155g Sierra Palma Matchking, IMR 4895, Starline .308 Brass, CCI #200; Thompson Center Compass Load Development Part 3

Preface

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.

Today we will be conducting our third test on the Thompson Center Compass in .308 Winchester in its factory configuration using the components listed below. Since we tested a relatively cheap hunting load in the last post/video, today we are going to be testing more of a match load using some Sierra Matchkings. The 155 Palmas weren’t my first choice, but I had plenty of them on hand to do the test so they are up next.

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. Risencitizen.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.

Components Used

Brass- New Starline .308 Large Rifle Primer
Bullet- Sierra Palma 155g Matchking Hollow Point Boat-Tail
Powder- IMR 4895 40.5 – 44.5g
Primer- CCI Large Rifle #200
Cartridge Overall Length- 2.775″

Loading Process/Case Preparation

Resizing

I always resize my brass before loading it, even when it’s brand new. It’s really easy to ruin your day when you are seating bullets in some brand new brass and all of the sudden your case mouth gets crushed. So, I am using Redding Imperial Sizing Wax since I have a small batch of 50 pieces, and I am resizing the brass using an RCBS Full Length Resizing Die Set (Group A).

Tumbling, Chamfering, and Deburring

Next, I tumble the lube off the cases using a Hornady Tumbler (dry media) and Hornady Media Sifter. Once the lube has been tumbled off using walnut media (corn cob media works fine as well), I chamfer and deburr the case mouths using a Lyman Hand Tool. I use the Lyman Case Prep Express when I have large quantities of brass to do but for 50 pieces the hand tool works fine. Normally I don’t trim brand new brass, so this brass won’t be trimmed until I have probably fired it a few times.

Priming and Measuring Powder

After resizing, chamfering, and deburring the brass, I use a RCBS Hand Primer (non-universal shell holder) to prime each case with a CCI #200 Primer. I make a mental note to check each one to verify it seated deep enough and that they are in the correct orientation (make sure they didn’t seat upside down). If you feel resistance when priming, something is usually wrong. As with everything in reloading, you can never be too careful. Take it slow because nothing is too easy to screw up.

Now that all the cases are primed and ready for powder, it’s time to break out the RCBS Uniflow Powder Measure, RCBS Beam Scale, and RCBS Trickler to begin charging our cases with powder. Working from 40.5g to 44.5g of IMR 4895 in half grain increments, five cases are loaded with each charge. I like to throw a rough charge using the powder measure and trickle up to the exact charge I want on the beam scale. Once all the cases are charged with powder, the bullet seating die needs to get setup on the press for the last step.

Bullet Seating

The RCBS Bullet Seating Die (in the group A set) has a crimp built into it, but I am not going to be crimping these rounds, so the seating stem is the only thing I am really going to adjust to get the depth I’m trying to hit. 2.775″ seems to be a pretty standard COAL with these bullets, so that is the length that I’ll be running with. I usually adjust the depth on one round until I get it where I want it, verify on the next round that it’s repeatable (or close enough due to variances in each bullet), and seat the rest once that’s confirmed. Now that all the bullets are seated, it’s time to shoot.

Shooting Process

The same process is followed for all load development up to this point. I usually place a Champion Redfield Style Precision Sight-In Target on a piece of anchored cardboard 100 yards away from me in a field, stretch out my Midway Shooting Mat, kick out my bipod legs, toss my ol’ sandbag/sock on mat, pull my Impact Electronic Ear Muffs out of my bag, and get comfortable behind the gun. In reality, I have to get up constantly to check camera equipment batteries and whatnot, but we’ll just pretend that part doesn’t happen.

I usually load up some sighter rounds to confirm zero and eliminate the cold bore variables that people will argue about in the comments if I don’t do it, so I do it. Once the barrel cools down, I shoot the first load, which is the lowest powder charge, feeding from the magazine as I have in the previous tests, then go mark the target for reference later and allow for the gun to cool off before the next group is put on paper. This is how all of the shooting is done to maintain consistency as much as possible.

Results

Below is a picture of the final target after the shooting is concluded and a video of the shooting with target footage. Each group is measured edge to edge with calipers and the bullet diameter is subtracted to get the final measurement. These Sierra bullets offered the best results so far out of the three tests we have done with this gun, so it’s nice to see improvement in the results.

9 5-shot groups with 155g Sierra Palma Matchking
Group Average: 1.3″
Group Average Minus Outlier: 1.15″

Please feel free to comment with any questions, and check out the YouTube channel or Facebook page for more content on this topic and others. Thank you for reading. Stay Risen.

Video of Load Development with Target Footage