375 H&H Virgin Brass Stretch

[RSL]

Some of you may have seen my previous thread about my first time firing my M70 Classic Express. I am just now getting around to checking the brass from that range day. I fired virgin Norma brass I handloaded with 58.6g H4895 powder and Hornady 270g Interlock bullets. The virgin Norma brass measured 2.455 inches from the case bottom to the shoulder datum. The once fired brass measured 2.4712 inches from the case bottom to the shoulder datum. That's a difference of plus .017 inches. More than i expected. I am trying to figure out how much if any i should bump the shoulder back when i resize this once fired brass. The once fired brass loads into the chamber ok as it is. No resistance when closing the bolt. I am open to suggestions. TIA.

Stan

 

[Hunter4752001]

Undoubtedly there'll be different views on this, however I adjust my dies to bump the shoulder back around 2 thou.

 

[LeftySixgun]

I’ll be following this thread. I’ve been wondering the same thing. These belted cases (which I’m new to) head space off of the belt. My rifle is also a 375 H&H Winchester M70 Safari Express.

 

[BryceM]

For a bolt rifle I intend to hunt with, I full-length resize and bump the shoulder 0.002”. In actuality, there’s a bit of variance, frequently 0.001 or so either way.

For DG, I weigh each finished cartridge (to ensure they all have powder) and chamber each cartridge to make sure the bolt closes easily.

Setting the shoulder back more than 0.002 or 0.003” really isn’t necessary. Setting it back 0.017” would be a bad idea - leading to thinning near the base and an eventual case head separation.

 

[LeftySixgun]

So, what tools are used to measure the amount of shoulder bump? And where do we get them?

 

[RSL]

So, what tools are used to measure the amount of shoulder bump? And where do we get them?

I use the Hornady lock n Load Headspace Gauge Set and a digital caliper from Amazon. There are You Tube vids showing how to do it.

 

[Hunter4752001]

The 375 H&H was designed to headspace off the belt and to have a lot of clearance between the shoulder and the chamber. This was so it would reliably chamber even in the presence of dirt and carbon etc. It was designed as a dangerous game cartridge where reliability was critical, brass life was irrelevant. It was also before reloading was common thing which meant the fired cases were throw away items. Unfortunately, full length resizing a 375 H&H without reference to the fired length will quickly result in a case head separation.

These days most of have to reload for financial reasons. Cartridges and chambers are still made to the original specs. As a result we have to size our cases to both headspace on the belt AND the shoulder in order to maximise case life. In practice, bumping the shoulder back a few thou extends case life, but minimises the risk of a case sticking in the chamber.

 

[Accidental Villain]

The 375 H&H was designed to headspace off the belt and to have a lot of clearance between the shoulder and the chamber. This was so it would reliably chamber even in the presence of dirt and carbon etc. It was designed as a dangerous game cartridge where reliability was critical, brass life was irrelevant. It was also before reloading was common thing which meant the fired cases were throw away items. Unfortunately, full length resizing a 375 H&H without reference to the fired length will quickly result in a case head separation.

These days most of have to reload for financial reasons. Cartridges and chambers are still made to the original specs. As a result we have to size our cases to both headspace on the belt AND the shoulder in order to maximise case life. In practice, bumping the shoulder back a few thou extends case life, but minimises the risk of a case sticking in the chamber.

I think you are pretty much spot on there.
I`ve zeroed a number of 375 H&H rifles for customers back in the day with different kinds of ammo.
This is one of the great party tricks of the 375H&H. You can sometimes make it work with a combination of bullets without changing zero that is, provided factory spec cases I guess? I`ve never tried it with anything else. Like a combo of 300 grain FMJ/SP and for example 270 grain SP.
Because the 375H&H head-spaces on the belt the bullets will usually hit the rifling at the exact same angle provided factory spec cases.
For hunting I`ve always sized the cases to exact cartridge specs. Shorter case life yes I know, but its for hunting so who cares.

 

[BryceM]

Shorter case life isn’t so bad….. it’s the way it fails that’s the problem. A case head separation immediately turns your fancy rifle into an awkward club. Usually a cleaning rod and brush will dislodge the broken case from the chamber, but if you’re unlucky, it will require the services of a gunsmith. If you’re going to full-length resize and push the shoulder back a long ways, you should inspect the inside of the case. A while before they fail, you can see and feel a thin spot in the wall of the case. Usually it’s around 1/8 inch beyond the region of the belt. You can make a “feeler gauge” from a bent paper clip or something similar. You can also sacrifice a case and saw it open to visually look.

I learned all of this the hard way. I did it reloading .257 Wby - a perfect bottleneck design for this problem. It’s a belted cartridge and headspaces from the belt. Before I understood all this, I was pushing the shoulder back WAY too far. Somewhere around reload 4 or 5, the problem manifested itself when the bolt removed the base but not the rest of the empty. Done shooting for that day. I sawed open a few of the reloads and found a thin spot in all of the ones I checked. It’s a big inconvenience in a PG situation, but potentially a huge problem when hunting DG. Even with perfect reloading technique, I don’t think I’d push it. 4 reloads is about all I’m comfortable with when it comes to DG hunting. Maybe I’d “stretch” this rule a bit if I was carefully checking the brass. Most of the nitros and the .416 Rigby have the advantage of low chamber pressures. They’re also not terribly over bore, so that helps.

One clue is the need to constantly resize brass. If you’re trimming a lot of material to get back in spec, realize that brass is coming from somewhere. That somewhere is usually just beyond the belt where the case stretches back to fill the chamber.

 

[Accidental Villain]

Shorter case life isn’t so bad….. it’s the way it fails that’s the problem. A case head separation immediately turns your fancy rifle into an awkward club. Usually a cleaning rod and brush will dislodge the broken case from the chamber, but if you’re unlucky, it will require the services of a gunsmith. If you’re going to full-length resize and push the shoulder back a long ways, you should inspect the inside of the case. A while before they fail, you can see and feel a thin spot in the wall of the case. Usually it’s around 1/8 inch beyond the region of the belt. You can make a “feeler gauge” from a bent paper clip or something similar. You can also sacrifice a case and saw it open to visually look.

I learned all of this the hard way. I did it reloading .257 Wby - a perfect bottleneck design for this problem. It’s a belted cartridge and headspaces from the belt. Before I understood all this, I was pushing the shoulder back WAY too far. Somewhere around reload 4 or 5, the problem manifested itself when the bolt removed the base but not the rest of the empty. Done shooting for that day. I sawed open a few of the reloads and found a thin spot in all of the ones I checked. It’s a big inconvenience in a PG situation, but potentially a huge problem when hunting DG. Even with perfect reloading technique, I don’t think I’d push it. 4 reloads is about all I’m comfortable with when it comes to DG hunting. Maybe I’d “stretch” this rule a bit if I was carefully checking the brass. Most of the nitros and the .416 Rigby have the advantage of low chamber pressures. They’re also not terribly over bore, so that helps.

One clue is the need to constantly resize brass. If you’re trimming a lot of material to get back in spec, realize that brass is coming from somewhere. That somewhere is usually just beyond the belt where the case stretches back to fill the chamber.

Case separation is something one definitely want to avoid.
The trick is of course to at least keep the brass separated and eventually keep track of how many times the cases have been reloaded. And only use at the most once fired brass for hunting rounds.

 

[Wyatt Smith]

Since the 375 headspaces from the belt, assuming that’s correctly set, an oversized chamber (or undersized case) should not lead to a case head separation. All that should happen is the case shoulder will be blown out forward to fill the chamber, with base being snugly heal against the bolt face by the belt.
The neck should crack from being overworked long before the case head separates.
For DG I would use new brass and fully resize the cases. There is enough taper in the 375 that if you screw the die out to get the shoulder set correctly, you are not sizing the case body as much.

 

[RSL]

Another interesting thing i discovered measuring the virgin and once fired brass is that the virgin brass was longer overall than the once fired brass.

Virgin = 2.837
Once fired = 2.833

Not sure i know what's happening here.

 

[Rafiki]

Eh, when taking a hunting trip that you've spent thousands on before even getting there spend a few extra bucks on new brass.

 

[BourbonTrail]

Another interesting thing i discovered measuring the virgin and once fired brass is that the virgin brass was longer overall than the once fired brass.

Virgin = 2.837
Once fired = 2.833

Not sure i know what's happening here.

That could be a measurement goof or Poisson’s ratio kicking in with a dry chamber; might try checking the diameter on that one.

My 416 Rem only moves forward .005” but my weatherby will move .050”-.1” regularly on first fire.

I only bump my Wby .002”, but full length resize for the 416. I anneal both necks to help delay neck cracking.

 

[Grumpy gumpy]

That could be a measurement goof or Poisson’s ratio kicking in with a dry chamber; might try checking the diameter on that one.

My 416 Rem only moves forward .005” but my weatherby will move .050”-.1” regularly on first fire.

I only bump my Wby .002”, but full length resize for the 416. I anneal both necks to help delay neck cracking.

I would tend to favour Poisson's ratio in this instance
Fun facts, the mathematician and physicist Poisson was a brilliant man, for fun look up poisson's kicking horses
Gumpy

 

[LeftySixgun]

Another interesting thing i discovered measuring the virgin and once fired brass is that the virgin brass was longer overall than the once fired brass.

Virgin = 2.837
Once fired = 2.833

Not sure i know what's happening here.

A fired rifle case often measures shorter than a resized case because of fire-forming and brass spring-back. When a round is fired, the brass expands outward to seal against the chamber walls. This radical outward expansion pulls the shoulder of the case backward slightly.
When you go and resize the case, the case is then formed to a smaller diameter with the sizing die and then "grows", in a sense in length.

 

[Bob Nelson 35Whelen]

Some of you may have seen my previous thread about my first time firing my M70 Classic Express. I am just now getting around to checking the brass from that range day. I fired virgin Norma brass I handloaded with 58.6g H4895 powder and Hornady 270g Interlock bullets. The virgin Norma brass measured 2.455 inches from the case bottom to the shoulder datum. The once fired brass measured 2.4712 inches from the case bottom to the shoulder datum. That's a difference of plus .017 inches. More than i expected. I am trying to figure out how much if any i should bump the shoulder back when i resize this once fired brass. The once fired brass loads into the chamber ok as it is. No resistance when closing the bolt. I am open to suggestions. TIA.

Stan

@RSL
DO NOT BUMP THE SHOULDER BACK
The case is now formed to your chamber dimension. If you keep bumping the shoulder back you will end up with incipent case seperation and eventually you will have a total seperation.
It appears you have an oversized chamber.
With magnum cases especially the 375 with its long sloping case are supposed to headspace off the belt but chambers vary and ALL cases should be head spaced off the datum line in the shoulder not the belt.
This issue is more common than you think.
Bob

 

[Bob Nelson 35Whelen]

I’ll be following this thread. I’ve been wondering the same thing. These belted cases (which I’m new to) head space off of the belt. My rifle is also a 375 H&H Winchester M70 Safari Express.

@LeftySixgun
That's a common mistake that people make and end up with ruined cases within three firings and have case head seperation.
ALL rimless cases be they magnum or not need to be sized off the datum line on the shoulder.
Bob

 

[Bob Nelson 35Whelen]

So, what tools are used to measure the amount of shoulder bump? And where do we get them?

@LeftySixgun
The tool I use is the brain
If my cases be they rimless or rimmed become hard to chamber I trim to length then full length size until I have very slight resistance when I close the bolt. This is done by sizing the case in very small increments

The 375 H&H was designed to headspace off the belt and to have a lot of clearance between the shoulder and the chamber. This was so it would reliably chamber even in the presence of dirt and carbon etc. It was designed as a dangerous game cartridge where reliability was critical, brass life was irrelevant. It was also before reloading was common thing which meant the fired cases were throw away items. Unfortunately, full length resizing a 375 H&H without reference to the fired length will quickly result in a case head separation.

These days most of have to reload for financial reasons. Cartridges and chambers are still made to the original specs. As a result we have to size our cases to both headspace on the belt AND the shoulder in order to maximise case life. In practice, bumping the shoulder back a few thou extends case life, but minimises the risk of a case sticking in the chamber.

@Hunter4752001
Unfortunately you can't headspace off both the belt and shoulder. I agree with your initial assessment on the design but the position of the belt can vary from brand to brand and chamber dimensions are different for every rifle regardless of calibre. For rimless and magnum cases you should always headspace off the datum line in the shoulder.
Bob

 

[Bob Nelson 35Whelen]

Another interesting thing i discovered measuring the virgin and once fired brass is that the virgin brass was longer overall than the once fired brass.

Virgin = 2.837
Once fired = 2.833

Not sure i know what's happening here.

@RSL
Sound like a slightly oversized chamber to me.
When the shoulder moves forward the case length shortens.
I know this happens with my 25 when I fire form cases they actually become a bit shorter because the datum line moves the case shinks.
Bob