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Attempting to clone GP11 in my K31

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KneverKnew
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Attempting to clone GP11 in my K31

#1 Post by KneverKnew » Sat Aug 25, 2018 9:45 am

Trying my hand at working up clone loads of the GP11 ammo which shoots so well in my rifles.
Please advize if I’m starting in the right place or if I should adjust or try something different.
Using Resized GP11 brass and Tula KV-762N Berdan Primers and several powders I have on hand. Bullets seated .004” off lands. Cases full length sized with shoulders set to same length from base as GP11, 1.777”.

1. SMK 168 , IMR 4064 - 40.5gr , TTL 2.179” , OAL 2.268”

2. SMK 168 , IMR 4895 - 40gr , TTL 2.179” , OAL 2.268”

3. SMK 168 , Varget - 42gr , TTL 2.179” , OAL 2.268”

My Sierra book doesn’t list 7.5 Swiss so I had to use Hornady book values and dillagent research. Still, I’d like a second opinion before I try these at the range. Thanks.

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Re: Attempting to clone GP11 in my K31

#2 Post by professrh » Sat Aug 25, 2018 11:08 pm

You might want to check out this thread: https://www.tapatalk.com/groups/theswis ... ate#p25722

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Re: Attempting to clone GP11 in my K31

#3 Post by slowbob2 » Sun Aug 26, 2018 11:09 am

First K-31's are not .308 rifles they are .306 . If your barrel has any wear on it , it will shoot regular .308 bullets fine . If it is a very tight replacement barrel you will get better results with a .308 VLD type bullet . The 168 SMK is a very good bullet for loose bores , it will out shoot GP-11 . 40.5 grains of I-4064 is a little light , 44.5 will get your velocity up to GP-11 standards . Varget acts a lot like I-4064 . I-4895 is a little fast for the heavier bullets and will pressure up quicker , more so with a tighter bore . With GP-11 cases I like them to be trimmed to 2.176 < . Fired GP-11 cases will be too long with some .308 bullets an jam the neck , even though they will clear with .306 bullets . I have had real good accuracy with the 135 SMK and tight bore rifles , so you are not limited to heavy bullets .

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Re: Attempting to clone GP11 in my K31

#4 Post by ammolab » Sun Aug 26, 2018 6:42 pm

The Nosler 175gr RDF .308" bullet is a good candidate for your GP11 clone work up. It has a slender ogive which allows seating further out than many bullets. Shotersproshop.com sometimes has "over-runs" for around 20cents/ea. A great price for match bullets there.

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Re: Attempting to clone GP11 in my K31

#5 Post by Smokey » Mon Aug 27, 2018 7:36 pm

I believe Swiss GP11 used the equivalent of Reloader 17 for propellant. While it sort of falls in the burning rate range of H4350, IMR4350 and WW760, it has a different pressure curve. The peak pressure is a little lower and the curve is flatter.
Arguing with someone who denounces reason is like administering medicine to a corpse.

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Re: Attempting to clone GP11 in my K31

#6 Post by KneverKnew » Tue Aug 28, 2018 4:30 pm

ammolab wrote:
Sun Aug 26, 2018 6:42 pm
The Nosler 175gr RDF .308" bullet is a good candidate for your GP11 clone work up. It has a slender ogive which allows seating further out than many bullets. Shotersproshop.com sometimes has "over-runs" for around 20cents/ea. A great price for match bullets there.
All I see currently are the Nosler 168 grain bullets

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Re: Attempting to clone GP11 in my K31

#7 Post by ammolab » Wed Aug 29, 2018 12:49 am

KneverKnew wrote:
Tue Aug 28, 2018 4:30 pm
ammolab wrote:
Sun Aug 26, 2018 6:42 pm
The Nosler 175gr RDF .308" bullet is a good candidate for your GP11 clone work up. It has a slender ogive which allows seating further out than many bullets. Shotersproshop.com sometimes has "over-runs" for around 20cents/ea. A great price for match bullets there.
All I see currently are the Nosler 168 grain bullets
They will be available discounted only when blemished or over-run stock is available. The online retailers will have them at "retail" prices if you want to buy a hundred or so to see if they are worth waiting for.

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Re: Attempting to clone GP11 in my K31

#8 Post by KneverKnew » Wed Aug 29, 2018 7:15 am

I may do that. Thanks.

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Re: Attempting to clone GP11 in my K31

#9 Post by KneverKnew » Sat Sep 01, 2018 8:59 am

I ended up pulling the 34 rounds that I loaded for my K31. I’m going to do some OCW increment testing with Varget and IMR 4064. Those loads take me to one increment past Max listed load in the Sierra load book for their 168 grain SMK‘s . If all works out and there are no pressure signs I will continue in increments of .1 grains towards the 44 grains of IMR 4064 that everyone seems to like.

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Re: Attempting to clone GP11 in my K31

#10 Post by ammolab » Sat Sep 01, 2018 1:25 pm

Understand that all the milsurp rounds and rifles developed around 1900 have maximum operating pressures (45-50,000psi) that are WAY below what you have when you see "pressure signs" (60,000+ psi).

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Re: Attempting to clone GP11 in my K31

#11 Post by slowbob2 » Sat Sep 01, 2018 8:18 pm

Going up by .1 of a grain is a waste of time . You will get more variance from the case , neck tension , barrel heat and so on .

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Re: Attempting to clone GP11 in my K31

#12 Post by KneverKnew » Sat Sep 01, 2018 9:57 pm

So if not .1 grain increment then what you suggest?

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Re: Attempting to clone GP11 in my K31

#13 Post by slowbob2 » Sun Sep 02, 2018 8:47 am

Most US loading manual information is way on the light side for military rifles . As the other guy said , the K-31 is good for more . Militaries did not load to a certain rifle's max , they just wanted a certain level of performance and ammo that could be used in all of their rifle models in use at the time . Even though the load I gave you has been used for years and 1000's of rounds at our shooting club , you should start lighter and work your way up . A .5 increase of I-4064 is small enough not to get you in any trouble and will go five times as quick for testing .

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Re: Attempting to clone GP11 in my K31

#14 Post by KneverKnew » Sun Sep 02, 2018 2:14 pm

That sounds good
To me. I appreciate the advice. I usually use a .5 grain increment when doing my typical ladder load
Workup. I just want sure with the OCW method as it’s a new thing to me.

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Re: Attempting to clone GP11 in my K31

#15 Post by KneverKnew » Sun Sep 02, 2018 2:22 pm

One other question. My Sierra book doesn’t list any load data for varget using the 168 SMK’s. My reading says that I
Can use IMR 4064 data since they are so close. That is what I am doing and think I’m safe since I’m starting low with both powders, reducing from max by 7% for start load. Does this sound about right?

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