Accurizing Marlin 375

[coyote nose]

Got a 375 Marlin a few months ago. So far accuracy with the few jacketed bullets I could find and a lot of cast bullets of various alloy has been dismal. It wears a 2 1/2X Weaver and I get occasional 3 shot groups around 2" at 100 yards but so far all AVERAGE groups have been in the 3 1/2" or greater range. Factory ammo, limited tests of course, has been around 4". Now i dont expect benchrest accuracy but when I can get average groups using tang sights of under 2" in a 33 WCF 1886, 2 1/4" in 45-75 replicas and original 1876 45-60s and 2 1/2" in original trapdoors with rude crude open sights......something just isnt right here. I am expecting 2" average at 100 yards for 3 shots. Online all Marlin lever accuracy tips center around the barrel band and floating the barrel. This 375 doesnt have a barrel band, it has the forend cap. The trigger is fine, as is the crown. Im thinking of taking off the forend and mag tube and do a few groups that way to see if the problem goes away. At least then I know where to start. Any thoughts?

[JimT]

I suggest reading this if you haven't ....

https://www.amazon.com/McPherson-Leverg ... 395&sr=1-2

[RIDERED350r]

While I don't have experience with the Marlin I do own a Winchester 94 Big Bore in 375 Win and my first shots with it were not satisfactory. It came with a box and a half of factory ammo that I fired off in an attempt to get a baseline sight in and work with handloads beyond that. My initial handloads set to specified COL netted the same results... 6" or larger shotgun patterns at 50yds.

So after doing a lot of looking around and conversing with folks on another forum, I decided to see if my action and chamber could tolerate a longer COL. After checking to see where the lands began with a shallow and lightly seated bullet and figuring out the chamber had ample room, I then experimented with a dummy round and found that my rifle would cycle and safely chamber a COL of 2.555". It was cycling from the mag to the chamber that didn't allow the full 2.600" that is the generally accepted limit of a Winchester 94 action. Bullet type and profile I figure can cause that number to wiggle about a bit. The 2.555" COL gave me about .010" margin of error for cycling...

Anyway all of that said, developing my 2.555" COL rounds using the Vollmer Precision 220gr JFN led to much better groups. My rifle likes the bullet seated out a bit further. I can now shoot 1.5"-2" groups at 100yds using the buckhorn open sights from the bench using sandbags for a rest.

You might want to look into the possibility of a longer COL if your rifle will tolerate it.

[TedH]

You are correct to expect more from that Marlin. Mine will consistently group around 1.5 moa with loads it likes. Have you checked the basics? Scope mounts tight? First thing I would do is mount a different scope and see if that helps.
Another easy thing to do is remove a slight bit of material off of the receiver end of the mag tube to ensure it "floats" as the barrel heats. You didn't mention any particular pattern to your groups. Vertical stringing could indicate mag tube binding.
The Marlin 375 have a very generous throat to fill. Cast bullets with a wide meplat seated long to fill the throat should shoot well. The Ranch Dog 235 gr mold was designed for this.

[Griff]

I gotta agree with TedH. It's been quite a few years since I've shot my 375 Marlin, but... It was capable of much better accuracy than I can produce. I replaced the 1970s era Weaver 4X with a 2019 Bushnell 1-4X and on 2 power was getting 1-¼" - 1-½" groups with the last of my Hornady 220gr. FN bullets. Since then, I've been waiting on Hornady to bring the 220 back... I don't recall ever shooting any factory ammo with mine. So can't comment on what you could expect.

[RIDERED350r]

Just a side note for my fellow 375 Win shooters. Vollmer Precision 220gr JFN is stated to be a near identical copy of the Hornady 220gr. Mr. Vollmer is a super nice guy to do business with but he is a small operation so orders take time to fill. I've been using his bullets pretty much exclusively in my 375.

I am not affiliated with Vollmer Precision. Just a satisfied customer figured some of you fellers might want to know. I appreciate the fact he is offering bullets for those of us who have these less common rifles.

https://vollmerbullets.com/

[6pt-sika]

I had a pair of Marlin 375’s one was jacketed only and the other was cast only . Two inches at 100 yards for three shots from the bench was not difficult with handloads in either , atleast in those two rifles . Don’t think I ever fired any factory in either rifle . I will say all my cast bullets were sized at .379” .

[AJMD429]

.
The Marlin 'XLR' series had the dovetail stud that attaches the tip of the magazine tune VERY loose - enough that the magazine tube tip could easily be pushed left or right by light pressure. Almost 'rattly' loose. The opening in the forend wood and cap was also 'generous' so although the wood was firmly attached to the receiver and barrel, the magazine tube was sort of 'loosely captured'.

I believe those things were done to improve accuracy

I do agree that one good troubleshooting step would be to simply fire the gun without the four end, or even the magazine tube, attached.

As far as scopes, I had a 32 or 36 x scope that was inexpensive and the windage adjustment had broken. But what I would do is mount that scope on pretty much any new long gun, even things like a 16" 45 Colt lever action, or a collapsible stock 16" AR-15. It looked pretty goofy, but I could tell very quickly if the gun was going to group nicely, or needed more work. I would shoot at a 4-ft square target at 50 to 100 yards with just a quarter inch black aiming dot, and I would shoot off of a homemade version of the lead sled shooting rest. So pretty much all of the variables aside from the actual firearm and ammunition were eliminated.

[coyote nose]

Ok guys thanks. Deer season started here in Ohio and I already missed my first doe! Using a 45-60 Winchester 1876. So with that going on my work on the 375 is on hiatus for awhile. Anyway, Vollmer bullets looks good and I will try an order there. I do size my cast bullets to 0.379". Will have to look to see if the forend cap is inflicting stress. And the groups (if you can call them that) are not vertical but triangular. Good point on the scope....I never had it on any other rifle. Will take that off first and mount another and try out a few groups. I do believe my brother in Montana has that McPherson book but I guess it is time I order my own. Nephew is asking what I want for Christmas and that looks like the ticket. THANKS TO ALL.

[marlinman93]

First thing you need to do is slug the bore on your Marlin 375! Without knowing the groove diameter it's impossible to know if the factory bullets fit well. After slugging the bore, pull a bullet and mic it to see how close it is. Then reassemble the cartridge without powder and seat the bullet out further. Check that the assembled cartridge functions to feed through the mag tube and cycle properly when seated out as far as the chamber will allow it. Sometimes with a levergun you can't seat a bullet out as far as would be needed for best accuracy, so you're stuck stopping at a point that it cycles reliably.
Once you begin reloading for the 375 you can play with bullet shapes, weights, powders, and seating depth until you get the best accuracy.