The accelerator rounds that you found are not very safe. I know a few people who used them and once in a while one would decide to be drunk and go out of the side of the barrel. They stopped using them after replacing a few barrels. Not sure about rifling being the reason for discontinuing, since there's other platforms that don't give impressions on the projectiles like black powder and shotgun, but the safety issue was definitely a part of the reason for discontinuing them.