doublegunshop.com - home Forums General Discussion German & Austrian Sporting Guns @ doublegunshop.com 9.3x72? Chamber cast shows convex walls?

My recently acquired no name hammer drilling was listed as a 9.3 x72 at so yesterday good friend Tom Hall and I tried to slip a new Sellier and Belloit cartridge in and it stopped with about 3/8" to go. I put some black marker on the cartridge, pushed it in until it stopped and then rotated the cartridge in the chamber and it showed a ring about 1-3/4 up from the rim, this is where it's binding.

I slugged the bore and it's .366. The S&B bullets are also .366 but COTW show the 9.3x72R as using .376 bullets.

I then made a chamber cast and the chamber is .430 at the base diameter, the S&B ammo is .424, COTW shows .427 and another dimensional drawing I found shows .422.

The neck diam. of the chamber casting is .386 (this was kind of hard to see on the casting, what I did was take the case length from COTW, 2.84, and measured up from the bottom of the rim, marked it and then measured). COTW says it should be .385, the S&B cartridge is .382 and the dimensional drawing says .390.

So all my chamber dimensions are larger than the S&B cartridge except at that tight spot where the S&B is .495 but the chamber is .492.

Tom tells me he remembers reading something about older guns not being chambered with perfectly straight walls but rather had a slight convex curve to them. The base and neck diameters are the same but are not connected by a straight line.

I held a straight edge up against the chamber casting from the top of the rim up about 1-1/2"(I used a straight edge razor blade with the edge blacked out) and sure enough the wall is curved, I can see light through the gap. The straight edge touches at both ends but is a few .001's shy in the center.

So I have a few possibilities.

• I have a 9.3x72R with a proprietary chambering from years ago that has curved walls, will running a finishing reamer clean this up?
  
  
• I thought there was a possibility it's a 9.3x70R but that's hard to determine as the only difference between the two is case length (.009) which is very hard to tell on the casting, and neck diameter (.386) which is right between the two COTW standards, .385 for the 72R and .387 for the .387R.
  
  

All thought and opinions welcome as I would like to get this hammer gun shooting.

first, forget COTW when it comes to old German cartridges! It is incomplete and inaccurate.
There was not only one 9.3x72R case, but at least five! The 9.3x72 Sauer & Sohn is easily dismissed, as it is of bottleneck shape, essentially a sligtly shorter 9.3x74R. Then there was the 9.3x72R D = Deutsche = German shape. This had a rapid taper from the base for about 1" and then was straight to the mouth. Apparently you have a D chamber. Next we had the 9.3x72R E = English. this one had a very slightly smaller base diameter than the D, but a straight taper to the mouth. Then the rare 9.3x72R Nimrod with a shape similar the E, but a smaller rim. About 1905 the German gun and ammo companies agreed to create the fifth, the 9.3x72R N = Normalised, designed so that all the older chambers could be easily rechambered to the new standard design. Of course, all "modern" post-WW2 loads by both RWS and S&B are of the Normalized type. Normalized cartridges usually do not enter tight D chambers for the same reason you describe.
To add to the confusion, there also were 9.3 x70R D and E shapes, a 9.3x75R Nimrod with a slightly larger base, and then three 9.3x82Rs again!

Thanks for the lesson Kuduae. I forgot to mention that the cut for the rim on my gun seem is only .040 deep, thinner than the rim on the S&B cartridge (.047)and the dimensional drawing I found shows .051. COTW doen't list a rim thickness

Can I cleanup this chamber and deepen the rim cut by running a 9.3x72R N reamer into it?


thanks,

Rob

Yes, this is what the N was designed for!Ask Mike Ford through the German Gun Collectors Association forum www.germanguns.com

Kuduae,

I have a message in to Mike but have not heard back yet. I started looking around at reamers for sale or rent. Is it safe to assume that a modern 9.3x72R reamer is going to be for the Normalised chamber?



thanks,

Rob

Don't touch those chambers! Find or size brass to fit the chambers that were machined in the gun originally. If you need some help in doing that let me know. I hate to see a beautiful gun messed up by somebody reworking it unless you absolutely have to. I have quite an assortment of brass as well quite a few original boxes of vintage factory ammo & I will bet that the orignal old Norma that came in the 10 rnd boxes with the red label will fit your existing chambers. Where are you located? I just came out of the shop making up some 13mm brass for a H Scherping double rifle from the 1860's. Started out with some 24 ga brass shot shells & cut them down to 1.450 long, then formed them, then turned the diameters to fit the chambers. They are similar to a .577 Snider but a bit shorter & a .550 bullet dia.

m-4

Am I going to find a set of dies to fit those old chambers? And how am I going to know what make of brass will fit? Any brass made for these chambers is going to be close to 100 years old if the chambering was standardized in 1905.

I'm in NY State on the CT border.

Hi Rob,
Once you discover what your original chamber was cut to fit, you can have Dave at CH4D build you Dies to fit it as well as find original vintage cartridges to go with it properly if you wish. Once you cut the chambers it is no longer original nor will it ever be again. There is no turning back, if this is not a expensive gun or has no historic value & your not worried about resale value and it is just planned to be a shooter and access to factory ammmo is necessary then opening the chambers might be the way to go for you. I understand your concerns, I used to think the same way until I thought about the history of the fine old guns and the fact that they have existed for around 100 years without the chambers being messed with. Then the satisfaction that comes with mating correct ammo together with an old gun that may have been years since it was shot last & making the correct ammo to fit the gun is half the fun! Your Call, just some food for thought.

m-4

I'm with m-4. As with classic sports cars, they're only original once. You will no doubt have a little more invested in the firearm but it will be "right" and not altered. There's even a little "gloatability" that comes with it!

Hello all.
I am still going to stick with what Rob and I looked at which is that the lower part of the case below the very long neck is concave. I remember reading somewhere that this was something that was not uncommon. I think that I actually saw diagrams from older German cartridge lists that showed this as well. Regardless, I could be imagining all of it.
M-4, agreed that the cost of a reamer (and changing the rifle) is about the same as having dies cut to match the chamber. It is easy enough to thin the rims on the lathe as well.
But as Kuduae said, many of those rifles were normalized while still in Europe, so who knows how many aren't in original condition.
Kuduae, were there nitro versions of the older chamberings? This one is nitro proofed.
Last, whose proofmark is a crown over a B?

Tom