.375 H&H Fireform to .375 WBY?

[benchracer]

Looking at the .375 Weatherby, it appears to have a shorter neck and presumably more freebore than the H&H. Will this have an effect on accuracy and/or velocity?

Here are some results from a guy shooting .375 Weatherby:

http://www.longrangehunting.com/forums/f17/375-weatherby-dialed-121054/

It looks like he used a custom reamer, so he may have had less freebore than a normal Weatherby chamber. However, it may still give you an idea of what the .375 Weatherby is capable of.

 

[longestrange]

Thanks for the link benchracer,

The accuracy looks good!

 

[MagnumManiac]

The order of case capacity is: H&H, Ruger, 375 Weatherby, RUM, 378 Weatherby.

One parameter that is not measurable for most shooters is pressure. Most hand loads are high pressure and most factory loads are far from it. Most recent experience with factory loads (most of my guns never see factory ammo) is with a friend's 7mm RemMag. Hornady Superformance 162 gr SST was closest to claimed velocity (-22 fps and the barrel was 2" shorter than factory) and the Remington Corelock was the least (2700fps vs. 3000fps claimed). Factory ammo not performing up to par is S.O.P. That's why I recommend to beginners to get a chronograph as their first purchase. Apples to apples has both cartridges at the same pressure.

When two same caliber cartridges are compared the higher capacity case wins. Short fat cases don't deliver higher velocities (as proved by P.O.Ackley) but they are MUCH more consistent. Fat cases deliver very low shot to shot variations. But Weatherby's claim of venturi effect has never been proven. It is based on the PMVF wildcats of the 30's.

Start pouring powder into both the RUM and 375 Weatherby and when the primers start cratering the RUM will be burning more powder and developing more velocity. To really do this right you would use the same barrel and rechamber.

Just the history of wildcaters and reloaders pushing the limits speaking here. If there was a magical case shape someone would have found it and the ammo companies would have made them rich with licensing fees.

KB

As I stated, the testing that I did was with factory ammo! I was using Weatherby factory ammo, and my buddy was using Remingtom factory ammo, the difference between the 2 were 20-30 fps with 300gr pills.
And, yes, you are correct that the RUM case SHOULD produce higher and higher velocities with handloading, but my buddies rifle gets pressure signs well before I do. Even on my Pressure TraceII his rifle is running at max pressure with factory velocities, which I believe is due to the case capacity, or better put, the expansion ratio not being able to burn the powder efficiently enough to sustain the push for those higher velocities. A slower progessive powder is needed to get the full potential out of the RUM case in 375, I think the same is true of the 338 RUM to a lesser extent, maybe RL17 is the type of powder needed, but a slower version?
There is a point when adding more powder just doesn't increase velocity because the burning rate influences the peak pressure to rise too sharply and the bullet just doesn't accelerate as fast as the pressure rises, what was coined overbore is nothing more than the expansion ratio being too large for the powder to burn progressively for maximum bullet acceleration.

Longestrange,
The 375Weatherby actually has a longer neck than the H+H, but due to fireforming, the neck actually is pulled back and shortened when the rest of the case and shoulder are blown out to match the new chamber, with a few loads the brass grows back to proper length.
Also, the standard 375Weatherby chamber has 1/2" of freebore, which is what mine has and my rifle has not suffered in any way from this, it shoots one hole groups regularly and clover leafs the rest of the time. As long as you headspace off the shoulder after fire forming you will have good case life.
I seat my bullets to max mag length, in my case 3.610", with all bullet weights and it doesn't make any difference to accuracy if I juggle seating depths, so I just leave mine as is.

Cheers.
gun)

 

[Kennibear]

MagnumManiac

From your last post it is clear you understand the "overbore" concept which is difficult to explain to newcomers. Just between you and me I have never been impressed with Remington's ammo offerings. I have never clocked any that was close to velocity as advertised.

I am curious why you went to RL17 for powder as its burn rate is faster than you need for the Weatherby? Most of the contributors to this site using 375 RUM's start with slower burn rates- more in the Retumbo/H1000 speed range. With 1/2" freebore the Weatherby 375 and RUM are pretty close in case capacity. As you know, that 1/2" is case capacity not surrounded by brass. With that much boiler room don't you feel the RL17 is too fast? The 375 Ruger is between the H&H and your Weatherby in capacity and it develops max pressure with powders of that speed with less than 100% loading density. I am about to try Superformance/RL19/RamShot Hunter speed powders (pending availability) because of it. RealGuns used RL19 w/ the 300gr Sierra in Joe's 375 Ruger data and it worked well. I have some of that load awaiting range testing.

Like you I seat to max mag length as long as the bullet does not jam the rifling. Some loads are seated deep enough to use the crimp groove as the recoil is heavy enough to back out the bullet if the neck tension is not sufficient. Roy Weatherby avoided a lot of problems by adding free-bore. To the nay sayers who think it harms accuracy I can tell you of several that shoot as well as I can hold.

If you don't mind could you post some of the data for your tests of the factory ammo? What are they doing with 300gr? It sure would help to know what can reasonably be expected. Thanks for your input!

KB

 

[MagnumManiac]

Kennibear,

Sorry, I didn't mean that I was actually using RL17, just the concept of it being developed for the WSM's, which I believe the RUM's would also benefit from.
I have a 338Edge, it is in it's infancy as far as developing loads for, I've barely sighted it in as yet, but I have found that it doesn't produce the velocity I expected with the powder selected. Unfortunately, here in Australia we are far behind the eight ball regarding new components, including powder and data, other than what's on the net. I would like to try RL33 in my Edge, but have no data for it, even on QL. I can't even find an approximate burning rate for it, but anyway, I guess I'll just have to wait.
This is the only RUM based cartridge I will ever have, with a COAL of 3.720" with either the 225gr or 250gr Accubond to be within .020" of the rifling it doesn't fit my magazine, I would need either a Weatherby MKV or CZ550 Magnum action to have them fit in the mag, and I won't be altering my mag to suit because it's just too much trouble.

From memory, the factory loads I had were running at 2830fps with a 300gr pill, can't remember what they were. My buddies rifle ran between 2850fps and 2860fps with the 300gr pill. This is all off the top of my head as it was a number of years ago when I used to help out a gun shop in their smithing room testing rifles after being worked on, it was a slow day, so we had a play with my own rifle and a newly acquired Rem 700 with a 26" barrel, my rifle has a 24" barrel. BTW, that 375 RUM is the only rifle I have ever seen from the factory over here, it's a rare bird.

Cheers.
gun)

 

[Kennibear]

MagnumManiac

I am surprised that with ADI producing most of the world's civilian supply of tubular powder that you Down Under don't have an excellent selection available.

Alliant has produced a slug of new offerings and I cannot find data on most of them. there is limited data for 300 MP and my son and I load for 357 & 44 magnums. it is ideal because it does not require magnum primers. They have a CFE 223 equivalent that has no data either and I wonder if it is as insensitive to temp as CFE.

My initial attempt at 300gr slugs from the 375 Ruger did not yield more than 2650 fps but none of the loads was anywhere near maximum pressure. Some of them did not register on the Pressure Trace II! All were not less than one grain under max in the books as the Data Manuals list loads safe for all bullets of the same weight/ maker. Straight sided round nose bullets generate pressures at much lower load levels than the sleeker SpBT offerings. The NRA tested this extensively in the '60s.

Keep checking Alliant's website as loads are appearing there for powders they have offered for sometime without proper data.

Good shooting!

KB

 

[Lefty7mmstw]

Kennibear,

Sorry, I didn't mean that I was actually using RL17, just the concept of it being developed for the WSM's, which I believe the RUM's would also benefit from.
I have a 338Edge, it is in it's infancy as far as developing loads for, I've barely sighted it in as yet, but I have found that it doesn't produce the velocity I expected with the powder selected. Unfortunately, here in Australia we are far behind the eight ball regarding new components, including powder and data, other than what's on the net. I would like to try RL33 in my Edge, but have no data for it, even on QL. I can't even find an approximate burning rate for it, but anyway, I guess I'll just have to wait.
This is the only RUM based cartridge I will ever have, with a COAL of 3.720" with either the 225gr or 250gr Accubond to be within .020" of the rifling it doesn't fit my magazine, I would need either a Weatherby MKV or CZ550 Magnum action to have them fit in the mag, and I won't be altering my mag to suit because it's just too much trouble.

From memory, the factory loads I had were running at 2830fps with a 300gr pill, can't remember what they were. My buddies rifle ran between 2850fps and 2860fps with the 300gr pill. This is all off the top of my head as it was a number of years ago when I used to help out a gun shop in their smithing room testing rifles after being worked on, it was a slow day, so we had a play with my own rifle and a newly acquired Rem 700 with a 26" barrel, my rifle has a 24" barrel. BTW, that 375 RUM is the only rifle I have ever seen from the factory over here, it's a rare bird.

Cheers.
gun)

rl33 is a few % slower than retumbo, so you can take retumbo data, start at mid-load, and work to a few grains over the top. Talk to azshooter on this as he has worked more with rl33 than I have.
One instance I have used rl33 in is the 300rum with 225 grain hornady hpbt bullets. I was able to go to 95 grains rl33 at normal pressure getting 3000 fps using rp brass and a 215. Hodgdon is getting retumbo to 89 grains at 2900 fps with the 220 partition.

 

[MagnumManiac]

rl33 is a few % slower than retumbo, so you can take retumbo data, start at mid-load, and work to a few grains over the top. Talk to azshooter on this as he has worked more with rl33 than I have.
One instance I have used rl33 in is the 300rum with 225 grain hornady hpbt bullets. I was able to go to 95 grains rl33 at normal pressure getting 3000 fps using rp brass and a 215. Hodgdon is getting retumbo to 89 grains at 2900 fps with the 220 partition.

Thanks, Lefty7mmstw, good to know, unfortunately at this time there isn't any RL33 available here.

Kennibear,
Even though ADI powders are plentiful, they still don't produce the kind of accuracy or velocity I have got with Alliant powders, double base powders are more predictable, H1000 is a good example of only working in a narrow pressure window, I'm still yet to try Retumbo in anything, but suspect it will be the same.
Cheers.
gun)

 

[longestrange]

Now I guess the question is whether it is possible to ream the chamber of a 375 H&H to .375 RUM.

First is the question of rim diameter - whether the H&H bolt head / extractor will fit or will not fit the RUM case?

Obviously there is the issue of whether the base diameter of the RUM is going to be excessive - less chamber wall thickness to handle pressure after reaming out an H&H - potentially very dangerous?

Finally, there is a question whether the shoulder of the H&H will clean up with the RUM reamer.

 

[garry cooper]

Given the cost and lack of availability of .378 Weatherby brass, is it possible to fireform .375 brass in a .378 and then reload?

 

[HARPERC]

No!

It is possible to fireform .375 H&H brass to .375 Weatherby, which is not the same as the .378 Weatherby.

 

[Axl]

No!

It is possible to fireform .375 H&H brass to .375 Weatherby, which is not the same as the .378 Weatherby.

True. Just like 2014 is not the same as 2021! LOL