POI drop?

[moonbogg]

I had a great weekend camping and shooting my .223. I started with a near perfectly clean bore and saw the gun was shootin about a half inch to the left, so I gave the scope a few clicks to the right and the gun was driving tacks all weekend long out to about 200 yards.
At the end of the trip someone was using my gun for a few shots and they were missing a small plate at 180 yards and I took a few shots to see if it was the gun. Sure enough, it was missing. I had to aim a few inches higher and the gun was then hitting with regularity again.
So, it appears that after about 175 rounds, the point of impact dropped maybe 1.5 to 2" at about 200 yards from when I started with a clean bore. These little things confuse me and I try to understand why they happen. So, could I have simply misjudged things or could the POI have actually became lower after 175 rounds going down the tube without a cleaning? Either that or the scope shifted which I wouldn't have expected.

[eddiesindian]

Id have to say the semi dirty bore is the culprit

[stangfish]

Id have to say the semi dirty bore is the culprit
+ 1

[LoneWolf]

Slight drop in FPS due to the dirty bore? Never thought of that in the equation before. Interesting!

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[J.Baker]

How much temperature difference was there between when you were shooting and when the other person was at the end of the trip? Any major change in barometric pressure? How hot was the barrel when you were shooting it the first go-round? Sure he didn't screw with the scope?

Lots of factors to consider and it's probably a combination of many of them.

[joeydasniper]

What scope? I've had scopes change POI, don't know why, sometimes I think they need to settle in!!!

[moonbogg]

Nikon Monarch 5-20 x 44 with DNZ single piece mount.

[coldmaker]

I have a monarch 4-16x42 SF. Once my rifle was leaning muzzle up on a tree trunk.
It slipped to the forest floor on a thick bed of dry leaves. I didn't ear anything loud, no banging at all.
Next time i shot the rifle (luckily on a target, not on a trophy buck) it was shooting 12" high at 100y...

So sometime it doesn't need much to throw the zero off.
I bought i new scope for my big game rifle after that and put this one on my 223 :)

[GaCop]

+ 1 +2!

[Ackevor]

I had this happen to my rifle last year at the range. Sighted it it in with the new scope (rifle came with scope base). Next trip it started shooting where I left it. As the day went on it began drifting from shot to shot.

I unmounted the scope, put it on another rifle to see if it was defective, it shot fine. I Go to set it back on my rifle and what do you know, the base was a tad loose. The guy at the gun shop said it was all torqued and and thread-locked down so I never thought anything of it. I cleaned up the threads, added more locktite and torqued it back down. Shot great from then on.