In the spring of 2012 I was one of the first guys to buy some. I reported my findings here.
A little background on this powder at the time it was introduced:
RL-33 is the second of a line of unique powders offered by Alliant. Borrowed this line from an ad: "New Reloader 33 Delivers More Speed in Big Magnums"
Now Alliant is introducing a new powder, Reloader 33, that uses the same kernel-impregnation technology first pioneered in Reloader 17. Alliant Reloader 33 is a new powder created by Rheinmetall Nitrochemie.
Many of us were stunned at the higher velocities we obtained with RL-17 in mid sized cases. I looked forward to trying this powder in larger magnums!
Alliant's data was limited. I knew it was slower than Retumbo so I used Retumbo's mid range loads for a starting point.
I tried it with a 7 Rem mag, 257 Weatherby and a 6mm-284 for the first trials.
There was a small gain with the 7 Rem mag and 162 gr bullets. But ran out of room in the case. The load that worked caused the OAL to be .010" longer even when using a drop tube.
I began to realize there was a reason Alliant's limited data had the heavy bullets paired with the magnums. Lighter bullets don't see the gain.
The 257 Weatherby (28" barrel) and the 6-284(28" barrel) had gains in velocity over Retumbo or RL-25. The 257 gained 90 fps over the maxed out load of RL-25 with 115 Bergers. The 6-284 had a very significant gain of 177 fps over Retumbo with 105 Bergers. These comparisons were with the most accurate loads for both rifles with no signs of pressure.
Later on, myself and several on LRH reported excellent results with RL-33 in a 300 RUM and 230 gr Bergers.
More recently posters on LRH reported using RL-33 in the 338 RUM, 338 Edge, 338 Norma and 338 Lapua with heavy bullets.
I just looked at Alliant's current load data today 7-16-25. While based on my experience with the 257 Weatherby it should work well in your 264 Win mag with 140 or heavier bullets but
there is no data on their site. 300 win mag will work with heavy bullets again,
NOW they don't list any loads for RL-33 and the 300 Win mag. Originally, they did see below.
They list load data for the 338 LM on their website.
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When you look at the data Alliant originally supplied, you will see they show heavy for caliber bullet loads.
Hope this helps
Ross
L! 
