Thread: Speed loss/gain per grain

My old 6.5x47 load of 42gr 2209, 140gr Amax .25mm off the lands, CCI 450, shot really well, and I was loathe to change it for a long time, stupidly, despite the fact that it would pierce maybe 1/20 primers on days over 30 degrees and bolt lift could be sticky on those days.

Because I'm lazy and I hate load development I shot it with that load through winter (no problems in cold weather, which was when I worked the load up initially). But this summer I thought I should get around to changing it so I threw some loads in some new brass and tested them.

40.9gr of 2209 shot extremely well with no pressure signs and I have decided to go with it. I didn't shoot my accuracy testing rounds over the chronograph so I have no idea how fast it is going. Because I'm bored between trainings today I decided to see what I can come up with to estimate it.

ADI book speeds/charges, mid size 6.5s, 2209, 140gr bullets

Cartridge: min/max. Min speed/max speed. Change in speed per grain

6.5 creedmoor: 36/40. 2465/2660. 48.75fps

.260rem: 39/42. 2530/2675. 48.333fps

6.5x55: 39.5/44. 2420/2620. 44.444fps

6.5BR doesn't have a charge for 2209 but with 2208 it shows about a 70fps loss per grain

Now this is totally unscientific and doesn't take into account the burn characteristics, pressure curve and relation to my barrel length etc, but in my past experience I remember speed gain being a fairly linear relationship with powder gain, so I am going to make the bold step of estimating that my new load is doing something like 2740-2760fps

Yup, I'm bored