Clean your barrel thoroughly prior to firing your test shots. HOWEVER, many people will tell you to take one or more 'fouling' shots before commencing your test. In essence, they are correct....but, not exactly. Most shooters believe fouling shots tighten up your groups (and they do), but you'll hear a hundred-and-one reasons as to why. The reason is very simple, yet easily overlooked.
Having cleaned your bore, you're going to finish it off with a protective coating before storing. When you take the rifle to fire, you'll also dry patch out any of that coating to clear the bore to attain a true shot. But dry patching only removes most
of the protectant. A slight residue remains. When you fire, the burning gases burn off the residue, oftentimes requiring more than one shot before 'fouling' the barrel.
Try this: Prior to shooting, dry patch the bore just like you'd normally do and then patch it with 100% denatured alcohol. Push the alcohol patch from breech to muzzle only
and alcohol patch it a few times followed by a few dry patches. Allow the bore to 'air' for a few minutes, then fire. It works for me and I save money by not having to expend ammo for several 'fouling' shots.
If you're serious about long range accuracy, I recommend against using a COL. A COL is a basic measurement reloading manuals use for generic ammunition. Remember, these manuals must provide measurements for all
firearm manufacturers. Their load data, like factory loads, must be safe for use whether chambered in Remington, Winchester, Smith and Wesson, Glock, etc. Therefore, their measurements (such as COL) have to be within a broad spectrum and allow for large tolerances
to safely operate in all brands of firearms.
In addition, a COL isn't very accurate because different bullet types have different lengths even when the grain weight is the same. Even with the same brand of bullet.
Take your 168 VLD, measure a few of them with your calipers and log the results. Now take a different bullet type, but of 168 grains and do the same. You'll likely find a great difference, especially when measuring soft tip hunting style bullets. Those soft tips crush very easily and shorten the effective length of the bullet. Your COL's won't provide consistent bullet seating.
Instead, if you were to use a bullet comparator (about $30, but well worth it), you can measure off the ogive of the bullet. That is the part of the bullet that makes the initial contact with the rifling upon ignition. The meplat, tip of the bullet used when measuring a COL, sticks inside the bore and never makes contact with the bore. Measuring off the ogive will be far more consistant, therefore accurate.
Instead of loading 24 cartridges and working a ladder test, you can load 15 and accomplish the same goal. First you'll need to get your hands on a headspace gauge, or you could go the 'ghetto way' and use a marker or a birthday candle. (That's what I did)
What you're looking to do is find the edge of the lands just past your throat. To do this, take a dummy load and leave the projectile protruding a bit too far. Try to bolt it into the chamber, but don't force it. With each attempt and the bolt won't close, seat the bullet a couple thousandths deeper and try again. When you're getting close (by measurement), lite a candle and allow some of the smoke to adhere to the ogive and body of the bullet. DO NOT ALLOW THE FLAME TO HEAT THE BULLET. Just get some soot on the bullet, then bolt it again. Wipe the bullet with a clean rag to clear the soot and repeat, each time seating a couple thou deeper. Eventually you'll be able to bolt the bullet in without resistance and you will have rifling marks on your soot bullet. Now measure with the comparator. THAT IS THE EXACT CHAMBER DIMENSIONS OF YOUR PARTICULAR RIFLE. Log that for reloading reference.
You want to seat your loads to start 0.03" (a little excessive, yet safe) deeper, giving you that distance of a 'jump' to the lands and do 5 loads with those lengths. Load another 5 with a 0.02"...another 5 with 0.015" and finally 5 more with 0.010". Fire those in order and check each case for signs of high pressure. Your rifle will fire best with one of those loads, that is what your 'sweet spot' will be.
MOST IMPORTANT!!! When trying your 'jump' loads, do not
use maximum listed loads. I recommend using a mediocre amount of powder listed in your manual. This will allow for any possible pressure spike without endangering you or your rifle.