Lead angle question. 1°30 or ??

[FatBoy]

Most of my reamers have had a lead angle of 1° 30. My current 284Lapua match reamer has .206" freebore with a 1° 30 As well but I had it made in 2005, when you either shot 168s or the 175SMK. Since then, I see some of the new reamers listing 1° 47-33. I'm not familiar with this, can someone enlighten me?

I haven't shot 7mm since '06 so I send JGS a dummy round for a new no-turn reamer for an upcoming project. They will be calling me in the next week or so to approve the print. I want to make sure I'm up to date on what is shooting. Plan is to use the Berger 180 hybrids, which didn't exist in '05. I think I have the body dims down as they haven't changed for the Lapua brass and I have set freebore off the a chamber I know to shoot but I want to make sure the lead angle I pick is right for the current crop of bullets.

Any advice from someone who's BTDT lately.

Thanks,

Chris

 

[Alex Wheeler]

The saami lead angle is 47 minutes 33 seconds. Its a hair over 3/4 degree per side. It works very well by the way. 1.5 degrees is standard now but theres pros and cons with different angles. If your not looking to experiment stick with 1.5. I have done different angles, dont be afraid to, you may just learn something

 

[FatBoy]

Thank you, Alex. I am going to Google the conversation to make sure I understand the differences you listed. I'm unclear if 1° 30 = 1.5 or if there is a difference so time to do some Googlefoo and do some match learning

 

[Alex Wheeler]

Degrees minutes and seconds, 60 seconds in a minute, 60 minutes (MOA) in a degree

 

[Brians356]

The saami lead angle is 47 minutes 33 seconds. Its a hair over 3/4 degree per side. It works very well by the way. 1.5 degrees is standard now but theres pros and cons with different angles. If your not looking to experiment stick with 1.5. I have done different angles, dont be afraid to, you may just learn something

Browsing through SAAMI drawings, the newest cartridges (Nosler) have the following leade angles denoted:

26 Nosler: 3.0 deg.
27 Nosler: 1.5 deg.
28 Nosler: 3.0 deg.
30 Nosler: 1.5 deg.
33 Nosler: 2.0 deg.
35 Nosler: 3.0 deg.
36 Nosler: 1.5 deg.

I'm curious how these angles were chosen for a particular cartridge.
-

 

[M-61]

Browsing through SAAMI drawings, the newest cartridges (Nosler) have the following leade angles denoted:

26 Nosler: 3.0 deg.
27 Nosler: 1.5 deg.
28 Nosler: 3.0 deg.
30 Nosler: 1.5 deg.
33 Nosler: 2.0 deg.
35 Nosler: 3.0 deg.
36 Nosler: 1.5 deg.

I'm curious how these angles were chosen for a particular cartridge.
-

As Lance said to Vincent in PULP FICTION:

" I'm kinda curious about that myself...."

 

[Alex Wheeler]

Well a larger angle will erode slower. If they put a 1.5 in a 26 Nosler I can imagine how fast the throat would move.

 

[Brians356]

Well a larger angle will erode slower. If they put a 1.5 in a 26 Nosler I can imagine how fast the throat would move.

So what's to choose between 27 and 28 that warrants 1.5 vs 3.0 I wonder? Seems arbitrary.
-

 

[BoydAllen]

As you all probably know, there are 360 degrees in a circle. Each degree can be divided into 60 minutes, and each minute into 60 seconds. This sums it up pretty well.

I found this a the top of results of of a Google search for "degrees minutes and seconds notation"
"The first method divides each degree into 60 minutes (1° = 60'), then each minute into 60 seconds (1' = 60"). The symbol for degrees is ° , for minutes is ', and for seconds is ". "

So, a degree and a half is one degree thirty minutes, and a 20 MOA (minute of angle, or in math minute of arc) base is angled a third of a degree 20/60= 1/3.

 

[FatBoy]

I went with 1°30 on the new reamer. Thank you all for the assist.

 

[Alex Wheeler]

So what's to choose between 27 and 28 that warrants 1.5 vs 3.0 I wonder? Seems arbitrary.
-

I do not know why the designers did what they did. It could be as simple as two different people designed those reamers. I have a 3 degree in my 28 noslers, they shoot better than a case that big should.

 

[EXTREME]

Has anyone determined the COAL on 26 Nosler Rounds with the 140 Berger Hybrid, 143 ELDX or 147 ELDM seated to the 3 degree Saami throat?

 

[dkhunt14]

Has anyone determined the COAL on 26 Nosler Rounds with the 140 Berger Hybrid, 143 ELDX or 147 ELDM seated to the 3 degree Saami throat?

I believe that depends on freebore. Matt

 

[EXTREME]

I believe that depends on freebore. Matt

I would like the measurements taken in a relatively new 26 Nosler Saami chamber which has a 3 degree throat angle and 0.118" FB. This FB would be the same for all Saami chambers.

 

[Doug Beach]

In general, when a throat is listed as 1.5°, is that .75° per side, or 1.5° per side? Stated another way, would a JGS drawing showing 1-30-0, be referred to as a 1.5, or a 3.0?

 

[hogpatrol]

Well a larger angle will erode slower. If they put a 1.5 in a 26 Nosler I can imagine how fast the throat would move.

Alex, I don't know if it makes any difference. Mine moved almost .040 in a couple hundred midrange loaded rounds "gently" shot and that was with a melonited barrel.

 

[EXTREME]

In general, when a throat is listed as 1.5°, is that .75° per side, or 1.5° per side? Stated another way, would a JGS drawing showing 1-30-0, be referred to as a 1.5, or a 3.0?

When a throat is listed it is listed as 1.5° it is drawn as a 1.5° angle to the Freebore where it ends and the throat starts. There are no sides as the bore is round so think of it as a long cone that the nose of the bullet fits into. However the reamer only cuts the lands and a bit of the bore. Another way to look at it is a brass with a 30° shoulder which is cut 30° to the chamber starts at the chamber and ends at the shoulder/neck junction. If a 45° angle is drawn it would be like a right angle triangle.

Here is a 25 caliber drawing with a 3° shoulder drawn to the 0.2575" diameter FB for 0.235" (Freebore or Leade). I had it throated this way to optimize it for the rounder ogive hunting bullets seated out in the neck, which requires Freebore so the bearing surface can protrude past the case mouth more than in a Zero Freebore situation. Large for caliber bullet VLD type bullets would likely seat properly to the lands but the lighter ones would seat outside the case mouth.


Here is a drawing of a 25 WSSM with 0 FB, starting at 0.261" with a 1°-43' throat. With the .300+ neck light hunting bullets may fit in the neck as would heavier VLD bullets as they would go further into the tapered throat. Heavy hunting bullets would protrude into the case whereas light VLD bullets would be barley into the neck or off the lands.



Hopefully this will give some incite into how changing throat angle affects FB and bullet seating in the neck or to the lands.