I have purchased a new Sig Sauer P320 X5 Legion in 9mm. Thought I would determine the lowest powder charge that will work the slide and at the same time look at grouping. Five loads of 5 rounds, between 3.4 grains of Unique and 4.2 grains of Unique were balance-weighed for the test. I am shooting a powder coated Lee 358-125-RF which weighs around 132 grains as sized to 0.358”. Loads shot from lowest charge to highest charge.
The loads were shot off a bench with a Case-Guard plastic pistol rest. Not the best but all I have to work with. Target distance was a measured 50 feet and a 1” target dot was used as a target.
The Legion has the heavier 14-pound slide spring installed. All loads worked the slide properly. The 3.4 grain load is about as low as I can go with the 14-pound spring. The spent cases just clear the port and lands about 1 foot from the pistol on the bench.
There does not seem to be a lot of difference in the group sizes. Will probably select the 3.6 grain load for the next loading session.
I had previously loaded some rounds using the 0.5 cc (4.6 grains?) Lee dipper. Shot eight rounds and got a center to center spread of 3 inches at 50 feet. The best 7 rounds gave me a 2-inch group. Does not look like weighing provides much improvement over dipping.
Powder Coated 132 gr Lee 358-125-RF
Unique powder
Powder Charge 5 Shot Group; Inches Best 4 of 5; Inches QuickLoad Vel.
3.4 .....................2.75 ........................2.25 ......................827
3.6 .....................2.75 ........................1.25 ......................869
3.8 .....................2.13 ........................2.13 ......................910
4.0 .....................2.25 ........................2.13 ......................950
4.2 .....................2.25 ........................1.25 ......................989