K31 Dies for 7.5x55 Swiss

[kbuilta]

Who reloads for their K31 and what dies do you use?

I have read about the (alleged?) difference between K31 and other 7.5x55 Swiss chambers and that particular dies are best if one wants to minimize working the brass. The problem I found is the Hornady K31-specific die set (their number 546361) is not in production and they say they don't know what they'll make more of them and the Redding is pretty expensive.

My question is: is there another alternative to those 2 for K31-specific dies?

I'm not desperate - I have enough GP11 for this shooting season and well beyond - but I want to get ready to reload.

Information

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[Parashooter]

Any decent 7.5x55 sizing die will work just fine for the K31. The idea that only the Hornady or Redding die is correct for the K31 chamber has been way overdone at some sites. In practice, the most often cited benefit of the wide-shouldered "K31" die is very slight - for the simple reason that it works the neck no more or less than a 1911-style die and it's the neck that fails first from work-hardening, not the shoulder. Proper annealing takes care of both neck and shoulder - and has to be done for the neck anyway, long before the shoulder actually needs it.

Those who argue that the "K31" die necessarily gives greater accuracy fail to recognize that a carefully FL-sized cartridge is centered by the cone of the case shoulder mating with the cone of the chamber shoulder. This occurs whether the major shoulder diameter is .455" from a 1911-type die or .472" from a "K31" die.

A few handloaders claim that the "K31" die, by doing less work, requires less force on the press handle. That's undoubtedly true - but if you use the right lube, sizing a K31-fired case in a 1911 die isn't difficult anyway. Of course some handloaders are addicted to pretty ineffective case lubes and aren't eager to change to one that works better and costs less (e.g. castor oil).

The only practical difference is that cases fired in a K31 normally elongate more during FL sizing in a 1911-type die than in the "K31" die. Brass displaced when shoulder diameter is reduced goes in the only direction open to it during sizing - forward. Consequently, less frequent trimming is required with the die that reduces the shoulder less. Many careful handloaders trim often simply for greater uniformity. Those who find trimming especially onerous are probably better off with the larger "K31" sizer.

[kbuilta]

Thanks for the details, parashooter. I'll keep thinking about this.

[kbuilta]

I wound up buying a Redding set and have run a small batch of GP11 brass through the sizing die. Will make some test rounds to validate that I can do all the steps and set a Berdan primer to the right depth and make something that goes bang safely. I don't have any Berger VLD bullets so I'll try either some 168gr or 175gr Nosler CC's that I have. Another challenge will be to find the right bullet seating depth since the ogive is not the same as the VLD.

[Bruce_in_Oz]

Just be aware that the K-31 (and the ZfK-55) have SHORT throats that are meant to accommodate the GP-11 bullet with its SECANT ogive.

Any suitably-weighted bullet with a TANGENT ogive, like the Sierra Match-King series, will probably give you problems with seating / overall length measurements. A K-31-owning friend found this out the hard way after he loaded up a batch of ammo with 168gn Sierra MatchKings and the found they would not chamber. They fed fine through K-11s, both his and mine.

The earlier G / K-11 series have a LONG throat because, when they were introduced, there was still a vast amount of the earlier "torpedo"-bulleted ammo in the system.

Lee Enfield owners will also be aware that this happened with their favourite rifles. The long throat needed for the round-nosed Mk6 bullet was carried over in the SMLE series until final production. No4s seem to have a throat more appropriate for the profile of the MK7 bullet.

The US "Springfield" went through the same transition: the first '03 was chambered for the same long, heavy round-nosed bullet style that everybody else was using.

Then those craft German chaps turned the ballistic world on its ear and introduced "spitzer" bullets driven at considerably higher velocities. Thus, everyone who wanted to stay in the game had to turn around and re-engineer their rifles and machine-guns (sights, feed systems for starters), and re-think their range tables.

Hence "'03-A3" Springfields.

[Bruce_in_Oz]

Oh, and regarding dies, I use the Lee version for my K-11 reloads.

Well-made gear; no problems here.

I doubt there is any significant difference in CHAMBER dimensions between the K-11 and the K-31. Throats; yes; chambers; no.

[Parashooter]

. . . I doubt there is any significant difference in CHAMBER dimensions between the K-11 and the K-31. Throats; yes; chambers; no.

There is a significant difference in taper and consequent diameter at the body/shoulder junction -



FWIW, the GP11 bullet features a tangent ogive, not secant. It's a long-radius ogive that begins pretty far back, but it's a tangent.

[Bruce_in_Oz]

Well, there ya go!

Except....

By that diagram, there is NO parallel bearing surface anywhere on that bullet; there is a slight taper starting at the forward end of the boat-tail. This then changes to the 70mm ogive radius..

So, the GP-11 bullet is not your "basic" bullet by a long shot. I don't have a CAD package on this computer yet, so, is anyone out there capable of whizzing up a quick (but accurate) profile from the sketch provided in order to ascertain exactly where that 70mm ogive radius runs?

[Parashooter]

. . . there is a slight taper starting at the forward end of the boat-tail. This then changes to the 70mm ogive radius.

. . . is anyone out there capable of whizzing up a quick (but accurate) profile from the sketch provided in order to ascertain exactly where that 70mm ogive radius runs?

That "sketch" is a vintage Swiss mechanical drawing that accurately describes what we find when measuring GP11 bullets - "a slight taper starting at the forward end of the boat-tail" that "changes to the 70mm ogive radius" after some 6.2mm of a conical section 7.82mm diameter at its base and 7.70mm at the tangent ogive junction. While the design may be too unusual for some tastes, the Swiss seem to have been pleased enough to keep it in service for over 80 years - essentially unchanged except for playing around with cannelures.

Attachment 62483
GP11 bullet variations from 1911 to 1978

[Bruce_in_Oz]

GP-11: Worked for them since 1911; last heard of still feeding the "Rolex-grade" MG-51 GPMG as well as a slowly diminishing fleet of "Reserve" K-31s, ZfK-55s, StG-57s etc.

These bullets should work quite well in a .30-06.

I would definitely not be complaining were the elves to leave a pallet of those "oddly-constructed" GP-11 bullets under my Christmas Tree.

The good wife may inquire about where her .224" 69gn SMKs were, however.