A few thoughts here. One is that the 19-3 is old enough that it won't be covered by the S&W lifetime warranty unless they decide to do it simply to prove yet again that S&W has superb customer service. Basically, it's worth a call to inquire but don't expect that they will do warranty service on a revolvers made in the 70's under different ownership.
Second, sometimes a mild to moderate overcharge can cause bulged chambers in the cylinder. Unfortunately, the only solution for this problem is a new cylinder and that may be difficult to find, especially a recessed cylinder. To check for this you'll have to carefully measure the cylinder at various depths using snap gages and micrometers. If you don't know what snap gages are, talk to a machinist and he'll show you a set of spring loaded T's that can be locked with a knurled knob on the stem. Because modern rimmed casings provide a lot of additional "meat" at the base these bulges usually are found deeper in the chambers, say from 3/8 inch in to near the front of the chamber. What you should measure is a very slight taper from front of case to the rear opening of the cylinder. If you find the chamber gets larger as you check deeper, the chamber is bulged and you'll need a new cylinder.Second thought pertains to the period when your 19-3 was made. People complain a lot about S&W Quality today and seem to have a bit of reverence for older revolvers produced during the Bangor Punta ownership. If they had actually been purchasing revolvers during the late Bangor Punta ownership they'd probably be running into traffic in frustration. There were times during this ownership when Quality was just awful. One recurring issue was poor surface finish in the chambers in the cylinders because Banog Punta wouldn't replace a reamer until it stopped cutting completely. Take a good close look at the surface finish in your chambers, if you see deep gouges honing the chambers may provide a solution. However, you do NOT want to go overboard with that honing, just do enough to solve your ejection issues and stop. In some cases trying to remove all traces of gouging from a dull reamers will only result in chambers that are oversize. I would take a very conservative approach and plan on multiple trips to the range. Start with 20-30 revolutions on each chamber, test for ejection, and then repeat until the ejection issues are resolved. Keep in mind, try as I might, I've never had any success in getting my "material putter backer" to work, so only remove what is needed and stop there.
Third thought. Never been really impressed with Magtech ammo. Also not real impressed with Winchester White Box. Ammo's that do impress me are American Eagle, Federal Champion, and Speer Lawman. I would suggest you try any of these 3 before doing anything else. Fact is that cruddy ammo will crud the chambers and cause problems, especially in an older gun that may have a bit of a finish challenge in the chambers.
BTW, Speer Lawman is the ammo that I find most impressive, however it's a bit spendy and VERY difficult to find in my area in 38 spl.. The Federal is every bit as clean shooting as the Lawman, just not quite as accurate as the Speer ammo.
