Ideal bullet position within the case

[Educated Redneck]

I'm sure this has been answered before but I can't seem to find the answer:

Throat, jump, coal , and saami specs all aside, where is the ideal bullet position (boat tail to the base of the neck) from a velocity stand point? Said another way, where is the ideal bullet position within the case to produce the highest velocity? At the neck base/boats tail base junction??? Just forward or back a bit???

Essentially the same question, but for accuracy vs velocity. I assume the full bullet bearing surface within the neck would be most concentric and accurate???

Again all the throat, freebore, saami spec stuff aside. I want to know the answers purely from a case engineering/physics theory point of view, everything else equal.

Thanks,
Jake

 

[Pdvdh]

There is no one size fits all answer, which is why you can't find one. Each rifle can be unique in this regard.

I presume you hand load your own ammo. Maximum velocity can usually be obtained by giving the bullet some running distance before it hits the rifling lands. Best accuracy seating depths can only be determined by trial and error, and they could be different with different bullets in the same rifle.

Having said this, most will claim that a reasonable starting position is to seat the rear baring surface of the bullet in the vicinity of the neck/shoulder joint.

 

[JeffVN]

+1 Assuming the chamber is throated sufficiently long, I try to start with the boat tail / bearing surface junction just above the neck / shoulder junction (if you have any chance of developing a doughnut this location puts you above the doughnut).

My default starting point is roughly 10-15 thou jump to the lands, and I start off with 2 thou neck tension for bolt actions (3 for semi-auto).

JeffVN

 

[dkhunt14]

If throat the gun so the pressure ring or boatail body junction is ahead of the neck shoulder junction you will gain more velocity with less pressure because you gain capacity just like blowing a Case out like in an Ackley. You can go out to about half the neck but you need enough bullet in the case to hold it. When we throated out a Dasher and a 300 WSM we gained about 100 feet more withe same pressure. The WSM took about 2more grains of powder and I believe we throated it about .100housandths out farther. I can't remember how much more powder we got in the Dasher but we throated it from 104 freebore to .155 freebore. If you throat it out you also don't have to worry about a donut because the pressure ring is in front of it. Matt

 

[corsair4360]

The real puzzle is what is your chamber like and what does the gun tell you (takes time and patience to learn). Each manufacturer uses slightly different chamber reamers, especially in the throat and leade areas and magazine length.

For instance I have a Savage 110 Predator Hunter in 6.5x284 that has a very long throat and 1 in 9 twist with a double box detachable magazine that has lots of room even at a 3.160 overall length. For that 6.5x284 I have found seating bullets to be near the lands difficult, particularly Bergers, much better success with Sierras and Noslers which I can seat close to the lands (0.010" so far). The gun seems to like bullets close to lands (I got a 3/4" group at 100yds yesterday with Sierra 140gr Match Kings with the bullet 0.010" off the lands).

I had a 7mm Remington Magnum that had a huge chamber (took four full power loads to really fire form the cases). Because of the huge chamber and moderate throat it shot the 154gr Hornady soft points really well (5/8" group at 100 yds from a cold wet barrel every time). That load I will not repeat, it was way more H870 than any book lists, but in that gun it was low pressure, and lightly compressed. All I did for seating length was maximum magazine length.

I have a 1917 Enfield with the original military 30-06 barrel, it has a relatively short throat, apparently for the 150gr military loads of WWII. I have yet to shoot it, recent rebuild, awaiting a new scope for elk hunting here in Utah.

 

[corsair4360]

The real puzzle is what is your chamber like and what does the gun tell you (takes time and patience to learn). Each manufacturer uses slightly different chamber reamers, especially in the throat and leade areas and magazine length.

For instance I have a Savage 110 Predator Hunter in 6.5x284 that has a very long throat and 1 in 9 twist with a double box detachable magazine that has lots of room even at a 3.560 overall length. For that 6.5x284 I have found seating bullets to be near the lands difficult, particularly Bergers, much better success with Sierras and Noslers which I can seat close to the lands (0.010" so far). The gun seems to like bullets close to lands (I got a 3/4" group at 100yds yesterday with Sierra 140gr Match Kings with the bullet 0.010" off the lands).

I had a 7mm Remington Magnum that had a huge chamber (took four full power loads to really fire form the cases). Because of the huge chamber and moderate throat it shot the 154gr Hornady soft points really well (5/8" group at 100 yds from a cold wet barrel every time). That load I will not repeat, it was way more H870 than any book lists, but in that gun it was low pressure, and lightly compressed. All I did for seating length was maximum magazine length.

I have a 1917 Enfield with the original military 30-06 barrel, it has a relatively short throat, apparently for the 150gr military loads of WWII. I have yet to shoot it, recent rebuild, awaiting a new scope for elk hunting here in Utah.

I corrected the actual overall length, not case length. Me bad

 

[Canadian Bushman]

If throat the gun so the pressure ring or boatail body junction is ahead of the neck shoulder junction you will gain more velocity with less pressure because you gain capacity just like blowing a Case out like in an Ackley. You can go out to about half the neck but you need enough bullet in the case to hold it....... If you throat it out you also don't have to worry about a donut because the pressure ring is in front of it. Matt

^ This