Phathead
The QLA is on the muzzle end of the barrel - it is a section of the barrel that has been bored larger than the bore itself so that you can drop you sabot/bullet combination into the barrel for easier loading. Anotheravantage (suppose to be) is there is now crown on the end of the barrel. Most crownson ML's are subject to damage by the ram rod rubbing them as you load or patch a barrel. Wearing the crown un-equally will cause loss of accuracy.
The QLA was actually thought of a long time ago by old time rifle builders and when it is installed correctly it is not normally a problem. My hunting partner has a TC Hawken with a QLA on itand shoots Bull Shop conicals very well - but the guy is also an excellent shot - he pops the headsof grouse with it all the time- 10/15 yards - not much of shot but for a open site ML he impresses me. He can shoot clay pigeon targets at a 100 yards with a 460 BullShop with out any problems (from a bnech and rest).
If you plan on shooting conicals then I would be some what leary of the QLA but there are TC's out there that shoot them just fine and visa-versa...
I have two Omega's but I have never shoot a conical from them so I can not tell you about mine, but then again I have no interest in shooting conicals from them.