1.First thing is first: Make sure it has the upgraded firing pin since they had a recall back in 1991 due to some safety issues. They are very easy to replace yourself or you could just take it to a gunsmith.
2. Shoot factory stuff through it. If you reload don't run max loads in it (learned the hard way and cracked an extractor). My handloads consist of:
- full length sizing my brass
- 45 gr RE 15 powder
- cci 200 primers
- rem or winchester brass
- 150 gr. hornady sp flat base bullets
3. Bed the forend like this, it helps with accuracy:
4. Make sure your mags work properly, a bad mag will result in jamming and failure to feed problems.
5. Keep it clean and keep an eye on the piston that operates the gas system (if it is pitted you need to replace it).
Here's a few pics of how mines shoots:
This was before sight adjustment (3 shots) at 50 yards using factory irons:
full magazine (4 shots) after drifting and adjusting sights:
And at 100 yards with a cheap simmons aetec which I don't have on there any more due to a tracking problem:
These targets are not very typical of the accuracy of the model 100 but like I said, the bedding will help out greatly. 4 shots into less than 3/4" works for me
Good enough for any pig or deer that walks this earth.
Lastly, I love my pre 64 model 100 and it works flawlessly as long as you follow what I've outlined. I'm sure there is a lot more I could add but I'm sure someone else will chime in. By the way post some pics of your new rifle if you can. Good luck with it.