I am a reloading instructor with 35+ years experience.
The 5.7x28mm is a semi-auto version of the 22 Hornet - and use the same diameter bullets as the 223, 5.56mm, 22-250 etc etc etc etc etc - it is a .224" bullet. You just cannot use the same bulelts from these other calibers in a 5.7 'cause the 5.7 likes 27gr to 40gr bulelts - 55gr for subsonic.
I have a ton of experience loading 223 for NRA Highpower Rifle competition to 600 yards - and I can tell you the 5.7x28mm is a very very difficult round to reload. The factory outside coating interfers with full length sizing. The case is too short to accomplish FL sizing, de-priming, and neck sizing all at once like normal reloading easily - your better off performing these steps individually, or, wreck 20+ cases getting the die dead on perfect.
The full sized brass always needs trimming. The primer pockets are military crimped and need to have it removed with a swagger.
The big problem - FN has never relieased their pressure data to United States manufacturer's - this means none of the powder or bullet companies can publish a load with 100% confidence it is safe. I've talked at lenght with Hodgon and Sierra about this.
There is some load data on the internet, and, a few magazines - but these almost always use a local powder like 'True Blue' that is only found on the East Coast and not on the West Coast, Alaska - or sold by mainstream companies like Midway. This makes loading for this caliber very dangerous!!
Bottom line. There just isn't enough info available for anyone to reload this round 100% safely. Just take a peek at your factory once fired brass and you will notice they all show signs of over pressure. I've never blown up a rifle or pistol reloading in 35 years, but, this is a real possibility for me as I continue to work on this caliber. By the end of June I should have some safe loads for 30gr Midway Dogtowns, 40gr Nosler BT's, and 55gr subsonics for people using suppressors. I will post them in this Five-Seven area. Lots of nice folks here. I have 24/7 access to a nice range just minutes from my house..
American gun shop walls and ceilings all over the country are decorated with blown up rifles and pistols - mostly from reloading. These are guns blown up that had published data available. The 5.7x28 is not for the novice reloader - and - if you can't afford to have your gun blown up - you shouldn't be reloading for this either.
Hope this helps! You can email me at the end of June and see where my load data is at.