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Swiss M-78 Load Development and Results

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KneverKnew
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Swiss M-78 Load Development and Results

#1 Post by KneverKnew » Mon Apr 29, 2019 1:41 pm

This will be about my load developments in my Swiss M-78. I will post more range reports as they happen.

4/29/2019 First Firing.
I couldn’t wait to make it to the range so went out on my river deck and fired several rounds past the LabRadar.
I just shot into the white powder sand down the river bank from the house at about 50 yards. Was Definitely hitting high as expected. Everything was loaded single shot since I can’t crimp just yet.

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Powder - 2400, 16.5 grains
Bullet - 320 grain cast .430
OAL - 2.200”
Lebel cases formed in Lee 41 Swiss dies. Fireformed.
CCI 350 primers
Case lengths vary. 44mm and 40mm
V= 1054 FPS (subsonic!)

Obviously lots of room to increase load.
I plan to pull the rest of these loads and up the charge.

My fired brass had two things of interest I want to point out and get opinions on. First, the shoulders have a noticeable bulge that is larger in diameter than the case body. I assume this is caused by too low a charge not obdurating the entire case.
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Second, my firing pin seems to be puncturing the primer. I believe this can be remedied by me polishing the tip to a more roundish profile. I don’t think the pin protrudes too much though.
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Re: Swiss M-78 Load Development and Results

#2 Post by KneverKnew » Mon Apr 29, 2019 6:31 pm

I upped the load a bit, to 17.2 grains of 2400.
Same everything else.
Velocity was 1115 fps.

I also polished up the firing pin and tried to round it more. I checked protrusion and it’s .050”. This time I only had two of the five primers puncture. Any ideas? I’m thinking I may need to reduce the firing pin protrusion to .045 or .040”. Ideas?
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And yes, my firing pin is off center. The drill bit walked a bit.

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Re: Swiss M-78 Load Development and Results

#3 Post by KneverKnew » Tue Apr 30, 2019 12:55 pm

I did more work on my firing pin. Shortened it from .045 to about .029” and polished it nice and round as best I could. You can see where my pin hole is off center in both the bolt and the Teflon “pin carrier.” I have an extra carrier and may drill it with a smaller drill bit just slightly larger than the pin and stay on the side of the bolt hole closest to the center. That should bring the firing pin strike away from the edge a bit. For now I will see how this adjustment works. If it ignites reliably I will leave as is.
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Re: Swiss M-78 Load Development and Results

#4 Post by KneverKnew » Tue Apr 30, 2019 1:05 pm

Can someone recommend an IMR 4198 load for my current supply of 320 grain bullets? I see mention of 22 to 25 grains 4198 with a 310 grain bullets. And one mention of a 22 grain load of 4198 with 335 grain cast bullet doing 1350 FPS. Any thoughts what a safe start load would be?
I’m thinking 20.5 or 21.

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Re: Swiss M-78 Load Development and Results

#5 Post by DaleH » Tue Apr 30, 2019 3:40 pm

No idea on the 4198 load, but on the SMLE Enfields, rimmed case, I put 1 thin dental/braces elastic at/above the rim for the 1st firing, to keep the rim up against the bolt, or breech block in your case. Fireforms the case to the chamber, then I neck-size only.

I do not know/own a Vetterli .. but could a similar approach work for you?

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Re: Swiss M-78 Load Development and Results

#6 Post by KneverKnew » Wed May 01, 2019 1:09 pm

Todays test results:

I tried 22 gr IMR 4198. Same 320 gr hard cast bullet at 2.2” fired single shot at 100 yards. Group hit about 2’ high and 6” left. What’s best way to adjust windage?
Average V= 1185 FPS. Discounting flyer the group was about 4”, but I was getting some leading and my cases were not all the same length. Not sure why leading is occurring at such a slow velocity and with a lubed, hard cast bullet (.430”). No I haven’t slugged my Bore yet.
This will be a mystery to solve later.

But to end on a good note, it looks like my primer piercing problem (say that ten time fast!) has been resolved.
Image

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Re: Swiss M-78 Load Development and Results

#7 Post by KneverKnew » Sat May 11, 2019 8:31 am

I tried 20 grains of 2400 the other day. I tried three shots at 100 yards. Average V= 1352 FPS.
I’m noticing a trend for a first shot flyer on a cold clean barrel, with subsequent shots being much closer together. Including first round flyer, the group for three shots was 3-3/4”. The last two shots measured 1-3/4”. As is typical, with rear sight at lowest 225 meter setting the group was about 24” high, and about 4” to the left. Still wondering if rear sight can be drifted in its dovetail???

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Re: Swiss M-78 Load Development and Results

#8 Post by KneverKnew » Wed May 15, 2019 11:50 am

I retested my 20 grain load of 2400 powder at my local 100 yard range. I loaded three extra to shoot first as fowlers. After the fowlers, I waited a few minutes for barrel to cool and to get my LabRadar set up and organize my junk. I then loaded the five rounds in the tube magazine and got busy. I checked after the first shot to see where it landed. Sure enough it was about 24” high near the top of the target sheet, which is why I had set my black bullseye at the bottom of the board for my aiming point. I fired the remaining four, recorded my velocity data and went down to check the results. I was quite pleasantly surprised.
Discounting the first round flyer, the group size was 1-1/4”!!
Average V= 1324fps with 20 gr of 2400.
9D71B740-5643-4733-A46F-337048CC0CD0.jpeg
Big target
6CBDB747-4583-47A6-B8FD-B70422E7E576.jpeg
Group
EEE3FE85-7AF7-4469-AD6B-BD09E3A7A825.jpeg
M78
You can see my group is still hitting left of center. I did drift my rear sight to the right a bit which did move the POI a bit but obviously it needs a little more adjustment.

After letting the Vetterli cool down while shooting my M96 Swede, I shot another group using 21 grains of 2400. This time the group opened up quite a bit. There was the expected first round flyer low and right, but the remaining four shots spread out to about 3-3/4”. The average V=1358 FPS. Pressure signs looked fine, so will try slowly increasing to see if group closes up any before reaching max. I don’t plan on going much higher, hoping to reach the original swish ammo’s 1425 FPS or so. But if group doesn’t close up I will be quite happy to leave it at 20 grains 2400.

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