wildcat help

[.44 RF Express]

Hi everyone!
i have a bit of a problem that i hope the people in here can help me with...

i´ve designed and made a wildcat caliber for my double rifle. it was a .444Marlin,
now it is a .429 RFExpress (se pics)
my problem is developing a load for this caliber..
att the moment i´m driving a 270gr speer deepcurl bullet att 2200fps

anyone here good with load development?

i´m not looking to increase speed (maybe upp to 2300fps )
mostly i wanted to have a bigger case and maybe drop the chamber preasure slightly (it isn´t high now)
and keep the speed.

[.44 RF Express]

regulating the rifle won´t be a problem (did it when i made the rifle so can do it again)
built it during my year att the Swedish gunsmithing school
the donor gun was a 16ga brno sidelock shotgun. i don´t have the measurements here (it´s in the gunsafe and i´m att work)

the new cartride is made from a .45 basic case (used for making 45/90 and so on)
it has a .43" long throat and a total length of 2.48" with a taper from the neck to the base.

my biggest question is can i start with the same load i used when it was a .444 marlin
and work from there?? or should i back of 10% or more ?

will be using it for everything from roe deer to swedish moose

[Barry54]

You may run lower pressure, but by increasing the cartridge diameter you could still have the same thrust on the breach face.

You’ll have to calculate the area of each and multiply that by the operating pressure to determine the thrust.

The Thompson Center Contender is a good example to study. It’s chambered in 223 Remington on up to 45-70. These are two of the pressure extremes, and surface area on the breach extremes as well. You can’t just say it’s a 55,000 psi frame and built a 243 Winchester barrel and go. It will destroy a Contender frame!

[bruce drake]

Your wildcat's case length and volume may be close to the American designed .40 Whelen wildcat cartridge or the European 9.3x62 Mauser cartridge. With all wildcat designs, start at the lowest charge on the powder table and work upwards.
If it has been proofed already at 444Mag, you could start with the light load and work your way up the charge table.
Another unknown is the shotgun boxlock action that you have. It may require you to bush the firing pin holes with stronger steel to halt primer flow if you start developing issues with difficulty opening as you work up the load.
trying to work that up to 2400fps with that shotgun buttstock. Your shoulder may not appreciate long range sessions

[357Mag]

.44RF -

Howdy !

You might want to consult the on-line version of the old Tyne “ Powley Computer “.
kwk.us>powley

Powley invented and developed his analog “ computer “ with wildcatters in-mind.
He provided a means of predicting load pressure and velocity for such cartridges.

*** Be sure to checkout all of the “drop down” boxes highlighted in blue. ***

The computer was set-up principally using IMR powders, however…placement of other manufacturer’s powders by “ burn rate “ can be interpolated from a current powder burn rate chart; also viewable online.

A copy of the computer’s instruction manual is available for viewing online, too !
embscomputerart.com>pdfs>powleysmanuals1

***;Be sure to read & use the manual’ instructions ***

With regards,
357Mag

[357Mag]

.44RF -

Howdy, again !

Forgot to mention…. On the Powley Computer Instructions Manual link I mentioned above;
Be sure to scroll down to pages 3-9.


Regards,
357Mag

[John Taylor]

Be careful with larger cases and rifle powder. To much air space and you can blow up the gun. My brother did this with a 45-70 and a light load of RX7. The barrel looked like the banana peel, the top of the action was gone and about 4" of stock was missing. Luckily no one was hurt.

[Jedman]

Your case volume is now quite a bit larger than a 444 Marlin so an equal charge from the 444 will be less pressure and less velocity. I have a similar wildcat to yours built on a 45-100 case and necked to use a .375 dia. bullet. It is 2.6” long and I mainly shoot 250 - 300 gr. bullets.
So you have a very large case and not really asking for performance that should take hi pressures to achieve. Not knowing what powders you can get in Sweden I would start with a powder that is easy for you to get that’s on the slow side in burn rate to what you can find data for that’s used in the 444 and start there. Accuracy is usually what you are looking for and a load that will be regulated well for your double rifle. You should have a good bit of room working upwards with the powder charge from a maximum 444 charge if the same weight or similar bullet is used.
If you can get your case capacity in H2O and find someone with the quickload program to run some information for you it would save quite a bit in components used to get in the ballpark of what you want.
Jedman

[Shawlerbrook]

Sounds like quickload would be beneficial here .

[Larry Gibson]

"my biggest question is can i start with the same load i used when it was a .444 marlin
and work from there??"

That is what i would do. I also would use a dacron filler if the powder used is in the burn rate of 4198, RL7 or slower. I would work the load back up in 1/2 or 1 gr increments until the velocity was the same 2200 - 2300 fps as with the original 444 load.

If you want lower pressure at that velocity level, then a slower burning powder will be necessary.