.375 H&H Cast Shooters:

[Tusker]

Anyone use the Lyman “M” neck expanding die or something similar to expand the case mouth before seating a bullet for this cartridge-GC or plain base?

Lyman claims increased accuracy-but I just don’t need another die languishing on my shelf that I don’t use if it makes little or no difference.

[Larry Gibson]

I shoot quite a few GC'd and PB'd cast bullets along with some RBs in my M70 three six bits. I always use the Lyman M-die to expand the case neck and flair the case mouth.

[JonB_in_Glencoe]

I used a custom made expander insert (or maybe it was a NOE product, I can't remember?) that goes inside a Lee universal Flare die.
For my gun it was needed, since my gun was foreign (Czech). The Interarms Barrels are known to be larger than the spec .375
After slugging my barrel, I found I needed to size the boolits to .378 and the FL size die I had would make the neck way too tight for that fat of a boolit, so Neck expanding was very necessary.
That's my 2¢

[stubshaft]

Yes, I use a NOE expander to open up the neck to load cast bullets. Without it you run the risk of the case neck sizing down the bullets and bullets hanging up on the case neck.

[Tusker]

I appreciate the responses. I should have listened to Dad, he’s been shooting one or another since 1962. “Trust but verify”. RWR

[rockrat]

Yep, use an M-die. I size to .379" and it will shave lead off the boolit if I don't use it.

[reedap1]

Piling on with another "Yes, I use the M die for the 375 H&H". It is especially important if you are loading powder-coated bullets to avoid scaping off the powder. I first inside chamfer the case after trimming (if needed) and then neck expand. Lately, though I have been using the NOE expanders for my other cartridges.

Good luck

[mehavey]

Another "YES" for proper expander/bell die/use for anything cast.

[wmitty]

To elaborate somewhat, the full length sizing die will/can size the case neck to the point that a soft alloy boolit can be distorted, especially if the groove diameter is larger as JonB mentioned. It is crucial to flair the case mouth to prevent the neck from shearing alloy from the sides of the boolit when it’s being seated in the neck. The neck tension on the boolit is determined by the diameter of the smaller shank of the M die. I prefer a very light neck tension and make up larger pins than the M die and place them in a collet type bullet puller to open the sized neck slightly larger. Then flair the case mouth with a tapered pin. Loosing a piece of H & H brass these days to a split neck is a major deal!

[Tusker]

My M70 classic slugs to the fat side of .376” the length of the bore, near as I can tell. I have a single cavity 375449 and a MP .375-275. I also have for my Lyman .450 .376”, .377” and .378” sizing dies.
Snow is still deep and I have not shot anything through it yet.
Here is the question:
1.what size boolit do I want to size to shoot (the MP mold will throw a .378” bullet and the 375449 throws a .376”)
2. What size mandrel/expander for the neck?
Just trying to make the best educated guess without much education.
Bullets will be GC, about BHN 19-22. I’m guessing.
I have 3031, H4895, AA5744-shooting for a velocity of ~1800-1900 fps.
Maybe faster if it allows.

[JonB_in_Glencoe]

my best guess is to size boolits to .377
NOE carries a .380 x .376 expander plug
https://noebulletmolds.com/site/shop...-376-exp-plug/

[Larry Gibson]

My M70 Classic groove diameter runs .3755". My 375449 drops C)WW + 2% tin at .377. My 375248 cast of 20-1 drops at .378. I GC, size and lube in a .377 H&I die. I use a standard Lyman 37R M-die and have no probles seating either bullet or RBs.

With the 375 249;

I use 36 gr 5744 w/dacron filler for 1860 fps.

46 gr 4895 w/dacron filler for 2150 - 2200 fps.

4 gr of Bullseye (no wad or filler) under a 80 gr RB lubed with LLA for 900 fps.

[TurnipEaterDown]

4 gr of Bullseye (no wad or filler) under a 80 gr RB lubed with LLA for 900 fps.

How do you find the accuracy (say 25 yd) w/ the roundball, and did you have trouble getting there?
I tinkered a bit last summer w/ roundball loads in the 8x57, but moved on to others things before I intended to revisit, because of dismal initial results.

[rp85]

good morning:

Fireform a large number of 375 H&H case to 375 wby. With cast bullets the H&H and Wby gave the same speeds, accuracy and performance. Only when loading jacketed bullet does 375 Wby comes into its own.

Data based on 285 grain bullet, lubed\gas checked. BHN 15 (air cooled) can increase to BHN 18 with water quench. Cheap Walmart pencil set for BHN number, $9 + tax.

Wby rifle has a 26.5” barrel. The bore of rifle is .377 so I ordered .379 mold from Arsenal bullets mold. Very nice product. They do not answer e-mails, placed order on inter-net, mold showed up 4 weeks later after placing order.

Arsenal mold is a 375499 clone, gas check design, weight is 285 lubed and gas checked. Lube is red but don’t remember exact name. Bullets drops at .381” sized to .379”. Just try your .378 sizing die might work!

Using Gator copper gas checks, because they cost less than Hornadys.

Sizing dies, using a Lee 375 H&H, tapered expander for fireforming process and then final sizing with a RCBS 375 Wby sizing die. There is a difference in OD of the mouth of a sized case, Lee is .400” and Wby is .395”. Been using the RCBS sizing die for loading fireformed Wby cases. Using Lee expander to open mouth of sized cases to .408-412”. If case mouth not expanded very possible to shave lead off side of cast bullet. After loading a bullet the mouth is re-sized to .401-.403”.

Repeat with cast H&H & Wby same speeds, accuracy and performance the same. Bulk of information came from H&H cases, with 285 grain Arsenal bullet. The following gave best accuracy;

Red Dot (Lyman Cast bullet Manual), top end + a little extra, speed 1450. Extremely accurate, very little recoil, NO FILLER.

3031, mid-range for 1685, + extra powder speed 1805. Mid-range very accurate. USED A FILLER.

5744, just above starting loads for cast bullets speed 1950fps. Accurate, NO FILLER.

Bullet length, max chamber length less .020"

Finial note, 375’s with cast bullets is a black hole for $$$$. Enjoy!

rp

[Tusker]

Larry, is that a BACO gun or one of the “older”ones? In other words, any idea what year it was made? Mines from the ‘90s and serial # G15**** (6digits).
I’d like to know when exactly it was made but for some reason Winchester (whoever that IS now) is stingy with certain records it seems, AFAIK.

[pworley1]

I almost always use the m-die for everything. It keeps the bullet from being swagged by the neck.

[Tusker]

Yes! Thanks for the reminder about those pencils, I forgot I do have a set.

[Larry Gibson]

How do you find the accuracy (say 25 yd) w/ the roundball, and did you have trouble getting there?
I tinkered a bit last summer w/ roundball loads in the 8x57, but moved on to others things before I intended to revisit, because of dismal initial results.

They run about 1 1/2" - 2" at 25 yards and hold minute of grouse/ptarmigan at 50 yards. Somewhere abot 70 - 75 yards they'll turn into a slider, sinker of curve ball with which was "pitched" being unkown..... Wasn't hard getting there as I had previous experience with RBs in 7.8, 10 and 12" twist barrels. I knew best accuracy was going to be in the 850 - 950 fps range. I also already knew that Bullseye powder was the best choice. For such loads I use odds n end case with the flash holes drill out with a #28 bit.

With RBs in the 8x37 I had some that were .328 +/. that did about the same at 900 fps.

I should note I seldom use RBs anymore in any cartridge as I've found a light weight for caliber cast bullet 800 - 1050 fps performs much better.

[Larry Gibson]

Larry, is that a BACO gun or one of the “older”ones? In other words, any idea what year it was made? Mines from the ‘90s and serial # G15**** (6digits).
I’d like to know when exactly it was made but for some reason Winchester (whoever that IS now) is stingy with certain records it seems, AFAIK.

"BACO" ?

I bought it new in '94/'95 [ G28XXXX] and it had the cheapo moulded stock on it. I found the stock was flexing with full bore 300 gr jacketed loads and accuracy wasn't what it should be. I found the finished Winchester stock at Numeric Gun Parts. It was a "blemished" for $85 or $90 so i took a chance. Turned out the "blemish" was some of the stock inletting was chipped away at the steel recoil lug. Since I was steel bedding the action in the stock that "blemish" is under the bedding. The 300 gr jacketed load then shot moa. I love the rifle......

[TurnipEaterDown]

They run about 1 1/2" - 2" at 25 yards and hold minute of grouse/ptarmigan at 50 yards. Somewhere abot 70 - 75 yards they'll turn into a slider, sinker of curve ball with which was "pitched" being unkown..... Wasn't hard getting there as I had previous experience with RBs in 7.8, 10 and 12" twist barrels. I knew best accuracy was going to be in the 850 - 950 fps range. I also already knew that Bullseye powder was the best choice. For such loads I use odds n end case with the flash holes drill out with a #28 bit.

With RBs in the 8x37 I had some that were .328 +/. that did about the same at 900 fps.

I should note I seldom use RBs anymore in any cartridge as I've found a light weight for caliber cast bullet 800 - 1050 fps performs much better.

Thank you for replying Larry.

I was attempting a "gallery load" equivalent for the 8x57 (at least that is what I would generalize it as), and I already had a RB mold on hand. Wanted something I could hand a small kid or similar, and experience little to no recoil. Only real bullet mold I kept for 8 mm is the Saeco 081, and if I get another it will be a custom WN "throat fitter". Perhaps I just started way too high w/ the RB: 6 gr BE and a WLP gave me 10" groups at 25 yd, and it got worse as I went to 9.

I have some LEE healed BP revolver bullets that come out to 0.377", and I have been meaning to goad my friend into trying these in his 375 H&H which he complains about the poke on. Figured I would donate him some 700X, some of these LEE w/ LLA, and get him to make plinker loads for "familiarization"...