Case forming question - .41 JMP

[AJ]

Has anyone ever made cases for a .41 JMP (also known as a .41 AutoMag). A friend has a barrel for his .44 AutoMag. We are thinking of taking a .357AMP case and necking it out to .41. The putting a light load in it to form a .41JMP. He needs five fired cases to get a die manufacturer to make custom dies for the pistol.

As an aside does anyone have any .41JMP cases or dies that they are willing to part with?

 

[Hair Trigger]

According to L.E. Jurras, developer of the .41 JMP, the cases are made by necking down a .44 AMP case, just as the .357 AMP case is also made. I suppose if you have .357 AMP cases, you could neck them up to .410 as well, this article talks about both.

https://www.amtguns.net/wp-content/uploads/2011/12/Newsletter-Volume-2-No-13.pdf

 

[AJ]

According to L.E. Jurras, developer of the .41 JMP, the cases are made by necking down a .44 AMP case, just as the .357 AMP case is also made. I suppose if you have .357 AMP cases, you could neck them up to .410 as well, this article talks about both.

https://www.amtguns.net/wp-content/uploads/2011/12/Newsletter-Volume-2-No-13.pdf

Thank you. I forwarded it to him. Next week he picks up his new purchase. He has .357 AMP and .44 AMP ammo , so should get to shoot it then.

 

[Alk8944]

The simplest way if he only needs 5 cases is to simply shoot several of his .357 Auto-Mag rounds in the .41 barrel. Voila, fire-formed cases! They should be full-power loads, not down-loaded! This will not do any damage to the .41 barrel! Tell him, though, to do this where he can shoot the gun vertically! I have fire-formed hundreds of cases in several bottle-necked calibers and for some reason they fire-form more thoroughly when shot vertically! I have no explanation for this, just many years experience!

 

[6string]

Did you read the Kent Lomont articles I posted in your other AutoMag thread?
On page 4 of the 1st article it says cases are formed by necking down .44 AMP cases.

Here’s the article:

AutoMag_Story_pt1.pdf - Google Drive

By the way, RCBS made AutoMag case forming dies.
Their intended to form straight-wall .44 AMP cases from any 308/30-06 parent case.
From there, you can neck down and neck turn your newly formed .44 AMP cases to any of the derivative AMP cartridges (357, 41, or even the rare 30 or 22 AMP).

Again, the Lomont articles will walk you through the case forming process.

Midway used to sell them:
Access Denied

I suspect there are specimens out there to be had.

Or, you can just buy new Starline .44 AMP brass and neck it down.

44 Auto Mag Brass - Large Pistol - Brass Cases

 

[AJ]

Did you read the Kent Lomont articles I posted in your other AutoMag thread?
On page 4 of the 1st article it says cases are formed by necking down .44 AMP cases.

Here’s the article:

AutoMag_Story_pt1.pdf - Google Drive

By the way, RCBS made AutoMag case forming dies.
Their intended to form straight-wall .44 AMP cases from any 308/30-06 parent case.
From there, you can neck down and neck turn your newly formed .44 AMP cases to any of the derivative AMP cartridges (357, 41, or even the rare 30 or 22 AMP).

Again, the Lomont articles will walk you through the case forming process.

Midway used to sell them:
Access Denied

I suspect there are specimens out there to be had.

Or, you can just buy new Starline .44 AMP brass and neck it down.

44 Auto Mag Brass - Large Pistol - Brass Cases

I will remind him. I am not doing this, myself.

 

[BEEMER1]

Don't mess with forming brass from 308. You have to ream it and it is a PITA and you end up with an inferior product anyway.

The Starline brass is excellent and all you need to do is run it into the 41 JMP die to form your brass.

Again, the headspacing on Auto Mag chambers varies a lot from pistol to pistol so make sure your handloads fit your chamber correctly.

 

[AJ]

Don't mess with forming brass from 308. You have to ream it and it is a PITA and you end up with an inferior product anyway.

The Starline brass is excellent and all you need to do is run it into the 41 JMP die to form your brass.

Again, the headspacing on Auto Mag chambers varies a lot from pistol to pistol so make sure your handloads fit your chamber correctly.

Got a .41 JMP die set for sale?

 

[BEEMER1]

Got a .41 JMP die set for sale?

I only have the one set and it's not for sale. They rarely come up for sale on the secondary market.

Try CH4D, they list them and might have one in stock. If not, they have the drawings and could make them.

Here is Lee Jurras's personal 41 JMP Silhouette pistol. It has an 8 1/2" vent rib bull barrel and a serial number of "JURRAS".

 

[jcelect]

Fire forming

The simplest way if he only needs 5 cases is to simply shoot several of his .357 Auto-Mag rounds in the .41 barrel. Voila, fire-formed cases! They should be full-power loads, not down-loaded! This will not do any damage to the .41 barrel! Tell him, though, to do this where he can shoot the gun vertically! I have fire-formed hundreds of cases in several bottle-necked calibers and for some reason they fire-form more thoroughly when shot vertically! I have no explanation for this, just many years experience!

When fire forming brass the best method is measure some powder into the brass! Then use tissue or a very small wad of cloth packed over the powder charge. Fill the case with corn flour(or equivalent) to about 1/8" below the rim. Now light a candle and drip some wax over the corn flour to seal the package. Discharge the round into a barrel or container or outside in a safe direction. I have fire formed many .224 Harvey K-Chuks from Hornet brass and .256 Win Mag from 22 Jet brass. I never use more than 3grs of junk powder for the process!
jcelect