School me on the K31 and 7.5x55 Swiss

Awesome rifle. Really great cartridge. Consider it very similar to a .308, maybe halfway between there and a .300 Savage. It certainly falls squarely into the list of 100 or so cartridges that would make for a really great deer rifle.

The 7.5x55 is plenty good enough for deer. Its nearly a ballistic twin of .308 Win which is just a great deer round.

As to the rifle itself - its VERY accurate. Its a bit large and heavy to lug around as a deer rifle, but it'll work (IMHO the Mosin Nagant M44/M38 is a better choice for an off the shelf milsurp for deer hunting just due to the size).

From a recoil perspective it is very much in the .30 caliber full power range. Recoil is like shooting a Garand or M14.

As the K31 is a bolt gun and doesn't have a semi-auto gas system to help spread out recoil time and force, you will feel that steel butt plate. Shoulder it wrong once when you light it off, and you won't want to shoot much longer. Just like many bolt action mil-surps.

Something like this makes range sessions last longer.

http://www.pachmayr.com/home/deluxe-slip.php

I have one of those on my K31.

The K31 is the only rifle I own where handloads did not improve the accuracy. That is not a complaint, the Swiss GP11 ammo is that good. Off a rest 1.5 moa is no problem at 200yds for me. I am sure a scope would shrink that down. They are a beautifully designed and built rifle, and the cartridge will compete with any of the .30's. The 7.5x55 was way ahead of its time. Look at the short, fat case, and sharp shoulder which didn't really become popular until 80 years later with target shooters.

To the OP, if you are interested in the K31, then get one while they, and GP11 ammo, are still available. Prices have gone from $89 to $3-400 for a decent example, and are sure to keep going up. GP11 is still available for ~60¢ a round in bulk, and it is probably the most accurate standard military round ever made.

The only downside of the K31 besides weight is that the bolt design makes properly mounting a scope very difficult. The machine work on the rifle is stunning for a milsurp.

+1 to the warning about recoil with the steel plate. Though a "ballistic twin of 308" the case capacity is very close, so recoil is above a normal 308 load. Some stocks are better than others; upon inspecting a couple, I found some variance in how "sharp" the sides of the buttplates were, mine being a sharp one, leaves little red lines on my shoulder if I don't wear extra layers.

There is a good aftermarket for these guns"
-Mojo makes replacement sights
-Diopter sights are available for mucho dinero
-Several companies now make reloadable brass and ammo
-Takes 308 bullets and probably loads similar to 308 and 30-06
-Boyds makes replacement stocks, IIRC
-Excellent non-corrosive match grade milsurp GP11 ammo is still around for .55/rnd (don't buy any though; I want it ALL )
-St. Marie makes and excellent non-marring clamp on scope mount
-Stripper clips are available and the best ever designed; expensive for what they are, but well worth it
-Milsurp rifle cases are still out there, as well as slings, bayonets, muzzle covers, and cleaning kits
-Numrich has replacement parts, but it's doubtful you'll need them

Strong arguments for the guns over others are:
-prices have risen, but have stabilized ~300$ for at least the time being
-ammo is "obscure" but available online, and never spiked in price or disappeared during the Banic
-GP11 is Berdan primed, but you won't gain anything reloading (money or accuracy, and all rifles are left stock)
-Ring safeties, straight-pull bolt actions, and T-handles are just better
-Will go toe to toe with any Finnish Mosin or Swedish Mauser --and stands a good chance of winning (especially if speed is a factor)
-You can practice marksmanship, and play catch with your rifle simultaneously
-It's auto-loading big brother the STWG57 shoots the same fantastic ammo, has the same quality of workmanship, and even the same bolt handle
.Excellent, excellent two-stage trigger design is probably the best of the War

(I dare anyone with a K31 to not try catching their brass at least occasionally)

Important stuff:
Like all straight-pulls, there is no way for the bolt handle motion to indicate the bolt locking lugs have fully rotated. It is imperative that this rifle (and other straight pulls) are inspected for damage or wear on the camming surfaces. The K31 also allows the striker to fall with the gun slightly out the full-forward position. Normally, the striker momentum kicks the action closed the rest of the way before the primer could ignite, but not so if certain parts are broken or worn. No different than any autoloader as far as its safety, but different from manually-rotated bolt guns. Unlike other straight pulls, the K31 is safer in that gas pressure from a blown case or primer will not itself unlock the action--it's as safe as any Mauser/Mosin design in this regard. One last bit; be sure to keep ammo and the chamber clean. The straight pull cam action reduces the bolt's leverage on the extractor, and a stuck round could tie up the action a bit easier than a turn bolt you can force open (to a point). A K31 is plenty tough to cycle as fast as you want, but it should never be forced open or closed (the latter can be an issue if certain 7.5 Swiss reloading dies are used to resize brass, since IIRC Lee spec'd them on an oversized model 1911 chamber, leaving the cases too big for the K31 match chambers)

TCB

Interesting posts guys, I just picked up one of these beauties last night. It is built like a Swiss watch. Can't wait to shoot it. I ordered some GP-11, debating on whether I'll reload for it.

Reloading Experiences

I have two K31 rifles, and both barrels and chambers will accept .308 diameter bullets. With these foreign rifles of unknown chamber dimensions, it is a prudent safety check to verify the neck expansion on a fired case mouth. A bullet should enter the expanded case mouth without resistance. If not, the case neck is pinching the bullet during ignition and pressures may be dangerous.

Cartridge OAL

American reloading guides provide inconsistent information on the 7.5 * 55 Swiss cartridge. I suspect all their data is based on reverse engineering from the older, M1896 and M1911 rifles. The K31 has been on the market for only a short time. I found , as many others have found, the maximum cartridge lengths of 3.060”, listed for the 168 Match Bullet in the third edition Hornady Manual were much too long. When I loaded the US military .308 174 gr FMJBT bullet anywhere near this length, the bullet would jam in the barrel throat. I finally found an OAL of less than 2.900” work in my rifles. I have standardized on an OAL of 2.850 with nothing greater than 2.900” and have had no problems. I have used this for 165 grain hunting bullets, 168 grain Sierra and Nosler Match bullets.


I purchased INDEP 7.5 Swiss, Lot 9001, loaded with a 170 FMJBT bullet. These cartridges from the factory have an OAL just below 2.900”, the spread between five I measured went from 2.880” to 2.894”.

Trim Length.

The manuals state that the maximum case length is 2.180”. The instructions that come with Lee Dies state that maximum trim length is 2.185”. My third edition Hornady Manual gives a 2.140” case length. From unfired INDEP ammo, the case length of 20 cases, the spread was between 2.167” and 2.1765”. Most of the cases were just about 2.170”. I believe that any trim length between 2.180” and 2.160” will work.

It is important to trim your ammunition on the first reload. I have found that cases grow the most on the first reload, and become over length. The consequence of over length cases is that the case neck will extend into the tapered throat area, pinching the bullet. Excessive pressures will develop because of this obstruction. This can lead to blown primers and/or sticky extraction.

Brass

7.5 * 55 Norma brass and loaded ammo is ridiculously expensive for this rifle. However, 284 Winchester brass can be sized, necked up and fireformed for use in this rifle. Even though the OAL of a 284 Win case is supposed to be 2.165”, I found that the sizing process made them overlength and cases needed trimming. 284 Winchester brass has same case rim diameter as the 30-06, which is smaller than the Swiss round. I measured three 284 Win case rims and found them to be 0.427”, 0.470”, and 0.470”. Three Norma case rims were 0.498”, 0.497”, and 0.495”. This dimensional difference has caused occasional failures to eject. The cartridge will extract out of the chamber, but will fall off the bolt face into the action. I encountered no feeding problems with 284 brass. The case capacities of my 284 Win brass are less than the Norma 7.5 cases. Behind a 174 gr FMJBT it took 55 grs of WC852 in the 284 brass to give the same velocity as 57 grs of the same powder in the Norma cases.

INDEP ammunition has been available on the US Market, and a measurement of five cases gave a case rim measurement spread between .4935” and .494”. All the INDEP cases ejected positively due to this big rim. The weight spread, for twenty INDEP cases, was between 180.0 grains to 184.1 grains. My Norma and 284 Winchester brass is all loaded up, so I cannot make a weight comparison between them and INDEP brass.


Bullets

Different manuals give different bullet weights. I have found in reloading for military rifles that the best results come from loads that duplicate as close as possible the standard military loads. This makes sense if you think of it. Both the rifle and the ammunition were developed together, and then over the years, military rifle acceptance tests were conducted with the military ammo, and the military ammunition makers tested their ammo in the military rifles. So, in time, the rifle and ammunition evolved together to give optimum performance.

Standard .308 diameter bullets have worked well in my rifles. The fourth edition of “Cartridges of the World”, by Frank Barnes claims that a 174 grain .308 bullet was adapted in 1911. The web site www.swissrifles.com has more current information, that is “The GP11 was loaded with a 174 grain spitzer bullet. The round could travel at 2640 fps. The diameter of the bullet was increased to .307 inches, and the length of the case was increased to 55m. The GP11 generates around 45,500 psi of pressure.” The site provides the warning “ Under no circumstances should GP11 rounds be fired in Model 1889 Schmidt-Rubins!! “

In my rifles, point of impact, with bullets from 165 grain to 174 grain, shoot to the mechanical point of aim.

Reloading Dies, and Sizing.

I am using the Lee Sizing Die and Lee bullet seater. The table reflects my load development. I followed the load data included with the Lee Die, and found it unsatisfactory. The loads are too slow for the K31, only the IMR 4895 load was close to an acceptable velocity. And it happened that the WC852 I purchased from Jeff Bartlett, http://www.GIBrass.com/, turned out to be a champ with this cartridge. WC852 is military surplus 30-06 ball powder. Accurate Arms purchased a different 90,000 lb lot of this, repackaged it, and sold it as 2700. 2700 was the same basic powder but had a faster burning rate than my lot of WC852. Since I found a very satisfactory load with WC852, I stopped experimenting with other powder combinations. But, if I get tempted to start experimenting again, I expect the powders that have a good probability of providing good results to be IMR 4895, IMR 4064, and IMR 4350. The velocities that I want to get to will be just below 2600 fps with a 168 or 174 grain bullet. My groups definitely tightened up as bullet velocities approached this speed.

The Indep load, that I recently tested, actually shot better than I thought it would. It was Lot number 9001, and purchased from SOG. Cases only had 33.1 or so grains of an unknown ball powder. The case was less than half filled with this powder, and ball powders usually do not work well under 80% loading conditions. The 170 grain FMJBT bullet was .3075” in diameter, except at the boatail edge, where it was .308” in diameter. When I pulled the FMJBT bullet, and substituted a 168 Nolser bullet, I got a better group. Unfortunately the Indep factory load is a low powdered load, giving an average of 2155 fps, and my rifle shoots best with faster loads.

Temperature effects velocity, and I believe the loads that I chronographed at 52  F would be at least 100 feet per second faster at 70  F.

My rifle was sensitive to bullet velocity. The slower 2100 fps loads, printed about 2” low and to the right of the 2500 fps.




Cartridge Comments:

Loaded 7.5 * 55 Norma cartridges boxes claim 2650 fps with a 180 grain bullet. Any rifle/cartridge combination that can send a 180 grain bullet to 2650 fps should be considered high power. I believe the basic case design goes back to 1889. The current cartridge configuration seems to have been set in 1911. It has some desirable characteristics for automatic gun mechanisms: It is shorter than the 30-06 and has a very thick rim. A compact action with less mechanism travel can be designed around a short cartridge while a thick rim is harder to pull off during extraction. These are characteristics that drove the replacement of the 30-06 with the 308 Winchester as a military round. I wonder if the 7.5 * 55 would still be in our military inventory if the US had copied it instead of creating the venerable 30-06.



One weekend turned out to be warm enough to go out and chronograph some loads. My Chrony Chronograph does not do well in forty degree weather, which is normal for this time of year, but we got a 58 F weekend, and so I was able to do load development with my chronograph.

I have a keg of AA4350 and was curious to see how it does in the 7.5 Swiss. Based on case capacity, the 4350 series looked like it should give good results with 168 grain and up bullets in the 7.5 Swiss. AA4350 is advertised to be equivalent to IMR 4350. I have found that to be in the main true, accepting the differences you normally have with lot variations. That is, you have to be very careful with maximum loads if you change to a different lot of powder, even though it is the same powder by the same manufacturer. Accurate Arms has told me that they keep lot to lot variances within 5%, and claim that is half the industry standard. If that is true, then it is possible to change powder lots, and have a pressure increase of 5000 psi for a load that normally produces 50,000 psi. Then of course, a max load that is safe in 58 F weather may be too hot in 90F weather. These are things you just have to check out, unless you own a pressure barrel and a thermal chamber.

Anyway I looked at my Sierra Loading Handbook for load data and found that Sierra had an extensive section for the 7.5 Swiss. Sierra had tested their loads in several M1911 rifles. They claim a maximum load of 51.0 grains of IMR4350 with their 168 Match Bullet. The velocity they publish is 2700 fps out of a 29” barrel.

Since the K31 is a much stiffer action , it is a front locking action whereas the M1911 is a rear locker, I was not afraid to use their maximum load, and than go one grain above it to see what happened. Also, I used the 168 grain Nosler Match Bullet, which is an exact copy of the Sierra, except perhaps, jacket thickness. Glen Zediker (http://www.zediker.com/) claims in his book “Handloading For Competition” that the J4 jackets are thinner than the Sierra.

I have found that the 168 grain Sierra Match bullet is one of the most consistently accurate bullets in .308 caliber rifles. It is a truism that if you own a 308 Winchester and your rifle will not shoot a 168 grain Sierra Match, in front of 40.5 grains of IMR 4895, then something is seriously wrong with the rifle. I have had excellent results with the less expensive Nosler copy of the Sierria bullet in 308 and 30-06, and I have been using it in my 7.5 Swiss with good results.

Anyway for a load of 168 grain Nosler, 51.0 grains AA4350, INDEP Brass, Fed 210S Primers, OAL 2.850”. I measured an Average Velocity of 2536 fps, with a standard deviation of 17fps. Accuracy was within two inches at 100 yards with iron sights. For 168 grain Nosler, 52.0 AA4350, INDEP brass and Federal Primers , OAL 2.850”, I got a velocity of 2632 fps with a standard deviation of 24 fps. Accuracy was good, five shots falling within .075” * 1.5”. Considering that all groups were shot with iron sights, I do not believe that there is any significant difference in accuracy between the two loads. Extraction was easy on both loads, and primers were rounded. When doing load develop with a bolt gun, if the rifle design allows it, I will pull the cocking piece back and then open the action. This gives me a more sensitive feel to extraction resistance. If it feels like you are extracting a cork from a bottle, your pressures are way too high. I miked the case heads, comparing them against unfired brass, and was unable to determine any conclusive patterns. Everything was within .001” of unfired brass, and I do not know if that is significant or not. I have never had any luck determining pressures from case head measurements though such authorities as Ken Waters use it in load development.

I think the 51.0 grains of AA4350 may turn out to be a pretty good load. The velocities spread was fairly even and it shot to exactly to point of aim at 100 yards with the rear sight set at its 100 meter mark. A six O’Clock hold gave a group exactly at 6 O’clock in the bull. When it gets warm again, I may try some IMR 4064 loads with the 168 grain Bullet.

Accuracy:

While I have shot groups that were less than 1 MOA I consider this to be just a statistical aberration. While the K31 Swiss rifles are exceptionally accurate for a service rifle, but, in the end, they are service rifles. I don't know the Swiss Army requirements for accuracy, but no one builds a general purpose service rifle with a 1 MOA requirement. (Well, I don't know of one) Typical bolt gun era service rifle requirements were around 3 MOA. That was way inside the hold of the untrained cannon fodder sent to the fronts. Accuracy requirements were even worse for gas guns. The M14 was a 5 MOA affair, as issued. I don't know if an SKS will hold 8 MOA. It is possible the Swiss wanted 2 MOA rifles but no one should expect consistent true target rifle accuracy out of one of these things. What they can expect is outstanding accuracy for a service rifle.

Incidentally, the Swiss greased their bullets up to the 1980's. They claimed better accuracy and a longer barrel life. I don't have any GP1890/03 rounds, but from pictures, it looks they were greasing bullets all the way back to the 1890's.

"It is built like a Swiss watch"
Don't let the rifle here you say that; it could stomp that watch into little pieces --and keep on ticking

Thanks for the reload info, Slamfire. I've heard that it's not as much a novice's cartridge as say, any old bolt 308. IIRC, the OAL has to be watched to ensure that the bullet doesn't jam up on the lands and increase pressure. The K31 was built for accuracy, and therefore had tight chambers and very short free bore before the lands. I believe that the original profile of the bullet vs. the shape we normally use today had something to do with it

"I have found that the 168 grain Sierra Match bullet is one of the most consistently accurate bullets in .308 caliber rifles. It is a truism that if you own a 308 Winchester and your rifle will not shoot a 168 grain Sierra Match, in front of 40.5 grains of IMR 4895, then something is seriously wrong with the rifle. "

Indeed. That is actually my preferred 308 load for both my R700 and FNAR (works great in both--happy coincidence). Haven't seen 168's in months (of course) . When I get dies for 30-06 and 7.5 Swiss, I'm tempted to try the same load/bullet in all three and see how it stacks up. They're so similar, that I'm convinced a load could be developed that would suffice for all three (and 7.5 French, too )

Greasing the bullets helped aid the weaker extraction mechanism in the straight-pulls, and was probably critical to function in the blow-back STGW57 machine gun (which still stretched the heck out of cases). I've been told the Swiss were huge on grease, using for everything from case lubricant, to bore cleaner. It's staying power compared to oils and great high-pressure performance are a big reason why Swiss milsurp guns are in as good a shape as they are today. My STGW57 parts kit --cut up and imported decades ago--still had plenty of grease on the interior, mixed with blowback soot. Apparently oiling those machineguns instead of greasing them can actually lead to more soot buildup, to the point the locking recesses no longer work safely

"I don't know the Swiss Army requirements for accuracy, but no one builds a general purpose service rifle with a 1 MOA requirement."
I can't find the source off-hand, but I think it was 10cm at 300meters, so 4" ~ 328yds --pretty close to 1MOA . Since their tactics have always been defensive in nature (neutrality), accuracy is emphasized more strongly than in most other nations (the STGW57 had greater accuracy than the H&K G3, and the SIG550 even better than that)

TCB

tuj, moa maybe, more comfort more pad, and yes
You have gotten plenty of good info.

barnbwt, the 1931 has the oversize(sloopier shoulder) chamber not the 1911. Not much about the chamber or resize die but the 1911s had very long thoats while the 1931s are very short. Other than rethinking whose die maybe oversized, you post a lot of good info, But yet comes another even gooder info post.

Slam, no offence meant, but some things get printed, repeated and believed which may be incorrect even at our venerated swissrifles.com, which I've been part of for along time. There have been .304 groove/bore diameters reported for years.
No 7.5 Swiss ammo GP-90. GP-90/03, GP90/23, or GP-11 was less than .307" in dia. The velocity of 2640-2650fps is generally given as the speed from a 1911 long barrel with either GP-11 or Norma's fodder. Norma or GP-11 with the K-31 should produce speeds more like 2550fps,YMMV.

The infamous170grain Lot#9001 ammo box(lol) proudly stating made IN Portugal. It was better than not having brass and it wasn't much worse than the later 174 grain INDEP(FNM) Lot # N o(I can't do justice to the/a small zero). Lot # N o states made FOR FNM(Portugal)

Case lengths went from 53.5mm(GP-90 & GP-90/03), to 54.5mm(GP-90/23), and finally to 55.5mm(GP-11). 55.5mm is real close to 2.185" Trim length consistancy is important, but I think a chamber cast on just about any K-31 will show that bulletbarrelcase pinching should not be a worry for any case length used even going well past 2". Shorter case length=more throat/chamber erosion,Longer case length=less throat/chamber erosion.
Good postings all
Best

The .304 groove diameter figure was based on the original SR 1889, which was rifled with three grooves about equal in width to the lands. So a typical slug measurement would come up short. The original loading was a paper-patched bullet about .310 diameter, later with a metal cap on the nose to comply with The Hague Convention banning expanding bullets. The jacketed GP 1923 ammunition had a 190gr bullet, and had the distinction of having non-corrosive priming, which continued in the GP 1911 ammunition. Since the Swiss citizen-soldier kept his rifle as long as he was in service, the pre-1911 rifles and the ammunition for them stayed in service for many more years than would be the case in other nations. SR1911 rifles and carbines were still widely in use as late as WW2.

As far as reloading, Redding was the first maker to make dies correctly dimensioned for the K31 chamber, I don't know about the current manufacture of the other suppliers. Loaders should keep in mind that although the K31 action is very strong, the GP11 ammunition has a maximum operating pressure of around 45,000psi. This is probably based on the weaker initial extraction that is an inevitable result of the way straight-pull actions work. The plus side of keeping pressures at this level is longer case life and a much longer barrel life. If you have to kick the bolt open, your handloads are definitely too hot! At the same time, remember that the rifle is intended to be cycled from the shoulder, with the bolt operated "with great violence", as the British would say. Trying to lower the rifle and operate the bolt with fingertips, as is often the case with turn bolts, will result in sticking and frustration.

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What they said.

Ed, recheck your source. The Swiss never used any corrosive perchlorate or chlorate products. They used non corrosive mercury fulminate until 1951. You are right however in that the Swiss did make a change to a less erosive primer mixture early on in the GP-90 series.Best

barnbwt/SlamFire1: Your knowledge and presentations are superb.

barnbwt/SlamFire1: Your knowledge and presentations are superb.

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Thanks! Just trying to be helpful, and when outstanding posters such as barnbwt add to the discussion, I learn a bit more.

The 7.5x55 is very, very close to the .308. Search on it, and you'll find at least one member here who built loads based on .308.

The K31 is an excellent rifle. It shoots better than it ought because of an excellent barrel and trigger. The surplus 7.5x55 ammo doesn't hurt either, it is match quality.

If you want to scope the rifle, the clamp-on mounts are good, but they take some finesse when zeroing because they are about 1/2" - 3/4" to the right of center.

If I could change anything about the rifle, I'd shorten the barrel length. Modern powders, etc.

You can absolutely improve on GP-11. For powder, Reloader 17 is the way to go. It's the civilian analogue to the powder found in GP-11.

I have never tried it but PRVI makes brass for the 7.5x55.

The Swiss K31 is one of my favorite military rifles and I have experience with the Mosins, 1903A3, M1A, and Enfield. Just a well built sweet shooting rifle.

"outstanding posters such as barnbwt"
Gawsh, fellas, you're makin' me blush . Thanks for the compliment, I'm glad my trivia is useful to others. Anyone interested in these guns should head straight to swissrifles.com and theswissriflesdotcommessageboard.com (after of course, seeking appropriate info here ) for a veritable font of information from very experienced shooters and even former servicemen who trained with them.

"You can absolutely improve on GP-11"
I definitely believe this to be the case, but I also believe it's pretty tough unless you're a very good/experienced loader. Yes, the GP11 wasn't tuned for an individual rifle like a worked up load, so it's potential is limited. But the stuff is so dang ridiculously consistent that it's hard to improve upon if the standard load happens to work well in your rifle. Unless doing true blue competition, it's hard to justify the time/effort of reloading just yet as a pure cost/benefit question (which ignores the pleasure most folks get working up and loading a custom recipe )

Luckily I'm too crummy with irons to know in any case, so I get to kick back with a happy/stupid grin on my face (and a bruise on my shoulder ) no matter what I do

TCB

old 1911

I have the older 1911 rifle, made in 1915. Love the way it shoots. Have had it over 40 years. Only paid $14.50 fort it. One good buy. Glad to find out technical changes in newer one.

The k-31 is the finest of all the milsurps. I love mine. I had plans of reloading but gp-11 gives me fist sized groups at 100 yards standing with open sights. That's plenty good enough for me. As long as there is a supply of surplus I couldn't justify reloading unless you just want to tinker.
I think they are a good investment. Well made and unique. You will enjoy it.

fireman 9731 said:

The k-31 is the finest of all the milsurps. I love mine. I had plans of reloading but gp-11 gives me fist sized groups at 100 yards standing with open sights. That's plenty good enough for me. As long as there is a supply of surplus I couldn't justify reloading unless you just want to tinker.
I think they are a good investment. Well made and unique. You will enjoy it.

Click to expand...

My reloads give me golf ball sized groups, you can definitely out step GP-11