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

If I estimate it's doing between 2500 and 3000fps , do I get anything for being correct.

Its not linear, its the inverse tan log of the flux capacitor quotient dummy!

Originally Posted by Cyclist

Its not linear, its the inverse tan log of the flux capacitor quotient dummy!

That number is not available for the 6.5x47.


Like factory load data, or rifles, or loaded ammo, or

New brass FL sized. I haven't noticed any difference in anyway between my new brass/once fired but I don't have any info in front of me now and I lost my old notebook anyway, which is why I'm thinking about this bollocks instead of just looking at my old chrony data

Originally Posted by jakewire

If I estimate it's doing between 2500 and 3000fps , do I get anything for being correct.

Only if it actually is. We don't know yet.

Considering I have the actual rifle/scope combo in question under lock and key at my house I would suggest a rather large cash prize be in order, whether I am correct or not.

If the cash prize is larger than a certain point, I'd be better off buying a new rifle

Although then I'd have to do load development again and that's tedious as hell

Nah, your luck you'd fill it with powder and it would work fine.

Gimp, I hear that adding 5mls of Mekong to each load can smooth out the pressure curve, but the muzzle blast is somewhat eye-watering...

What if I drink half a bottle of Yoong Thong before firing?

Or is SsangSom more appropriate for my calibre?

Originally Posted by jakewire

Nah, your luck you'd fill it with powder and it would work fine.

It's not good luck, it's sensible life choices.

Originally Posted by jakewire

Nah, your luck you'd fill it with powder and it would work fine.

I thought thats how it is

41gr of 2209 with a 130vld gets me 2777fps from a 24" barrel. So I'd say you will probably be in the high 2600"s with a 140 and a short barrel.

My barrel is slow for its length compared to others.