Be careful with your speculative math on total rifle weight. The CZ mini action is only 1 ounce lighter than a Rem 700 short action. The Howa is supposedly 3 ounces lighter. Mag choices obviously play into this discussion - but a blind 700 could conceivably be built lighter than the DBM CZ, as light, or maybe lighter than the Howa. That’s even before lightening mill work is done to the 700, or any consideration of Titanium clones. Personally, for 1-4 ounces of action weight, let alone break even weight, I would much rather have a 700, the bolt action rifle with an infinite aftermarket, instead of the two rather obscure and poorly supported mini actions. Bolt fluting, skeletonized bolt handle and knob, and some lightening mill cuts on the 700 action could bring it right in line for weight with these mini’s.
Your statement lumping the 700 and 70 together in one breath is foolish, as there’s 3/4 pound more steel in the 70 than the 700 - a full pound in the long actions. Ruger 77’s, Win 70’s, and Savages are fat - the 700’s, not so much.
Single shot bolt actions are often heavier than an equivalent blind mag action, as the light sheet metal mag box of an ADL is replaced by a thick steel belly of the action. Be careful with this math as well.
I could be convinced of some modest utility at short ranges to be garnered from a 16” 300 Blackout bolt rifle. Just dumb to build it as a 25” rifle, considerably silly even above 20”.
Getting under 6lbs takes work, and is rarely reached with even a light sporter contour barrel of 20”, let alone accomplishing it with a 25” tube. most polymer stocks will be 1.5-2.25lbs, add a quarter pound for proper bedding and forend reinforcement (add 1.5lbs if you’re lazy and stiffen the forend by filling with epoxy). Wood or composite a half to full pound more. Bare actions are 25-32oz at the light end. Even blind mags or aluminum floorplates can add a quarter pound or more, plus a few ounces for the lockwork. A 24” sporter barrel will typically run 2.5lbs in itself. Cutting down to 20” would cut off almost half a pound for you, 3/4 pound for cutting down to 16”, which is still more than you need to get the best in-field performance out of 300blackout. Even if you figure 2lbs for a 20” sporter, 2lbs for the action and bottom metal, and 2lbs for the stock, you’re already at 6lbs. It’s not magic, it’s pretty simple math, really. You could get under 6lbs with a 25” barrel if you milled an action to be a true 1.5lbs, but I’d only do so if the cartridge really needed 25” to perform - which your 30 cal 5.56 variants do not.
The Rem Model 7 action is a half inch shorter, and commensurately lighter than the 700 action - I’d expect it’d give the Howa a run for its money on total weight, if not be lighter, and it remains to be considerably more supported in aftermarket parts than the Howa.
