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Range Report - 10.15x61R Cape Gun
Old 03-23-2015, 07:43 PM
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gitano gitano is offline
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Default Range Report - 10.15x61R Cape Gun

I started the workup on the Cape Gun today. I'm pleased with these initial results.

First, the "issues".

1) It's an obsolete cartridge. Dies are "custom".
2) No brass.
3) Bore is 0.400", groove is 0.406". No bullets or molds in those dimensions.
4) No load data except from sources that I don't particularly trust. QuickLOAD is "off" for cases like these - big and cylindrical.

1) CH4D had dies IN STOCK. Got them very quickly. They work very well!
2) Can make the brass from .348 Win with nothing more involved than fire-forming.
3) Squoze .427 Hornady 205-grain "Cowboy" lead bullets down through .424 and .410 Lee sizing dies. Final diameter 0.409+".
4) Made a stab in the dark with QL and 'adjusted' powder characteristics per QL's author to get real QL estimates to match actual results.

I fire-formed 6 cases using the process I usually use: 15 grains of Bullseye and Cream of Wheat to the mouth and a plug of toilet paper on top.

As most here at THL know, I don't like to "beat" guns up, especially old guns like this one. There are two primary ways to beat guns up, and they are related. Most people 'worry' about max pressure, but that's not the whole story. Most guns, even old ones, can 'handle' more pressure than most people understand and WAY more than the Chicken Little "experts" assert. However, attendant to pressure is "recoil". The kinetic energy (ft-lbs) the bullet has as it exits the muzzle defines the force being exerted to "pull" (or push) the gun apart, "beating it up." That energy is "pushing back" on the breech while at the same time trying to shoot the barrel 'off'. So while this firearm could easily handle 35 kPSI, I decided to set the ceiling at a muzzle energy of 2500 ft-lbs.

I can reach that figure with the 205-grain Cowboy bullet using I-3031 and only generate 21,877 PSI MAX pressure while still getting 2345 f/s from that bullet. Those are great numbers as far as I'm concerned. And the firearm is "fun" to shoot.

Turns out, when one gets away from the typical "modern" case - .30-06 Gov't, .300 Win Mag, etc. - QL starts to get 'off'. Estimates of parameters for small cartridges like the Hornet are a problem, and large cases like the .50 Alaskan or this 10.15x61R Jarmann are too. However, the author of QL is aware of these anomalies and has figured out the appropriate adjustments that need to be made to the powder parameters to get good estimates of pressure and MV given a specific charge.

In this case, I started with a charge of 62.2 grains of I3031. According to QL, that should have generated a MV of 2345 f/s with a max pressure of about 28000 PSI. HOWEVER, the MVs were; 2794, 2766, 2836, for an average of 2799 f/s. That was the OPPOSITE way it was "supposed" to move. Nonetheless, armed with that data, I could make the appropriate adjustment and try again.

After adjusting the Ratio of Specific Heats, QL estimated that a charge of 52.4 grains of I-3031 would give me the desired 2345 f/s and 2500 ft-lbs of muzzle energy. The actual MVs were; 2454, 2477, 2396, for an average of 2442. About 100 f/s faster than I'm after, but still 'good'.

After much finagling (adjusting Ratio of Specific Heats), I was able to come up with an Accurate 2495 load of 55.2 grains. That produced the following MVs; 2568, 2430, 2457, for an average of 2485 f/s. Again 'high', but still 'good'.

It wasn't difficult to get the MagnetoSpeed attached to the Cape gun:

(I love that thing! Thanks again, drinksgin!)

I wasn't interested in "target" shooting because I was going to be 'all over the place' with loads, but I did want to see if I could hit anything, so I set up a 'target' (an old poster of my daughter that she threw out). I fired all shots at 30 meters and off-hand, and the MagnetoSpeed strap was covering the front post, so these aren't too bad.

This is the first shot from the gun:

Here are the three last shots.

I shot a half-gallon plastic milk jug filled with frozen water. It was VERY impressive! Blew the jug at least 15' into the air and blew a big chunk of 'dirt' from the frozen ground. This is a thumper, for sure.

I am working on getting an NOE mold (www.noebulletmolds.com) of the right dimensions and about 350 grains. I'm not holding my breath on that one.

When I shoot this at 100 yd, I'll post another range report for 'accuracy'.

Then you will know the truth, and the truth will set you free. John 8:32

"We make men without chests and expect of them virtue and enterprise. We laugh at honor and are shocked to find traitors in our midst. We castrate and bid the geldings be fruitful." ~ C.S. Lewis.

Do not confuse technical skill for wisdom and do not confuse strength for skill. Paul Skvorc

Last edited by gitano; 03-24-2015 at 01:06 AM..
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10.15x61r, cape gun, hammer gun, jarmann, magnetospeed, range report

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