Im going to pull some and load them into empty shells to see how far the bullet has to be seated to chamber
Like RC20 mentioned, if they drop in the barrel correctly (the plunk test) then its not a chambering issue, its a FEEDING issue.
Too many people overlook the fact that while the max length to fit in the chamber is an important number, the max length that will feed from the magazine CAN BE DIFFERENT, usually shorter than the max length that will chamber.
And your rounds need to be short enough to fill the magazine and feed without issue. The amount of difference in length needed will vary between different guns and calibers.
One fellow wrote in the other day, he had gotten a COAL from a website (or a manual, I forget, but in this case it doesn't matter), his rounds passed the plunk test, but when loaded in the gun he found only 3 rounds could be loaded in the magazine, before they began binding against the mag body.
His COAL was over the SAAMI listed max, as it turned out, he rechecked and found he had missed the * in the data that led him to a footnote stating the length was over SAAMI spec...
HOWEVER, the same result CAN happen when rounds are at the SAAMI spec. Remember that the spec for max COAL is just an agreed upon industry standard, one that should work in everything.
Should work, is not the same as will work. There are guns and ammo that varies from the SAAMI spec.
There's no taper on the bullets until almost to the nose of the bullet.
This is most likely the cause of your problem. Essentially your gun is trying to slam an almost un-tapered cylinder into a hole just barely bigger than it is, and does it by coming up from underneath at an angle. The round has to "turn the corner" to line up with the chamber and hard lead doesn't "slide" as well as a copper jacket, making the amount of clearance (and in the needed place) between the round and the barrel even more critical.
Loading the bullet a little deeper MAY give you enough "room" and solve your feeding problem.
The bullet can't be seated much lower without problems
This has me a little confused. OK, I don't know the exact bullet you're using, but if it is so blunt as it seems from your description, what problems would you get from seating it a few thousandths deeper?
(and if your answer is raising the pressure too much, the answer is reduce the load appropriately. There's no free lunch.)