smart cover, healing, sticky bomb, or something you use.
i want to try to improve my characters toughness etc as im currently at toughness 343,969 but he still seems to lose his health quickly, i do use skills as a health skill but is there any other way to make my guy tougher.
Toughness is basically made up of your health, which comes from your stamina and from any health bonuses your gear provide, and your damage mitigation, which comes from armor. There's no cap to your health, so increasing your stamina and adding as much bonus health as you can from gear and mods is an easy way to increase toughness. Armor, however, is capped at 5354, which provides 75% damage mitigation. Any armor that you have over that is a waste and you should try to recalibrate the armor to some bring else or use mods that have a bonus other than armor.
You can also make your character more durable by increasing your protection from elites, which reduces the damage you take from yellow bar enemies, and by increasing your exotic damage resilience, which decreases the damage you take from non-bullet sources (like grenades, fire, etc.). To see what your values are for all of the above (health, armor, protect from elite, EDR), bring up your character stats and then scroll down to the section called "Survivability".
also when i was in missions on the underground recently some strangers i was playing with kept enablign explosive bullets to the whole team all the way through the mission, could somebody tell me what talent/perk this was as id love to have it as makes a big difference to the emenines
All characters can carry 3x incendiary (fire) rounds and 3x explosive rounds as a base. These can be equipped by hitting right on the D-pad (PS4) and selecting them from the consumables wheel that comes up. This is the same place where you can eat energy bars to remove status effects, drink water to cause more damage to elites, etc.. I'm not sure how you bring up the consumables on XB1 or PC, buy you should be able to figure this out by looking at the controls and seeing what activates rbe consumables.
The specific phenomena you are referring to so something different. One of rbe people in your group was using rbe reclaimer gear set. Here are the reclaimer set bonuses:
Set Bonus (2):+100% Support Station healing speed
Set Bonus (3):+50% Consumables Duration
Set Bonus (4): Talent | Reclaimer Consumables and special ammo used now apply to the whole group and are not consumed on use.
They were utilizing 4 pieces of reclaimer and using the Reclaimer talent which means whenever they pop a consumable (ammo, water, etc.), everyone in the group gets the benefit of the consumable and the consumable isn't consumed from their inventory. Typically, when you use a consumable, it only affects you and it reduces your on-hand for that consumable.
It's my understanding that only the person wearing the reclaimer gear can pop an item, give everyone the bonus, and not have the consumable consumed. So, if you popped the item, it would only work for you and it would be consumed, since you weren't wearing the reclaimer gear.
Hopefully this info helps. Feel free to post up any further or follow-up questions you might have.