leade angle

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b moulds

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i have just calculated the correct leade angle for the 180 gn berger 7mm bullet using the method described by james boatright.
the minimum angle (at which the ogive touches the lands at groove diam) i get is 5.165 degrees per side, and the ideal angle as described by james (at which the ogive touches the leade at groove diam) is 5.7 degrees per side.
this seems very steep to me, and as a non mathematician, i can only presume i got it wrong.
has anyone with any skill calculated these angles, and would they be prepared to share the answer?
thanks,
bruce.
 
Just my opinion but don't believe everything you read. There's a lot more involved in throat angles than what may theoretically be ideal for centering up the bullet in the bore. Boatright has some interesting and valid ideas, theories and writings, but I have never felt he was 100% on with all that he espouses. Some of the throat angles that you get when you "run the numbers" are way more than are typically used and found to be in the norm of what is workable.

Query:

What the steep angle does for pressures? It elevates them.

Does the steep angle stresss the whole projectile more as it forces it to deform more quickly as it passes through the lands? I bet it does.

Have you taken one step forward in one place but maybe 1 or 2 backwards by using a steep throat angle? I think that may be the case.


Robert Whitley
 
Steep

To tell you the truth ,the only way you will really know is to have the reamer made.We have and find no minuses and so far i think the barrel life is extended but it is to early to prove ..Still over 3000 competitive 1000yd Benchrest cartridges later with a 80 gn powder charge is not to be sneezed at, about the last time this barrel was shot it recorded 2 back to back 7 inch 10 shoters at 1K..JR..Jeff Rogers
 
I've been using a custom .223 chamber with a 4 deg per side leade for the last year. Accuracy was the same as a 1.5 deg leade, as was the throat erosion rate. My loads worked as always, with no change in velocity and no signs of elevated pressure. The sole advantage I've found is that the bullet engagement is "cleaner" as the throat erodes; the shallower leade would feel "sticky" when using a Stoney Point gauge to check seating length, holding the bullet quite firmly. With the 4 degree leade, the bullet releases easily and the seating depth is more definite (less deviation between measurements). I suspect that the accurate barrel life will be somewhat longer, but I won't know until I fire another thousand rounds or so.
 
Bruce,

Listen to the guys who've done it not the guys who dispute one theory with another. I've had otherwise similar reamers ground to several different leade angle and have found ZERO pressure correlation.

Just My EXPERIENCE

al
 
alinwa said:
Bruce,

. . . . I've had otherwise similar reamers ground to several different leade angle and have found ZERO pressure correlation.

al
Click to expand...

Interesting - my experience has been exactly the opposite - the steeper the throat angle, the greater the initial pressures. This has been especially so with smaller cartridges I have worked with. Now maybe a big 7mm to shoot the 180 Bergers has enough capacity to buffer things a bit more so the issue does not present so prominently.

Robert Whitley
 
thanks all for the input. allthese things are food for thought, & must be considered.
has anyone done the sums for the berger 7mm vld. i really need to check my numbers with those generated by someone who's mathamatical ability can be trusted.
perhaps an interesting approach might be to grind a reamer for the berger 168, & experiment with regrinding it, reducing the angle several times, and then grind it for the 180 berger at the best angle.
bruce.
 
rcw3 said:
Interesting - my experience has been exactly the opposite - the steeper the throat angle, the greater the initial pressures. This has been especially so with smaller cartridges I have worked with. Now maybe a big 7mm to shoot the 180 Bergers has enough capacity to buffer things a bit more so the issue does not present so prominently.

Robert Whitley
Click to expand...


Ok, so let me backpedal a little :D I came on a little strong yet unclear. AND, I'm no engineer nor do I have testing equipment. I'm an experimenter.

Robert if you've actually measured this or recorded it with a strain gauge mounted to an oscilloscope then I'll agree that instrumentally there may be differences noted BUT........ these same minuscule changes my be had with small adjustments in seating depth. When comparing ogive grinds the only way I've got to "equalize this" is to seat such that hand pressure against the bolt handle is "similar" between loads. Doing it this way I find no measurable velocity changes, from your original post I assumed that you meant "significant changes", changes which would equate to velocity changes or to dangerous pressure excursions.....

6BR, 5 reamers all with different leade angles, no velocity differences to be noted from one to the other. I have thirties ground one with a 1.5* and another with a fitted compound angle designed to actually cradle or conform to the ogive. I'll be testing these soon.

al
 
bruce

My suggestion is speak to the reamer makers on the idea of running a steep shoulder angle like Boatright theorized was ideal for centering the bullet in the bore (yes, it is a theory). Many of the reamer makers know about this whole situation very well.

Since Boatright published his articles, many shooters tried what he suggested, and most of the reamer makers will tell you that many of the guys who ordered those reamers and chambered up rifles with those steep throat angles were back later having the reamers re-ground with a milder throat angle and/or buying milder throat angle throaters and/or setting back and rechambering their barrels (many expressing that they "spun their wheels" trying out the steep throat angle theory).


Robert Whitley
 
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I seem to recall Boatwright's name in PS long time ago, but don't recall the articles in question. Please identify the month and year or other identity of the articles on this subject. Thanks.
 
hello 10ring
the date of part 2 of boarright's article is october 2006.
the biggest problem i had was estimating how much to add on to the nose length where truncation occurs due to the meplat. i estimated 0.080.
bruce.
 
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