Thanks again for all the replies. I've fired about 10 rounds through the rifle. All chamber and eject smoothly. All look identical once fired; all look like the fired brass in the photo in my 1st post. (Both those rounds are sitting level on a flat surface). Saving the brass is not an issue at this time; I am using factory ammunition that has functioned perfectly in other rifles. I would like to solve the problem as I really like the rifle, but am not sure what the problem is! Would a cast of the chamber likely help solve the question of what is going on? I don't have access to a gunsmith unless I mail it to someone.
A Chamber Cast would be definitive concerning the dimensions of the chamber, particularly the Freebore and Leade, but there is an easy way to approximate them.
First off, your fired cartridges give you a good idea of the dimensions of the chamber (there's always some "spring-back", typically a few thou depending on pressure and the brass itself). For example, you already know that the chamber neck is at least 0.343" at one point, which is more than 0.009" clearance, which is plenty (more than preferred in fact).
What would be most interesting is to determine the distance from the end of the chamber to where the rifling is bullet diameter (total Freebore+Leade distance). Here's what you do:
- remove a bullet from an unfired cartridge. If it's flat-based, you're in luck. Measure the diameter of its body at its greatest - it should be 0.311" or 0.312";
- insert it backwards into the chamber until it engages the rifling and hold it there gently with the eraser end of a long pencil;
- insert a dowel or cleaning rod into the muzzle while holding the bullet in place, and carefully mark the place on the rod where it's even with the muzzle ( I use masking tape);
- remove the bullet and repeat the measurement with the dowel or cleaning rod pressed against the bolt face; and
- measure the distance between the lines. If should exceed 2.222" by at least 0.100" (which is still very short - I have rifles where that measurement is 0.250"+).
Tell us the number you came up with. This method is an approximation that's accurate to perhaps +/- 0.020", and can at least rule out too little Freebore+Leade (Throat).
To be honest, the absolutely quickest way to know if this is the problem is to chamber a round and then extract it unfired. The vast majority of Factory ammo will have more than 0.100" of full-diameter bullet seated outside the neck - I just can't tell if that's the case looking at the picture you provided of unfired ammo. If the act of chambering seats the bullet deeper, to the point where the full diameter part of the bullet is pushed into the neck or next to it that's evidence of a very short Throat.