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Part I

Discussion, Rifle, Cartridge and Some Measurements

Often, a priority Mil-Surp cartridge slips into relative obscurity when few rifles are available on the market.  Of course, there were always a few grizzled characters that did acquire the hand full of rifles available.                                                                            

Lapua 7.62X54R, great quality, but, expensive

To shoot the gun; a somewhat similar boxer primed case was often reformed and or trimmed to fit (Note.1).  Some paid bootleg prices for new, limited production, very hard to find, boxer- primed cases.   Others went to the trouble to deprime berdan-primed brass and locate a supply of proper diameter berdan primers.                

A few, (very few) went to a lot of trouble, and actually machined the berdan primer pockets of Mil-Surp brass to accept and function with standard size boxer primers.

Each of these guys had one thing in common; they jealously guarded their hoard of brass cases like treasured family heirlooms!  

Odd diameter bullets were a similar story.  Home cast or home swaged worked for some.  Small lots of odd sized, jacketed, commercial bullets could sometimes be acquired.    Small companies imported these bullets from Europe on an irregular and unreliable schedule.  Needless to say, the prices on such items would choke a Vegas high roller! 

Surplus Swiss GP-11 ammunition, clean, accurate, non-corrosive, BUT Berdan primed

Right now there are large amounts of Swiss K-31 Karabiner Rifles on the US market. Most I’ve seen appear in good to excellent condition.  Additionally, there is Swiss Mil-Surp ammunition currently available for the K-31 rifle (Note.2).  This Swiss Mil-Surp ammo is clean and non-corrosive.  That’s the good news.  The bad news is the cartridges are Berdan primed, and the primer is slightly larger then an American primer.  Yes, this brass can be reloaded. My friend Ted wrote a fine article wrote about reloading Berdan primed brass:

http://www.surplusrifle.com/shooting2005/berdanreloading/index.asp

I was on the lookout for clean Swiss K-31 Karabiner Rifle.

Randy Ward, proprietor of WEST TEXAS MILITARY SURPLUS, 2413-34^th St, Lubbock, Texas 79411, 1-(806)-785-4867, www.gunsandblades.com had a very fine example of a Swiss K-31 on his rack.  An examination (see article: http://www.surplusrifle.com/shooting2006/barrelprimer/index.asp) revealed a barrel in about new condition.  A deal was struck, and I gained title to said rifle.

With the release of large amounts of Mil-Surp rifles, a sufficient market is created for retail companies to locate a vendor willing to tool up and produce non-corrosive, boxer primed ammunition and empty brass for a metric caliber once considered obscure.   With a large market share, such ammunition and brass can be offered at popular prices. So it is with the 7.5 X 55 Swiss cartridge (Note.3).

On the 7.5 X 55 bullet front, it’s all good news.  The 7.5 X 55 Swiss round uses a “standard size” (standard size for the US and 7.62 NATO rounds) .308 (.30 caliber) diameter bullets.   Readily available jacketed; or cast bullets from standard molds are the ticket for this cartridge.  Now let’s look at commercial brass and ammunition.

Privi Partizan ammunition is Boxer primed, non-corrosive

Commercial, boxer-primed, brass and ammunition for the 7.5 X 55 is now available from several sources.  Prvi Partizan ammunition is manufactured in Eastern Europe.  Graf, www.grafs.com and Wolf sell this ammunition.   Here in the US, Hornady manufactures 7.5 X 55 ammunition.  Graf also sells Prvi Partizan 7.5 X 55 brass (Note.4).

I called Graf’s trying to get some empty brass.  They were sold out of their last shipment.  I ordered some Prvi Partizan loaded 7.5X55 ammunition that they did had on stock. 

Straight pull action is fast to operate, grasp beer barrel shaped knob on the right…

Pull knob and bolt back…

Push knob and bolt forward to chamber a round

In the event a chambered round doesn’t fire:

Grasp finger ring, pull back to re-cock the action

A quick review of the Swiss K-31 Karabiner Rifle and its locking system are in order.  The K-31 is designed on the Schmidt Ruben “straight pull” system.  No raising a bolt handle, pulling it back, pushing it forward and turning it down here.  Simply push straight forward on the handle to chamber a round, press the trigger to fire, pull straight back to eject the empty brass and push straight forward to chamber the next round. 

How does it work?  The separate bolt head rotates within the receiver during the loading, ejecting and reloading cycle.  The fit & finish of the K-31 action is extremely well executed.  It’s buttery smooth, and very fast to operate!    That’s the good news.  The bad news is this design has nowhere near the caming power of a bolt gun.  The K-31 is very sensitive to Over All Length (OAL) of loaded cartridges, case shoulder position and total length of brass cases.

Right after I acquired the K-31, I had a phone conversation with a fellow that owns several different models of Swiss rifles.  We were discussing K-31’s and loading the 7.5X55.

“Whatever you do, DON’T load a cartridge to the OAL listed in most of the reloading manuals.   The lengths listed in the manuals are all too long.  Swiss rifles have short throats.  Most bullets loaded to the OAL’s in most of the manuals will get jammed into the leade!  The olgive of the Swiss bullet doesn’t increase in size to .308 until a lot further back; so the long bullet of Swiss GP-11 ammunition doesn’t interfere with the short throat.  Most US made bullets reach .308 diameter much closer to the nose of the bullet.  If you attempt to eject an over-length, unfired cartridge from a K-3, the cartridge will de-bullet, and powder will get spilled in the action!”

I replied:  “Oh, I never pay attention to the OAL’s listed in the manuals (I always pay attention to the charge weights listed, and NEVER exceed them).  My friend Ted and I developed a procedure to check for proper OAL in any rifle with any bullet (article: http://www.surplusrifle.com/shooting/oal/index.asp).  I always determine the proper OAL by our procedure before doing any loading.

He added something else thing before “domestic issues” required him to get off the phone in a hurry.                                                                                                                      

“One other thing.  There is a slight difference between the 1911 chamber and the later K-31 chamber.  Make sure the dies you get match up with the chamber of your rifle.  K-31 chambers have a wider area at the case shoulder.  Some dies reduce brass too much for the K-31, and there have been misfire problems.” 

I know this fellow to be very knowledgeable.   However, at Surplusrifle.com we are like the guys from Missouri.  It was time to “Show me”.  I went down to Randy’s and checked the throats of all the K-31’s on his rack.   I used a 150-grain Nosler bullet to take the measurements.  

In the above referenced article Ted & I recommend seating a bullet .015 to .030 back from leade engagement.  This gives the bullet a good running start before engaging the leade and rifling.  However, for this article I calculated the OAL’s for this random group of rifles by supposing the bullet was seated back only .005 from leade engagement.  That is bare minimum free travel in any rifle.  Look at the results in the chart below!                                                                                                                 

You can easily calculate what the final OAL’s would have been reduced too had I calculated using the .015 or .030 figure.

Next, I grabbed all the manuals I have that list OAL’s for the 7.5 Swiss.  Here are the results.

This is one of those few (very few) cases where just simply accepting the OAL’s listed in some loading manuals may get you into trouble!  A cartridge loaded to the OAL’s listed in some of the manuals will jam a bullet in the leade of the rifling in the barrel! 

Apparently Swiss K-31’s, due to an extremely streamlined bullet in GP-11 ammunition, do have a tendency for very short throats.  Most Mil-Surp rifles tend to have roomy chambers & long throats, NOT the Swiss.     

An over length cartridge may not even chamber in a Swiss rifle due to the reduced camming power of the action design.  If an over length cartridge is forced into a chamber and fired, pressure may go sky high!   We recommend in the strongest possible terms you check the chamber length for your rifle and determine proper OAL before seating a bullet (this applies to ALL rifles, Mil-Surp or sporting, but, especially to Swiss Mil-Surp’s). 

Let’s recap the main points so far.

► Swiss K-31’s are a straight pull action.  While extremely fast to operate, they don’t have the camming power of bolt guns.

► Reasonably priced boxer primed Prvi Partizan ammunition and brass is sold by Graf, www.grafs.com.

► Swiss K-31’s have slightly different size chamber then Swiss Model 1911 rifles.

► Swiss K-31’s use .308 diameter bullets, BUT, have a short throat, and require a very careful adjustment of the bullet-seating die.

OK, I had rifle and reloadable ammunition.  I also had bullets, appropriate powder and primers a plenty.  What I lacked was reloading dies. 

Part II

Tools, Some More Measurements, Die Adjustment & Loading

I put in a call to Redding, www.redding-reloading.com, Redding Reloading Equipment, 1089 Starr Road, Cortland, NY 13045 • Phone (607) 753-3331 • FAX (607) 756-8445,

Kurt Nelson, Director of Marketing at Redding took time out of his busy schedule, and discussed Swiss rifle chambers with me.  I told him the dimensions of brass fired in my rifle.  I asked about the differences between 1911 and K-31 chambers.

Kurt stated: “Yes, there is a difference between the Swiss 1911 chamber and the K-31 Chamber.  Redding is the only company producing 7.5X55 Swiss dies cut specifically for the K-31 chamber.  Other brands of dies are cut for the 1911 chamber.”

Redding 7.5X55 Swiss dies.  The only brand of reloading dies specifically cut for the K-31 chamber

Redding dies have a lifetime warranty, come with an Allen wrench and a spare decapping pin

Kurt supplied a set of Redding, Series A, Full Length 7.5X55 Swiss Die Set in support of this article.  A bit later, we will see just how close Redding dies come to the chamber size of a K-31 (the guys from Missouri thing again). 

But, before we go to the reloading bench and adjust the dies, let’s check out the size of a case fired in the K-31.

Fired case mouth

Fired case shoulder

Fired case about mid-point

Now, ya’ll remember those sizes.  OK, it’s time to head to the reloading bench!

In a previous article, http://www.surplusrifle.com/shooting2006/dieprep/index.asp we cleaned the shipping preservative from the new dies, now its time to adjust them.        

We will cover all adjustment first, all the way through seating a bullet.  Powder dispensing will get covered last, even though all powder dispensing would actually be accomplished after resizing / de-priming and re-priming, BUT before seating any bullets.

Insert shellholder

Raise ram to top of travel

(Redding Ultramag 700 press)

Thread FL die in until it touches shellholder…

Turn down lock ring…

Allen wrench tightens set screw

The 7/8-14 threaded lock ring can now be turned down against the top of the press frame, and its setscrew tightened with the Allen wrench.      

Either a patch soaked in resizing lube, or a cotton tipped swab…

Lubes the inside of the case neck

Lube outside of case, BUT, keep lube off the case shoulder

(I have enough lube on my finger for 3 cases)

A thin coat of lube on the case…

Ram raised, case pressed into die, case is resized and de-capped

If the old primer doesn’t pop out, lower ram about ½ inch, turn in the decapping stem a tiny bit and raise ram again…

When old primer pops out, tighten finger nut

Check to make sure the old primer is expelled.  If not, lower ram about ½ inch, turn down the decapping/expanding rod a bit at a time until the old primer is expelled.  Once the primer is expelled, tighten the finger nut to secure the decapping rod.  Wipe cases clean of resizing lube after resizing and de-priming.

Re-priming of cases can be accomplished with either with the on-press primer arm, or with a hand-held priming tool.

Now our cases have been FL resized and re-primed, but, before moving on, let’s see how close the Redding dies come to our K-31 chamber.  Remember our fired sizes?  No?  Don’t worry; I’ll repost the pictures.  First the measurements taken from a fired case, immediately followed by the measurements taken on same spot on the case after being full-length re-sized in the Redding die.  Ready? 

Fired case mouth

Resized case mouth reduced 6.5 thousands

Fired case shoulder

Fired case at mid-point

Resized case at midpoint, reduced 2 thousands

Check out the pictures above.  Redding dies are made specifically for the K-31 chamber.  The pictures prove it!  OK, Redding dies measure up (literally) for the K-31 chamber; what about other brands of dies?                                                                                                          

A fellow I know has a set of 7.5X55 dies produced by another company.  I asked him to resize a handful of my 7.5X55 cases in his dies; again, his dies ARE NOT Redding.  He sized them, and I checked it with my calipers.  The pictures show those other brand of dies resize the case much smaller.  Check out the pictures below.

Case on left resized in Redding die.  Case on right resized in other brand of die.  Notice difference in shoulder width and angle.  Redding die has correct shape for K-31 chamber

Other brand of die (not Redding die) reduced shoulder width a whopping 19 thousands!

Other brand of die (not Redding die) reduced mid-point 12 thousands

Other brand of die (not Redding die) reduced case mouth 7 thousands

Other then the case mouth, the other brand of dies really reduced the case much more then was required for the k-31 chamber.   I tried these cases with the same load, bullet, & primers as those resized in the Redding die.                                                                           

I had an extremely high percentage of misfires with the cases resized in the other brand of dies.  An examination of the cases showed the primer with a faint indent.  The excessive sizing by the other brand of dies allowed the brass to go deeper into the chamber; and firing pin strike to be weak.  I had ZERO misfires with cases sized in the Redding die.  I can’t say this will happen with every K-312 out there!  I know a few people who have bought a K-31, got dies and lived happily ever after.  However, I have spoken with a number of people about their experiences with the K-31 and resizing dies. The general consensus is; resizing with most brands of dies, other then Redding, can get a bit dodgy. 

Resizing with other brands of dies usually means playing around with die adjustment until a happy medium can be found.  The problem with that is the action doesn’t have the camming power of a bolt gun.  Chamber size will ultimately dictate what will, or will not work in your K-31.  

Let’s get back to finishing up our die adjustments.  Adjusting the seating die is next.

Resized and primed, ready to adjust seating die

(Powder would be added before seating a bullet)

Bring die down until it just touches the shellholder, then…

Most bottleneck rifle, rimless cases don’t require crimping.  Therefore, back the die up ¼ turn, now the 7/8-14 threaded lock ring can now be turned down against the top of the press frame, and its setscrew tightened with the Allen wrench.

168 grain Nosler bullet

Now we are to the point where we can adjust the bullet-seating stem.  Recall we only turned the bullet-seating stem in a couple of turns initially?   In this way we can turn it down a bit at a time, and not chance driving the bullet too far into the case all at once.  Place you bullet in the case neck and slowly raise the ram.                                            

Initial seating with seating stem only a couple of turns into die

Turning stem down, and seating bullet deeper

We have a way to go yet

Turning stem down a bit more…

Getting closer…

Turning stem down a little bit more…Got it!

Tightening finger nut to retain adjustment

Die adjustment is complete.  Once all the cases are charged with powder, then all the bullets will be seated. 

Redding # 3 Master Powder Measure

(Notice measure stand is bolted to a 2x4 block, block is C clamped to the bench)

My Redding # 3 Master Powder Measure is the most accurate, and most repeatable adjustable powder measure I own. This particular one is rather old.  It, and its cast iron stand rolled out of the factory in Cortland NY just about the time the Woolly Mammoth went on the endangered species list!  Mine is painted brown, and has a nickel-plated spindle.  Fear not, the Redding # 3 Master Powder Measure is still being produced.  Redding’s newer measures are painted green.  The adjustment spindles are now blued.

Cast iron & steel

(OK, the hopper and drop tube are plastic)

I made a longer handle for my measure

(See article http://www.surplusrifle.com/shooting2005/powdermeasure/index.asp for the full story on powder measures)

For charges to be accurate, the measure must be on a rigid, heavy, cast iron base.  That base must be well secured to a heavy bench.  Vibration throws measure repeatability all over the map!

Speaking of charges, I consulted my loading sources; and used the bottom load of IMR 4895 for the 168-grain bullet.  I felt this would be a bit light, but always start with the bottom load. 

Resized and primed cases on the left, powder charged cases on the right

Always draw one charge right after the next.  Charge the cases in a slow, deliberate manner.  The steady rhythm makes the charges very repeatable.  After charging a case, move it to the block on the right.  Once all cases have been charged, and you have verified each case has a powder charge; to accomplish this; hold the charged cases under a strong light, or use a flashlight.  Any case with too much, not enough, or no powder will stand right out.  Bullets are to be seated in a separate step 

Seated bullets

Part III

Shooting

The usual West Texas wind was blowing at the range; however, good shooting was still to be had!  The initial charge of IMR 4895 did turn out a bit light.  Next time I’ll add a bit more (still within book limits) and see if groups tighten up.

Ready to launch some bullets

Sand bags keep aluminum-based rest secure

Best 5 shot group at 100 yards

Good old West Texas winds!

More West Texas wind!

Part III

Wrap up

I’m extremely pleased with the performance of Redding’s 7.5X55 dies.  They are cut with the K-31 chamber in mind.  Now that I have the best dies made for the K-31, I plan more load development with the 168 grain Nosler, and also to play around with some lighter bullets in my K-31.  Stick around; the fun’s just begun!

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