I purchased a used JM manufactured Marlin 336w in 30-30. I installed XS Ghost Ring Sights on the rifle. I already had to install a higher front sight which was provided by XS. I went to the range the other day and was maxed all the way out on the windage adjustment to my rear sight. My rounds were still impacting left of the target. I contacted XS while at the range and they informed me that they have experienced this before with their sights. The customer service rep said that the barrel was not installed straight. So when I installed the rear sight to the receiver the front is not straight. The customer sevice rep said they have a front sight that can fix this issue and sent one to me. Apparently this front sight can adjust fir windage and i believe its a dovetail sight. Has anyone else had this issue? Is this something I should contact Marlin(Remington) about or a gunsmith to fix? Or will the nee XS Sight Fix this issue?  Thanks.

It's entirely possible the barrel on your Marlin is not straight. Most likely the threads in the receiver weren't cut straight, a gunsmith could most likely fix it (if that is indeed the issue) but it wont be the cheapest project. I'd try the new front sight and see if it has enough adjustment to fix the issue first.