Lead angle cost/benefits?

[Medium rare]

I have been looking at some reamer prints and seeing different lead/throat angles. Most I see are 1.5°. Would anyone mind helping me understand what the positives and negatives of going in either direction. For instance what would the trade off be for 1° vs 2°?

 

[DaveTooley]

I have some reamers with a 2 degree lead. Never went as far as 1. The only absolute would be a change in free bore length at groove diameter. Accuracy, barrel life etc. are areas that are to broad to define.

 

[Alex Wheeler]

Dave is correct, there is no one size fits all answer. If you find a particular angle to work well with one case/bullet/caliber that does not mean it will work well in another. The only way you will know is to spend a couple grand on reamers and barrels and do the testing. I can tell you from my experiance that the 1.5 degree lead was not an accident, and it is in my opinion the most versatile.

 

[Shawnba67]

Didn't someone do some testing where throat erosion seemed to be at 1.5 degrees. Meaning in a few hundred rounds your leade is gonna be about 1.5° anyway.

 

[Alex Wheeler]

They do wear and change shape, but not into a 1.5. Its more of a radius.

 

[Lucky Shooter]

I've noticed that all the PTG/JGS reamer prints I've looked at are 1.5 degrees------some of the SAAMI prints are 3 degrees.

There is a bit of common sense suspicion that the 1.5 degree throat might give the bullet a less abrupt start.

Since I don't have any first hand knowledge over the best choice, I go with the popular 1.5 degree throat on my reamers.

Also suspect the shallow angle throats might wash out sooner that a 3 degree throat.

Alex opines that the 1.5 degree throat is not an accident-----good advice I think.

A. Weldy

 

[spclark]

Also suspect the shallow angle throats might wash out sooner that a 3 degree throat.

Sooner?

No, I believe it’s generally accepted that the opposite is true: 1.5 angle work well enough for most modern cartridge/jacketed bullet combinations that it’s become the go-to choice because it erodes slower than more abrupt profiles.

3 degrees may be a holdover from an older, lower-pressure era where a steeper land profile wouldn’t cause a dramatic chamber pressure spike.

Keep in mind that as a bullet enters the lands it must alter its shape to conform to that of the lands and grooves. The more extreme this transition the greater any resistance to forward motion becomes.

There may be other angles chosen for use with particular cartridge/bullets combos. Hugh Henriksen specified a 0°-45’ angle for use with 115/117 grain bullets of the 2003 era on his 6XC reamer design, 1°-30’ otherwise.

 

[DaveTooley]

Sooner?

No, I believe it’s generally accepted that the opposite is true: 1.5 angle work well enough for most modern cartridge/jacketed bullet combinations that it’s become the go-to choice because it erodes slower than more abrupt profiles.

3 degrees may be a holdover from an older, lower-pressure era where a steeper land profile wouldn’t cause a dramatic chamber pressure spike.

Keep in mind that as a bullet enters the lands it must alter its shape to conform to that of the lands and grooves. The more extreme this transition the greater any resistance to forward motion becomes.

There may be other angles chosen for use with particular cartridge/bullets combos. Hugh Henriksen specified a 0°-45’ angle for use with 115/117 grain bullets of the 2003 era on his 6XC reamer design, 1°-30’ otherwise.

I think you meant David Tubb. David was soft seating his bullets. Meaning when he closed the bolt he was seating his bullet further into the case. I'm pretty sure he went away from that several years ago.

 

[Alex Wheeler]

The angle doesnt change pressure much at all. The 28 Nosler is a 3 degree and they sure dont pressure up, that angle worked really well with the 195s. There are no rules here I have found. Break out the check book and start testing.

 

[DaveTooley]

Tangent ogive bullets tolerate different leade angles better than Secant ogive bullets. Or at least that's been my experience.

 

[DaveTooley]

The angle doesnt change pressure much at all. The 28 Nosler is a 3 degree and they sure dont pressure up, that angle worked really well with the 195s. There are no rules here I have found. Break out the check book and start testing.

Can I hit the like button twice?

 

[Medium rare]

Thanks for the help. I’ll be saving to test some different lead angles. Hopefully I will be able to draw some conclusions from the test.