The 7.5x55 Swiss

[FAsmus]

Gentlemen;

I've just purchaced a K-31 Swiss in excellent condition - all matching numbers and the soldier's name it was issued to under the butt-plate.

I know a few things about the rifle and how to load for these military outfits but naturally I don't know it all!

I'm requesting the membership's input about successful cast bullet loads and techniques for feeding this particular design. Please to include any special treatment of bullets and diameters such that they will enter the throat consistently and accurately.

Thanks in advance,
Forrest

[Storydude]

K31's are each unique. what works in mine may not work in yours.

I never used any cast in mine, but45G Varget under a 168 pill worked great for mine. OAL must be changed to allow the tight throat.

[rmaster14145]

i like a 150gn (308) jacketed bullet over 30gn of H4895.

for cast i have been shooting a .313, 115gn LFP over 9gn of unique

i have some 170gn .309s over 7.5gn of unique but i have yet to try them .

rm

[twotoescharlie]

get a bump die from Smokem Joe, as these rifles have a almost nonexistant throat.

TTC

[Calamity Jake]

First thing, clean all copper then slug it. You will find it to be about .297-8 bore by
.307-8 groove.
I have 2 K31's, both slug to the above Ø's, in one I use 311291 that casts .298 on the nose by .311 body, the .298 nose will not fit in the bore, I gas check and size to .3095(my smallest 30 cal. sizer)lube with FL and load in cases worked with Redding dies over 18.0 Blue Dot.

FYI, the K31 action design fired with low vol. loads(cast or J'ed) will shoot to the right, if loads are worked up to 2000-2200 then there is enough windage adjustment in the front sight to bring POI to POA @ 100 yards.

With the above load and my 59YO eyes I can put 5 into about 3.5 inches @ 100. I know it will shoot a lot better than I can see.

[45 2.1]

I would suggest you take a lead throat slug and see what you are dealing with. That rifle does not have a standard throat. I think you will find a long chamber neck with a shoulder at the throat, what little you will find. It has an abrupt entrance into the rifling. The RCBS 308-165-Sil has worked fine for fit and reasonable accuracy with Unique for me. These shoot fairly well with cast, but are not the equal of the earlier versions.

[Maven]

Forrest, Search this site's archives as there are many posts on the K-31's. You also may want to get in touch with Joe Wiest (Smokemjoe here) and have him make you a bump die* once you know bore and throat dimensions of your rifle. K-31's handle a variety of CB designs well, but some, e.g. Saeco #315 and RG-4, exceptionally so.


*This one swages the nose down to allow greater OAL. E.g., prior to obtaining the die from Joe I had to seat Ly. #311291 to ~2.70" OAL in my K-31's to get the bolt to go into battery. With Joe's die, I can size the nose if needed and the first driving band enough to allow me to seat to 2.90" OAL.

[Bret4207]

Not cast, but the GP11 Swiss ammo is some fine target ammo. I was amazed that even this half blind shooter could keep 5 in just over an inch with the GP11 at 100 yards. I used my favorite "V" shaped aiming point and punched the tip of the "V" out with 10 shots- just under 1.375 inches!!

[FAsmus]

OK everyone;

Thanks for taking the time to write.

In my initial experimentation with dummy rounds loaded with various cast bullets I had already determined that the throat was unusally square and close to the case mouth.

As you say this was easily fixed by use of a nose sizing die - mine is a Ed Wosika Coaxisizing die that not only sizes the nose but tapers the first band so as to enter the bore consistently every time .. I've used the Coax dies a lot and they really do help accuracy but I dislike all the extra procedures necessary to get my bullets prepared for loading.

There was no way a 0.301 nose would fit into the muzzel but the origin of rifling at the breech end is worn enough to accept anything under 0.3005, which happens to be the Coax die's size .. so what if the bullet gets rifling cuts all the way to the nose by the time it exits the barrel?

For initial testing I plan on RCBS 30-150-GC since it is short enough to avoid the bullet base extending into the powder space.

I did search the site for other M31 material before posting my request. It seems to me that there are lots of mild-to-squib loads being used. I plan on the standard old things like 21 grains 4759 or 30 grains Varget for starters and I'll post on this thread for those of you who might be interested to see what happens.

I plan on using the rifle for long range shooting; Things like 395 to 830 yards here in my home town rifle range.

Good evening,
Forrest

[runfiverun]

27 grs of h-322 with a filler makes mine happy with the rcbs 165 silh and no alterations to the nose.
the body of the boolit sits in the neck and the nose engraves just enough to keep it straight.

[FAsmus]

Runfiverun;

I don't have a 165 grain RCBS at all but a fellow shooter loaned me his 30-150-FN yesterday - good for initial testing. Things like buying a SAECO 316 or something will have to wait.

The intent here will be to find a good load to shoot practice at our 350 yard Offhand target - even the blunt 30/30 RCBS should work for this.

As for fillers in a bottle-neck case; no thanks. I load and shoot thousnads of rounds of fillered ammunition in straight cases and I know how its done - I just draw the line at the bottle necked design.

Good morning,
Forrest

[KCSO]

The Lee 165 spire point bullet that was made for the SKS also works well in the K 31. I seat mine to just lightly engrave the rifling at the nose and back it with 12 grains of Red Dot and spark it off with LP primers. The bullet is sized to 309 in the body and no nose sizing is necessary. These will group well enough to win most military rifle matches, my iron sight groups are averaging under 2 1/2" at 100 yards and i saved one target that had 5 in 1 3/4" c-c at the 100 yard mark.

[leadman]

I also have the RCBS 30-150-SP mould and this boolit works very well in my K-31s. Never had some of the problems that others have mentioned.

[FAsmus]

Leadman;

I got up early to beat the heat and ran off 200 RCBS 30-150-FN this morning. As the design is intended for 30/30 they measure pretty close to what I was hoping for, going 0.2995 on the noses and 0.3085 on the body.

These dimentions will allow me to shoot them without going through all that time-consuming Coaxisizing stuff addressed previously in this thread.

Right now I'm waiting for delivery of the Serbian 7.5x55 cases I ordered from Graf.

Good morning,
Forrest

[FAsmus]

Gentlemen;

The day has gone well - I cast up the trial run of the RCBS bullets described above and then, time seeming to be on my side I pulled the bullets from a box of Hornady commercial 7.5x55, threw away the powder, lubed and loaded the fresh-cast bullets over 22 grains 4198 into the cases thus made available and headed for the range for initial testing.

For just 20 shots in an untried rifle things went OK. The first two groups were strung somewhat but the next two tightened up quite a bit with the 4th one going into 5 x 2.320 with (naturally) the issue sights.

The groups aquired show what I call indications that the rifle "wants" to shoot. That is, the typical five shot group would show four good and one flyer. One such example today had three holes touching. When this happens I know that eventually I'll find what caused the flyers, eliminate it and go to shooting consistently as well as the rifle is capable.

I looked for and found three spent bullets from this shooting. My! they certainly showed complete mushrooming; nothing much left but the gas check shank and mushed over remains. ~ Pretty soft alloy ~

Good afternoon,
Forrest

[FAsmus]

Gentlemen;

The K31 has been up to the range with 80 test rounds since last addition to the thread.

Things continued as per the post just previous to this one: The rifle indicated it "wanted" to shoot by giving me the occasional group as tight as I can hold with as-issued sights and then tossing semi-wild flyers with good sight picture.

I tired various components and sizing as per the intent specified in the thread. Some were definitely better than others and I think I have at least a preliminary idea about what is going to work as regards the bullets, sizing and seating stuff.

However! I pretty much shoot a rifle first and then (if necessary) look it over. It was obviously time to inspect the rifle thoroughly.

Upon disassembly I was first impressed with the fine way Swiss put this rifle together and then amazed at finding what I feel is the reason it fired groups the way it did in spite of the overall good engineering and design of the piece;

The recoil lug initially showed no contact with the wood at all. In fact there was some loose foreign material in the place where normally you'd find only the impression of the steel against the wood.

I got curious once I proved that this was in fact the case; How much of a gap is there? I asked myself, so, I installed progressively thicker shims between the lug and the rear portion of the stock where it would normally fit up against.

I quit when I reached 0.125 gap between wood and steel in this critical area and still no contact - there was no point really - over an eighth of an inch is such a gap that a semi-major rework is indicated anyway.

My question to the members is: Has anyone else seen this sort of problem in their K31s? If so how did they fix it? How did the fix work out?

Good afternoon,
Forrest

[twotoescharlie]

would suggest going to the" Swiss rifle forums" as they have articles pertaining to the swiss bedding and accuracy tips. some as simple as loosening and tightening a screw.

TTC

[runfiverun]

i bedded mine.
i have been watching this go along as i have that rcbs 150-***/c boolit also, and my wifes 0-6 will shoot it better than any other booit i've tried so far.
does it feed from the magazine for you?
i think that it would, it feeds in my bolt action 30-30 fine.
if you wanna just see quick if it's that use some hot glue for a quick bed just in that area,with some car wax for a release agent.

[35 Whelen]

Regarding the bedding, it has been my habit (right or wrong)when bedding rifles to relieve the front, sides and especially the bottom of the recoil lug. I learned this in my Dad's Gunsmith Kinks book and it's always worked for me. I tuned and bedded my '53 K-31 into a match rifle and bedded it as described. I also left quite a bit of upward pressure under the barrel at the end of the forend.
As far as flyers go, for me at least, they just seem to be a way of life. In fact, in most of my 10 shot groups, I expect about 80% "success", with typically a couple of flyers. Sometimes I have 3 flyer, and sometimes only one. And incidently, I weigh all of the bullets that I cast for High Power matches. They are then sorted and grouped with 20 of exactly the same weight being set aside for Slow Prone, then if possible 20 of identical weight for Rapid Prone. I'm not quite as particular for Rapid Sitting and Offhand, but even these bullets vary no more than +/- .3 gr.
Here are a few groups fired from my '53 K31. Maybe this will give you an idea of what to expect.





Good luck,
35W

[Bob S]

Good afternoon Forrest,

The "recoil lug" isn't. It's more appropriately called a "bedding block". The bottom of that block (only) contacts the stock, or a metal shim placed there to regulate the pressure at the fore-end tip. The recoil thrust surface in a military K31 is the back of the trigger housing. If you study the receiver bedding carefully, you'll see that the only places that metal contacts wood are the bottom of said bedding block, the recoil surface at the back of the trigger housing, and the tang. Nothing else touches wood. All of the gun scribes and pharisees seem to think that the K31 barrel should be free floated. They are wrong. Looking again at the military bedding, the only contact point that keeps the barreled action from moving in yaw is the contact with the barrel at the front of the stock. It acts like a Vee block. The Swiss armorers used different thicknesses of shims to regulate the pressue there, not to remove it. The military bedding system is a little odd, but it required absolutely no hand fitting of wood to metal ... the only semi-skilled labor required in asembly of the barreled action to stcok was the choice of thickness of the shim ... I believe there were three choices.

If you are interested in keeping the carbine legal for US-style "as issued" competition, there are some limited tweaks you can do; if you don't care about the US CMP rules, you are limited only by your imagination (and good engineering judgement!). First make certain that your stock isn't warped. A lot of them are. Just remove the bands and handguard and see what happens to the front of the stock. If it looks like, this, start looking for a replacement:



If the stock remains straight and pushed up on the end of the barrel with about 9-10 lbs force, you're good. If the contact at the end of the stock seems light, remove the metal shim that is under the bedding block.

Replace the handguard and bands and try to push the front of the barrel up and out of the Vee block. If there is insufficuent clearance to move the barrel up (and there probably isn't), remove some of the wood from the handguard. Repeat until you can push the barrel up at least .020" or so. The barrel should reseat itself once you stop pushing up on it.

Check for clearance from the rest of the barrel. Remove the handguard. With modelling clay, make a few small "snakes" about 1/16 in diameter, and place these on the top of the exposed barrel, cicumferentially. Make certain at least one of these will be under the rear band. Replace the handguard and bands and tighten down the screws; remove the handguard again and note if any of the clay snakes have been totally smooshed ... if so, relieve wood, and repeat until you have about 1/16" clearance between the barrel and the handguard.

Next, make certain that the handguard rabbet will slide under its mounting surface without levering the barrel up. Place the handguard on the stock about 1" forward of its normal position, and slide it back to seat under the rear sight base. If you have to lift the front of the handguard to get that little tab to seat under the rear sight, you will need to remove some material from the tab, or sand the bottom of the entire handguard. If you need to sand the bottom of the handguard, you may need to recheck barrel clearance again.

Having done the above, the barrel will free of all unintended stresses; and barreled action will be stable in the yaw axis.

Regarding "tuning" the rear bedding screw ... if the action was properly bedded, there would be uniform contact in the Z direction (up and down) at the bottom of the bedding block and the tang. That would be the ideal, but as discussed, the Swiss only paid attention to the height of the bedding block. In most cases, the bedding is not uniform fore and aft. With the only the front action screw installed, the action will be sitting only on the bottom of the bedding block, and the tang will be dangling in thin air ... It may only be .005 or .010" of thin air ... but even that little isn't good. Now when you tighten down the rear bedding screw, you are trying to lever up the whole barreled action; the bedding block is the fulcrum. In extreme cases, the tang can actually become cracked. If you experiment with the torque (or lack of it) of the rear screw, you may find a point where the action is just stable without trying to rock it around the bedding block. This is a weakness of the bedding system, but if you want to stay "as-issued" you're stuck with it: you can't add shims back there because the Swiss armorers never did that.

If you're not interested in keeping the carbine "as-issued", you can epoxy bed it as you would a Springfield or a Mauser and get great results. You may still find that the relatively light barrel needs some pressure at the front to give the best groups, but if you epoxy bed the receiver so it is stable, you at least have the freedom to try free floating to see if it works for your barrel. One enterprising shooter (I think he postes here sometimes) bedded the under side of the rear sight base, so that would be the "vee block" point to stabilze the action in yaw, and he has gotten phenominal results ... but I don't think he shoots cast in it. I recently put a Swiss Products damper on a K31 that has been bedded in a Boyd's sporter stock (no longer made) ... and it improved the balance of the rifle, which is why I put it there. It didn't hurt grouping, and it might have improved it slightly. The jury is still out on that one; but that's another option to consider for non-"as-issued" carbines.

These are some pix of the bedding of my K31 CISM rifle (7.62x51). It is "conventionally bedded" with Marine Tex, and despite the erroded throat, it is still shooting high Master (not High Master) class scores for me on reduced range courses with the Ideal 311291.







The heavy barrel on this one really is free-floated. Note the the tang had to be shortened in order to use the close-set vertical pistol grip. That leaves insufficient wood between the trigger housing and the rear bedding screw, so the military recoil surface could not be used as such ... the "conventional bedding" that uses the bedding block as a recoil surface was a necessity in this case.

Hope this information is useful to you ....

Resp'y,
Bob S.