Thank you for the information and experience. I don't have dies for this cal. As of yet but it is on top of my list. I'm an avid reloader when time presents itself. Next question is it was my first thought of over charging the round and had my wife slowly charge then use forward assist to complete. Every time she does it will not eject the round like the extractor is not grabbing the rim. Thought she may have not been putting enough forward pressure on the forward assist so I tried myself a few times and when I pull back charging handle the round remains chambered until you tip the gun barrel up then falls out??
Another classic issue chronicled over the years. There are theories about this and they all have merit. I experienced this myself on my original Bushmaster upper. My theory among all the others is that the single extractor is the culprit. My factory 450b had a very generous chamber. Holding a round by the rim, I could lower it into the chamber and wiggle it side to side a small amount. I'm not sure why Bushmaster made them that loose, other than to add a degree of reliability to the extraction process once the chamber becomes dirty. True to form, I rarely if ever had a failure to extract a fired round in over 2k of reloads. I did experience a high degree of resistance to well lubed cases when resizing which testified to their expansion. However, I could never extract an unfired round, despite it falling out if I tilted the muzzle upward. My theory it that the extractor pulls the smaller
unfired case on one side, tilting it ever so slightly in the chamber and making it bind just enough to overcome the tension afforded by the extractor spring. This does not happen with fired cases as they have already expanded to the chamber diameter after firing and despite having shrunk back away from binding (by design) they do not slop around.
That having been said, there are holes in my theory based upon your observation. In my upper, it did not matter whether I eased the bolt into battery of let it slam into battery. Neither unfired rounds would extract. In your case, I am wondering if your chamber is cut a little on the long side. Its not unheard of. If you ease the round into battery, it needs to run into the end of the chamber to stop the case from going forward enough so that the extractor can reach around the rim and fall into the extraction groove far enough that it takes hold of it. If the extractor is not cut exactly right, or if the chamber is too long to allow it that last couple of thousandths reach to slip over the rim, then it will not be able to thoroughly engage and hold on tight enough to pull the case out. Another theory: In slam chambering, the case is rear-ended by the bolt and bottoms out against the bolt face momentarily, allowing the extractor to grab properly. The other possibility is that the case may not bottom out against the bolt face during slam chambering, but scoots ahead of the extractor engagement point. However, as it races ahead of the bolt into the chamber all the way to the end, the case mouth encounters the lip of the chamber, stopping its forward travel and bouncing it backward back into the still advancing bolt, to the extent that it allows the extractor hook to engage it.
Not having a transparent chamber, these theories are just that, theory. Regardless of the reason, it is one of the issues resulting from shooting rebated rims, straight-walled cases in a semiauto action. Unlike their bottle necked cousins, they headspace on the mouth. All that verbosity adds up to no simple solution for your circumstance. I just got used to tipping my barrel upward and catching the unfired round as it fell out. If that is an uncomfortable situation for you and your wife, then you're going to have to get used to rotating your case sequence over the course of a hunting outing, assuming you have to load and unload a lot. It is as you observed, a cumulative problem.
FWIW, I am now in possession of a Bartz Manufacturing upper. The aforementioned issue no longer manifests in it. My observation of the bolt, barrel extension and chamber is that of having been more precisely manufactured than my stock Bushmaster upper. Tolerances are much better adhered to and the extractor firmly engages the rim regardless of whether I ease the case into the chamber or slam it in.