Time to make the donuts....

[geo.ulrich]

Randy or George, can you explain the preforming process? I am taking a guess here, but is the core seat die(obviously no core) used with a special punch? Lubed?

yes

 

[geo.ulrich]

The best path for BT is to preform both the jacket and the core: this results in punch fit/selection & seating/bleed-by results very similar to making FB.
Poor quality, however, this pic displays the heel-radius variety due to seating without and with prefromed materials. The preformed are easy to spot: squarer is better - especially regarding BC uniformity . . . 'ball-tail' bleeds performance.
RG View attachment 1672779
View attachment 1672780

Randy great pictures and yes they are easily picked out once you see the difference

 

[geo.ulrich]

Is there a rule of thumb on how much lead you should fill your jacket with to get maximum accuracy?
I cutaway a few to give you an idea, comparing them to Sierra and Berger.

***Sorry for the quality of the photo

1-155,5 grains ogive 7 J4 jacket 1.150"
2-155,5 grains ogive 13 J4 jacket 1.200"
3-175 grains ogive 13 J4 jacket 1.300"
4-200 grains ogive 13 J4 jacket 1.400"
5-185 grains 0give 13 J4 jacket 1.300"
6- 185 grains Berger juggernaut
7-175 grains ogive 7 Sierra jacket 1.220"
8- 168 grains ogive 7 J4 jacket 1.200"
9-168 grains ogive 13 J4 jacket 1.200 "
10-175 grains ogive J4 jacket 1.200"
11- 175 grains ogive 7 J4 Jacket 1.300"
12- Sierra 168 grains MK



View attachment 1672809

I'll go out on a limb and say 60% you can go a little less as long as the jacket doesn't push down during point up. going up on weight always makes the handle harder to pull

 

[ridgeway]

Great info here!! Now, if one would preform the BT, will the core need preformed with BT geometry?

 

[geo.ulrich]

Great info here!! Now, if one would preform the BT, will the core need preformed with BT geometry?

it can be but not really, either way the force is greatly reduced during core seating because you are not stretching the jacket. we are talking about long range not short range

 

[Kiwishooter]

it can be but not really, either way the forde is greatly reduced during core seating because you are not stretching the jacket. we are talking about long range not short range

Thanks George, the nugget I got from the above

Has anyone tried this is short range?

 

[RGRobinett]

Whether point-blank, or, LR, preforming both jackets and cores will produce the most uniform bullets your dies can make. The jackets are formed in the core-seat die, using a punch taper 'close' to the BT angle - here, exact is not necessary.

The concept is to obtain fluid dynamics very similar to when seating FB cores. When the core is used to form the BT, the [core] face must move forward to accommodate the reduced volume in the BT - considering jacket-wall taper, this dynamic makes punch 'fitting' more problematic: lead will be flowing around the punch prior to filling out all of the die cavity . . .

Whether near, or, far, uniformity rules. RG

 

[geo.ulrich]

Whether point-blank, or, LR, preforming both jackets and cores will produce the most uniform bullets your dies can make. The jackets are formed in the core-seat die, using a punch taper 'close' to the BT angle - here, exact is not necessary.

The concept is to obtain fluid dynamics very similar to when seating FB cores. When the core is used to form the BT, the [core] face must move forward to accommodate the reduced volume in the BT - considering jacket-wall taper, this dynamic makes punch 'fitting' more problematic: lead will be flowing around the punch prior to filling out all of the die cavity . . .

Whether near, or, far, uniformity rules. RG

Randy, I agree somewhat in a short range bullet you are only moving the jackets a few thousands maybe .006 to .010 when core seating a s.r. bt the length only grows minimally. on a long range when you seat the core it stretches about .050-.060

 

[tom]

 

[tom]

^^^^

Haven't used it yet, but may play with it soon....especially on Sierras.

Tom

 

[jackieschmidt]

“

Randy or George, can you explain the preforming process? I am taking a guess here, but is the core seat die(obviously no core) used with a special punch? Lubed?

I am curious too.
I seat the cores the regular way on my 68grn BT and they shoot really well.

But then, they really don’t have much of a Boat Tail when compared to bullets built on 1.150 jackets in the 103 grain+ range.

 

[liseo]

^^^^

Haven't used it yet, but may play with it soon....especially on Sierras.

Tom

Tom
Why use it especially if it is Sierra? Is the jacket thicker or harder, making it difficult to form the boat tail?
In the batch of Sierra I used, it seemed to form the boat tail more easily.

 

[liseo]

When George sent the tool to do the preforming, I modified the shape of the core to make it more similar to the preformed jacket(for ogive 13 200 grains bullets 30 caliber)
My concern was to avoid trapped air. I don't know if it makes a difference, but it made me feel more at ease.

 

[tom]

Tom
Why use it especially if it is Sierra? Is the jacket thicker or harder, making it difficult to form the boat tail?
In the batch of Sierra I used, it seemed to form the boat tail more easily.

I haven't tried to many lots/manufacturers/lengths, but the 6s i have of each j4 and Sierra i would say are thicker at that end. I know I wasn't happy with the boat tail without lubing the cores. Not that that's a bad thing, as I have had bullets out of this die shoot extremely well when Jason had it made that way. I just don't "love" doing it that way if I don't have to. It may not be a thing with the 6 though, so I might need to just get over it lol.

Tom

 

[JoeDuke]

View attachment 1672898

And this comes along just when I thought I had a grade school grasp on making bullets.

 

[geo.ulrich]

Tom
Why use it especially if it is Sierra? Is the jacket thicker or harder, making it difficult to form the boat tail?
In the batch of Sierra I used, it seemed to form the boat tail more easily.

Liseo the sierras are a steeper taper making the base a little thicker so its just about impossible to get the radius on the base down smaller

 

[liseo]

Speaking about the boat tail angle, is there any advantage/disadvantage between a bigger or smaller angle?

Does the bigger or smaller angle influence the BC?

 

[geo.ulrich]

Speaking about the boat tail angle, is there any advantage/disadvantage between a bigger or smaller angle?

Does the bigger or smaller angle influence the BC?

In b.c.no in gyroscopic stablety yes, flatter is better but not for punch longevity

 

[Catawampus]

Joe, I generally judge the corner radius, bleedby, and diameter. if I get a stretch mark at the lead line its to much. I am also a big fan of cutting open a bullet length ways to see how the core looks when seated. If theres a problem thats where you will find it. I also use a bullet spinner to check runout of the seated core. it usually works out when they are spinning true they are seated correctly...

Any recommendation on a source for a bullet spinner? Can we see some examples?

 

[liseo]

I always imagined that longer jackets would have a thicker base.
In this case, they both have the same thickness (J4 30 caliber 1.200" and 1.400")