This is Alliant's new powder made in Switzerland. 6mmbr has a great tech article on it here: http://www.6mmbr.com/reloder17.html
RL17 is different in that the chemical that controls burn rate permeates the entire kernel, as opposed to previous powders where it's pretty much only on the surface. What the claim is for this powder is that it will allow for higher velocities with lower peak pressures because the burn rate has a flatter curve. Supposedly designed originally for the small caliber magnum rifles, it has seen a lot of testing in other calibers, such as the 6xc, 6.5x47, 6.5x284, .284, and .260 Rem. A couple guys I shoot long range matches with shooting the 6.5x47 are getting great results and have switched over to RL17 completely.
So I thought I would give it a try in the 6.5x55 in my CG80 with a 26" barrel. I'm a big believer in the RL22 for this cartridge. I get very good accuracy at velocities of 2500fps to (at 90 degrees F) 2725-2750 fps using a Sierra 142gr SMK at a C.O.L of 3.125". The load at 2725 fps is what I use for 1000 yard matches and gets the bullet to 1000 yards with 30 MOA of come up from a 100 yard zero.That velocity is getting close to the max published limit for a small ring Mauser. So I thought if this new powder does as claimed, I could get more velocity without increasing the pressure. And hopefully still have good accuracy.
Alliant lists a max load of 38.5gr RL17, out of a 24" barrel, shooting a 140gr Speer SP bullet with a Fed 210 LRP, giving a muzzle velocity of 2508 fps. Alliant gives a C.O.L. of only 3.000" for the Speer bullet. MUCH shorter than my standard load COL.
Using the 142gr SMK at my normal COL, I started my load work up at 36.0gr and worked up to 38.5gr in .5 gr increments, and then in .2gr increments up 39.7gr. Since I only have 1 pound of powder to work with I only made up 3 rounds at each charge weight. The initial results were disappointing as to velocity. At 39.7gr I was only getting 2450 fps. There were NO signs of excess pressure at all on the brass. The primers had only a hint of flatness to them. I was shooting at a distance of 200 yards, and the vertical string from the lightest load to the heaviest load was about 6 inches, with a slight curve to the right as the load charge increased. The loads at 39.5 to 39.7 all grouped within 1-1/2".
I figured the lower velocities than Alliant's data was probably due to my longer COL.
I worked up another batch and went back out today, but was only shooting at 100 yards. Cooler than the previous trip, with temperature right about 60 degrees F. - Note: my range is about 200 feet ASL.
I started this load group at 40.5gr, went up to 42.0gr in .5gr increments, and then in .2gr increments up to 42.6gr. At 41.5gr and 2500 fps I hit an accuracy node - all 3 rounds overlapped. At 42.4 - 42.6 I hit another accuracy node. All 6 rounds were inside a 3/4" paster. The velocity at those charge weights 2560 fps and 2575 fps respectively.
I also fired some of my standard load for baseline comparison today. At today's temperature I was getting 2650 fps for a 5 shot average.
Velocity is still 75 to 200 fps less than what I am shooting for. The max load I shot today actually grouped BETTER than my RL22 load. The brass still shows no pressure signs - no blown cases, no case separations, case measurement just above the case head is the same as my RL22 cases. The primers are still a lot less flat than my RL22 loads.
My next work up will be 5 round groups starting where I left off at 42.6gr, and I'll work up to 44.5gr and see what I get. The velocity increases from one load to another seemed to be very linear. No sharp jumps as I've seen with some powders. Right now this powder looks very promising. As it is, I would have no issues using this powder at 42.6gr for my silhouette matches (out to 500 meters) if further testing gives the same accuracy results.
One interesting thing I did notice. Normally at light loads, the case neck, and in some instances the case itself, will be heavily sooted, indicating the case is not expanding enough to give a good seal. With the RL17, from the lightest load to the heaviest load so far, there was minimal soot on the neck, and none on the case.