I have a 16hh 3yo ex-racehorse called Avon. Recently I have been having troubles with her bit. When I first had her (5 months ago) I rode her in a loose-ring plastic happy mouth with the rubber bit guards, and she was fine for about 2 months. I then changed her bridle (keeping the same bit but with no more rubber bit guards.) to one with a flash and a sore split in the corner of her mouth appeared.
I gave her some time off for it to heal, which it did and then bought a metal snaffle (no loose ring) in the same size, but within a month she had it again. I also used Vaseline in the area but didn't seem to help that much. I have now bought her a bigger size metal snaffle which I haven't tried yet.
My riding instructor tells me it is not my riding or her feed that is causing it but the bit.
I was wondering if anyone had any similar problem or had any advice? I would rather not have to ride in a bitless bridle.