There's a few, Short or Long action?
I use Kwik-klip long action ones because they have 10 rounds mags available, and HS precision short action because they have 10 round mags available. They are good, but the mag release's are small and tough to get with gloves on.
There's a few more companies out there that make them. Check on the Precision rifle section, lots of those guys have them on their long range guns.