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I've been working on loads for a new M70 375 HH and am experiencing some issues. All primers are flattening regardless of powder charge - sounds like the shoulders are pushed back a little far. Next, fired case length to the datum point is .012" longer than the new brass measurement - sounds like excessive case stretching. Thirdly, fired cases are showing the frosty ring above the web - sounds like excessive case stretching as well. My problem is all loads have been fired with new, never sized brass. Does this sound like a minimum size brass issue or a maximum size chamber issue or combination of both? What are them SAAMI specs on the 375 HH? I could always throw more money at the problem and just buy a different batch of brass but I'd like to understand what is going on first. Thanks

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"Does this sound like a minimum size brass issue or a maximum size chamber issue or combination of both?"

I believe you have named your problem. The .375 headspaces on the belt, and if the brass is too short in the neck area to fill the shoulder, the brass will stretch between the belt and neck, causing the problem you are having.

As you mentioned, it could be brass that is too short, or a chamber that was reamed too deep. Or both.

I had a .300 Wby. that did that. Cases fired in this rifle, even after FL resizing, would not chamber in another .300 Wby. I had.

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Almost all belted magnum cases are short to the shoulder as they have to be able to fit in a super tight chamber. As they headspace on the belt, this is not an issue unless you reload. The way to avoid this issue with any belted case is to take the following steps.

1. FL size, trim and chamfer NEW cases.
2. Lube the inside of the case neck
3. Run you case into a neck expanding die. In your case (and mine) a 41 magnum pistol die works fine. Don't "bell" the mouth, just use the portion of the expander to open up the whole neck to +-.409"
4. Now get out your rifle.
4. Start running the case into you 375 H&H FL die to reduce the neck back to 375 H&H dimensions. It's a try and reset process. You want to leave a ridge below the neck and above the shoulder that is just enough to let you close the bolt with a positive feel. Now you are headspacing on the ridge, not the belt.
5. Load em up (full loads) and bang away.
6. You will now have cases fitted to your chamber, that headspace on the shouder.

375 H&H cases are very durable and will last forever with reasonable loads.

The same method is not a bad idea on ANY new case belted or not as brass is always made to minimum size whereas chambers vary a lot.

I even do it on my ancient M-1 and the LC NM cases last forever.

Just be sure to function test any ammo you plan to use for hunting or self defense.

As for the brass you have already fired and stretched. Probably okay for cast bullet loads but were it mine, I'd trash it.

There is another way to do this that also works in bolt actions (more camming power) if you have long enough bullets and a short enough throat. Seat the bullets way out so they firmly engage the lands. The cartridge is now headspaced by the bullet, not the belt or shoulder. Use about a 75% load as there is no bullet jump.

Finally either method works fine with cast bullets or pistol bullets. On my 35 Whelens I use the "ridge method" with 158 gr FMJ .357 revolver bullets seated BACKWARDS.

Great gun, great caliber, good shooting !


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Mathman
Thanks for the SAAMI specs. That is what I was looking for. It looks like my brass is a little on the short side by about .005 (2.452" new out of the bag).

Interthem
If I am understanding your process, you are blowing the shoulders out instead of stretching the case body. Then you use a standard FL sizer on the fired brass, setting the die up for minimal resizing. I am correct?

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The initial resizing of NEW brass, followed by trimming, is with the die set to bump the shellholder.
Once the case is fireformed to the chamber by the "ridge" method, the die should be set to only size enough to allow easy chambering. Better yet, use a Lee Collet or other neck sizing die. There is some stretch as the case is enlarged to fully fit the chamber, but nothing like takes place when a case that headspaces on a belt has a shouder a long way from the chamber's shoulder. (The 300 Win Mag is among the worst "stretchers".)
The 375 H&H is a low pressure cartridge and full length sizing should not be required as long as loads are reasonable. I have loaded 375s 10 times or more, just neck sizing. Trimmed em' once after 5 loads. BTW, brass being a bit short is not really an issue in the 375 H&H.


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I had 2 375 H&H with different chamber sizes. Had several incipient case failures when I was not segregating brass to rifle.

Once I kept brass segregated and sized brass to rifle had no more case failures.

375 H&H case is prone to stretch due to the taper of the case. One of the reasons I sold the 375 H&H and went to the 375 Ruger.

My large chamber Savage 99 in 250 Savage has same issues in a tight chamber bolt action, long brass life and less trimming.

In my large chamber 250 Savage I create a false shoulder and fire form 22-250 brass to have it fit chamber on first firing.
Would be much simpler to have a proper size chamber.


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What interthem is talking about is creating a false shoulder. If you size the whole neck up so that it wouldn't chamber and then set a NECK SIZE die to size only enough of the neck so that it will chamber with a crush fit, then you will be holding the case tight between the case head and the false shoulder.

A Lee Collet will not work since it is factory preset to size all of the neck (unless you had just the right size washer between the shell holder and bottom of the collet tube)

False shoulders are often used in cases like the Gibbs cases where you take new brass and set it up for fireforming. For instance, I form 30 Gibbs cases by taking 35 Whelen and setting a neck sizing die to size just enough of the neck to hold it tight in the chamber. Keeps the primers from backing out and the case from thinning too much on the initial firing.


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This thread and the one (currently) right next to it about the Chargemaster are interesting in that they both deal with problems inherent with the design that would be something that I think it would be valuable for a new person (or us old people, for that matter) to know. Has anyone ever done an article on "Quirks in Reloading that Aren't Generally Known" or something to that effect?


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The Lee collet die is ONLY used after the cases are fireformed to the chamber (as I said).

The "false shoulder" method will work with any case that has any shoulder.

As for 99 issues with the 250 Savage, 243, 22-250, 284.... the cartridges are all hot rods. The action was designed around a 30-30 class cartridge (303 Savage) and the action has a bit of "spring". In my 303 1899, cases last forever. In my 300 and 250 pre mil 99s, full hunting loads require FL sizing every time and brass is tossed after three reloads.

For those of old enough to remember when the 25-06 was still a wildcat, 30-06s were necked to create the false shoulder and fireformed with full loads. Chamber necks were cut larger, than today, as the neck was thicker than today's 25-06 factory brass. Bottom line is: the tighter the cartridge fits the chamber the less brass working takes place.

Last edited by interthem; 12/10/11.

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Originally Posted by BC3
Next, fired case length to the datum point is .012" longer than the new brass measurement - sounds like excessive case stretching.


That's not real bad from my experience. Best I've ever encountered is .015" short, the worst near .040". Mostly on belted mags the shoulder is around .018"-.025" on everything I've ever bought.



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My experience with .375 H&H is that the brass stretches more than other rounds. Because of the kind of game I would hunt with a .375, I want it to work and chamber and extract every time, so I full legnth size and trim after every firing and toss the brass after of the second firing.

Also, when hunting, I use new .375 brass.

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So...sounds like what I'm experiencing is fairly common with the 375 HH (or any other belted magnum). One way to deal with it is to create a false shoulder so the cartridge headspaces on this false shoulder. If I prep my cases using this method will the stretch not occur? Where does the brass come from that blows the shoulder out - the neck? The second way to deal with it is to treat it like any other cartridge and just set the should back .002 or so after the first firing and live with the initial stretch as the case forms to the specific chamber. If I follow this course of action will that initial stretch greatly shorten case life?
With a cartridge design (belt) that has been around for a hundred years or so one would think there would be a standard setup procedure for dealing with this idosyncracy.

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Your problem is designed into belted cartridges to ensure they will work. As I noted, the 300 Winchester Magnum has the same issue and there was even an extensive article in Handloader a while back saying all the same things that have been retold here.
The remedy for your issue is simple and has been well explained. Your issue did exist in 1912 (read up on how cordite powder cartridges were made)
The belt and set back shoulder (along with the body taper) reflected the genius of the cartridge's designers. The cartridge was designed to ALWAYS feed and chamber even in nasty humid places like India & Africa, into rifles that were just tools and treated as such. The combination of cordite powder, humid air, lots of dust and dirt, low tech cleaning methods and non-anal owners frequently lead to crud and rust in the chambers. With the set back shoulder and good old Magnum Mauser actions, you could be almost 100% sure that you could chamber a round and extract an old one before Mr Buff stomped on you. Nobody reloaded (generally illegal) so case stretch was a non issue.
Given the same conditions and ammo technology many of our modern wonder cartridges would result in "bad things". Sorta the same reasons a well used 1873/6 Winchester from out of own old West is almost never found with a perfect chamber and bore.
One of the reasons so many PHs are carrying 458 Winchesters today is the same. Simple, a big belt to headspace on, no issues keeping a straight sided chamber clean, big bullet moving slow, typically built on a Mauser or Mauser clone action that always seem to work when the chips are down.


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interthem - Thanks for you patience in explaining what is going on here. I appreciate you spelling out the detailed explanation on the procedure. It looks like I need to pick up a 41 magnum neck explanding die and give it a shot. Now, what caliber neck expander would you use for a 7mm Rem Mag?
Brian

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30 caliber.
35 for 338
375 for 35

You can buy ONE die with the threaded stem and buy the individual expanding plugs.

I use the Lyman ones. By a "long" M die. (really designed for expanding necks for using cast bullets)

http://www.midwayusa.com/product/194950/lyman-neck-expander-m-die-405-winchester (these were not made when I started doing this, hence I used a 41 Magnum pistol die)

The actual expanding "plug" is threaded onto stem that goes through the die body. You can buy additional "plugs" in various diameters directly from Lyman.
Say you wish to build a false shoulder on a 300 Win Mag, buy a 32R or 33R plug, unscrew the 405 Winchester one from the stem, replace it with the 32R or 33R one and you're ready to go.

Die bodies for handgun calibers are called "short", they will work but the ram will only be partially raised and it's easy to go too far.

Here's another site with some good pics and tables: (you can use a "pistol plug" on a "long" rifle die as the threads are the same). The tables are dated as there are more plugs available today.

http://www.lasc.us/Brennan_LymanMDies.htm

As Joe says, Lyman is a nice place to do business with.

Sounds a lot more complicated than it really is. Good luck !


Hey NSAQAM, Larry is very "IN", LOL
You also dishonor the 28th division by using the unit patch as an insult.
As for the liar, welcher Bricktop, his day is fast approaching.
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