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Discussion Starter #1
I've been thinking lately about working up a decent 38-55-Level load for the 375.  Up until now I've been looking for top velocity but was thinking lately of a good "'round the house" load since black bear trash can season is about here.  I live out a few miles and don't have to worry about over penetration too much (an exception might be an encounter in the house!).  Now don't get me wrong...I'm not trying to think of a good reason to shoot a bear, but they've become a nuisance here since the spring bear season was closed.  Some people in the area have had close encounters and even some breakins.  I've had them in the garage before and generally around the house unexpectedly.  It doesn't hurt to be prepared.  I'll also admit that some lighter loads would be fun to shoot sometimes too.  The 375 can be pretty respectable in the recoil department.

Does anyone have a pet cast lead load that produces something in the 1300-1600 fps range with good accuracy?  Will 21 bhn bullets (as BTB) cause leading at these lower velocities (ie will the bullets obturate)?
 

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Bart,

First thing is about leading at the reduced velocities.  Absolutely not.  If sized to be a minimum of  0.001" over groove diameter they will not lead, and won't need to obturate to fill the bore.

Now about the .375 Winchester and reduced loads... that is a sore subject with me.  You'd think after all these years, and being in the business of making bullets, that I'd have come up with a great reduced cast bullet load.  Sorry to say that every attempt at loading under about 1350 fps with the Marlin .375 Winchester has resulted in neat profile type impressions of bullets at 30-75 yard targets!  I've never managed to get a 250 grain bullet to stabilize below 1350 out of my assortment of Marlin .375's.  Yes, I've tried many powders, but still lack satisfactory results.

Something I have had outstanding results with is a .380" hard cast round ball, lubed with Lee Liquid Alox.  I've used several fast buring pistol powders for 1200-1600 fps with these loads and had excellent accuracy almost universally with all loads tried.

Perhaps results would be better with a 200-220 grain bullet, but I find it rather strange that my reduced loads were almost identical replicas of .38-55 type loading density and velocities that deliver such outstanding accuracy in the .38-55, yet have failed so miserably in the .375 Winchester.

I simply don't have the answers here, perhaps I've not been interested enough to make it a passion for success.  In either case, I can't guide your success in this venture.

If you succeed, please let us know!

God Bless,

Marshall
 

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Discussion Starter #3
The reports of 375 Win being less accurate than 38-55 have always puzzled me.  After all, dimensions of the cases are so close that it shouldn't matter.  Maybe it's the rifle.  Has anyone tried the Winchester BB or Savage 99 with light loads?  I wonder how the twist rate of the Marlin 375 and the Marlin 38-55 compare?  A lot of people here were just telling how accurate their Marlin Cowboys were.  One has Microgroove and the other Ballard...another difference.  Doesn't seem like there's too many other factors.

If I find something that works I'll be sure and report it here.  In the meantime I need to figure out where to start.
 

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Discussion Starter #4
After my first outing "working down" some loads I have begun to wonder something: At what point does detonation become a concern using RE7?  I started at 28.0 gr and worked down to 25.0 this weekend without a problem.  Accuracy is still there and I haven't noticed any bullet stabilization problems yet.  My tripod decided it didn't want to participate and so couldn't set my chrony up...don't have a clue as to velocity.  Seems like the 28.0 gr load was listed at about 1700+ in some rifle with some components, somewhere.  These must be getting down into the 1400-1500 fps range.

BTW, a 260 gr slug moving at even those pedestrian velocities is still a pretty good thumper.  When my supply of bullets gets refreshed...by next weekend I hope...I'll pick up the quest again.
 

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I have been working at this off and on over the past  8 months or so. Last night, I finally felt some breakthrough at the range.

Much seems to depend on how your rifle is chambered, as 375's seem to show a lot of variation. 2 Contender barrels I have had seem to have been chambered "normally". My current rifle is a pre safety 94 Big Bore. It will feed and chamber 38-55 ammunition no problem. I have, in fact, used 38-55 brass in it when I was short on 375 brass. The chamber is loooong.

This got me thinking about seating depth. The experiment last night entailed 250 gr. RCBS FPGC's cast in water quenched wheel weights.  I did not use gas checks. With the identical charge of approx 20 grains of AA1680, group size was about 8" when the bullets were seated to the crimp groove.

I also loaded some with the bullet seated out to the first lube groove, and used a Lee crimp die. Group size was 1/2", a dramatic difference.

I did not chrono these loads, but my guess would be about 1500 fps. I am finally feeling like I am on a track with this. It just seems like you really need to experiment with seating depth, bearing in mind that you will probably want to feed through the mag. I am going to see if I can get that bullet a little closer to the start of the throat.

If the group is interested, I can keep you posted as I play more.
 

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Good Observation,

Long ago I had to lengthen the cartridge carrier stop on my 375 Marlin to accomodate the longer cartridge overall length which I load for the .375 Winchester in my guns.  The differences are dramatic as Jem270 has posted.  It is nothing short of amazing what happens when you get that bullet up to the lands before launching it out the bore!  Group sizes dramatically shrink.  As an added bonus, you also increase available case capacity, and can thus acheive higher velocities with equal pressures as ammo loaded to standard length.

It opens a whole new realm to those shooting the .375 Winchester cartridge in leverguns!

God Bless,

Marshall
 

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Discussion Starter #7
A little update on this project.  I have reached the 20.0 gr level with Re7.  My F1 Chrony clocks this load out in the 1225 - 1395 fps range.  Accuracy from shot to shot has been what I can usually expect from the Marlin...in the 3-4 inch range at 100 yards.  I think loading density is about to  become a problem with this powder and it's probably time to switch to something a little bulkier at lighter loadings.  Note the extreme spread of velocities is around 200 fps with half full cases.  I haven't experimented with powder orientation in the case or anything, which may help consistency.  But the main point is that accuracy is pretty consistent, even though velocity is all over the board.  I had to adjust my rear sight upward considerably to even hit the target at 100 yards, and have no idea of what the midrange trajectory might be.  I have not witnessed any keyholes.  For these tests I've been using a 260 gr RNFPGC from Bonus Bullets out of Canon City, CO.  Can't afford to use up my supply of BTBs with elk season coming up.

I'll try this again once I get my firelapping supplies and get a chance to smooth the bore up some.  Hopefully the expected accuracy of this rifle will improve with completion of that project.  Marshall, are lapping supplies now on the backorder list too?
 
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