Plastic Stock Accuracy Test: Thompson Center Compass .308 Winchester Load Compilation and Shooting Groups Part 4


This is part of a written compilation of a series of accuracy testing with the Thompson Center Compass bolt-action rifle, chambered in .308 Winchester, which will include load development using numerous different components and the installation and glass-bedding of a Boyd’s Prairie Hunter stock. We will establish 3 different loads using different components (each with it’s own post and video), then we will use those loads to get a baseline of accuracy with the stock that comes on the factory rifle. Once we do that, we will test those same 3 loads with the Boyd’s stock installed. Last, we’ll glass-bed the stock and test those same 3 loads again to see how the accuracy changes throughout each step of the process. In theory, we should see a linear increase in accuracy, but this is going to be a way to see first-hand if that will actually hold true.

This test will be the portion where we compile the best loads from the previous three batches of load development (four if you count the retesting of the Z-Max bullet where our scope mount came loose) and shoot several groups with each load and average them out to get a baseline of accuracy with the plastic stock.

The Specifics

Recently, we had done some accuracy testing/load development with 3 different load combinations including two kinds of powder, three kinds of bullets, three kinds of brass, and one primer. The best “accuracy load” from each day of load development is the load that gets to move on to this portion of the testing, as well as the rest of the shooting for this process.

So, now that we have our best loads compiled, which will be listed below for reference, we are going to shoot 20 rounds of each load (in four 5-shot groups) and average out the groups to get the baseline accuracy for each particular load with the plastic stock installed. Once this test is concluded, the same test will be conducted with a Boyd’s Prairie Hunter Stock installed, and finally the same test will be done one last time with that Boyd’s stock glass-bedded to the rifle action.

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. 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.

Components Used/Loads Chosen

Load 1

  • Brass- PPU/PRVI Partizan
  • Bullet- Hornady 168g Z-Max
  • Powder- Varget 42.5g
  • Primer- CCI Large Rifle #200
  • Seating Depth- 2.800″

Load 2

  • Brass- Winchester
  • Bullet- Hornady 150g Hornady soft-point (flat base)
  • Powder- Varget 45.5g
  • Primer- CCI Large Rifle #200
  • Seating Depth- To cannelure

Load 3

  • Brass- Starline .308 Large Rifle Primer
  • Bullet- Sierra Palma 155g Matchking Hollow Point Boat-Tail
  • Powder- IMR 4895 43.5g
  • Primer- CCI Large Rifle #200
  • Seating Depth- 2.775″

Loading Process/Case Prep

All of the loading/case prep has already been covered in the previous posts, so I won’t go in-depth on what we did for each load, but the same equipment was used to load all the rounds with the exclusion of the PRVI/PPU brass. All the brass was neck-sized except for the PPU because all the PPU brass that I have used will stick in the chamber if it isn’t full-length resized, and this brass is no exception.

Here are links to the previous posts for those that would like to see how each batch of rounds was loaded…

Part 1: PPU Brass

Part 2: Winchester Brass

Part 3: Starline Brass

Shooting Process

Up to this point, all of the shooting has been conducted in the same fashion. This test will maintain the same basis of fundamentals, but I will be shooting one load per target in four 5-shot groups. A Champion Redfield style paper target is placed at 100 yards and all shots are fired from the prone using a bipod and a rear sandbag. All rounds are magazine fed, time is alloted for barrel cool-down between shot strings, and all shot groups are fired on the same day to keep environmental conditions as consistent as possible.


Below are pictures of the targets after all the groups were fired and measured. One of the targets actually had 8 groups fired into it instead of the 4, but the averages are still listed on the left side for reference (written in sharpie, sp stands for soft-point and mk is matchking). Included is a video of me discussing the results, but not of the actual shooting as I was down a camera at the time.

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