308 Winchester 175 Sierra MatchKing and IMR 4064 load development

308 Winchester load development with the Sierra 175 grain MatchKing (SMK) and IMR 4064 Powder.

In this post, I’ll be developing a load for my M40A3 clone. Built on a customized Remington 700 receiver, the rifle has a 25″ long barrel and used the following parts from Brownells:

It was chambered with a Manson Precision Reamer 308 Match reamer on a Grizzly gunsmithing lathe. To see how the rifle was built, see Building a USMC M40A3: Cloning the Marine Corps Sniper Rifle from 1999-2009.

A good starting point for 308 load development is always the 175 Sierra MatchKing (SMK). For decades, the 168 SMK was the go to match bullet for the 308 Winchester, however, the newer 175 SMK provides the shooter with a greater likelihood to achieve consistent hits at 1,000 yards. This has made the 175 SMK the most frequently encountered bullet for 308 match rifles and Sierra’s top selling bullet in 2015.

Varget has been my go to 308 Winchester powder for nearly a decade, but I am always looking to improve. I’ve heard great things about IMR 4064. It has a strong following in high power rifle competition circles and has proven accurate in my past experience with it.

All shooting was done at 100 yards, prone, with a bipod and rear bag. The Timney 510 trigger was adjusted to 2.5 pounds and the Nightforce optic was set at 15 power magnification. The target was a 2″ orange dot on white paper. Each charge was fired for one, 5-shot group. Muzzle velocity was recorded with a MagnetoSpeed barrel mounted ballistic chronograph.

WARNING: The loads shown are for informational purposes only. They are only safe in the rifle shown and may not be safe in yours. Consult appropriate load manuals prior to developing your own handloads. Rifleshooter.com and its authors, do not assume any responsibility, directly or indirectly for the safety of the readers attempting to follow any instructions or perform any of the tasks shown, or the use or misuse of any information contained herein, on this website.

I used the following reloading components:

My loading process is fairly simple. I don’t do a lot of prep work when I load ammo. I don’t weigh brass, sort bullets or double weigh powder charges (Specifically; primers were seated with a Sinclair hand priming tool, powder charges were dropped with a Harrell Culver Powder measure, and bullets were seated in a Forster press with Redding match dies). I simply open a box of Lapua brass, seat a primer, drop a powder charge and seat a bullet. That’s it. I like to shoot, not reload.

I get a lot of questions about using Russian primers like Wolf and Tula. Some shooters view them as “cheap”. In my experience, these are the most consistent large rifle primers available, offering lower standard deviations than other brands.

The rifle’s chamber was measured with a Hornady OAL gauge and the cartridge overall length was adjusted so the bullet was seated at the lands.

Range conditions were overcast, 45F, with half to full value 10-15 mile per hour winds.

I like to fire 5-shot groups of each load during the load development process. In the past I have used 3-shot groups, which I have found too small for reliable results, and multiple 5-shot groups, which I have found take too much time and utilize too many components for initial load development. A 5-shot group for each load during the initial work up seems like the best bet.

NOTE: The Sierra load manual lists 42.8 grains of IMR 4064 as the maximum load for the 175 SMK in 308 Winchester. Proceed with caution, the last shot of the 44.1 grain load required a mallet to open the bolt! Reread the disclaimer above, these loads are only considered safe in the test rifle.

175 grain SMK and IMR 4064 41.7 grain through 42.2 grain groups at 100 yards (above).

175 SMK and IMR 4064 43.5 grain through 44.1 grain groups at 100 yards (above).

The 42.0 grain load shot very well, .421 MOA.

The 42.6 grain load shot the best, .351 MOA.

I was really impressed with the standard deviation (SD) of all seven loads tested. The average SD was 10.5. Not bad considering this was factory brass with no prep work and all powder charges were thrown!

Velocity was decent. Having a 25″ barrel, I expected numbers that were slightly higher. However, these will certainly meet my needs.

So, which is it IMR 4064 or Varget? The jury is still out. For comparison purposes, using a 15 round sample (3, 5-shot groups), 44.2 grains of Varget was 2717 feet/second with an SD of 10.7 (avg size of 3, 5-shot groups was .605″) and 44.8 grains of Varget was 2755 feet/second with an SD of 13.2 (avg size of 3, 5-shot groups was .974″) from this gun on the same day. So Varget seems to give shooters a velocity advantage over IMR 4064.

IMR 4064 shows a lot of promise. So much so, that I ordered a couple 8 pound kegs of it too keep me busy. Moving forward, I’ll spend some more time working with loads in the 42.0 to 42.6 grain range. Once I find a favorite, I’ll play with cartridge OAL.

If you shoot a 308 Winchester and see a can of IMR 4064 on the shelf, I suggest you pick it up. You might be surprised!

To read about load development in a 22″ 308 using Varget and RL15, see: 308 Winchester Load Development Part-2: 175-grain Sierra Matchking, Varget and Reloader 15