Okay, on the serious side...if by "worst" you mean the most difficult to find a load for, here is my submission:
The .25-06 was a real "bitch" to get to perform to my wishes!
It took me almost 6 years to finally find a load that would shoot a 5-shot group at 100-yards of less than 1/2-inch!
The Ruger 77, out of the box was miserable. Probably the worst rifle I had ever purchased. The trigger was way too heavy, at around 10 pounds, the creep and backlash was extremely excessive.
I did my usual "Ruger Trigger Tune-Up". After careful application of files, emery paper, polishing compound and Colgate toothpaste I finally managed to get the trigger down to around 2-1/2 pounds, with absolutely no creep and no backlash. A trigger this light and sensitive is not generally advisable on a hunting rifle, however, that is where I set all my rifles for working up a load. There is enough adjustment on the Ruger trigger to bring it up to around 4 pounds, which is much more safe for a big-bore rifle used for hunting purposes.
As usual I wanted to use Remington brass, Remington primers and the fantastic Sierra Hollow Point Boat Tail bullets. So I purchased 1,000 pieces of Remington Brass all of the same lot number, and 3,000 of the Sierra bullets, again of the same lot number. I loaded 150 cases with around 37 grains of IMR-3031, and used these loads to fireform the brass, and to lap and break-in the barrel.
After I fireform my cases I only neck size them just enough to firmly hold the bullet, which usually only resizes about half the neck.
Then I started selecting powders...first I loaded some IMR-3031, in 0.3 grain increments from 37.0 grains to 43.0 grains. Results were lousy!
Next powder selection was IMR-4064 from 39.0 grains to 45.0 grains. Results were lousy!
I broke open a canister of IMR-4350 and loaded from 44.0 grains to 51.0 grains. Results were not that great...
I then tried H-450 from 49.0 grains to 54.0 grains. Results were lousy!
H-380 (what the hell, I had a ton of it...) from 39.0 grains to 44.0 grains. Results sucked!
I went back to IMR powders, this time 4320, and loaded from 39.0 grains to 45.0 grains. Same-o, same-o!
Next in line was IMR 4831, from 43.0 grains to 53.0 grains. Disgusting!
With all these powders, and all these loads, the 5-shot groups ran from 3 inches to, would you believe, 7-1/2 inches!
I was beside myself! I figured I would try one more powder, H-4831, so I loaded from 44.5 grains to 55.0 grains. WHAT? All the groups with this powder, regardless of the load, ran between 2 and 2-1/2 inches! I was amazed!!
To see if this was a fluke, I ran those loads again, and received the same results. So it looked like H-4831 was the powder of choice.
My next step was to take the most accurate load and start playing with seating depth, varying .001 inch down to .01 inch under my measured "ideal" overall length. (The way I find "ideal" overall length is to carbon up a bullet, semi-firmly set it way out in the case, and then gently close the action of the rifle. I want the bullet just touching the rifling...no free-bore for me!
Well, it turned out that my "ideal" length was the most accurate, but I still only got groups of 2 inches at 100 yards...4 times larger than my requirements.
I had just finished loading some .257 Roberts for a friend, and he specified the Nosler 120 grain bullets for his loads, so I had a bunch of them laying around. I decided to see what would happen with them. Was I ever surprised when the group sizes dropped to 1-1/2 inches! (I'm not a Nosler fanatic...) But, a 25% improvement was worth noting.
Still not satisfied with a 1-1/2 inch, 5-shot group at 100 yards, I started working on the bedding of the Ruger. I did what I have done to every other Ruger 77 that I have ever owned. I sanded off that damn knob at the end of the forearm! And free-floated the entire barrel from the front of the receiver to the end of the forearm, enough to fit 3 thick business cards all the way down without touching metal and wood.
Groups dropped to 1-inch!
Still not satisfied, I decided that I would try different primers...first Remington large magnum rifle...groups flew all to hell!
Next Federal regular and magnum...a total disaster!
CCI weren't any better, regardless of regular or magnum.
I had a thousand or two of the Winchester WLR primers, and before I used the rifle for a crowbar I decided that I had tried everything else, so why not them?
HOT-DAMN!!! Groups dropped to 0.489 inches instantly! And they stayed there!
I loaded a bunch more, using the Nosler bullets, the Winchester primers, Remington brass, and 53.3 grains of H-4831. Groups continually ran between 0.357 and 0.489, for 5-shots at 200 yards...
I had found my load...but it wasn't with the Sierra bullet...AND I WANTED TO USE THAT SIERRA BULLET!
I loaded some more cases with the Winchester primers and again used H-4831 powder, loading in 0.1 grain increments from 52.3 to 54.3 grains...stuck the Sierra bullet on top.
At 52.5 grains the .25-06 started printing 5-shot, 200 yard groups of between .258 and .308 inches!
Being kinda partial to IMR-4350, I decided that I wanted to try that powder once again...this time with the free-floated barrel and the Winchester primers, and naturally the Sierra bullet. I found that 47.7 grains of IMR-4350 gave the exact same velocities, and accuracy as the H-4831 loads! I was impressed!
After several hunting trips, and many, many one-shot kills, that load with the Sierra bullet is my favorite .25-06 load. It took 6 years to find it, but I have been using it ever since. As a matter of fact, I made my longest 1-shot kill several years ago on an antelope. The distance was 704 yards...measured by me and two witnesses, FIVE times!
As usual, once I find a load that I like, that is where I stay...generally for life, since I have several thousand bullets, tens-of-thousands of primers, and cases of powder all of the same lot number...and 1000 cases will last a long time...
I don't know how any of these loads will work in your .25-06...but think they are worth a try if you are not totally satisfied with what you are now shooting.
