The Oryx DOES in fact fit bottom bolt release SA. This newer chassis made by MDT is a FANTASTIC less expensive option. MDT has many different to choose from. Each one is a great option in its own right. I use the TAC21. XLR is another with several options and just as good as MDT. At the upper echelon are the KRG & MPA Chassis, both running in the $1K+ range.

What you should know of chassis is they differ in price based on features. EVERY one of the known high quality chassis, whether $400, 0r $1K+, will provide accuracy potential higher than even competent shooters are capable of. Every chassis provides a SOLID aluminum bedding, and perfectly free-floated barrel. My best advice is to look at various options, read up on and choose based on the features you want for the price you can afford.