So, I ended up chambering a barrel in 6x47L. Got my own no-turn reamer with a neck that is 0.2765 at the mouth tapering to 0.2775 at the neck-shoulder junction. It has a 1 deg. throat angle with 0.083 freebore. Seats the 105 Hybrid perfectly 0.050 in front of the donut area. Over 300 rounds down the barrel so far and I'm quite pleased. The brass is built like a tank, tougher than my Lapua 308 win brass.
So far, I've only shot 105 Hybrids, but I've tested them with H4350, IMR4451 and RL-26. Have used Rem 7.5 primers exclusively. This was after some investigation. Notably, this experiment by German Salazar (which I repeated with Rem 7.5s, Fed. 210Ms, and CCI BR2s): http://www.6mmbr.com/primerpix.html
The small Rem primer creates a bigger spark than either of the two popular large rifle primers I tested, even through the 0.062 hole in the x47 brass. I can't see how it would have trouble lighting powder if those primers don't. Temperature tests confirm no ill effects in cold weather. I cooled rounds to the low 20's F and heated them to above 100 F, in addition to firing them at the ambient 38F on the day I ran the test. H4350 varied by 0.69 fps/F, IMR4451 varied by 0.45 fps/F. SDs for IMR4451 were higher, but still only 12 at most, H4350 had SDs in the singles, and ES of 16 at most at each temperature. Measured with the LabRadar. I did not test RL-26 because the node was at the same velocity as the other two and the larger powder change created noticeably more muzzle blast.
I worked up to 45.0 gr. of RL-26 under the 105 Hybrid. This gave me 3201 fps. out of a 26.5" 7.5 twist MP 5R Bartlein barrel. Grouped ok:
This was during break-in, when the H4350 load I've settled on was giving me 3015 fps. That load now gives me 3089 fps., so I suspect the RL-26 load is also faster. 3201 fps. is already above the 3150 fps. limit of most PRS matches, so I didn't pursue it any further. I will look at RL-26 again when my throat wears enough to shoot the 115 DTACs without seating them into the case.
As for brass forming, it's simple: just lube a 6.5x47L case and run it into the 6x47L die. The die does make a difference though. I bought a Forster regular FL sizing die and a Redding type-S FL Match set. The regular Forster dies over-sizes the neck and the case comes out short and with a really crooked mouth. The Redding die with a 0.269 bushing does a nice job. Cases come out with good neck tension, straight mouths and are 1.846" long. They grow to 1.850" (trim length) after a couple firings. Most of the loaded virgin rounds have had runouts of 0.002" or less. I'm going to have the Forster die's neck honed to give the right neck tension once I settle on one.
Highly advise using a bolt with a 0.062 firing pin. Primers were cratering at starting loads with a regular firing pin. I only blanked one primer so far, but the piece stopped the firing pin from hitting the round after it and it failed to fire. Had to take the bolt apart and remove it. Have since ordered a bolt with the small firing pin.
I can see why this round has been popular in PRS. It loses nothing to bigger 6s within the 3150 fps. velocity limit of most matches, and recoil is noticeably less than my 6mm Crusader, which makes a difference in spotting shots when shooting from unstable positions like off of barricades. I will be running it in PRS this year. Well worth the initial pain of the cost of the brass (which I still need to stock up on). I may try some N150 since I'm not wild about the IMR4451 SDs and H4350 is hard to find.
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