That's all very well and good, but better for people that don't actually lift.
They're designed to get civilians moving and used to bracing and using their core as required... not really for lifters who have to be particularly strong in certain positions.
A number of things could be causing the bar to roll forward: if this is due to fatigue, then Delvis is right.
There are some other things to bear in mind...
- Trunk position: if you're hips aren't suitably greased, you will have a hard time keeping a nice (elatively) upright torso, meaning the bar will roll forward more easily...
- Shoulder/trap/rhomboid strength: if these are weak, you won't be able to keep your shoulders up, supporting the bar...
- Shoulder mobility: you're using the California (fatman) grip which suggests your shoudlers don't move properly, meaning more lat stretching and external (and probably internal - let's face it) mobility is required.
If you want a bullet-proof core for front squats (specifically) there isn't much better than doing paused front squats. Take your weights back to around 70% RM and then do paused triples feach for a 5 count. They are all the more miserable because they do an excellent job of (pretty much) compeltely removing the back from the lift which is why they are so much harder on the core... and why actually doing core work for them is quite a toughy: what other exercises simulate a compressive vertical load? A fully-braced plank is probably as close as you're going to get, but it's not the most interesting exercise in the world.
