6.3X48R cape gun

[mike ford]

Thanks Diz.
Mike

[Diz]

Alright, I made a mess of this the first time and here are the numbers the right way:

117 grain bullet / 23 grains Viht N-140 = 2450 bar (35530 psi) and 2234 fps

117 grain bullet / 22 grains Viht N-140 = 2130 bar ( 31470 psi) and 2144 fps

110 grain bullet / 23 grains Viht N-140 = 2270 bar ( 32914 psi) and 2250 fps

My apologies as I had too many notes on my desk when i was doing this. Note the difference a single grain makes. Thanks, Diz

[Axel E]

I doubt the basic data on the 6.5x48R underliing the Quickload calculations. Where did the Quickload designers get the basic data on bullet diameters, barrel dimensions and pressures? The cartridge appears in no half way modern proof table. Max pressures were fixed in 1939 only, five years after the cartridge was declared obsolete. Before, the gunmaker who sent a gun to the proofhouse had to specify the service load the gun was to be prooofed for. Ql apparently calculated pressures using 6,7 mm = .264" and 6.58 mm = .259" max, and barrels of the different modern dimensions for such bullets.Only this explains the different expansion ratios appearing in the Ql calculations. If te same case is used with the same barrel, merely with different bullet diaameters, the expansion ratio remains the same. But according to 1920s literature the bullets loaded in the 6.5x48R were the same old German "6.5" of 6.64 mm = .261" diameter. In the 1920s barrels were often made undersized by todai's standards. Such is apparently the barrel of the drilling discussed here. The proofmarks give the land diameter as 6.3 mm. As the grooves of German smokeless rifle barels are usually .1 mm deep, the groove diameter of that barrel must be 6.5 to 6.6 mm = .256 to .260", a bit tight even for the old .261" bullets. I have encountered this situations more than once with barrels chambered for the 6,5x58R and 6.5x70R cartridges. Such undersized barrels were ok with the proofhouses before 1940: If the thing passed firing the proofload without damage, it was accepted. They usually shoot .257 bullets quite good.
Mike, the gun here is a Blitzlock drilling. I have still to see such a drilling with the rifle barrel firing pin mounted on the hammer like a hound's tooth. This would make assembly nearly impossible.
No, you can not reliabley convert pressure units like bar, at, cup, psi or tons per square inch by pocket calculator and fixed conversion factors. "Measuring" peak pressures inside a gun barrel is not real measuring like that done with a caliper or micrometer. It's still more an educated guess, the readout depending on exact apparatus and protocol. The readout even differs markedly from modern SAAMI to CIP methods, both using the most modern piezoelectric transducers. All guessing is based on a piston moved by the pressure, applying pressure in turn to an pessure sensitive object, be it a transducer or a deformable copper cylinder. Then the reaction of the object is compared to it's reaction under a static load. You try to calculate the short time peak pressure inside the gun by using the area of the piston involved. But everything is influenced by the mass/inertia of the parts that have to be moved by the pressure and the exact position of the piston in relation to the cartridge. As SAAMI calculates all dimensions in inches and pounds and lets pressure blow a hole intothe brass case, while european CIP uses metric units and bores a hole opposite the piston, pressure readouts often differ by a substantial margin. So American ammo that is to be imported to Europe has to be rechecked by an European proofhouse using CIP procedures, while European ammo has to be rechecked by a SAAMI approved institute.

[mike ford]

Axel,
The gun is a BF, does that make a difference as to whether a blitz action with "hound's tooth" firing pins are possible? The reason that even came to mind is because my ca. 1911 Sauer BF in 9.3x72R Sauer blew a primer with 9.3x74R ammo and I had to have it converted. That exercise made me leery of that type firing pin for rifle calibers. If the BF has a "gas tight bushed firing pin", there is no reason the gun would not hold the same pressure as generated by any other 360 based cartridge it was available for. I'm guessing the same gun was available for 6.5x58R and it should hold those pressures. Commercial ammo in Germany was limited to pressure established IAW the proof law, but handloaded ammo, here, is not so limited. What do you think?
Mike

[Diz]

Axel,

I have to differ with you on two points. First, the areas of the two groove diameters differ and so does the swept volume in the barrel as the bullet moves along and so the expansion ratio differs because of that. Calculated bullet travel for a 24 inch barrel in this chambering is 22.553" adjusted for each bullet. The volume of the .257 barrel is 1.15239 cubic inches and the .264 is 1.216012 cubic inches. This doesn't seem like much but it has an effect on the burning rate and pressure curve. Even given the same case volume it is the expansion of the volume within the barrel that makes a difference. The actual volume of the case between the 257 and 264 differs by my own calculation of about one grain of water due to the taper changing slightly. On the second point, you can correlate pressure values between the various measurement values. Denton Bromwell wrote a very interesting paper describing the correlation between ANSI CUP and ANSI PSI pressure measurements. I have my own method for doing the same from back in the Powley Calculator days. Piezo and the newer strain gauge measurements can be calibrated very accurately and the resolution can be down to hundred thousandths of a second with a fast computer. Back while I was working, I observed the running of a trial on a high pressure extruder using a standard pressure transducer of that time and was able to resolve pressure differences of several pounds at one ten thousandth of a second and that was ancient technology compared to today. A modest Pressure Trace system can measure pressures quite accurately above 10K psi and with one millisecond resolution. If the engineers at QL got this bullet diameter wrong than they are still batting 99.9%

Thanks, Diz

[Tom H.]

Has the chamber been cast? That should clarify if the rifle was a 25 or 26 caliber. I have a 9.3x72r that easily chambers modern factory ammunition but the barrel slugs at .358. It shoots far better with the correctly sized bullet even with the oversized neck made for the larger diameter.
Tom

[Axel E]

Mike, sorry, I erred on the drilling /cape gun question. I looked at Leatherman's photos again. In his last, scope mount, photo you can see the small set trigger adjustment screw. So the gun was built as a Büchsflinte = cape gun for use with smokeless, jacketed bullet cartridges. Not a set of barrels fitted into a shotgun action as an afterthought. This pretty much rules out a hound's tooth firing pin.
Diz, no question, modern equipment has little inertia and high resolution compared to the old crusher systems . But there is still the problem of protocol. Pressures differ widely if taken at different places of the chamber. CIP and SAAMI both have strict rules where exactly the pessure is bled off from the cartridge case, but these rules differ. You may find the current CIP specifications here http://www.cip-bobp.org/homologation/de/tdcc_public
The Ql calculations impute using .264" bullets from .264" pressure test dimension barrels and .257" bullets from .257" barrels. That is not the problem here. We are talking about shooting .257" or .261" bullets from the same barrel. That barrel has a groove diameter of .257" (Leatherman's first post, I tend to believe that) to .260" ( maximum calculated from the proof marks). Shooting fitting or even slghtly undersized .257 bullets from that barrel will not rise pressures, but lower them, compared to the original .261" bullets. So I would try .257" 117 gr rn bullet first, loaded with about 22 gr VV N140.

[Diz]

Axel, I completely agree about the difficulty of placing the instrument properly in the chamber to get a standardized reading. I think the best unit I have seen is one that fits in the face of the breech and measures back-thrust. it eliminates the problems of different case lengths. However, that technique is subject, as all of these measurements are, to how the operator sets up the trial. I can calculate in QL a 257 bullet through a 264 barrel and vise-versa and it gives warning that there is a miss match. You can continue the process and the pressures derived are higher or lower than normal based on the combination but as far as accurate calculations go I have never tried to verify the numbers. Interior ballistics have been a passion for fifty years and I am still learning. Thanks, Diz

[mike ford]

It looks like you guys are going to make me get some of that "new fangled" N140, instead of the "old school" powders I normally use. I don't see anything wrong with trying the 117gr RN bullet, but I am still anxious to see how the new 110 gr Flextip bullet works out. Also, Nosler makes a 100 gr .257" Partition bullet, if there is any question of sufficient penetration. In my experience, using Partition bullets in small case cartridges steps up performance. This was true with 60gr .224" Partition in my 5.6x50R and 85gr .243" Partition in my wildcat 6x40( a shortened/improved .222). The partition bullet made these varmint rifles into Whitetail rifles and would likely do so with the 6.5x48R.
Mike

[Leatherman]

Holy Moly! This cartridge and rifle has really opened a can of worms. Great conversation and a lot to absorb. I have N140 powder as well as some of my favorites like 3031, 5744, 4895, 4227 , 4350 and Trailboss. I have only tried the N-140 in some of my 9.3X72R drillings but got better accuracy using 3031 and 5744 using jacketed bullets. I got the two Hornady bullets in and the 117 grain is longer than the 110 grain by .100". The 110 grain is a boat tail and the 117 is a flat base. Both are Spitzer design. I may get a box of the 100 grain Nolsler Partition if I am not happy with the accuracy of these Hornady's. I have been impressed with the wound damage I have seen using the Hornady FTX and SST bullets out of 270 and 6.5X55 both 130 grain bullets going 2900 and 2600 fps respectively. This was on Mule Deer and Pronghorn. Full penetration through the rib cage and massive wound Chanel and exit. Hornady advertises the FTX bullets in the 25 caliber to be designed for the slower velocity cartridge, so my thinking at 2100 to 2200 fps. it should expand as quick as the faster calibers . Im looking for exactly that as I try to take the best ethical shot I can so the rib cage of our deer is only about 12" to 15"wide. I want as much expansion without fragmentation out of a bullet and I believe these new bullet designs will deliver if you pick the proper bullet for the caliber and what game your going after. For example I met some guys at the airport going in to a hunt in South Africa last year. We compared what calibers and Bullets we all were going to use. Most of us had bonded premier bullets or Barnes TSX as there were some larger animals on the menu. One guy in the group had Hornady's SST in a 30 06. We met them again going out and found out the guy using the SST bullets had a terrible experience with the performance of the bullet on his larger game. (wildebeest, Gemsbuc, Zebra) Mostly lack of penetration and fragmentation and he spent more time chasing wounded animals. His PH told him to use a better bullet next time. I shot three Roebuck sized antelope with my 6.5X57R 129 grain doing 2400 fps using Swift Scirocco and the exit wound was very small yet still quite effective on such small animals. I too had some larger deer sized game animals on my menu but never got a shot with my rifle. When going after 600 pound and up animals I switched to my 9X57R 220 grain Swift A-frame and it performed fantastic. Again matching the caliber and bullet to the size game. Now this 6.5X48R having been called light for Roe Deer back in the day by some confuses me. The older bullets must not have expanded well. Any caliber shooting 2200 fps with todays designs of bullets Like the FTX in weights over 100 grains should be plenty for Whitetail given a broadside heart/ lung shot. I dont need a caliber that is going to pick up and slam the deer to the ground or a bullet that will penetrate a deer lengthwise. So I will start out with the 22 grains of VV N140 and the 117 grain bullet. On paper at least. I have a big Doe in my front yard every day but my wife and the game warden wont let me shoot her. Yet

[mike ford]

I guess now it's to the loading bench and chronograph to see how it works out.
Mike