.375 H&H Brass to .340 Weatherby Brass Conversion Question

[J E Custom]

JE, I am sorry but you are becoming a serious problem on this thread. I am trying to get conversion data, and you have countless times repeated yourself on an issue that is beat to death and distracting from the thread. Below are the 340 and 375 specs from SAAMI that you could have found merely by clicking on the link I provided above. As stated above, they are all 'voluntary' but nobody in their right mind would ignore them.
Please play nice in the sandbox or I will just delete every one of your posts.
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Sorry you feel that way. I was only trying to help keep you from encountering problems. Different opinions and experiences have always help me and others to keep them from learning the hard way.

If you don't want my comments, that's your problem. but if it will save someone else I feel that my experience has helped. I don't understand why you won't to do this, but that is your choice and not mine. If this is what you want, I will pass on anything you post.

On this web site we all try to help and if the reply is not what you wanted to hear or you don't want to hear it, don't post asking for help and then jump on someone for trying to give you that help. We all have our experiences and opinions and often they are totally different from ours but they can also be a benefit to all.

Sorry I cant help.

J E CUSTOM

 

[Swamplord]

Simple operation really, I've necked down and cow fireformed hundreds of 375 H&H cases to 8mm Rem Mag a number of years ago and ran same velocity/pressures as factory Rem 8mm RM brass, some cases lasted longer than others and it was usually directly related to brand quality rather than some overstated pressure rating on a cartridge..... and it's just one less step to make 340 Wby brass

recently made 50 pcs of 350 Rem Mag brass from Winchester 264 Win Mag brass but didn't like the ring left from the body/shoulder junction, hope it will fireform out and clean up by neck turning, just formed 50 pcs from Winchester 300 Win Mag brass and happy to see the longer body takes the ring up out of the case length of the 350 Rem Mag

but back to 340 Wby, simply run the 375 H&H cases into a 350 Rem Mag fl die just enough to size the neck down then fl size in a 340 Wby die, might need to trim a bit depending on length of parent brass but usually the brass length pull back to fill new wider chamber and leaves necks a bit shorter than trim length as I have experienced in making 8mm RM cases from 375 H&H brass


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[Swamplord]

the good ol' wildcatter boys used to do it all the time

..

 

[J E Custom]

OK, hopefully we've buried the pressure thing that's been beaten to death, let's move on to this as it is more closely related to my question.
I agree that you can neck down a 375 to 340, fireform and trim to fit nicely in the chamber. I have some serious safety issues with actually loading magnum charges into such a case.


Thanks for getting the point I was trying to make of loading an older designed cartridge to High pressures. People buy Weatherby for one reason "Velocity" and If a person wants these velocities, there are things that have to be done to the chamber that Makes there loading safe (At minimum of a factory chamber has to be cut for the necessary freebore).

If you had stated that you did not intend to load to factory pressures, I would never have mentioned the brass you wanted to use. Weatherby's have special chamber requirements In order to run the velocities they do, if these requirements are not met extreme pressure will be the results. Other Magnum cartridges don't have these requirement's and can be loaded to there limits with different results.

J E CUSTOM

 

[J E Custom]

the good ol' wildcatter boys used to do it all the time

..
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I agree that it can be done, but should it be done. Wildcatters normally know what to do to a chamber in order to get more velocity at Lower pressure, and as long as these things are done everything should be ok. But if they are placed in a chamber without the Weatherby design features, Problems will arise.

Loading can be a dangerous business and not very forgiving if not well thought out.

J E CUSTOM

 

[Swamplord]

I agree that it can be done, but should it be done. Wildcatters normally know what to do to a chamber in order to get more velocity at Lower pressure, and as long as these things are done everything should be ok. But if they are placed in a chamber without the Weatherby design features, Problems will arise.

Loading can be a dangerous business and not very forgiving if not well thought out.

J E CUSTOM

Not disputing the safety concerns at all, every handloader and especially wildcatter is responsible for thoroughly researching the rewards and very real hazards of wildcatting parent brass cases into other cartridges, every single design feature of cartridge & chamber is a required study before actual sizing down/up & fireforming takes place

such is my practice .... there is far more research and study that happens before cases pop into new shapes

 

[Swamplord]

I would like to convert .375 H&H (parent case) to 340 Weatherby Magnum Brass. RCBS formerly made a die(s) to do this, but has long since discontinued doing so. 375 brass is readily available and relatively cheap. 340 brass is costly and hard to find. I have attached the SAAMI specs for each case/chamber. Notable differences are that:
1. The 340 case has less taper, thus a fireform at some point is required
2. The 340 case uses Weatherby's double radius neck vs. the conical frustrum neck on the .375
3. The 340 case length and distance to neck are just a smidge less than the .375, a nice feature
4. LOA can be identical and be in spec
5. Both headspace off the stupid belt, but Weatherby's has tighter tolerances both for bolt and chamber

So what I have in my possession is a full length .375H&H (taper crimp) and a full length 340 Wby (taper crimp) two die set, along with a 340 Wby finish chamber reamer and a small lathe if needed.

So my first inclination would be to oil the cases and size them with the 340 die set sans plug/decapper. The die would be run down until the neck was all the way resized to the 340 dim's. on the outside. That would be .366 OD at 2.485 from the base. Not sure what the shoulder would look like at this point.
NOTE: If the cases were un-fired I would probably size them with the .375 die first to make the necks round.
Then I would 'somehow' ream out the inside of the neck to possibly .3353 or .3383 not sure, they are both in spec. I want to make sure there is enough case mouth thickness to grab the bullet when seating but not too much that it would push the case shoulder back instead of seating the bullet. Don't know what the standard practice is. Don't know whether the case mouth would have to be supported externally whilst reaming either.
Then I would trim to length.
Then I would anneal the cases and fire-form them. Do I need a real bullet for that? Then I would reload as normal except headspace off the shoulder if possible, maybe a full length resize would be needed on the first reload?
Anyway have never done a case conversion before so please add lots of comments even though it may seem obvious to you.


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The following took place last night after reading your post and replying to it... My experience with converting 375 H&H brass to 8mm Rem Mag was always a positive one, I have a 340 Wby but haven't formed brass for it yet and took it upon myself to do so, did not have any 375 H&H brass on hand... went out and bought the only available 375 H&H brass on the shelf, sadly it is Hornady chonk but will do for this project

 

[Swamplord]

Attempting to run Hornady 375 H&H brass directly into an RCBS 340 Wby Full Length sizing die resulted in cases getting crushed down instead of necking down, (first two cases in pic) unsure if crap brass or cases needed a bit more necking down ...

Not having 375 H&H dies I used a FL 375 Ruger sizing die (old story why I have these dies, don't ask , I'm ashamed.. lol ... old wildcat project ) with spindle & expander ball removed from die to round out the case necks without expanding back up to 375 cal via the expander ball, the 375 Ruger FL die was absolutely the answer as it allowed fully necking down the case neck, pushing the shoulder down and slightly belling the case mouth inward in order to allow necking down with the 340 Wby FL die,

I then deburred the outside of the case mouth to further reduce the possibility of crushing cases in the next smaller diameter necking down step......

this was accomplished by trial and error until desired results were reached... necking down in small increments and adjusting down with the 340 Wby FL die and running into chamber until the bolt closed with slight resistance without scraping the base of the case as I wanted a temp and positive headspace on the shoulder datum instead of the belt, to prevent the premature onset of insolent case head separation (incipient, lol)

primed with WLR primers & charged the cases with 10.5 gr of Blue Dot pistol powder and topped off with original Malt-O-Meal and capped with paraffin wax, then fired in my Sako TRGS M995 rifle to create beautifully formed cases !

** Note** not using bullets & rifle powder to fireform cases .....

Cases were fully formed but require trimming to 340 Wby "trim-to-length" ,

my Sako TRGS M995 340 Weatherby is a world traveler with a storied past, having been in multiple countries on the dark continent, Europe, NZ and Alaska multiple times, taking many heads of game in it's lifetime, I have no need to fireform brass from the 375 H&H to 340 Wby since I have plenty of WBY factory brass and have recently bought some more Nosler brass on this website

Just wanted to see if I can do it without needing custom case forming dies ..... Yup, sure can.... and I can neck the 375 H&H brass to 350 Rem Mag just as easily with a couple other dies

it sure is easy too neck down & fireform 375 H&H brass to 340 Wby ....
but..... reloading these fireformed cases will require you to use common sense, caution and gradual workup from lower charges/pressures until a known safe velocity/pressure threshold is achieved with converted 375 H&H cases

good luck

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[memtb]

Very nice presentation Swamplord! memtb

 

[Swamplord]

340 Weatherby factory brass on left and 340 Wby Nosler brass on the right

Hornady 375 H&H brass converted to 340 Wby in between the two , easy as cake ... or pie ?

 

[longestrange]

Attempting to run Hornady 375 H&H brass directly into an RCBS 340 Wby Full Length sizing die resulted in cases getting crushed down instead of necking down, (first two cases in pic) unsure if crap brass or cases needed a bit more necking down ...

Not having 375 H&H dies I used a FL 375 Ruger sizing die (old story why I have these dies, don't ask , I'm ashamed.. lol ... old wildcat project ) with spindle & expander ball removed from die to round out the case necks without expanding back up to 375 cal via the expander ball, the 375 Ruger FL die was absolutely the answer as it allowed fully necking down the case neck, pushing the shoulder down and slightly belling the case mouth inward in order to allow necking down with the 340 Wby FL die,

I then deburred the outside of the case mouth to further reduce the possibility of crushing cases in the next smaller diameter necking down step......

this was accomplished by trial and error until desired results were reached... necking down in small increments and adjusting down with the 340 Wby FL die and running into chamber until the bolt closed with slight resistance without scraping the base of the case as I wanted a temp and positive headspace on the shoulder datum instead of the belt, to prevent the premature onset of insolent case head separation (incipient, lol)

primed with WLR primers & charged the cases with 10.5 gr of Blue Dot pistol powder and topped off with original Malt-O-Meal and capped with paraffin wax, then fired in my Sako TRGS M995 rifle to create beautifully formed cases !

** Note** not using bullets & rifle powder to fireform cases .....

Cases were fully formed but require trimming to 340 Wby "trim-to-length" ,

my Sako TRGS M995 340 Weatherby is a world traveler with a storied past, having been in multiple countries on the dark continent, Europe, NZ and Alaska multiple times, taking many heads of game in it's lifetime, I have no need to fireform brass from the 375 H&H to 340 Wby since I have plenty of WBY factory brass and have recently bought some more Nosler brass on this website

Just wanted to see if I can do it without needing custom case forming dies ..... Yup, sure can.... and I can neck the 375 H&H brass to 350 Rem Mag just as easily with a couple other dies

it sure is easy too neck down & fireform 375 H&H brass to 340 Wby ....
but..... reloading these fireformed cases will require you to use common sense, caution and gradual workup from lower charges/pressures until a known safe velocity/pressure threshold is achieved with converted 375 H&H cases

good luck

.....

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Wow! All I can say is Wow! I was going to reply to your earlier posts with gratitude for the great info, but this is beyond that!

 

[longestrange]

Couple questions, but made some measurements first:
OK so have made a few measurements on some new/fired 375H&H and new 340Wby brass, along with the reloading die plugs. It is hard to measure the wall due to burrs and the roll crimp.
.340 'new' brass neck is .3605 OD and around a .011 wall, resize plug measures .3365 OD and the CNC bullet is .3380 dia exactly
The chamber specs are .369 ID near the mouth
.375 'new' brass neck is around .392 OD or so with again a .011 wall, resize plug measures .372 OD or so
The chamber specs are .404 ID
fired neck is .403 OD or so with the .011 wall
So if I add 2X wall thicknesses to the bullet dia's I get .360 for the Wby so .009" dia difference to the chamber
On the .375 I get .007 dia difference.
Thus it there seems to be a bit more room in the Wby chamber near the neck, probably deliberate.
Another thing to note is that the new hornady .375H&H brass isn't very round, being tossed loose into a bag in a box. The 340 Wby brass is put in the box in plastic holders, complete with the radius, which will make a great shellbox once reloaded.
Both have burrs on the inside of the neck, and I have noticed burrs on the outside of some necks.

Comment: Thanks Swamplord for pointing out the need for resizing to .375 prior to necking down. If you got hornady 375 like mine it's not round. Am also going to push it into the roll crimp a bit just in case.
Comment: Thanks to 'somebody' above who said never anneal prior to resizing because the shoulder will tend to push in more.
Edit: This was Magnum Maniac:
'Yes, I anneal my brass prior to fire forming AND necking down, but a word of warning, in some dies that do not have a tapered expander, an annealed case can crush the neck, so depending on this, it may be better annealing after the neck is reduced.'
Comment: Thanks to somebody on another thread here back when who said that pushing the case into the resizer very slowly (15 seconds or so) will help eliminate collapsed shoulders. I guess brass gets 'harder' if you try to force it 'fast', like silly putty thrown against the wall.

Questions:
Swamplord: Can you please tell me what the resized neck thickness was on the 340 Wby brass, or at least the final neck OD after loading?
Anybody: Should I really be concerned about the so-called donut forming near the base of the neck?

 

[Swamplord]

after fireforming the 5 pcs of Hornady 375 H&H brass in my 340 Wby chamber, I used RCBS dies to full length size the cases and seat Nosler 265 gr ABLR bullets, at the same time did same with Weatherby & Nosler 340 Wby factory cases in order to get loaded case neck OD, looks like there is no need for neck turning but will need to trim to 340 Wby min trim length
there won't be a donut forming anytime soon in this process, primer pockets on the Hornady brass will give out way before any donut issues arise

cases from top down in first pic and left to right in others
375 H&H fireformed to 340 Wby
Weatherby factory brass
Nosler Factory brass


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[Swamplord]

Left to right, all Hornady 375 H&H cases

Barnes 250 gr LRX
Nosler 265 gr ABLR
Hornady 270 gr ELDX
Swift 275 gr A-Frame



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