Thread: Ladder Testing

Here is a ladder I did for my 6.5 Grendel last week.

I used 5 widely spaced powder weights and two sorts of primers.






Here are plots of the points of impact of the 5 shots with each primer type:


As you can see there is no real pattern or node. One is simply a 2cm group and the other an apparent 1 cm group. Who would need to measure powder weight when a range of 2 grains will group them pretty much together ?

I chose which powder weight I'd use by:
1. One full grain below the max I'd tested and hadn't ruptured on me.
2. Not a compressed load. I guessed this by measuring the length of the loaded round. I've found in the past that after seating the bullet the compressed loads are a bit longer than they should be. Perhaps the press springs a bit meeting a hard powder charge and can't seat the bullet as deep as it should. My target case base to ogive length was 1.700". The length OAL to tip was a bit more variable. I imagine that 28.5 gr was compressed here and one manual said it would be.
3. And I measured the case base diameters before and after firing, The calipers are only precise to 0.0005" ie half a thou. so expansion only takes values of 1 thou, 1.5 thou and 2 thou. I decided to accept 1.5 thou. Might regret it later if the cases deteriorate. Here are the figures I used:



I loaded up 50 rounds at 27.5gr of BM8208 and fired another 5 shot group off a simple front rest and rear bag at the bench:


The first shot was the bottom left one from a cold but dirty barrel. I won't read anything into it. It's a 23mm group and somewhat higher on the paper than my first fireforming load.

Next, I shot at 600yd (stepping out from 300 of course ) using a backpack rest, prone, holding the foreend:
This is the technique and equipment I would use for longer hunting shots. The grid squares are 1 MOA.



Elevation is about 1.5 to 2 MOA and horizontal somewhat more due to my rudimentary wind reading.

So, essentially, I checked a range of powder loads for safety, didn't find a "node" and chose a powder weight a comfortable margin below the highest I'd proofed at.
The grouping at 100m looks adequate, although of course I won't know for sure till I've fired quite a few more groups as I sight in and check zero over the next few months. Grouping at "medium range" , well beyond the working hunting envelope of the Grendel cartridge, using the backpack was also adequate. So, I will just use that first, almost random, load and not bother to experiment to try and improve it.