What do you all make of this ladder test for 7mm-08? I've see velocity go down slightly after a peak, but never this drastically, and never seen one stay down as I approached book max. Oddly enough I had some old loads (same components) from another gun at 46.5 grains and they chrono'd about 2910 fps several months back, but the groups weren't great.

Suggestions?

I’ll take a stab...one of two things:

1. You hit max at 46.5, and things went downhill afterwards. You didn’t list the powder, so hard to tell how likely. 46.5 isn’t a big charge for the 7-08, but charge size is relative to powder...not so much for H414, over for RL15

2. Your chrono got screwy from overhead sun angle/shadow or Ive even seen low batteries give odd numbers. Did the standard deviation go up when the velocity dropped off?

Big Game powder. Book max is 47.5. This was a new bottle of powder.
Magnetospeed chrono, so sun shouldn't be an issue.

I don't recall the speeds dropping a lot, not enough to matter anyway, but every time I hit adding powder and getting not much if any increase it means in that particular situation I am at the max and need to back off.

Book max vs a guns max can be quite a bit off...

This is what happens when the powder you are using too slow a powder for your rifle/component combination.

Step the speed of your powder up a notch. As an example, if you are using H4831, go to H4350, or from H4350 to H4895.

This should fix your problem.

Its pretty obvious that you are at max with your rifle and load at around 46.3gr. After that, your rifle just isn't burning all the powder you are throwing at it... I've seen that using RL26 in the 270w. On to a different powder if it were me. On a side note, you should probably be running a magnum primer when using big game in the 7mm08. You'll likely get a better burn and it has been highly suggested by guys that use the 7mm08 religiously... Pharm in particular..

Interesting. I learn something every day. I thought I would see pressure signs and excessive velocity before I got into powder not burning.

May try that and re-run ladder test and see what happens.

Did you start with a clean barrel, odd things can happen until the bore is seasoned with a bit of copper, especially a new one.
A layer of fouling reduces friction which can result in a corresponding drop in pressure and velocity

Wasn't clean or new.

Agreed. Once velocities start to plateau it’s time to call it a day and back off a grain or two. Maximum has been reached and you just have to accept what that load combination gives you.

Before commenting on your results, I would need to know number of shots fired per each charge weight.

40 to 50 fps can be no more than noise if using a single shot for a graph point. If each point on the graph is an average of five shots, that is a different matter entirely.

Only 1 shot per weight. This was the first try with this particular combination.

I would go back and load three each at least, preferably five each at 45.9 gr, 46.2 gr, 46.5 gr, and 46.8 gr. And I would be loading any relatively slow ball power with CCI 250 primers.

This will confirm if you are seeing actual decline in velocity with increased powder charge, or if you graph is simply the result of velocity variation at charge weight.

I have seen many bullet powder combinations which give 100+fps velocity spread with identical charge weights. Such large variations are more common in magnum capacity cases, but not unheard of in the 308 class.

Such variation will quickly rule out a powder for use in a particular bullet/barrel combination. But during load workup, it will produce some very quirky graphs.

Look at what these guys have to say: https://www.longrangehunting.com/threads/ramshot-big-game-7mm-08.216196/