I would expect to shoot better than that with that rifle and the correct slugs. Providing you can shoot better than that with a different rifle.

Maybe your not holding the gun right? Sorry couldn't resist.. ( that was meant to be a joke,not a jab, please don't be offended by it).

How does it shoot on cooler days? I have had rifles that would do that, but they normally string vertically. You could try messing with the barrel and action. Like free floating and bedding if it has not been done, or messing the with the torque on the screws. Keep in mind when you are hunting with it, it will not see these conditions. Well that depends on where you live I guess. With my ML I fire every shot from clean cool barrel. I fully clean it after every shot. I am only concerned what the bullet will do from a clean barrel, not a fouled hot one. It is time consuming, but it works for me.

Is this a repeatable thing, or could you have just been having a bad day? I normally try not to change anything or worry too much unless I can repeat it again under the same conditions. This is really the case with archery, but applies to guns as well. If you just can't get things to go right, when they normally do just stop and try again later.

Your a lo liket me. I am sure you are looking for 1 -1.5 inch groups at 100 yards. But like said above, that is plenty accurate if that is all it opens up to with changing conditions. Unless you want to varmint hunt with your slug gun.

Good luck figuring it out.

Paul