I have done a lot of testing on my factory barreled 223 Stevens. It has been shortened to 18" and a tensioning sleeve added to the barrel for stiffness. It is by far one of the most accurate rifles I own at the moment.

I can say that on MY gun it shoots way better with the bullet seated close to the lands.

My chamber specs:
With Sierra 69gr SMK= 2.46" OAL to the lands
With Hornady 68gr HPBT Match = 2.40" OAL to the lands (because of the different ogive angle)

Using 69gr SMK's I have tried seating at different lengths from 2.23" OAL to over 2.43" OAL. I settled on a load that is 2.43" OAL with Varget and CCI400 primers. The cases are R-P that are full length sized and trimmed to 1.755-1.759. Nothing shorter than 1.755 or longer than 1.759.

My groups with the 2.43" Sierra SMK loading is 1/2" at 100 yards reliably. When I take the same rounds from the same loading session and push the bullets back to a OAL of 2.23" the groups open up to over 1" at 100 yards. I have tried different lengths between the two and the farther the bullets are away from the lands the worst it gets with the 69 SMK's. This load is not the most accurate I have loaded but they are the most consistent. I have other worked up other loads that would be in the .2's then throw a flyer. I would rather have a consistent .5" shooter than a sometimes .2" shooter. The inconsistent loads were with a bullet maker that has some lot to lot issues from what I have been told.

I realize the 2.43" loads will not fit in the magazine and I am fine with that because I will never need to make fast follow up shots because I do not hunt, only puch paper or steel.

I was told early on in reloading to find the LENGTH you want then work up a load for that LENGTH. I tried that but nothing seemed to shoot well so I started lengthing the OAL and found a sweet spot, .03" off the lands for THIS gun.

Hope this helps
Dolomite