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Hello Jani

With the load mark of powder charge over bullet type the gun was built before 1912. My take on this is that the 248 has nothing to do with the chambering of the rifle barrel. Perhaps the proof house was practicing their binary coding??? <grin>

After some calculation, "248" IS the plug gauge pre-rifling diameter for 7mm. I didn't think to run the numbers until I noted that "Crown" over "N" beside "2,3g G.BP.(Gewehr Blattchenpulver) over "St.m.G." is the pre-1912 mark of smokeless proof of a jacketed bullet thru a rifled tube. Around 1910 plug gauge marks were exchanged for a truncated mm stamp and from this I saw there was a need for a pre-rifling diameter. If "248" was a proof date, it would also have the odd DDR mark. I learned something today and hopefully everyday.

Kind Regards,

Raimey
rse

The rifle bbl on my Miller & Val Greiss 9.3x72R is stamped as follows;
Eagle with crown over G beside it
Eagle
Crown over U
8,8mm/72 (/ =Solid line, showing 8.8mm bore dia atop case length of 72mm)
6,13 (June 1913)
240 (my understanding of this is it would have been the 240th gun proofed in June)

These marks are all between the forend lug & the hinge lug, & are read with breech to you & muzzle pointing away, each on seperate line. Turning muzle to left & rotating toward you, reading left to right just below joint with left shot bbl is
Crown over N followed by K.m.G/12,7gr for the nitro proof of a copper jacketed bullet weighing 12.7 grams (approx 196 grains), no powder charge given.
I can simply see no way the 248 relates to bore dia on a 7MM.

1st plug 181 into your plug gauge equation which is for 7.7X57R or .303 British. Then plug 248 in and it should approach a 0.26"-0.27" value which with about 0.01"+/- with rifling is going to approach 0.28?" Check the values as I may have miscalcuated but I'm doing it on a consistant basis.

Yours just by the marks, and not the date, is a post 1912 which checks with your 6,13.
Kind Regards,

Raimey
rse

Raimey;
You made your post while I was writing mine. Let me see if I am following you. When you say that ("248" IS the plug gauge diameter for 7mm) are you here referencing the older gauge system. If so then 248ga would translate to .266". This would make sense, but all references I have to this system only go down to .300" caliber & are in .010" increments with the gauges carried out to 2 decimal places. My 8x58R (1907) is marked 172.28 (.300") with the actual bore falling between that & 156.14 (.310").
Do you have references for other caliber markings used of smaller dia than 30 claiber, as several existed prior to the switch over in marking?

Well we were typing at the same time again, but do seem to be on the same page. 181 calculates to .295", but I also note many of these German sporting guns seem to have deeper grooves (smaller bore dia) than standard military guns, for some reason. Perhaps they were intended for use with bullets having thinner or softer jackets.

2-piper:

I was of course referring to the plug gauge pre-1910 German, old English method of identifying the diameter by the number of lead spheres of the same diameter which when their mass is summed together would equal 1 lb. The plug gauge equation has a Y = X^3 type dependence. I now see that a plot of the plug gauge equation might be beneficial. I've seen many pics of flats with "181" for 0.303" British and the lowest plug gauge number I've seen in print is "184,11" for "7,5 or 7,6 mm". Jani's drilling is the lowest number caliber and highest plug gauge number I've seen. Now I'm not saying they equate just that the plug gauge designation/pre-rifled value is found for a specific caliber. I'm going to calcuate the values down to 6mm, or maybe lower, and see if there are other integer values. I don't think bullet technology regarding jackets was too advanced and the jacket was thin and possibly soft.

Kind Regards,

Raimey
rse

Raimy;
A long time ago one cold winter afternoon I decided it would be more interesting than watching the idiot tube & I sat down with a programable calculator & played with the gauge vs dia chart from the Britisf proof house, which went down to the 172.28ga @ .300". I also have an early German chart which gives the same figures. I found that for every gauge to "Round" to the nearest 3 decimal place found on the chart it was necessary to carry the 1 ga to 6 places. Going to 5 places 1.66928 is too small & 1.66929 is too large. 1.669285 if cubed, divided by the gauge number then the cube root taken (your formula) will round to the 3 place dimension of every gauge on the chart from 1 to 172.28. Any other gauge can of course be determined by the same formula, which is how I derived at .295" for 181 & .266" for 248. I now have a calculator with 1.669285^3 (4.65148337) stored in memory on the desk by my computer. All I now have to do is pick it up & turn it on, hit MR, divide by a gauge # & take the 3√ & have the dia. To find the gauge of a given Dia I simply hit MR & ÷ D^3.
If you just take any one dia off the chart some others may be in error by as much as a "Whole .001") due to rounding error. Big deal I know, but it was more fun than watching some stupid TV show.

Wellll, it certainly is possible that whoever stamped that 248 intended it to be a gauge mark, but it wasn't an "official" proof law standard to do so. The gauge marks from .300" to .450" in .010" increments were established by the 1868 British proof law which Germany included in their first proof law of 1891. There's a table of 'em here at the bottom of the page. Gauge marks other than these within that diameter range would not be likely from the proof house.

A bore of 248 gauge, at .266-.267", seems pretty tight for a 7mm with a nominal .284" groove diameter, but those German gunsmiths did lean toward tight barrels.

2-piper, cube roots to six places really does beat TV!!

2-piper:

Yeah, but we get too technical with the values of pi, the mass of lead and the string of sig-figs . Without a doubt they were doing it long-hand and I'm sure rounded, which is difficult to determine to where or what they rounded. Therefore, somewhere there was a published chart that the proofhouses were using. Your mention of thin jackets and say the plug gauge value 181 for 7.7X57R or 0.303" British leads me to believe that below .30 cal they may have gone to 1/2 of the 0.01" interval which would be .005". That's about the only way the "181" stamp as well as the "248" and "468" for something akin to the 5.6 Vom Hofe; a stamp I haven't seen yet. As the calibres become smaller, the gauge heads toward infinity, quickly. For anyone interested who has been following this exercise in mathematics, somewhere around 0.261" the plug gauge equals 261.

Steven:

So when & where did the "181" for 0.303" originate, as well as the "184,11" for a 0.295"? All the "181" stamps I've seen were under the "Crown" over "U" as described on the drilling.

Kind Regards,

Raimey
rse