You shouldn't have any problem feeding with a COL of 1.155, since COL will range from 1.14 to 1.25 depending on the bullet. But I have found that WC's and FP's do seem to feed better if they are a little longer. I'd try COL at 1.20~1.23 to see how that works. Case pressure will be lower at the longer length so there is no hazard in experimenting with a longer COL.
It sounds like a typical three point jam, but you didn't say if the base of the cartridge was against the breech face, or whether the base was trapped under the breech and still in the magazine pressing on the round below it.
The second to the last round not feeding is an important clue, as that round and the last round are presented differently when cycling. It may occur on the third to the last round as well, depending on the magazines follower.
You can see this difference for yourself with a loaded magazine. You will find that you can push the nose of the top round down, and it will pop back up against the feed lips. It will pivot up and down since all the tension is at the base and there is no support at the bullet end. When the slides stripper rail hits the top edge of the base to push it out of the magazine the nose of the bullet dives down and it comes out of the magazine in a more horizontal position, usually hitting the feed ramp somewhere around the mid point.
Pushing on the top edge of the cartridge base you'll see each round dip as you push it forward out of the magazine. This will happen until you get to the last 2~3 rounds. At that point the nose is supported by the follower and no longer dives, but comes out of the mag in a nose up position.
Normally failure to feed the last 2~3 rounds is a magazine spring problem, as it is not able to get the base of the round up level and under the extractor in time. The nose of the round is high striking the upper part of the feed ramp, and spring pressure is at it's lowest value. Remove the follower and spring and drop two rounds into the tube, then replace the spring and follower. Then load 5 rounds and try it If the last two rounds now feed OK you need to replace the magazine spring.
But since you have 8 magazines in two brands, and it happens identically with all of them, I would guess the problem is not mag spring tension, that's about as likely as getting struck by lightning twice in the same day.
I would check the extractor and it's tension as that is the most likely cause if you have ruled out weak mag springs. Also check the breech face to make sure it's smooth with no carbon buildup. When shooting wad cutters a wadcutter or hybrid magazine with tapered lips will release the rounds base sooner as it moves forward and feeding will be smoother.
All this assumes you haven't had the ol' Dremel out "improving" on the feed ramp or breech face.
