Cast in 7.5x55 Swiss

[Macd]

While I wait for the only place up here that sells Sierra .358 bullets in 180 grain for my 35 Rem. to restock I have decided to return to a stalled project of getting cast to shoot well in my K31. Most cast designs have to be seated deep to account for the almost non-existent leade in these rifles. Even though my rifle was made in 1934 it has virtually no throat erosion. I have selected the Lee 309-150 F, traditionally lubed and water quenched WW with Hornady checks. Seated .005 off the lands the check is just below the neck in my trimmed to spec PRVI brass. Powder selection is a bit of a problem as I like 80% case fill. I am trying to keep velocities in the 2000 fps area. Powders in the mid-range such as Win748, Varget, BL- C(2) and CFE 223 are candidates. I plan on no crimp other than required to just remove the case mouth flare. The K31 was designed around the GP 11 bullet which has a spitzer profile. I will be watching for any problems with the feed of the flat point Lee bullet including setting the bullet further back in the case.

[RBHarter]

Did the Swiss adopt the 7.7/303/Russo 1-9ish fast twists or the slower US 1-10/12 twists ?

I ask I had an 06' and x39 with 1-8.5" and 1800 was where it came all undone , I could hurl boxcars at 230 gr but not very fast with even light bullets . The 308 I had , had a 1-12 and refused to shoot anything over 175 gr regardless of shape but 22&2400 fps wasn't a problem with 150-165 gr . All based on groups of course .

[Macd]

Twist is 1 in 10.23. The GP11 is 174.4 grains and runs at about 2450 fps. I worked up a load using the 178 grain A-Max but that bullet is no longer available. I then switched to 150 grain SST which I pushed at over 2600 fps with Varget. I was going to order some PRVI 174 FMJBT and attempt to duplicate the GP11 but got sidelined with other things.

[Macd]

Here is the bullet and where it will seat in case. I have seated below the neck before but not so far down as this. I do not expect any problems. also, after some QuickLoad work I can only get the velocity and case fill with slower powders. Both HV 100 and H4350 look promising although they are going to have some nice flashes at the muzzle.

&.&x%% L309-150 F.jpg

[larryw]

[larryw]

[AlaskanGuy]

is it required to get full case? when I had mine, i used 2400 and it shot very nicely... i know this sounds like a rookie thing, but is it that the bullet wont seat any farther out due to bullet dimensions in your throat? also, doesn't lee make a bullet more suited to the k-31? also mimicking the profile and such of the original GP?

[Macd]

is it required to get full case? when I had mine, i used 2400 and it shot very nicely... i know this sounds like a rookie thing, but is it that the bullet wont seat any farther out due to bullet dimensions in your throat? also, doesn't lee make a bullet more suited to the k-31? also mimicking the profile and such of the original GP?

I always try to get at least 80% case fill as a matter of preference especially for slower powders. This doesn't apply obviously to fast handgun/shotgun powders used to create reduced loads in rifle cases. 2400 would make a good choice but alas it is hard to find here. I also considered IMR 4227 which I have on hand.

I looked at the lee offerings and I couldn't find a better alternative. The 1896, 1911 and K11 rifles had more leade to accommodate the GP90 bullet. The K31 was made specifically to most accurately shoot the GP11 bullet which is a long spitzer shape. The transition from chamber to lands is really abrupt. I don't really worry about seating a jacketed bullet deep as long as I don't end up with a really compressed load. I have less experience with gas checked bullets that seat below the neck. I don't have any safety concerns but am not sure if the check having to transition the shoulder neck interface will cause deformation and therefore reduce accuracy. I am not planning to ever use the rifle for hunting. I am trying to get the best paper accuracy.

Lastly as far as powder choice, my other constraining factor is trying to keep velocity down to 2000-2100 fps while maintaining my 80% + case fill target. The mid-range powders I mentioned in my original post are better choices but give velocities above 2300 fps for that volume level. I just don't think the cast bullet will like this velocity. I have tried it in the similar volume 308 case at these velocities and accuracy was not very good.

[Macd]

Here is the finished sample cartridge. O.A.L. is 2.650 and this gives me a jump of only .005. I am going to load 5 rounds using 4 different powders. No ladder tests and the pressures, except one, are less than half of the maximum. I included QuickLoad predictions . I decided to load IMR 4227 and Trail Boss just for comparison purposes.

Hodgdon 4350
41.0 grns
79.9%
2111 fps
20,250 psi

Hodgdon HV 100
40.7 grns
80.0%
2091 psi
18,548 fps

IMR 4227
25 grns
51.9%
2058 fps
20,843 psi

IMR Trail Boss
17 grns
96.0%
1712 fps
31,189 psi

Lee 309-150.jpg

[Macd]

So I got to the range yesterday nice and early with no one else there. Beautiful day with no wind and the sun just right for shooting and my chronograph. The only fly in the ointment was literally flies; black biting evil creations that crawl on your face, down your neck etc. Hard to concentrate on shooting.

Here are the results: (All shot at 50 meters) (Five shots per powder)

Trail Boss
A complete wash. The group was a vertical ladder that spanned 4 inches.
Low: 1555 High: 1646 Avg: 1609 SD: 38
At 96% fill I think the deep seated bullet was slightly compressing the powder. TB doesn't like to be compressed. Velocity was under the 1712 predicted by QuickLoad.


IMR 4227
Group was 1.25" with 4 shots at 0.875
Low: 1875 High: 1906 Avg: 1896 SD: 13.4
Surprised by this load. Velocity was under the 2058 predicted by QuickLoad

HV100
Group of 4 was right at 1". The 5th POI was 5.5 inches up and 2.5 inches right. Either something went wrong (check fall off maybe?) or I simply aimed at the wrong bull. There are 7 bulls on each target and with the flies buzzing around my head I may have been distracted.
Low: 2135 High: 2179 Avg. 2151 SD 17.8
This powder has potential and gave the best velocity. Velocity was over the 2091 predicted by Quickload.

H4350
Group 1.5" with 4 at 1".
Low:1916 High: 1967 Avg: 1943 SD: 20
A bit disappointed by this powder. It may improve with a heavier charge. Velocity was significantly less than the 2111 predicted by QuickLoad.

No leading evident anywhere so I am happy. Going to work on the three powders a bit more.