I just started load developing for a new bullet in my 338 lapua. I Noticed yesterday while shooting a 12 shot string 4 groups of 3 and starting with the lowest charge my velocity continually gets lower and lower with each shot even though I'm going up in powder charge. My last group produced 1/2" at 200 yards so today I loaded up 9 rounds for 3 groups of the same powder charge. Same thing happened with the velocity, High at first then gets lower and lower. Ended up with a ES of 114 and groups no smaller than 2" at 200 yards. Does this sound like my rifle needs to be copper cleaned? The rifle has about 350 rounds through it but it's had about 300 rounds since last copper cleaning. Just don't understand why the FPS would keep getting lower.