I just bought a Lyman Mustang Breakaway inline late last year, and it's a very nice looking and handling rifle. My experience with Lyman is limited, I do have a Plains Pistol I've shot for years with no problems.
I got the new inline right at the start of our deer season so I was in a hurry to get it in operation. I slapped a Leupold 2-7 scope on it and headed for the range. The only bullets I had on hand were 300 gr Hornady XTP sabots. At 100 yards about a 2" group, not great but good enough to get to hunting if I watched my range. I also found I didn't have enough adjustment with the scope bases/mounts to get the eye relief I needed. Couldn't get the scope close enough to my eye for a full field of view.
This spring I decided to play around with it and find some good loads. I like to shoot 100 grains of loose pyrodex or 2 pellets for hunting. I took the scope off to sight in the fiber optic sights in case I ever needed a backup sight. It wouldn't zero! With the rear sight set at it's lowest setting I was still 4" high at 50 yards. I called Lyman and they told me the rights were regulated with 150 grain loads and no other sight options were available! [:@]
I went back to the range to shoot some more and after a couple shots with lighter bullets (250 gr.) I opened the action and the little magnet on the breech plug that keeps primers tight was stuck to the breech face in 2 pieces! - Called Lyman and they sent me a replacement.
Got the replacement a couple weeks ago and headed back to the range. Got set up at the bench, fired one round and started to reload. Rammed the bullet home and the ramrod snapped off at the tip! [:@]
Called Lyman and a new ramrod is supposedly on the way to me, but I haven't seen it yet in almost 2 weeks.
My overall impressions are that it is a decent rifle, but nothing to really brag about. The trigger was horrible, but some careful stone & polishing work improved it. The scope mount system is not favorable to compact scopes (I finally found an old Leupold M8-4X fit OK). The accuracy is acceptable for hunting, but it isn't a "tack-driver" by any means with any of the loads I've tried yet. I can get around 2" groups @ 100 yards with most loads, but haven't gotten much better than 2" yet. Most inlines I've owned will do better than that!