Convert Swiss K31 to 7.62 NATO
- Thread starter y2k
- Start date
burnt_servo
CGN Ultra frequent flyer
- Location
- right in the middle of b.c.
Not that simple, there are camming surfaces on the breech end of the barrel that are needed for the operation.♠♠
i was talking in tearms of just being able to clean up the chamber to be recut it to 308 .
looks like a person would have to rebarrel it to use it as a 308 .
thanks for the pics
I just can't conceive of WHY anyone would want to do it. With the availability of brass from TWO factories (Norma and Partizan) and one of them at a reasonable price, there is no reason not to be able to stockpile some brass. It uses same primers, powders and slugs as almost any .30-cal. military round.
PLUS, the bigger casing means that you should be able to get .308 performance with LESS pressure, which is always a bonus if you want your barrel to last.
The .308 is not all that wonderful a cartridge as far as performance is concerned. In its sniping/competiton loading, it mimics precisely the Mark 8 .303 round which it replaced. And everybody KNOWS that the .303 is an absolete piece of ****. You should be able to do just as well with the much larger casing of the 7.5x55, now that brass is readily available.
Just do yourself a favour and lay in a LOT. With the laws going strange on us, who knows how much longer we "free" citizens will even be allowed to buy such dangerous things as empty brass tubes.
PLUS, the bigger casing means that you should be able to get .308 performance with LESS pressure, which is always a bonus if you want your barrel to last.
The .308 is not all that wonderful a cartridge as far as performance is concerned. In its sniping/competiton loading, it mimics precisely the Mark 8 .303 round which it replaced. And everybody KNOWS that the .303 is an absolete piece of ****. You should be able to do just as well with the much larger casing of the 7.5x55, now that brass is readily available.
Just do yourself a favour and lay in a LOT. With the laws going strange on us, who knows how much longer we "free" citizens will even be allowed to buy such dangerous things as empty brass tubes.
While the ball is rolling on this topic...
A friend of mine has a K31 that i believe has been rechambered to .308. The problem with it is, it has a very tough time ejecting fire brass. You almost have to hit the charging handle with a hammer! But, the odd time it will eject just fine.
Would be nice to figure it out. It is a nice sporter passed down from his grandfather.
A friend of mine has a K31 that i believe has been rechambered to .308. The problem with it is, it has a very tough time ejecting fire brass. You almost have to hit the charging handle with a hammer! But, the odd time it will eject just fine.
Would be nice to figure it out. It is a nice sporter passed down from his grandfather.
burnt_servo
CGN Ultra frequent flyer
- Location
- right in the middle of b.c.
it is possibly the same problem that guys who use 284 win brass ......
the rim on the swiss round is a bit amount bigger than the 284 / 308 rim .
which means the piece that grabs the rim needs to modified a bit to grab the smaller rim .
- Location
- Tucson, Arizona
If you don't reload, you are flushing your money down the toilet.
Cutting that barrel thread and cam isn't too big a deal for a competent gunsmith. And by competent gunsmith, I mean one with their own lathe who is also at least a partially trained machinist who can cut threads from scratch and do chambering on the lathe. IT seems these days almost anyone will hang a shingle and call themselves a "gunsmith".
The question is, why would you buy a several hundred dollar blank and pay several hundred more in machining to be able to shoot .308 in a rifle that is already ballistically equivalent?
The question is, why would you buy a several hundred dollar blank and pay several hundred more in machining to be able to shoot .308 in a rifle that is already ballistically equivalent?
I'd say that the 7.5x55 is ballistically equivalent to the 30/06 not the 308, and about 80 years ahead of its time - the first "short magnum" IMO (years ahead of Newton's rounds and the 280 Ross). It and the 6.5x55 Carcano (a better 6.8 SPC) are "back to the future" rounds.
Nice to see somebody besides me sticking up for the Carcano round!
7.5x55 was designed by Maj. Rubin, same guy as designed the .303. That's why both are such truly great cartridges.
7.5 operates at lower pressure than the '06 OR the .308. This is, in good part, a function of the larger case diameter. Firing the same amount of powder in different casings WILL give different pressures, and they can be charted as lowest pressure with the biggest case. For proof, put 35 grains of 4895 into a .303, a .30-'06 and a .300 Weatherby and gauge them. But there also is a reverse problem as far as actions are concerned; you also have to watch per-unit thrust on the boltface: 50,000 pounds pressure on a square inch is 50,000 pounds thrust; same pressure on a fifth of a square inch is only 10,000 pounds thrust. 7.5 is bigger at the base than the '06, therefore per-unit thrust on the bolt-face will be higher at any given pressure than with the American rounds. Exact formula can be calculated quite easily.
The 7.5 has a number of advantages and it is also a very accurate round.
7.5x55 was designed by Maj. Rubin, same guy as designed the .303. That's why both are such truly great cartridges.
7.5 operates at lower pressure than the '06 OR the .308. This is, in good part, a function of the larger case diameter. Firing the same amount of powder in different casings WILL give different pressures, and they can be charted as lowest pressure with the biggest case. For proof, put 35 grains of 4895 into a .303, a .30-'06 and a .300 Weatherby and gauge them. But there also is a reverse problem as far as actions are concerned; you also have to watch per-unit thrust on the boltface: 50,000 pounds pressure on a square inch is 50,000 pounds thrust; same pressure on a fifth of a square inch is only 10,000 pounds thrust. 7.5 is bigger at the base than the '06, therefore per-unit thrust on the bolt-face will be higher at any given pressure than with the American rounds. Exact formula can be calculated quite easily.
The 7.5 has a number of advantages and it is also a very accurate round.
Here are some shots of the rifle that gives one much difficulty while trying to open the action after firing.. I havent seen enough K31's to know what the chamber and bolt head should look like. Maybe someone has some input on why this .308 conversion is doing what it is?
7.5x55 operates at well under 50k pressure, .308 operates at about 52k.
TEXT BOOK OF SMALL ARMS - 1909 gives operating pressure for the Swiss Model 1900 rifles and ammunition as 17.1 (British long) tons per square inch: 38,304 pounds per square inch.
LESS than a .303, which had an operating pressure of 18.5 tons.
Operating pressure of the .308 is 23.2 tons.
You are operating your rifle well above the pressure levels it was designed for when you shoot factory .308. Handload and drop your pressures a bit through use of a progressive powder.
Problem will disappear..... or should, anyway.
TEXT BOOK OF SMALL ARMS - 1909 gives operating pressure for the Swiss Model 1900 rifles and ammunition as 17.1 (British long) tons per square inch: 38,304 pounds per square inch.
LESS than a .303, which had an operating pressure of 18.5 tons.
Operating pressure of the .308 is 23.2 tons.
You are operating your rifle well above the pressure levels it was designed for when you shoot factory .308. Handload and drop your pressures a bit through use of a progressive powder.
Problem will disappear..... or should, anyway.
As to the actual mechanism of what is going wrong, consider the length of your bolt in FRONT of the locking-lugs. There is 3 inches or more of steel there.
Give it enough pressure and steel WILL compress.... and you are giving it enough pressure, believe me.
You fire, the cartridge goes off, the bolt compresses, the casing stretches so that it doesn't spew 52,000-psi gas all over the place, the bullet leaves, the pressure drops and the bolt TRIES to stretch back to its original length.
But it CAN'T because of this &&%$ cartridge in the road. So it COMPRESSES the cartridge-casing back into the chamber.
This jams everything up tight.
The result is that your rifle is trying to remove something that is jammed in absolutely tight. The normal elsaticity of cartridge-brass prevents this is pressures are safe. You have the problem because pressures are too high for this action.
You can handload to less pressure easily and still have ALMOST the killing-power for hunting purposes AND your rifle will stop doing weird things.
Have fun!
Give it enough pressure and steel WILL compress.... and you are giving it enough pressure, believe me.
You fire, the cartridge goes off, the bolt compresses, the casing stretches so that it doesn't spew 52,000-psi gas all over the place, the bullet leaves, the pressure drops and the bolt TRIES to stretch back to its original length.
But it CAN'T because of this &&%$ cartridge in the road. So it COMPRESSES the cartridge-casing back into the chamber.
This jams everything up tight.
The result is that your rifle is trying to remove something that is jammed in absolutely tight. The normal elsaticity of cartridge-brass prevents this is pressures are safe. You have the problem because pressures are too high for this action.
You can handload to less pressure easily and still have ALMOST the killing-power for hunting purposes AND your rifle will stop doing weird things.
Have fun!
You forgot to put a smiley there.....
....
I'd say that the 7.5x55 is ballistically equivalent to the 30/06 not the 308, and about 80 years ahead of its time - the first "short magnum" IMO (years ahead of Newton's rounds and the 280 Ross). It and the 6.5x55 Carcano (a better 6.8 SPC) are "back to the future" rounds.
I like the way you think....
....but the .280 Ross and the .276 Enfield were also pretty neat....
I like the way you guys think!
cyclone, I didn't put a smiley right there for 2 reasons: (a) I don't know how to put them where I want them.... will find out, and (b) which one should I use, anyway? Far as obsolete .303s are concerned, I pick up the junkers that everybody else wants rid of, taken them home and talk nicely to them, feed them carefully, all that. That nice rimmed case is just too easy for an action to handle; Brits found the same thing with the Vickers.
There have been a lot of really good developments which have come along..... it's just that folks have to have something 'modern', even if it repeats the errors of 80 years ago.
When the .220 Swift came out, it burned barrels out in a single day's varminting.... so they developed new steels to handle it. Now the Swift is 'obsolete' and you can get a ***NEW*** rifle that........ uses 55 grains of powder for a 50-grain slug....... and can burn a barrel out in an afternoon. Yet you can still pick up an old Swift, run it at a mere 3800 and the barrel will last two-thirds of forever. One of those obsolete .303 barrels will handle 12,000 rounds of highly-corrosive/erosive Mark VI Ball..... which is why God gave us cool-burning progressive powders and NCNM primers.... and now they lkast five-eighths of forever and still put out almost what a .308 puts out..... which has a barrel life of 3K.
There is still LOTS of room for the old ones.... and they still work well.
Gets interesting.
cyclone, I didn't put a smiley right there for 2 reasons: (a) I don't know how to put them where I want them.... will find out, and (b) which one should I use, anyway? Far as obsolete .303s are concerned, I pick up the junkers that everybody else wants rid of, taken them home and talk nicely to them, feed them carefully, all that. That nice rimmed case is just too easy for an action to handle; Brits found the same thing with the Vickers.
There have been a lot of really good developments which have come along..... it's just that folks have to have something 'modern', even if it repeats the errors of 80 years ago.
When the .220 Swift came out, it burned barrels out in a single day's varminting.... so they developed new steels to handle it. Now the Swift is 'obsolete' and you can get a ***NEW*** rifle that........ uses 55 grains of powder for a 50-grain slug....... and can burn a barrel out in an afternoon. Yet you can still pick up an old Swift, run it at a mere 3800 and the barrel will last two-thirds of forever. One of those obsolete .303 barrels will handle 12,000 rounds of highly-corrosive/erosive Mark VI Ball..... which is why God gave us cool-burning progressive powders and NCNM primers.... and now they lkast five-eighths of forever and still put out almost what a .308 puts out..... which has a barrel life of 3K.
There is still LOTS of room for the old ones.... and they still work well.
Gets interesting.
Larry Racine, http://www dot lprgunsmith dot com has done lots with these and they seem to be quite convertable to 308. I have a rear sight to test for St. Marie when the weather gets better. I have loaded 7.5 Berdan with good results and 284, they all can work really well. We were supposed to do a PS magazine article on one set up in our stocks for Course shooting in the USA but it has not happened yet.
