Boolit nose-throat relationship question

[Ed K]

Let's say you're wanting to design a bullet to fit a particulat throat. You have a design drawing of the throat, a chamber cast or both. The leade works out to be 1 degree. Here's the question: At what point along a tangent ogive will the nose contact the rifling of the leade? This question kinda boggles my mind :veryconfu Gotta believe it is at differing points for other nose profiles. Seems as knowing this reference point would be all-important for boolit base/neck relationship among other things.

Thanks, Ed

[Cherokee]

Too much math for me.:coffee:

[45 2.1]

Let's say you're wanting to design a bullet to fit a particulat throat. You have a design drawing of the throat, a chamber cast or both. The leade works out to be 1 degree. Here's the question: At what point along a tangent ogive will the nose contact the rifling of the leade? This question kinda boggles my mind :veryconfu Gotta believe it is at differing points for other nose profiles. Seems as knowing this reference point would be all-important for boolit base/neck relationship among other things.

Thanks, Ed

AutoCad, an electronic drawing program, lets you draw to more accuracy than you can measure to and lets you design to any configuration you can think of. All you have to determine is where you want everything and the clearance tolerances involved. Tangent ogives are not always the best thing to use and do not contact the leade or rifling for any distance. More than one contact point is involved also.

[fourarmed]

One option would be to design either boolit or throat profile so that the point of contact is as far forward as possible in order to better align the boolit with the bore. On the other hand, making the point of contact as far to the rear as possible would reduce the lever arm between the force of friction and the force of the powder gases, which would reduce any rotational or bending effect. My gut feeling is that the former makes more sense at low pressures, and maybe high pressures too. I have always heard that Loverin boolits do best at high speeds, and they are full diameter almost to the nose.

[BABore]

One of the first molds I had Mountain Molds cut me was for my 338 WM. I worked from a chamber cast and slugs to model up the chamber, case, throat, and bore/groove on AutoCAD. The boolit was designed to fit and fill all of these critical area and still work in Dan's (very limited) design program and machining techniques. The final casted boolit did indeed fit my gun well. Problem was it was fussy getting it to shoot well. I'm talking below an inch. It did pretty good in my buddy's 338, but had to be seated much deeper. To remedy this I machines a die to taper the front band in my RCBS press. Worked great. I tried some of these modified bullets in my gun and had to seat them out with a LG exposed to engrave. But did they shoot. Cut already good groups in half.

Bottom line, its sometimes a good idea to run a tapered front band and bore ride area to closely follow the whole throat, rather than just look for point contact. You will notice that several of 45 2.1's designs have a tapered front end. He didn't get it from me, rather me from him.

Best to view the concept of good bullet fit as pounding a dowel into a press fit hole. You stand up a dowel in the hole and try to keep it straight. Now hit it with big hammer. If all things are exactly perfect it may go straight in. With out any rear support, (i.e. loose chamber at the case neck) the hammer may cant it to one side. Single point contact, up front, will allow the rear to go where it wants. Now picture a taper dowel standing up in a taper reamed hole. Even with a little run in, odds are in your favor for it to go straight.

[leftiye]

What BaBore said, plus a little freebore. It all helps to keep the boolit from canting when the pressure hits. I've been thinking about a freebore long enough for the whole boolit followed by a case topped by a wax cookie to hold the powder in.

[Bass Ackward]

In order to survive the pressure wave produced by expanding gas, you need at least two points of support. The wider these points are, the stronger the bullet will be. In essence, allowing softer mixes to be used at the same pressure levels, or pushing higher pressures and velocities.

Remember, a tangent olgive design will have a radius based upon how long the nose length and meplat width are. So actual contact location will depend on the final design.

Tangents excel for increasing case volume by maximising weight outside the case. But a matching taper or a secant, both with the proper meplat sizes to maintain the angle, can increase the contact area strengthening the design better than a tangent.

[Ed K]

Well, the reason my question sounds a little hypothetical is because yes indeed, I am playing around with Dan's design calculator. Between that and searching threads here I'm trying to educate myself a little on bullet design. Too bad the do's, dont's and rules of thumb aren't all in one spot but that's OK. I'm getting pretty good with the search tools :)

The nose doesn't have to be a tangent ogive. A secant could work just as well for the purpose of the original question: still a mind boggler. I like the comment on simply using a little trial and error fitting using a CAD tool. I know I have a lot to learn on nose types, front bands and such too so thanks for all the input.

Ed

[45 2.1]

Well, the reason my question sounds a little hypothetical is because yes indeed, I am playing around with Dan's design calculator. Between that and searching threads here I'm trying to educate myself a little on bullet design. Too bad the do's, dont's and rules of thumb aren't all in one spot but that's OK. I'm getting pretty good with the search tools :)

The nose doesn't have to be a tangent ogive. A secant could work just as well for the purpose of the original question: still a mind boggler. I like the comment on simply using a little trial and error fitting using a CAD tool. I know I have a lot to learn on nose types, front bands and such too so thanks for all the input.

Ed

MM online design is extremely limited in what it will do. Whether you use a secant or tangent curve is irrelevant since you are trying to fit the throat which will dictate what arrangement you use.

[Ed K]

MM online design is extremely limited in what it will do.

Oh yes I realize this: MM design is not what I was hearing as the "CAD" tool to fit up throats.

[montana_charlie]

I've been thinking about a freebore long enough for the whole boolit followed by a case topped by a wax cookie to hold the powder in.
That's called "breech seated" ammunition. The bullet doesn't have to be laying in a 'freebore', either. Usually, it's (pretty much) 'fully engraved' in the rifled bore before the case is loaded behind it.
CM