Cape gun queastion

[Leatherman]

OK Diz, here is a diagram of what I got with measurements .
http://i828.photobucket.com/albums/z.../image_18.jpeg

OK I see now why the seller sold me this gun. I have loaded Springfield 45/70 loads of 5744 and 3031 powder and even loaded a black powder load and am having the neck expanding out so far as to not allow extraction of the cases by hand. The bullet matches the bore and all measurements seem to be within tolerances so I am putting it out there for anyone to comment what could possibly be going on. I have reduced the loads to where I am below 1000 fps on my chrony and am still not able to extract the case. My thinking is that it may be a pressure spike caused by the absence of a forcing cone in the chamber. See my picture of the chamber casting. I have never seen a chamber like this and I went back and looked at all my chamber castings I have saved and all of them have a gradual tapering into the rifling . This one just goes from the neck measurement to abrupt squared rifling. If that is it I can have a reamer made to take care of that but I dont want to spend the money if that isn't the problem. This rifle could never have shot as far as I am concerned and that is why it is in such pristine condition.

[mike ford]

Leatherman,
As the King of Siam said "is a puzzlement". I suggest you sacrifice one of your cases and shorten it to 50-52mm, and load it. Then smoke it, or color it up with a magic marker, and fire it in the rifle. It is said the British changed from 3 1/4" case to 3" in their 450-400( when changing to nitro powder) because of extraction problems. Since your case length was in question, this may be your problem. After firing, the smoke/magic marker should tell you precisely where the interference is, if it still doesn't extract. If it was intended for a shorter case, years of use may have resulted in some gas cutting/corrosion at the original case neck area, resulting in something similar to a bulge in the chamber with the longer cases. If this is the problem, the chamber may have been polished. Also, since cerrosafe shrinks, before it expands this could have hidden the problem. I am anxious to hear the results.
Mike

[Diz]

Leatherman,
Thanks for the drawing but I am at somewhat of a loss right now on what this is. The abrupt transition from neck to barrel is very strange. Stranger still is that there is zero taper from the very slight shoulder to the end of the chamber. At first glance I thought that the chamber to bore difference was excessive but from your drawing I could deduce that the case wall is .010” thick and that leaves .023” for expansion. This is quite a bit but not too bad if you think of it as a little over .011” a side. Still it’s going to be hard on brass.

It is the sharp lead that concerns me and the zero taper in the chamber. My guess is you are seeing a pressure spike due to the bullet movement being checked buy this sharp edge and possibly a reflected pressure wave compounding the chamber pressure due to it. Sometimes ADDING powder will take care of this as the bullet is accelerated to a higher rate before it is checked and drives right past the restriction. This becomes scary territory without any gauging to see what is actually happening.

If it is a pressure spike, then the lack of taper makes the case very difficult to remove because there is no clearance after any initial extraction and there is a lot of case neck to pull clear. I am speculating here and most of this involves unknowns. I am not afraid to admit that I am stumped at the moment. Mike's comments are all good possibilities.

Thanks, Diz

[Leatherman]

Way ahead of you Mike. I already shortened the brass to 53 mm about 3/16" so the end of the brass came to the shoulder of the bullet while still having about 1/16" of free bore space ahead of the rifling. I used a magic marker on the brass and on my hotter loads the entire neck from the slight shoulder forward had expanded tight against the chamber. Below is a picture showing the scrapping marks. On my lighter loads the area where the bullet was seated showed scrape marks. All of the loads could not be pulled and had to be driven out with a rod. The end of the case neck shows a crimp like curve which might be a sign of something. I did not crimp the case neck. Maybe I should shorten the case length more to allow the bullet to be seated deeper so it has more time to accelerate before it hits the rifling as Diz suggests. There is plenty of neck length on this cartridge. I still think the lack of a forceing cone and the way the bullet has to abruptly hit the square edges of the rifle lands can only cause a preasure problem. I will seat the bullet another 1/8" deeper and try that tomorrow. image.jpg

[Diz]

Leatherman,

Even more of a puzzle after looking at the cartridge but if it were me I believe I would shorten the case enough to place the bullet base at or very near the slight shoulder. This is a lot of trim but I think it will get the case out of the area where it seems to be making the most contact and give the bullet a good deal of free bore to start. I am still looking for something that matches up but haven't had much luck.

Thanks, Diz

[Leatherman]

Problem solved. I looked into the chamber with a flash light and saw the throat /neck area was pretty corroded so I got a 3/8" dowel and wrapped it with some 400 grit sticky back sand paper, put it in a drill and polished it out. I trimmed a case another 1/4" shorter and loaded with 43 grains of 3031 which is a starting load for Springfield 45-70. Wha-La case extracted perfectly. So now my total case length is 48 mm. So thanks to Mike and Diz I have a shooting gun finally. I am going to load up some more test loads to see how high I can go before any case sticking happens. Hopefully I can get it up to 1500 fps with the 335 grain bullet.

[mike ford]

Leatherman,
Please don't depend on traditional pressure signs, such as flattened primers, etc. to determine when to back off the load. By the time these signs appear, the pressures will likely be way too high for your gun. This is only one man's opinion, based on an abundance of caution. The bullet weight was determined, because heavier bullets wouldn't stabilize. If it will shoot to the sights, at less velocity than the target, I suggest stopping there. You have a fine rifle, it would be a shame if it were strained.
Mike

[Leatherman]

Yes I agree, I am going by the velocity of the loads and I figure it should have similar velocities and pressure as the 45/70 as it has similar case capacity. The lyman reloading book has 45-70 springfield low pressure loads using a 330 grain #2 alloy cast bullet which is as close as I am going to get for a comparison. I am stopping at 1500 fps if I get there before the max suggested load for the 45/70. I have loaded 43 grains and 46.5 grains of 3031 and will shoot it this week end over my chronograph . I already shot one out the garage door and the case came right out. I hit a white milk carton at 50 yards offhand so thats encouraging too. Quite a kick too. Light guns and heavy calibers You got to love it.

[sharps4590]

Maybe I'm oversimplifying this but it seems if the case neck is expanding that much it is too long. Who can answer for the chamber dimensions? I had a similar situation with the Outschar staking rifle and once I trimmed the cases back it was fine.....and exceedingly accurate. There is/was/has been/will be some strange "goin's on" with these old rifles.

[Diz]

Bravo! Sounds like it wants to work. A word of caution to add to what Mike and Sharps have to say. I failed to mention earlier that decreasing case capacity by trimming and moving the bullet in will increase pressure and sometimes quite a bit with the same charge. Also velocity is not the best indicator of pressure. I am going to try and run a couple of trials on my QL program with your altered case to see what it looks like.

I think you're free to name it what you wish as I think this is pretty much a wildcat cartridge now. The "476 Leatherman" has a nice ring to it.

Thanks, Diz

[sharps4590]

So I was late to the party again.... Sorry Leatherman, I didn't see the previous post where you got it working. Good deal!!!!!

[Diz]

Leatherman,

I made a few assumptions and ran the numbers on Quick Load. The closest I could find for a bullet was the Lee .476" x 325 grain #C476-325 RF which I think is a very good match. I assumed (guessed) a .400" seating depth. The case length is 1.890" based on what you said and OAL with this bullet and seat depth is 2.213". Case capacity on my model may be a bit MORE than actual because I cannot set the shoulder back without doing a LOT of work. I also used a 24" barrel length. So all that being said here is what the computer came up with:

43 grains - IMR-3031
66.6% Fill
1344 FPS
8580 PSI
57.87% Burn
16.4% Eff

46.5 grains - IMR-3031
72.0% Fill
1460 FPS
10079 PSI
63.32% Burn
17.8% Eff


I ran this in IMR-4064 just to see:

45 grains - IMR-4064
69.0% Fill
1348 FPS
9210 PSI
54.42% Burn
15.7% Eff

47 grains - IMR-4064
72.0% Fill
1410 FPS
10190 PSI
56.79% Burn
16.5% Eff

These numbers are all CALCULATED of course and don't correlate to any actual data so use it with caution as your results may vary especially since actual case capacity couldn't be computed.

However, hitting a milk carton at 50 yards is not bad at all for a first try and I am certainly interested in seeing more of this project. Good luck.

Thanks, Diz

[Leatherman]

Loaded two loads to try useing 3031. I used the minimum starting load of 43 grains and the max load of 46 . I recorded an average velocity of 1445 fps with 43 grains and 1630 fps useing 46 grains. A little higher than Diz's calculation. This cape gun likes the hotter load. I shot a 1 1/2" group at 50 yards with the fairly heavy front sight and with the sun on my right side. But dead nuts centered in the ten ring. The lighter load was closer to 3" and was 1" lower. I liked the recoil of the lighter load though! Now I want to reload some Balistic Products Dangerous Game 16 gauge slugs and see if they print any closer to the rifle. It is shooting 3" low and 4" to the right with Brenneke slugs. Does any one have experience trying to regulate a side by side cape gun? I would think it would be similar to a double rifle. If that is so, then I would have to speed up the slug or lighten the weight of the slug to bring it to the right. Maybe hollow point a brenneke to reduce the weight? I don't know about pushing it faster as I don't know what the preasures are on factory loads but I got the manual on reloading shotgun slugs from Balistic Products and they have reloading figures for one ounce Dangerous Game slugs that run 1200 to 1600 fps that stay under 11000 psi. It will be another interesting project.

[Leatherman]

Correction on the Brenneke group. It shot 4" to the left not right.

[mike ford]

To get a slug load to "regulate" would be unusual, these guns were made to use shot on a regular basis. If a slug were used, It would likely be as "back up" to the rifle, much closer than 50 yds; at which distance, the Brennekes will be OK. I would be a little uncomfortable with regular use of the 1630 fps load, I would be surprised if the original load was much, if any, faster than the 1445 fps load.
Mike