I'm back to report on my load development for my AHR DGR CZ 550 Magnum Rifle in 404 Jeffery. It's taken me a while to get back to the range since I posted the results of my load development with the North Fork 0.423, 400 grain Semi-Spitzer (SS) Bonded Bullets (Softs). I've been working a lot, and it's rained a lot this spring, and I'm just getting around to it. Oh well....
At the advice of the North Fork technicians, I targeted a reduced charge weight of 1.0 grains of IMR 4831 as a starting point for my loads utilizing the North Fork 0.423, 400 grain Cup Point Solids (CPS) which would have been 89.5 grains. I actually had a range of 88.0 grains to 90.5 grains (same powder charge as my softs) in 0.5 grain increments to play with. I loaded up several of the NF SS bonded bullets as a reference, and then for each charge weight with the NF CPS, I loaded up 3 rounds. I used a large sight in target at 100 yds with several aiming points, and for each point, I fired 3 softs, and subsequently 3 solids. I then went with the load with the closet POI between the 2 bullets.
I'm happy to report that I think I found a winner. The targets pictured below were shot at 100 yds:
View attachment 230241
For reference, the top left hole is the original cold bore shot from the rifle using my "soft" load. The 2 closet to dead-center/bullseye, are the other 2 softs. The small cluster of 3 bullets just above the bullseye to the top left, are the 3 consecutive shots I took with the "solids". The next closest "node" if you will, was interestingly the highest charge loads (90.0 grains). The target is below for that, and is still pretty darn good for a large bore, dangerous game rifle....
View attachment 230242
The softs are in the center, and the solids in the top right. The groups were very tight for a rifle of this caliber, and even the POI between the softs and solids were plenty good enough for a minute of buffalo rifle.
My final load recipe for the NF solids were as follows:
Rifle: American Hunting Rifles Dangerous Game Rifle (CZ 550 Magnum)
Cartridge: 404 Jeffery
Case: Norma (fully prepped, annealed and FL resized)
Bullet: North Fork 0.423 (400 grain) Cup Point Solid
Primer: Federal 215 (Large Rifle Magnum)
Powder: IMR 4831
Charge Weight: 88.0 grains
COAL: 3.610 inches
Ogive Jump to Lands: 0.040 inches
Crimp: Yes (Lee Custom Factory Crimp Die)
Chronograph Data:
Average Velocity: 2355 fps
Extreme Spread: 1 (not a typo)
Standard Deviation: 0.78
Group Size: 0.56 inches
Muzzle Energy: 4927 ft-lbs
The other thing that I am happy to report is that with much warmer temps than my original load development for the "softs", the CPS loads showed no signs of increased pressure. Ambient temps originally when I shot my rifle with the NF SS Bonded bullets were around 45 degrees F with 40% humidity. It was also very windy with sustained winds in the 10-15 mph range and gusts of 20 mph. The most recent session had ambient temps of around 80 degrees F, with 60% humidity, but calm winds of 3-4 mph.
Hopefully this load development data will help others shooting North Fork bullets in their 404 Jeffery, but per my usual disclaimer, what worked in my rifle may not work in yours, so be safe, be observant, and work up your loads slowly.
