Design question

[Wayne Smith]

When designing a mold on the Mountian Molds site do I want to design to my groove size + or design oversize and plan to size it down .002? I've got a .4145 groove diameter, thinking of a .415 diameter bullet on the site. Do I want to increase this to .416 and get Buckshot to make me a .415 sizer die?

[felix]

Wayne, you have to be very careful here. Groove size does not mean anything here, not really. If you are talking a lever gun, or any gun when shooting from the magazine, you have to know what is the maximum size boolit diameter you can get into the chamber from the magazine with the desired cycling rate. Then tell the Mountain Molds program that is the diameter of the boolit, and choose the +002 tolerance. ... felix

[Wayne Smith]

Felix

This is for the combination gun, essentially a single shot. No magazine, no problems with crimp groove, and being shot with PB or 777. Gotta find a mold for the 16 ga rb, as well.

[felix]

No problem, Wayne, you are in good shape then to fit the largest boolit that can be chambered in YOUR cases into the gun MINUS .002 for case expansion when fired. Whatever that diameter is, is what you enter into Dan's program, still with +002 tolerance. ... felix

[Wayne Smith]

Couple of things.

I have a diameter immediately in front of the cartridge of .419" with a groove of .4145" and a bore of .403".

Something has been bothering me about this chamber cast since I made it weeks ago, and it just clicked this AM. The throat is inconsistent. That is, the rifling starts on one side of the cast just a few thousands from the case mouth and on the other side I have .30 of throat. This means that the chamber is off a couple hundred thousands in concentricity to the bore.

Since I am planning to use nothing harder than air cooled ww I don't think this represents a problem. How does this inform my front band length?

Right now I've got two different designs, both 265 gr Tangential Ogive with no crimp groove. Both are .415" in ww. Both have front band bottom at .415 and top at .414. One has front band length at .130 and the other at .100. The first has a nose length of .500, while the second has a nose length of .430. The first has a meplat of 70%, the second at 68%. The first calls for a throat length of .258, the second for a throat length of .148.

I'm guessing I want a short front band given this situation, am I right? Of course, this can be adjusted by seating depth as well. Nose length/front band length ratio is important here, right?

Do I want to go with a nose riding design?

[Bass Ackward]

I'm guessing I want a short front band given this situation, am I right? Of course, this can be adjusted by seating depth as well. Nose length/front band length ratio is important here, right?

Do I want to go with a nose riding design?


Wayne,

Wosh. What an interesting situation.

You can either go with a nose rider if your OAL is not limited or you can go with a Trunicated cone design where the front band starts at the meplat and tapers up to .416 or so right at the crimp groove. How long the nose is going to be is dictated by your OAL, if you have one.

Either way, your bullet is going to look .... pretty unconventional if you design it correctly. But I wouldn't go by looks, I'd go by function. That's just me. I have an ugly 225 grain 44 that Dan thought wouldn't fly straight if the target was placed touching the end of the barrel. I hide the ammunition when people come around so they don't see it. But the holes it puts in paper look just the same.

The issue as far as I see it is to minimize bullet jump and have alignment begin with the bore and not touch the cone until you need it to slow down and improve ignition. That means that the nose must hit first and have enough strength to turn it. Or stated another way, the front band has to be weak enough not to impact until enough of the nose is inside to turn it. However you prefer.

On the other hand, the cone could be fairly straight and just oblonged if somebody went in with a throat reamer to clean it up by hand and wasn't careful. Is this a lever?

[Wayne Smith]

BA

This is a combination gun, one barrel 16ga x 2.5" with no choke and the other barrel is probably 10.5x47R. This is chamber I'm writing about. CH4D has my chamber cast and I'm expecting a response from them this week or next. This gun was made prior to April 1, 1892 because it has no proof marks and the proof law in Stettin, Germany came into effect then. It was made in Stettin, probably in the 1880's.

Before I make any changes to the gun I'll try it like it is. I doubt anyone has a throat reamer this size anyway. It would have to be custom made, this is not a common size. Historically there are at least 10 different chambers known for 10.5x47R! Not easy getting a reamer in this contry. Germany, maybe.

I'm looking to design a bullet that will do well in this chamber and throat without changes at this time.

[45 2.1]

When you get the mold made, perhaps you can make it a nose pour and have Buckshot put a hollow base pin on it to help expand the bullet into the rifleing and reduce the bullet weight if needed.

[Bass Ackward]

BA

This is a combination gun, one barrel 16ga x 2.5" with no choke and the other barrel is probably 10.5x47R. This is chamber I'm writing about. CH4D has my chamber cast and I'm expecting a response from them this week or next. This gun was made prior to April 1, 1892 because it has no proof marks and the proof law in Stettin, Germany came into effect then. It was made in Stettin, probably in the 1880's.

Before I make any changes to the gun I'll try it like it is. I doubt anyone has a throat reamer this size anyway. It would have to be custom made, this is not a common size. Historically there are at least 10 different chambers known for 10.5x47R! Not easy getting a reamer in this contry. Germany, maybe.

I'm looking to design a bullet that will do well in this chamber and throat without changes at this time.


Wayne,

I was not suggesting a throat reamer. Only offering it as a possible explanation of your current throat.

Because of the age, I figure there has been some wear that would minimise any misalignment. How is the wood on that piece?

I wouldn't go for a bore ride on that piece if you didn't have too. Might run into fitting issues if you keep it too close. You aren't going to horse it I doubt, so a narrow band would be fine. You can even put a taper on the front band if you are concerned. I didn't see where you mentioned throat length measurements anywhere other than your current designs. So when you get it, just stay under that point by a margin to ensure seating. Your idea is sound.

Bob had a good idea for low pressure apps. Then as Felix suggested I would go big to what will chamber for the rest of your length. This way you don't need much expansion anyway. Large diameters of up to +.003 seldom seem to raise pressures more than 2000 psi in anything else I ever ran. Obviously, the faster the powder speed and harder the bullet. Your cartridge isn't listed in Quickload or I would offer to run your number for ya. To get an idea.

[Wayne Smith]

Aye, age and cartridge limitations is why I am asking about 777 on another thread. I will load this with Black or equivalent, and with this small a case I want as much power as I can get, thus the question about 777. I'm guessing my options are 777, Swiss, and the new Goex. I've not used any of them, just the straight Goex.

So the consesus, so far, is that I can go as large as .416 without problem? It will certainly chamber in that throat, and with a tapered front band to ease it's entrance it may not be a bad idea.

Throat length is somewhat of a question, being constantly changing as it does. At what point do I measure? None of the designs I'm playing with impinge into the throat enough to prevent chambering, or at least I hope not.

What's the consensus on designing oversized like this and then sizing down to fit vs. designing to fit? I know Buckshot will cut me a sizing die any size I want.