tapering bullets

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  • Last Post 30 October 2008
cityboy posted this 11 February 2008

My experience indicates that how the bullet fits the throat/leade when the round is chambered is a major variable in the accuracy equation. There have been many comments made about the relation of the bullet diameter to the throat diameter. But I have seen very little about about the profile of the rest of the bullet in relation to the tapered section of the bore.

To my mind, the bullet should be tapered to match the throat, and the forward part of the bullet should at least just “kiss” the top of the lands. Achieving this

is not easy. I have a number of Eagan dies for use in a Lyman 450 sizer. It is a trial-and-error procedure, and it has taken me a lot of trial and errors and I am still not there.

What are your thoughts on the subject, and if you fit your bullets, how do you do it?

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CB posted this 11 February 2008

cityboy,

You are right and of course are talking about bore-ride CBs. The front square drive-band is 'old school' for competition accuracy, or should I say a National record goal. I mapped out my Egan taper die with a micrometer and honed out the tight spots to match the throat. Time consuming, but works.

A better way is to make your own on a lathe. Use the same chamber reamer or throating reamer used in the rifle to ream the taper die. Don't get too involved in micro-measuring to find fit. Fit can be found by feel. Push the bullet into the throat and tap in lightly. Knock it out and inspect under a lighted magnifying glass for the correct engraving and smears. This is what I've found anyway..>................Dan

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billwnr posted this 12 February 2008

Dan,  I like your suggestion of tapping a bullet into the throat to see how much contact there is. 

I'm using a bump die to mate my bullets to the chamber.  Lately I've been wondering how much of my throat is shot out.  I can check by tapping a bumped bullet into it and seeing where the contact is (or isn't).

Anyways.. my answer is I use a bump die to ensure full contact.

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CB posted this 12 February 2008

Hi Bill :coonskin:

Yup, that's another way if yer cb is smaller in diameter, to bump it up. The taper die was a fast fix for me since I never made a bump-press, but I have to lap out my moulds where they are small. You can't taper down what ain't there. :wnk: It shouldn't take much of a tap in (about .010'-.015"), since the fit should be what Ed Doonan called 'stop' when pushed in. 'Stop' should always occur at the back-side of the angle and base, not the nose on a bore-ride cb...................Dan

:}

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CB posted this 12 February 2008

I like Bill bump all of my bullets. Have one gun that is 1 degree and 2 that are 3/4 degree throats..

The bump process certainly removes the diameter variance from your bullets and makes em all fit in the throat nice and tight.

I was talking to Lester Bruno the other day about throats and bump presses, One of his better accuracy tricks even with jacket bullets is to cut the throat to allow the bullet to enter the rifling on a smoother less abrupt angle. He was out at the range here in Phoenix testing barrels and exactly what I described above... He had the whole back of his van full of barrels and was changing and headspacing them at the range. Sure was interesting to watch.

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cityboy posted this 12 February 2008

Dan

I contacted Donald Eagan about using my throating reamer to make a taper die. He told me it was not possible to use a throater to make a die. I have no idea why. Can anyone shed some light on this?

cityboy

 

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CB posted this 12 February 2008

I don't know?  It works for me.

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cityboy posted this 12 February 2008

I have another question. Does anyone know where I can get a taper die made for my Lyman sizer using my reamer?

Cityboy

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CB posted this 12 February 2008

What you need to find is a machinist in your area.. If you have the throating reamer, take him that and a sizing die and explain what you want..

Other than that, I would if I had a lathe, but I dont....Yet... Get ahold of Mistro_Jerry here on this forum, he has machining equipment and he may be inclined to do it for you, ask him..

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afish4570 posted this 29 October 2008

New to this bullet bumping business......What is needed to bump a 358 bullet to 360 or a 311 to 314??? I have the usual presses, 450 Lyman etc. afish4570:dude::dude:

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CB posted this 30 October 2008

To fatten up a bullet that much you need a dedicated bump press and a die made from a throating reamer.

I advise against trying to get a bullet to bump up that far, it will cause too many problems.

You need a mold closer to the size you need. .001 would be as far as I would try bumping up.

What is meant by the term bump is actually to remove the bump left in the base of a gas check caused by the sprue bump left after smacking the sprue to break it.

I have 2 dedicated bump or taper presses for my competition bullets, each cost roughly $350.00 dollars to make. You need a rock chucker press and a machinist willing to make the die.

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CB posted this 30 October 2008

I don't bump bullets but I do taper them to match the throat I cut. I used to use 7/8 x 14 threaded rod for my dies but bought a bunch of die blanks from Dave Kiff for $7.50 apiece at the time and use them now although the rod worked just as well and you can get a lot of dies out of a 3 ft length. The Kiff blanks look like RCBS dies with a 1/4 inch hole through them and are soft, probably 1018. The parts to convert a press will probably cost under 20 bucks and only involves drilling and tapping one hole in the ram and drilling a few others for the ejection system, not pretty but simple and cheap.

I think the purpose of a bump press is to bump the nose of a bore ride up so it contacts the tapered section of the throat but maybe there's more to it than that. I use LBT style bullets for my match shooting which are full diameter to begin with so there's no bumping up just tapering down. Same results from different directions. 

I don't know why Don Eagan would say you can't make a die using a throating reamer unless he was using some pretty hard material to start with which isn't necessary.

When I'm building a rifle or cutting a throat for a cast bullet only rifle I start by tapering the LBT style bullet so that when I run a mic set at .308 down the bullet, if we're talking .30 cal, it stops at the point where there's at least a .100 long front driving band. Then I make a dummy round so that the bullet sits about 1/2 the bottom band inside the case neck and cut the throat so it chambers.

It's my personal opinion that bump presses came along because people were trying to get accuracy with bore ride bullets that left too much to chance and you can get away with just tapering an LBT design. I also think people worry too much about shooting heavy bore ride bullets when a 1 inch long 170 gr bullet that fits the the throat will shoot just as well or better.

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cityboy posted this 30 October 2008

I have lapped out a couple of Lee rifle molds. Bulllets were cast in each mold using a fairly hard alloy. Then a hex-head self-tapping screw was run into the base and lapping compound applied to the bullet from the same mold. A power screw driver was used to turn the bullet. Trial casts can then be made to determine the change in OD. I have never tried this on an iron mold.

 

Cityboy

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