Home Forums Hunting & Shooting Custom Rifles & Wildcats 375 WSM

Mike at Manzella Precision just finished this up for me. I really hope to be able to hit the range with it this weekend.

I like it!!! It should be a thumper too.

Thank you! I finished the brass up last night. I should have some 270 and 300g loads made up this evening. It should do a good job on anything I decide to point it at.

Very nice! Would be interested in build details. What stock is that?

It is a Lone Peak Arms Fuzion short action.
Proof Carbon 22" 1:12 barrel
Trigger Tech flat face special trigger set to 2.5lbs
McMillan Game Hunter stock. 65% black 35% Light blue
Action is bedded and Mazella Precision special pillars for Lone Peak actions
Hawkins Precision Hunter DBM with extra magazine
KEY MO suppressor break with adapter for AB .375 Raptor 8 suppressor
ARC 1" scope rings


The dilemma I had was brass size vs. chamber size. 375/300 WSM reamers already existed, but I was worried about neck length. I found a couple hundred Nosler 325 WSM brass and knew necking them up would shorten the necks. The only dies I could find available were from CH4D (Redding makes them, but their lead time was pretty far out.) I annealed the cases. Then I necked the 325 brass up to .358 and then again to .375 using an expander mandrel each time. I then sized the brass in the .375 WSM dies without the expander ball. At some point during the sizing process, a donut had formed. I expanded the brass to .376 with a mandrel and turned the necks to .014 and kissed the shoulders to remove the donut. I then sized them again in the 375 WSM die and expanded the necks for .002 neck tension. (BTW this Nosler brass is hard AF, even after annealing) Satisfied that the brass would be something I would be able to reproduce with the equipment I had (and carbon ring because of neck length wouldn't be an issue), I sent several brass and dummy rounds to JGS to make a reamer. I specified I did not want more than .003-.004 growth in any dimension, including length to make sure my brass life would be as lengthy as possible. So, theoretically, I now have a chamber matched to the brass dimensions my dies will produce. This should eliminate the need to/mimic the results of fire forming so that I can simply full length size each firing, bumping the shoulder back .002. Again, theoretically. We will see what happens, real world.

I am using Quikload to get a good start load developed for 270g and 300g in both Sierras and Barnes TSX.

Now the search is on to find someone willing to trade a brick of Magnum Large rifle primers for a brick of CCI Large rifle primers. Wish me luck!

Impressive build, looks like it turned out great, looking forward to hearing about how it shoots, would like to see that loaded ammo!

Thank you. I'll post some pictures when I get them made up.

Curious... how close do you think this will be to my 375/350? I've decided on 235gr bullets for mine.

Best of luck on this WSM project OP. Beauty.

I had a .338 WSM built 20+ years ago. Shoots great. My son took it to Africa in June. I loaded 250 gr AFrames at 2500 fps. He shot a nice Gemsbok, a kudu and a caracal. All DRT.

I have yet to measure my case capacity so, I honestly can't compare the two. I had the reamer designed to accommodate 300G Barnes bullets seating to the bottom of the neck without passing the shoulder and still be .060 off the lands. This allows me to still be able to seat the shorter 270 and 300g Sierras an appropriate depth and still be close to the lands. I have a box of Speer 235g but they are so short the jump to the lands is quite far.

That is good to hear. I bet he had the time of his life.

53.0g of RL16 under a 300g Sierra Gameking. Using the 375 Noveske in Quickload with my own cartridge measurements, it should be sailing at around 2000fps at 30k psi. I thought this would be a pretty good trial run to make sure everything is Kosher before upping the powder/pressure load.

Great looking cartridge!

Agreed, that’s a sexy som’bitch!

Purpose, i.e., what do you plan on hunting with it?

I hunt in Arkansas and 125yds is a long shot in my area. I plan on hunting pigs, whitetail and bear (If I can get get to one before the quota fills). I plan on keeping the load between 2100-2300fps.

Awesome love a good wsm wildcat build! That’s a nice setup!

Man that's a chunk of lead, good luck, looks great!

I did my first OCW test and I'm pretty pleased with the results. Smallest group is .63" and had an ES of 9fps. The other 3 groups are 1" or less. I plan on testing these 4 loads again then moving on to seating depth testing if they prove out. I was using Ramshot Big Game powder. The charge weight velocities were between 2266 and 2390. The best group was with 60.2g at 2300fps. This leaves my 100 yd. velocity at 2100fps. It should have no problem expanding the 300g Sierra Game King.

That’s gonna make a nice thump when it hits meat. Cool rifle!