Re: RL-22 The Slow Burn
I have owned a Ruger Mark II in 7mm Rem Mag. for over 10 years and during that time I have learned quite a bit about loading the 7mm Rem Mag.
If you look at a number of reloading Manuals you will find a great deal of variation between what is given as a max load with the same powder. I know that each manual uses a different barrel and there are reasons for some variation, but it is greater for the 7mm Rem Mag. than almost any other caliber that I have loaded.
My gun has a long throat and it usually takes more powder to produce the velocity that I am looking for. I know that RL-22 has a reputation for variations from lot to lot so when I use it for loads in my gun I get some of the same things that you are getting--much lower velocity than your expected and much lower than the manuals say you should get.
Just recently I worked up a potential elk load using 160 Nosler Accubond bullets and RL-22. With the max load listed with a 160 Nosler Accubond bullet I was getting only 2700+ ft/sec velocity. So I worked up a load(1.0 grains and then .5 grains at a time) that produced 2900+ ft/sec. without pressue signs. I stopped without trying for the magic 3000 ft/sec which I think I should have gotten.
It took 68.5 grains of RL-22 to get 2900 ft/sec.. I know that this is way over the max and it can make you nervious, however that is what it took. I do not have pressure signs at all. IT IS A SAFE LOAD FOR MY GUN! I just checked the Alliant web site and they give a load of 65.0 grains for a 160 grains Speer bullet. They show 2976 ft/sec with this load.
If your gun has a long throat you could be experiencing the same thing that I am.