you can buy a random unupgraded stat roll of a weapon in the "brunts armory" tab of the armory exchange
they can be fully consecrated to get 2 random perks and 2 random blessings on it, and to change which ever of those you want on there, you earn the ability to do so via mastery, which is earned by using the weapon, or sacrificing matching weapons into that weapon archetype. mastery is also what allows you to empower a weapon to futher raise its stats closer and closer to its displayed potential.
99.9% of the time, the dumpstat is always the same for the type of weapon, the usual cases are mobility, defences, collateral, and warp resistance
any weapon that has collateral typically actually is better when the collat is lower, as the stagger can make you miss shots, so its always a higher priority dump UNLESS you are using a blessing that benefits from staggered enemies, like no respite or pinning fire.
some weapons have both mobility and defences, which comes down to personal preference, whether you want slightly further dodges, or slightly reduced push/block cost
the literally only case where damage can be dumped is on the flamer, because the 20% dump is a loss in 1 singular damage on the hit that applies the burn dot, which is absolutely hilarious that they have a stat for this that changes this little