In gunsmithing and gundom in general “Tuning” can mean several different things. The next few paragraphs are some of the things it could mean.
Double actions: to set your springs to complimentary weights for light target trigger pulls in both single and double action for double action revolvers. This can be for combat or defensive guns as well. These combat trigger tuning is not as precise and a bit heavier but the triggers always come out smooth and with far less “stacking”
Single action: tuning involves polishing, spring polishing, or spring replacing with springs that work together to make a good, precise trigger weight. This is for cowboy action or other styles of competition.
Tuning Semi Auto pistols:
Semi Auto/Pistol tuning involves feed lips on your magazines, polishing the chamber, the ramp, and the breach face, re-cutting the extractor hook to make it work better, balancing your recoil spring for the load’s powder factor, and setting the springs for the best trigger pull with the most amount of safety it can have.
Tuning triggers on rifles: this includes setting engagement (how far your secondary and primary sear overlap each other. your over travel and your return spring weight (trigger pull weight)
Definitions- chambering and chambers:
Headspace as defined is the distance between the breach face and what ever stops forward movement of the cartridge. This could be the shoulder, the belt, the rim, or the case mouth depending on case design.
Lead: consists of two parts; the free bore for the slug before it engages the lands and grooves of the barrel. The throat or forcing cone; this is the tapered part of the chamber that transitions the slug from the free bore to the lands and grooves so that the slug will stabilize outside the barrel.
Jump: is the length from the slugs Primary diameter to the forcing cone/lead of the chamber. This can be set if you know how to measure it. Optimally 0.005″ to 0.030″. What ever your rifle likes best.
The lands and grooves: consist of two parts, primary bore: this is the original polished hole down the barrel and is the nominal bore size (caliber) for example 30 caliber or 0.300″. The second part is the groove diameter, the grooves are cut into the barrel larger than the bore diameter so that we have a spiral down the barrel so the projectile has spine/rotation so rotational energy will keep the slug from tumbling down range after it leaves the confines of the barrel. We rate these spirals in “twist rate” these usually come in revolutions per a designated length in inches. For example 1:8″ (translated one revolution per 8″ of barrel length). A 30 caliber has a nominal bore diameter of 0.300″, and a groove diameter of 0.308″ the grooves are cut 0.004″ larger than the bore diameter to have enough surface area to hold on to the copper jacketed slug and impart rotation to it.
Lands: the small part of the bore, the original/primary diameter of the bore
Grooves: the larger part of the bore. Consisting of either cut rifling or rotary hammer forged.