7.5 x 55mm Swiss question

TRguy · February 1, 2010, 12:14 PM

Okay I have several differing opinions on Over All Length of a loaded 7.5 x 55mm Swiss Cartridge.

I am shooting K31 Schmidt Rubin Rifle.

Some info I have gotten has OAL listed as:

7.5 x 55mm Swiss OAL = 3.060"

and another source

7.5 x 55mm Swiss OAL =2.95"

and SwissRifle.com has

7.5 x 55mm Swiss OAL = 2.89"

Okay I loaded some to 2.95" and when I went to chamber a cartridge it pushed the bullet deeper into the case. I put the caliper to it and measured 2.86" exactly.

Knowing that, would you seat all your bullets down to OAL = 2.86" knowing that with the chamber closed and locked that the bullet is just at the beginning of the rifling? And the 2.95" is bunk and shouldn't seat my bullets to that OAL?

5R milspec · February 1, 2010, 12:31 PM

did you try the load?if so what kind of group did you get.and if it was a max load you might want to bump the load down a bit so that it want be a compressed load.

but loading at or in the lands should give you a better group.the rifel should be OK with that and handle what you feed it.

a friend of mine put a ghost sight for the front sight and it worked like a charm on his K31.and I think he was useing 4064 for his go to powder.

TRguy · February 1, 2010, 12:47 PM

using IMR 3031

founds some info on the OAL at

http://forums.gunboards.com/showthre...ing-for-a-K-31

and

http://www.thefiringline.com/forums/....php?p=2624795

Seems K31 have different chamber cuttings over the decades of production.

I have shot them and get a 3" group off of open sites at 100yrs shooting on a bag.

hodaka · February 1, 2010, 02:40 PM

It will depend upon the design of the bullet that you choose. You may as well go ahead and drop a bullet into the chamber to see where the lands hit that particular round. My K-31's were driving me crazy trying to go by the book lengths. I think the GP-11's are long and skinny. I shoot SMK's which are much fatter. They really shoot well, but you will need to play with the length to get the bolt to close easily yet still have minimal jump.

Slamfire · February 1, 2010, 02:50 PM

I seated my 168 SMK bullets to 2.850 and my 174 FMJBT's to the same depth.

Old gun manuals must have been loading for M1911's, or something that had a lot deeper throats than a K31. Attempting to copy their seating depths resulted in stuck bullets.

For this reason, I keep my bullets well off the stupid lands in this rifle. You jam a bullet into the lands, you will have problems. This action has very weak primary extraction to start with, and leaving a bullet in the throat will result in a powder spill inside the action. The locking lug area is deep inside the action, hard to get to, and even after wiping it, I still had ball powder particles in there. That stuff then got inside the bolt and had to clean that up.

TRguy · February 1, 2010, 03:01 PM

Quote:

I seated my 168 SMK bullets to 2.850 and my 174 FMJBT's to the same depth.

Old gun manuals must have been loading for M1911's, or something that had a lot deeper throats than a K31. Attempting to copy their seating depths resulted in stuck bullets.

For this reason, I keep my bullets well off the stupid lands in this rifle. You jam a bullet into the lands, you will have problems. This action has very weak primary extraction to start with, and leaving a bullet in the throat will result in a powder spill inside the action. The locking lug area is deep inside the action, hard to get to, and even after wiping it, I still had ball powder particles in there. That stuff then got inside the bolt and had to clean that up.

Great Info - I appreciate you sharing. I didn't think the action was inherently weak but the PSI I have been reading are in line with 7.62x51 Nato so maybe if you put a 8mm Mauser in that action it wouldn't hold up.

I agree the lugs are well far forward in the action, makes you wonder what tooling they had in the 30s to accomplish such fine machining not to mention the high grade high nickel content steel. These rifles are a true work of art.

I will re-seat my bullets at 2.85" that will back it off the lands .01"

Slamfire · February 1, 2010, 05:42 PM

Quote:

Great Info - I appreciate you sharing. I didn't think the action was inherently weak but the PSI I have been reading are in line with 7.62x51 Nato so maybe if you put a 8mm Mauser in that action it wouldn't hold up.

I don't think the action is "weak" in the sense that it cannot handle pressure. I do think the primary extraction is "weak" in that you are working through the action lever and camming surfaces in the bolt.

Something with a solid bolt, like a straight bolt Mauser, you can kick the bolt open. You may bust the extractor, but you can get the bolt open.

On these straight pulls, I would not kick anything.

Quote:

I agree the lugs are well far forward in the action, makes you wonder what tooling they had in the 30s to accomplish such fine machining not to mention the high grade high nickel content steel. These rifles are a true work of art.

I don't know about the steel or the heat treatment. But from the comments of others and my experiences, the bolts on these rifles are completely interchangeable over a production period of 30 years. This is incredible. I don't know of any other rifle where this is true. These are a work of art.

lonniemike · February 1, 2010, 09:20 PM

Weak actions indeed. With enough money you can/could get factory 31's in 7.5, 308, and both the longer cartridges of 30'06 and 300 mag in single shot versions. best-o-luck

Dave R · February 2, 2010, 11:35 PM

My opinion, on the K-31 the best thing to do for a particular bullet it blacken it, feed it, and see if you get rifling marks in the blackening. If you do, seat it a bit deeper until that stops happening.

That's how I derived the right COL for 150gr. bullets in my K-31.

BombthePeasants · February 4, 2010, 10:54 AM

I am still brand new to this whole reloading thing, but could you not just measure the C.O.L. of a factory loaded cartridge, and just copy that?

Dave R · February 4, 2010, 12:48 PM

Only for bullets with similar shapes. One reason people have trouble is the GP 11 bullet has a different profile.

TRguy · February 4, 2010, 01:16 PM

Well maybe I could but I haven't bought factory ammo in years with the exception of rimfire.

I got my Case OAL length worked and test shot some rounds yesterday....it prefers the 2.85 OAL. I am good to go.

Plus none of your main retailers or even most mom and pop shops don't have boxes of 7.5x55mm swiss sitting on the shelf.

Dave R · February 4, 2010, 11:24 PM

Be aware that you can also use re-formed .284Win brass. Not like that's any easier to find...

But that's all my K-31 has ever known. I scored some at a gun show the day my rifle arrived. Just run the .284Win brass through the resizer die and check case length, and you're good to go. The rim is 'slightly' smaller than a 7.5 Swiss rim, but I've never known anyone to have a problem with that.

AzizaVFR · February 5, 2010, 07:14 AM

When it comes to reloading for the 7.5x55 Swiss, you have to disregard the cartridge overall lengths stated in most loading manuals. The K31 have very short leade sections between the chamber and rifling, due to the nature of the GP11 bullet. You need to measure your cartridge ogive of the bullet you wish to use. Hornady now makes a modified case to use with their overall length gauge and carried by Grafs & Sons.

A good source of reloadable factory ammunition is the Prvi Partisan 174gr FMJBT. In my experience with the loads I have made, only neck resizing needs to take place on this brass once fired through your rifle. Also be aware of the loads. The safe maximum pressure to build would be equal to the GP11 ammo, at 45,500PSI.

They made the receivers and bolts from two different metals. If you look on your bolt and see a marking that looks like "+CN", your receiver is made from Chrome Nickel. A "+CM" mark denotes Chrome Molybdenum.

February 1, 2010, 12:14 PM	#1
TRguy Senior Member Join Date: July 15, 2008 Location: Concord, NC Posts: 682	7.5 x 55mm Swiss question Okay I have several differing opinions on Over All Length of a loaded 7.5 x 55mm Swiss Cartridge. I am shooting K31 Schmidt Rubin Rifle. Some info I have gotten has OAL listed as: 7.5 x 55mm Swiss OAL = 3.060" and another source 7.5 x 55mm Swiss OAL =2.95" and SwissRifle.com has 7.5 x 55mm Swiss OAL = 2.89" Okay I loaded some to 2.95" and when I went to chamber a cartridge it pushed the bullet deeper into the case. I put the caliper to it and measured 2.86" exactly. Knowing that, would you seat all your bullets down to OAL = 2.86" knowing that with the chamber closed and locked that the bullet is just at the beginning of the rifling? And the 2.95" is bunk and shouldn't seat my bullets to that OAL? __________________ Two is One, One is None Last edited by TRguy; February 1, 2010 at 12:55 PM.

February 1, 2010, 12:47 PM	#3
TRguy Senior Member Join Date: July 15, 2008 Location: Concord, NC Posts: 682	using IMR 3031 founds some info on the OAL at http://forums.gunboards.com/showthre...ing-for-a-K-31 and http://www.thefiringline.com/forums/....php?p=2624795 Seems K31 have different chamber cuttings over the decades of production. I have shot them and get a 3" group off of open sites at 100yrs shooting on a bag. __________________ Two is One, One is None Last edited by TRguy; February 1, 2010 at 01:19 PM.

February 2, 2010, 11:35 PM	#9
Dave R Senior Member Join Date: January 7, 2000 Location: Idaho Posts: 6,073	My opinion, on the K-31 the best thing to do for a particular bullet it blacken it, feed it, and see if you get rifling marks in the blackening. If you do, seat it a bit deeper until that stops happening. That's how I derived the right COL for 150gr. bullets in my K-31. __________________ I am Pro-Rights (on gun issues).

February 4, 2010, 12:48 PM	#11
Dave R Senior Member Join Date: January 7, 2000 Location: Idaho Posts: 6,073	Only for bullets with similar shapes. One reason people have trouble is the GP 11 bullet has a different profile. __________________ I am Pro-Rights (on gun issues).

February 4, 2010, 01:16 PM	#12
TRguy Senior Member Join Date: July 15, 2008 Location: Concord, NC Posts: 682	Well maybe I could but I haven't bought factory ammo in years with the exception of rimfire. I got my Case OAL length worked and test shot some rounds yesterday....it prefers the 2.85 OAL. I am good to go. Plus none of your main retailers or even most mom and pop shops don't have boxes of 7.5x55mm swiss sitting on the shelf. __________________ Two is One, One is None

February 1, 2010, 12:31 PM	#2
5R milspec Senior Member Join Date: December 11, 2009 Location: South Carolina Posts: 360	did you try the load?if so what kind of group did you get.and if it was a max load you might want to bump the load down a bit so that it want be a compressed load. but loading at or in the lands should give you a better group.the rifel should be OK with that and handle what you feed it. a friend of mine put a ghost sight for the front sight and it worked like a charm on his K31.and I think he was useing 4064 for his go to powder.

February 1, 2010, 02:40 PM	#4
hodaka Senior Member Join Date: April 23, 2006 Location: South Texas Posts: 2,010	It will depend upon the design of the bullet that you choose. You may as well go ahead and drop a bullet into the chamber to see where the lands hit that particular round. My K-31's were driving me crazy trying to go by the book lengths. I think the GP-11's are long and skinny. I shoot SMK's which are much fatter. They really shoot well, but you will need to play with the length to get the bolt to close easily yet still have minimal jump.

February 1, 2010, 02:50 PM	#5
Slamfire Senior Member Join Date: May 27, 2007 Posts: 5,261	I seated my 168 SMK bullets to 2.850 and my 174 FMJBT's to the same depth. Old gun manuals must have been loading for M1911's, or something that had a lot deeper throats than a K31. Attempting to copy their seating depths resulted in stuck bullets. For this reason, I keep my bullets well off the stupid lands in this rifle. You jam a bullet into the lands, you will have problems. This action has very weak primary extraction to start with, and leaving a bullet in the throat will result in a powder spill inside the action. The locking lug area is deep inside the action, hard to get to, and even after wiping it, I still had ball powder particles in there. That stuff then got inside the bolt and had to clean that up.

February 1, 2010, 09:20 PM	#8
lonniemike Senior Member Join Date: March 16, 2005 Posts: 138	Weak actions indeed. With enough money you can/could get factory 31's in 7.5, 308, and both the longer cartridges of 30'06 and 300 mag in single shot versions. best-o-luck

February 4, 2010, 10:54 AM	#10
BombthePeasants Senior Member Join Date: November 17, 2008 Location: Texas Posts: 351	I am still brand new to this whole reloading thing, but could you not just measure the C.O.L. of a factory loaded cartridge, and just copy that?

February 4, 2010, 11:24 PM	#13
Dave R Senior Member Join Date: January 7, 2000 Location: Idaho Posts: 6,073	Be aware that you can also use re-formed .284Win brass. Not like that's any easier to find... But that's all my K-31 has ever known. I scored some at a gun show the day my rifle arrived. Just run the .284Win brass through the resizer die and check case length, and you're good to go. The rim is 'slightly' smaller than a 7.5 Swiss rim, but I've never known anyone to have a problem with that. __________________ I am Pro-Rights (on gun issues).

February 5, 2010, 07:14 AM	#14
AzizaVFR Junior Member Join Date: February 5, 2010 Posts: 3	When it comes to reloading for the 7.5x55 Swiss, you have to disregard the cartridge overall lengths stated in most loading manuals. The K31 have very short leade sections between the chamber and rifling, due to the nature of the GP11 bullet. You need to measure your cartridge ogive of the bullet you wish to use. Hornady now makes a modified case to use with their overall length gauge and carried by Grafs & Sons. A good source of reloadable factory ammunition is the Prvi Partisan 174gr FMJBT. In my experience with the loads I have made, only neck resizing needs to take place on this brass once fired through your rifle. Also be aware of the loads. The safe maximum pressure to build would be equal to the GP11 ammo, at 45,500PSI. They made the receivers and bolts from two different metals. If you look on your bolt and see a marking that looks like "+CN", your receiver is made from Chrome Nickel. A "+CM" mark denotes Chrome Molybdenum.