Is it a Bent Barrel?

Hello all, I am new to this forum and look forward to hearing feedback and learning from other Marlin enthusiasts. I consider myself a rifle enthusiast with a basic knowledge of firearms and an above average shooting ability. Even though I'm a fairly avid shooter with great appreciation and respect for firearms, by no means am I an expert or scholar in the subject.
Three years ago my father gave me a Marlin 336 for Christmas to use as my primary hunting rifle. It's a beautiful gun that dates back to the 1950's and doesn't appear to have seen much use in it's lifetime. The only imperfections in the rifle are a couple screws on the receiver are very slightly scored/stripped, other than that the rifle is pristine. It really is a beautiful rifle.
Unfortunately, the rifle is quite innaccurate and I am not comfortable using it to hunt. After spending several weekends with the rifle that year I was unable to zero my shots on target. All rounds were a few inches high and equally left. Not wanting to alter the original condition of the rifle, I chose to add a Williams peep sight to improve accuracy. Cranked all the way down, the Williams doesn't seat flat on the top of the 336 receiver, so I ground out the inside edge of the peep so it sits flat on top of the receiver in its lowest possibe position (I'm far from a gunsmith or metal worker, but I was quite pleased with my modification to the sight, I looks like it was made to fit the reciever). I replaced the front pin a couple times increasing the height with each pin. Despite these changes the rifle continues to shoot high and left.
I'm not sure if there's a possibility of a bent barrel. But the other thought/possibility that's been on my mind is an improper seating of the barrel into the receiver. As mentioned earlier, the only imperfections in the rifle are a couple screws on the receiver that are very slightly scored/stripped. I'm wondering if someone took the rifle appart and did not reseat the barrel correctly. Any thoughts on this possibilty?
Resolving this problem has been on my mind for the last two years and I'm ready to tackle it. I expect that I'll have to send the rifle out to be serviced and fixed by a reputable gunsmith and was hoping someone might be able to recommend someone in the vicinity of southwestern CT. I also suspect that might be wishful thinking and am perfectly willing to send the rifle further away. Although, I am quite handy and would be willing to further inspect on my own with guidance.
I look forward to reading any feedback on this issue. Any recommendations would be greatly appreciated.

Thanks,

Caleb

 

Thanks for the responses, I really appreciate the questions and interest. I haven't shot the rifle since I gave up on sighting it in a couple years ago. There definitely aren't any obvious marks or indications of trauma to the barrel or any other part of the rifle. I'm going to shoot it this weekend to give an accurate response to your questions.
As for how the rifle shot with the original sight; it was high and left, but not consistent. It remained high and left with the peep sight and with taller front pins. I don't recall ever having any tight groups, with the original sight or peep. It also seemed as if the accuracy wandered further as the barrel heated up, but I couldn't fully convince myself that was the case.
I will shoot it again this weekend and get back to you.

 

I apologize for the delay, I didn't get a chance to shoot until this past weekend. Thanks again for the questions and shooting tips.
One important thing I did realize while shooting: I was out of practice, especially with iron sights. Since putting the 336 away, for the first time in my life I've been using a scope, mounted on an X-bolt, which I also have not shot this year. It took a few rounds before I was able to get a tight group, high and left.
Shooting from a soft rest at exactly 50yds, I was high 5", and left 4". With the Williams peep sight, I zeroed the windage (which does not line up over the notch in the rear iron sight). I was also able to lower the elevation a hair. After going through the 35 rounds I had, I am still hitting 3+" high at 50yds (my groups were also loosening up a bit).
At this point, the first thing I need to do is shoot the rifle quite a bit more. I was very disappointed with my shooting and need to improve that before I can accurately assess the rifle. Although, I am sure of the problem I had before putting it away a couple years ago.
A friend of mine who is an Army veteran is going to shoot with me at some point in the next few weeks. At that time I hope to have an accurate assessment of the rifle to report. Thanks again for the input and suggestions.