Alot of it has to do with the the wieght and body construction of the game your shooting. Nutons law "equal and opposite reaction" , the bullet can only expand and transfer energy as much as the animals mass is able to push back. For this reason , it's usually better to use a "softer" bullet on...
Looking at quick load, a 18" 338 lap with H1000 should be able to push a 285 Amax or eldm over 2600 and around 2700 with a 20". Totally viable numbers for what your wanting. Even shows you have 100% burnt propellent in an 18" barrel so your not loosing much efficiency
I have had this happen before as well over the years on a few guns, always turned out to be a bedding or action torque issue or a loose base and not an actual mechanical problem inside scope
18" carbon barrel tikka, supressed 7 saum shooting 180s just under 2800 is my all round gun. A mid sized 7mm varients shooting 160+ gr bullets is really hard to beat (280 ai, 7 saum/wsm, 7 rem mag, 284 win)
If a guy is shooting at a known range on flat ground you wouldn't use a rangefinder or any "gadgets" anyway.Wind reading "gadgets" don't usually work very well being wind is so variable between you and the target. You seem like you don't have a whole lot of knowledge on the topic other than...
Here's a video I took shooting a cow around 300 yards with a 20" barrel 7mm08 . Since it's a slow round, your best bet will be heavy and soft bullet like a 162 eldm or 160 tmk. This video is the tmk and it killed a bull at 495 as well, not on camera but one shot to the lungs and dead
I'd stick with the 280 but try a bullet other than A partition if you expect long range. Dropping to 1800 fps at 450 is insanely terrible performance for a .284 bullet, my 7mm08 with 160 at 2700 mv is doing 2050 at 450 yards and my 7 saum shooting 180s at 2830 is still doing 2400 at 450.
Heavy 7mms kill elk just as cleanly as 30 Cal's, sometimes better due to the longer bullet with higher sectional densitys. I've first hand witnessed at least 40 elk being shot from 243 on up list and 7mms run right with the 30s no problem. 6.5s I'm a little hesitant on.
I've killed elk with both calibers, both 22". They kill about the same but the slight reduction in recoil of the 7 coupled with the large gain in BC is a huge win. Long story short I don't own a 300 wsm anymore but j still have the saum