Thread: AR2209 Lot Variations in the 6.5 x 55.

Greetings All,
A few months back I was developing some new loads for my 6.5 T3 and found some significant differences in burning speed between the current production and an earlier lot of AR2209. Sorting through some old loads some were found that contained AR2209 from an even earlier lot. It seemed a good opportunity to chronograph the three lots of powder with other variances eliminated as far as possible. I found the results interesting hence this post.

The three lots of powder were purchased in 1,993, called original, about 2,000, called old and 2,019, called new. Two different projectiles were tested, 120 grain Sierra flat base and 129 grain Hornady SST. The 120 grain projectiles were loaded in once fired Norma cases with Winchester W120 primers. These cases came from loads assembled in 1997 which were broken down to provide the powder. The cases, originally full length sized, were neck sized to restore neck tension. The 129 grain projectiles were loaded in new Lapua cases with Federal 210 primers. The shooting was done yesterday in cool overcast but breezy conditions at 60 metres. Mid chronograph screen was 3.0 metres from the bench. Loads for the 129 grain old and new lot powder were fired previously.

Velocities recorded are as follows:
120 grain projectiles 46 grains AR2209. Original lot 2,806 fps. Old Lot 2,798 fps. New lot 2,870 fps.
129 grain projectiles 45.5 grains AR2209. Original lot 2,763 fps. Old lot 2,720 fps. New lot 2805 fps.

The powder loads were max form the Hodgdon on line data which is limited to 46,000 CUP. The old lot of powder produced velocities close to Hodgdons. The new powder velocities are closer to the Nosler on line data. Nosler seems to have reduced the loads for their 129-130 grain data perhaps due to some harder projectiles in that range.

Results: There is a little less than 100 fps difference between the fastest and slowest lots of powder, equivalent to adding roughly 1.5 grains of powder in this case. A powder load adjustment would be needed with close to max loads. All loads other than the 120 grain new powder loads went into a 17 mm group with individual loads moving around in this group, a little less than 1 MoA. The errant loads went about 5 mm high.

Conclusions: Yes we do need to make adjustments when a new lot of powder is started but we shouldn't need to work up from start loads if you have a chronograph. Checking a start load of each lot of powder over the chronograph should tell you if the lots are similar or not. Adjustments can then be made. Velocity is the best measure of pressure we have as hand loaders.
Regards Grandpamac.