Re: 300WM vs 300 RUM sendero
I don't know about whether or not you can expect better accuracy from and WM vs a RUM but I'll lay my experience on you anyway. My crowd started with Sendero's about 10 to 15 years ago. One buddy bought a blued 300 WM and after shooting about 500 rounds through it without ever getting better than about 1 1/2" gave up. Another buddy bought a Sendero SF in 7mm STW, he too shot the wheels off of that thing trying to get it to group and it too was about a 1 1/2" gun. My uncle bought one in 308 and parked it after a few hundred rounds of experimenting yielded nothing better than about 1 1/2". Knowing this, I kept reading this forum (and others as well) and all of these people kept claiming that they had many Senderos that grouped down in the 1/2" range. The general rule of thumb was that if your Sendero wasn't delivering at least sub MOA or often sub 1/2MOA, you simply weren't pointing it correctly or you needed to bed it or your trigger wasn't adjusted right. So I bought an SF II this year in 7mm Rem Mag.. I put a Seekins 20 MOA rail on it, Burris XTR rings, a 30mm 4.5-14 x 50 Leupold M4 with TMR reticle on it, a Jewell trigger and bedded it in Marine Tex. I put about 200 rounds through it (about 40 different 5 shot loads using H1000, Retumbo, H4350, H4831 and 154 IBs, 160 Abnds, 168 VLDs, 180 VLDs, and 150 TSXs) and only shot about 3 or 4 sub MOA groups with it. None of these sub MOA loads was repeatable. I had a local gunsmith spin a new crown on the muzzle and after about 25 more rounds am fairly convinced that this rifle will not shoot MOA. I have a binder full of 1 1/2" to 3" targets to prove it.
I knew that it was a factory gun to begin with and still decided to buy one because it has such a good action and stock to build from should things not work out but I'm still disappointed. I'm not trying to discourage you from buying a Sendero I'm just telling you what my experience has been.
Most people claim how good their 3 shot groups are. I can say that my new Sendero has shot lots of sub 1/2MOA 3-shot groups and almost no MOA 5 shot groups.