Extending the throat leade and its impact on harmonics

[Tiny Tim]

I misspoke some, concerning lowering pressures with more speed, not sure that is possible, lol. What I should have said was, a sizeable jump seems to reduce a hard initial pressure spike, which can hinder initial load development.

Isn't that the premise of most of the Weatherby cartridges?

 

[milo-2]

Isn't that the premise of most of the Weatherby cartridges?

Maybe, I think I have read something to that effect. I've never had the desire for a WB case, so no history at all.
I just had to correct a not so well thought out post, hehe. I don't think the OP is really losing much jumping what I assume is a Nosler bullet.

 

[A A Ron]

With 190 Nosler ABLR seated deep with .140" jump, I'm loosing almost 4 grains of powder capacity dependant upon powder bulk. Less with Staball 6.5 more with H4831 or Reloader 23. So the thought was seat past the neck shoulder junction and get the capacity back, eliminate any doughnut risk, and gain some safely. Although the gain on 4 grains is less than 100 fps at normal pressure.

With the 200 gr Berger HBT I can seat above the junction and still jump .100" for best accuracy. I get a higher velocity node than I can achieve with the 190 ABLR. I have had the best results jumping most bullets with this rifle, except Sierra Match King's. They are best close.

 

[marc357]

I'm sure you could get back to your happy place, but my guess is it would require re-working the load.

I am shooting a rifle with a very long throat so I can seat the bullets farther out so I have room to cram more powder in there

A long time ago I had a custom Win Model 70 .300WinMag built. I cut the block out of the back of the magazine that limits cartridge length to SAAMI length of 3.340". Installed a modified bolt stop so the bolt would come farther back- far enough to strip a round from the magazine

Then I determined the longest length I could seat the bullets and still have them feed and function.
That ended up being about 3.520".

I loaded a dummy round to that length and gave it to my gunsmith, he throated the rifle to accommodate this longer round.

I am shooting a Hornady 208 gr bullet @ 3006 fps using H1000, it is still jumping at least .100"or .150", I don't remember. Accuracy is fantastic.

I've never really chased the lands in any rifle, I just load to the longest length I can and tune the powder charge.

 

[Dirtrax]

I throated my 7mm Practical and additional .050" to good effect. It cleaned up the throat to like new although I had only about 250 rounds through the barrel. It placed longer heavy bullets at the neck junction which was my goal as well. I went right back to my initial jump and it proved to be very accurate.

 

[FEENIX]

Curious how close the relationship between the free bore and barrel harmics is?

For example in my rifle a 190 ABLR shoots best at .140" jump. That jump causes the bullet to be seated deeply in the case using up capacity and it is way past the neck shoulder junction.

So if the throat was cut .140" deeper or so could you move the bullet the same jump to get back to node? My guess is the changing pressure, changing velocity, and changing harmonics timing would necessitate a complete new work up.

Any change to our current set-up will also require a change in your load development.

Isn't that the premise of most of the Weatherby cartridges?

That is also my understanding. Except for a few cartridges, they were designed with long free bore.

I have a .257 WBY SAAMI spec, but I can load mine .015" off the lands with 145 Black Hole bullets.

 

[A A Ron]

Weatherby was ahead of his time. If he had done a few things differently regarding proprietary cartridges the whole line would have been much more popular.