Accuracy Throat/leade Relationship

[wboggs]

Is there a relationship between throat and leade lengths and accuracy? Relationship between bullet profile/caliber and these lengths?
I have noted some chambers have varying combinations of these to place the bullet diameter above the neck shouler junction to prevent donuts.
What is the experience of you that build for accuracy?
Thanks
Bill

 

[urbanrifleman]

Is there a relationship between throat and leade lengths and accuracy? Relationship between bullet profile/caliber and these lengths?
I have noted some chambers have varying combinations of these to place the bullet diameter above the neck shouler junction to prevent donuts.
What is the experience of you that build for accuracy?
Thanks
Bill

Get as far away from the donut as you can. Not only does this improve the donut to bullet relationship, it improves the overall neck tension relationship as the brass gets older and becomes more funnel-shaped. You do not see the funnel having nearly as much to do with neck tension if the bullet pressure ring is only about 2/3 the way down the neck.

Basically people are running too short of free bores. Across the board. For some reason they think that the further the bullet is down the neck the better it will shoot That is absolutely not true.

 

[SKWERLZ]

As above it’s good practice to avoid letting the neck/shoulder junction influence the bullet bearing area, it’s difficult to keep that area consistent.
That’s why 6BR is so nice, long neck give a lot of real estate to play in.

 

[Twdmar]

This is just my understanding and may not be complete but I will throw this out there and see what sticks.
I will leave the donut part because that's been touched on.
As far as the relation of the bullet and leade angle, I do think there is a relation that matters. It seems like a lot of leades are 1.5 degrees. I believe that people have just kind of seized on that because it works pretty well for most bullets.
I would suggest that there are some bullet and leade angles that will be incompatible and if the angle allows a gentle transition into the rifling, accuracy will likely be good.
If you compare the leade angles of 223 rem reamers, I think they are what they are somewhat based on what bullets they are aimed at using. A light 22 bullet is likely to have a sharper ogive along the length of the bullet and a sharper angle might be beneficial compared to a heavy one.
My guess is this is part of the reason that VLD bullets can be sensitive to seating depth while tangent ogives are more jump tolerant. The secant ogive has less room for that entry to his the sweet spot.
Now, that being said, this is my understanding and I am not certain it's correct. I do think the smith's who have found that the 1.5 angle works pretty well most of the time, while it may be anecdotal, their body of evidence is good enough for me.

 

[AckleymanII]

A guy has to remember his application and goals for accuracy that he needs.

Bullet pressure ring about .020 above the shoulder neck junction gives fantastic results in the 223, 223 AI, and 22/204. In fact, all of my zero freebore reamers in 223, 223 AI, 22/250, 22/250 AI, 6 BR, 6 Dasher, 6 BRX, 243, 243 AI, 6 Rem AI, 7 stw, 257 Weatherby all shoot groups that open up a single bullet hole.

Remember, bullet leade grows in length and diameter! So, if you start off with .020 freebore, 600 rounds down the bore, that freebore has grown, plan ahead for more useful barrel life.

I Quit shooting competition.

My 7 Mags with .110 freebore all seat the 140g-168g bullets into the shoulder area and all of them shoot dot size groups.

Truth is that it is just requiring way too much thinking/effort to ask a guy to monitor his brass for doughnuts....and that ain't no BS! Since most reloaders are not willing to monitor their shoulder/ neck junction for doughnuts, best to devise a methodology to keep them out of trouble.

NO one would believe the accuracy of the 7 STW and 257 Weatherby with zero freebores....no body.

There is a standard for competing for the ultimate in Accuracy in competition, and that standard should not be confused for Varmint Hunters and casual shooters, especially when barrels are running $600-$750, chambered.

Minimal freebore to meet your accuracy goal means more useful barrel life.

 

[wboggs]

A guy has to remember his application and goals for accuracy that he needs.

Bullet pressure ring about .020 above the shoulder neck junction gives fantastic results in the 223, 223 AI, and 22/204. In fact, all of my zero freebore reamers in 223, 223 AI, 22/250, 22/250 AI, 6 BR, 6 Dasher, 6 BRX, 243, 243 AI, 6 Rem AI, 7 stw, 257 Weatherby all shoot groups that open up a single bullet hole.

Remember, bullet leade grows in length and diameter! So, if you start off with .020 freebore, 600 rounds down the bore, that freebore has grown, plan ahead for more useful barrel life.

I Quit shooting competition.

My 7 Mags with .110 freebore all seat the 140g-168g bullets into the shoulder area and all of them shoot dot size groups.

Truth is that it is just requiring way too much thinking/effort to ask a guy to monitor his brass for doughnuts....and that ain't no BS! Since most reloaders are not willing to monitor their shoulder/ neck junction for doughnuts, best to devise a methodology to keep them out of trouble.

NO one would believe the accuracy of the 7 STW and 257 Weatherby with zero freebores....no body.

There is a standard for competing for the ultimate in Accuracy in competition, and that standard should not be confused for Varmint Hunters and casual shooters, especially when barrels are running $600-$750, chambered.

Minimal freebore to meet your accuracy goal means more useful barrel life.

Are you saying that a 7mag with 0.110 fb, seating something like a 160 accubond does not cause donuts that have to be removed to maintain accuracy? Donuts do not harm accuracy and I'm talking about competition accuracy? Looking at the list of cartridges you mention, I would thing they all form donuts with the heavier bullets, say 80 and above in the .224s. So a donut at 0.02 above ns junction inhances accuracy and this moves forward as your throat wears and you need to move bullet forward or have more jump
Thanks

 

[AlNyhus]

Basically people are running too short of free bores. Across the board.

Respectfully, nothing could be further from the truth.

Good shootin' -Al

 

[urbanrifleman]

Are you saying that a 7mag with 0.110 fb, seating something like a 160 accubond does not cause donuts that have to be removed to maintain accuracy? Donuts do not harm accuracy and I'm talking about competition accuracy? Looking at the list of cartridges you mention, I would thing they all form donuts with the heavier bullets, say 80 and above in the .224s. So a donut at 0.02 above ns junction inhances accuracy and this moves forward as your throat wears and you need to move bullet forward or have more jump
Thanks

Donuts do not harm accuracy????

Um.

 

[urbanrifleman]

Respectfully, nothing could be further from the truth.

Good shootin' -Al

Most people have no idea where the back of the bullet is at all. And I mean MOST. Not a small group of expert shooters.


Respectfully.

 

[Beiruty]

First state what bullet's profile you are shooting, then design the chamber and its lead accordingly.

 

[BoydAllen]

Is there a relationship between throat and leade lengths and accuracy? Relationship between bullet profile/caliber and these lengths?
I have noted some chambers have varying combinations of these to place the bullet diameter above the neck shouler junction to prevent donuts.
What is the experience of you that build for accuracy?
Thanks
Bill

Keeping the full diameter part of a bullet in front of the neck shoulder junction keeps the doughnut from having an effect on accuracy. It has no effect on the formation of doughnuts.

 

[urbanrifleman]

I'll take a slightly too long a freebore over too short any day of the week. After the brass forms a donut and the bullet is seated into the donut, you might as well be shooting a shotgun.

 

[BoydAllen]

In the process of keyboarding my first post in this thread, probably due to hitting backspace unintentionally, my reply ended up showing up like a quote from the OP, which only spotted just now.

 

[wboggs]

Do you turn brass to eliminate the donuts even when the diameter is above the neck shoulder?

 

[urbanrifleman]

Do you turn brass to eliminate the donuts even when the diameter is above the neck shoulder?

The ony fix for donuts is to not be near them.

 

[swd]

The ony fix for donuts is to not be near them.

My cardiologist agrees, LOL

 

[AckleymanII]

Over a span of cases in a Lot#, Rockwell hardness will vary. Soft brass experiences more brass flow, hence doughnuts form faster in the softer brass. I cull that brass, place in a box. When I have enough of doughnut brass, I deal with it by forcing the doughnut to the outside of the case and neck turning, saving the brass for longer freebore, or just tossing it if it has been fired 50x or more.

Serious competition demands to keep the bullet shank out of the doughnut area, high volume varmint hunters need longer barrel life, hence the shorter freebore still achieving 1/4" accuracy and smaller.

 

[AlNyhus]

Most people have no idea where the back of the bullet is at all. And I mean MOST. Not a small group of expert shooters.

It's basic 'Handloading 101' to seat a bullet and figure out where the base is in the neck. Heck, you don't need anything to measure with....just hold a bullet up alongside the neck. In a one-size-fits-all situation, the Easy Button is a lot of freebore length, lots of extra neck length in the chamber, generous neck diameters and throat diameters. The factories had that figured out decades ago.

In an accuracy situation (which is what the OP asked about), I can't imagine ever compromising on the throat/leade/free bore just to run away from donuts. Incorrect free bore/throat diameter will give you way more intestinal gas than an easy to deal with donut.

Of course, 'accuracy' means different things to different people. The OP could be asking about very minute (tiny) group sizes, Minute Of Angle, Minute Of Moose or anything in between.

For what it's worth from a 'Forbidden Zoner'.

 

[big5ifty]

Is there a relationship between throat and leade lengths and accuracy? Relationship between bullet profile/caliber and these lengths?

Bullet ogive and throat angle.

 

[WSnyder]

At one time Jim Boatright wrote an article on the this subject. I believe it was published in Precision Shooting. It was also available at one time on Jim's website but I have a feeling that is gone now. You might be able to find it if you searched for it.

I'll add that if I recall correctly not much came of those lead angles he had suggested.