History question - 10.75x57

[Diz]

Mike,

I have been wondering about that double rifle and the closest thing I can find is a 10.75 x 65 Collath with a head diameter of .486" and rim .543". But the bullet is wrong and I think the Collath was a proprietary cartridge and not very popular. Everything with an 11 mm bullet seems to big at the base. Any further thoughts or info about it? I'm trying to get these metric cartridges sorted out.

Thanks, Diz

[mike ford]

Diz,
I thought about that, but the 65mm case length doesn't fit. The difference in head diameter could come from him using paraffin for the chamber cast, rather than cerrosafe. The proof house marked it 10.4/60. I don't know who marked the nominal caliber of 10.75x60 R.
Mike

[Axel E]

Mike, I amconfused about the barrel dimensions and markings too. According to former posts the rifle is nitro proofed for a sevice load with a 17 gramm = 262 gr St.m.G = steel jacket bullet. You report the groove diameter as .432" = 10.97 mm. The proofhouse marked the land diameter as 10.4 mm, so it was at best 10.5 mm = .413". This results in unusually deep grooves for a barrel proofed for a smokeless load and steel jacketed bullets, made 1912 or later. But 10.4 would be quite correct for a 10.75 barrel. Is it possible the owner took the groove diameter from a paraffin cast? Such a soft cast may have been slugged up slightly on pushing it out.
The base diameter you measured , .484" = 12.3 mm, does not fit any known European cartridge. It is too large for the LK series, the 7x65R, 9.3x74R = 11.9 mm, or the 7x57R = 12.05 mm, or 8x57IRS = 11.95 mm. And it is too small for the next larger older bases, the 7.62x54R = 12.37 mm, 8x56R Mannlicher M30S = 12.5 mm. The new .30R Blaser = 12.2 mm may be the best fit, but that case did not exist when that Stiegele rifle was made.
Well, 12.48 mm = .491" is the maximum base diameter of the Gruendig cartridges as it is taken from books and tables. But someone on nitroexpress forum apparently measured an original Gruendig 10.75x60RG cartridge. He gives the base diameter as 12.3 mm. This would barely fit your numbers.

[Diz]

Mike & Axel,

I am constantly amazed by the variability of cartridge dimensions and especially bore diameters in these older guns. That and the reference books don’t always agree either. When questions like this come up I like to see what I can find for myself but I am a relative newcomer to these guns and it has not been easy. I for one appreciate the extra information that you provide.

Thanks, Diz

[mike ford]

Axel,
It's pretty obvious that I am badly confused. The groove diameter was measured by the owner, having slugged both barrels using .457 " cast bullets, which was pretty tough to do. They wouldn't likely have slugged up, and they were consistent with each other. There was one odd thing about the bore diameter marks. The 4 in the 10.4, for both barrels had been "overstruck", but neither of us could make out what had been the original mark. The stamp seemed to be from the same set, so was likely done at the proof house. The nominal caliber was obviously stamped using a different set of number stamps. We presumed it was done after the proof marks, but now I wonder. What if it came to the proofhouse with the nominal caliber marked, and the bore diameter stamped some number larger than 10.4. I would think it highly unusual, but possible that they "overstamped" it to match what it should have been for a 10.75. As far as the base diameter is concerned, I don't have as much confidence in it, since he used paraffin instead of cerrosafe. I didn't see the chamber cast because he dropped it and it broke. In anycase, I don't like paraffin because even if it didn't shrink on cooling, it is too easy to "squash" it with the micrometer. He did make a drawing before dropping it. The other odd thing was the chamber having no leade, which would require a bullet similar to the "express" type bullet. This would allow the nose portion to fit into the rifling, with a larger shank fitting into the case. A weight of 17 grams might fit such a bullet, whereas a normal bullet would be heavier. I was looking for a .330" bullet for an entirely different question, and ran across some 7.62x54R blanks with a bullet formed from the case. This brass would be long enough and close enough to the right diameter that simply turning the head would get it small enough to fit. Then it would be a matter of adjusting the rim to fit. He can make the 9.3x74 cases work. I believe someone makes 265 grain jacketed bullets for the 444. Maybe they can be swaged into an "express" type bullet to fit, even if it requires two steps to do it, in fact, it may only need sizing the neck portion to fit into the bore, even if the base is a thousandth under size. As the King of Siam said in the movie-" it's a puzzlement".
Diz'
We find these kinds of differences all the time, due to some dimensions coming from cartridges and some coming from chamber casts. This doesn't even consider different manufacturers. Check the base diameter of a 6.5x55 European loaded case against an American one.
Mike

[cordite]

Hi, new member here who also has a 10.75x57. I've posted about mine on the nitro express forum. Enjoy shooting it with cast bullets and have used 30-06 brass though I now prefer 9.3x62 brass.

[mart]

cordite,

Welcome. We'll have to compare notes once I get mine up and running. My friend is going to a huge gun show in Florida today and looking for a set of dies for me. We have a big show next weekend in Wasilla and I'll check there as well. If he or I do not find any dies I'll order a set from CH4D. I've seen your post on Nitro and enjoyed the write up.

I have a really nice LBT mold for a 300 grain 44 caliber WLNGC that I can resize for this rifle. It'll be interesting to to see how it does with a 300 grain bullet rather than the standard 347 grain. I'm thinking hard about having Mountain Molds cut me a 345-350 grain mold for it as well. I hadn't thought about using 9.3x62 brass but then I have a bucket full of 30-06 brass. I also have a couple hundred 375 Whelen on some LC Match brass that I would only need to anneal and trim to reform to 10.75x57.

[mike ford]

I just had a discussion with my friend about his fireforming of 9.3x74R cases for his double rifle. He was unable to fireform these cases enough to be satisfactory. This led him to recheck the head diameter he measured from his paraffin chamber cast. His recheck confirmed that his former measurement was in error. He fabricated and fireformed a case from a 45-90. This confirmed that his chamber is, indeed, 10.75x60 Grundig, as opined by Axel and others. He now agrees, with me, that while a paraffin chamber cast might be useful to show the general shape of a cartridge, you cannot depend on one for making precise measurements. He did express interest in my idea of trying cases from PRVI 7.62x54R blank ammo, which would be long enough to make 60 mm cases.
Mike

[Nathaniel Myers]

Mike, let me check, I think I have some x54 blanks he could experiment on. Probably berdan primed? Send me a PM.or email.

[mike ford]

Nate,
He has ordered some for himself, and some for me to try in my 5.6x61R vom Hofe SE. They might be berdan primer , but the other PRVI cases I have are boxer. I can handle berdan primers, but don't know about my buddy. I could stake hin to a few primers, I guess. BTW, he is back to his cartridge being smaller than the Grundig head size.
Mike