Why doesnt factory ammo have to chamfer the necks?

[Basic user]

I'd like to know about the three differences I see between factory match and our handloads.
1. Why do we have to chamfer necks but some of the best factory ammo out there does not? How do they get away with it?
2. Why does factory ammo have a ton of neck tension, but we're all kinda pressured to do 2 thou of tension? I hear from a few people that they run 4 thou and have noticed better groups; should we all be running at least that much then? When I try to pull bullets out of factory rounds to experiment, it's always really hard. When I pull mine, sometimes they're really easy.
3. I heard that a ton of neck tension increases pressure; does it? And by how much? Asking that because I pulled down some old 8mm Mauser ammo from Yugoslavia, and it was soo difficult I had to break the seal (due to the asphalt looking stuff) with a seater first, before any of the bullets would pull. Are those rounds experiencing a massive pressure spike because of that?

 

[wvfarrier]

 

[RegionRat]

1. Why do we have to chamfer necks but some of the best factory ammo out there does not? How do they get away with it?

Flare and crimp.

2. Why does factory ammo have a ton of neck tension, but we're all kinda pressured to do 2 thou of tension? I hear from a few people that they run 4 thou and have noticed better groups; should we all be running at least that much then? When I try to pull bullets out of factory rounds to experiment, it's always really hard. When I pull mine, sometimes they're really easy.

You do whatever works for you, there isn't a "rule" per se. If your neck works better at 0.002, or if it needs more, then you run what you need.

3. I heard that a ton of neck tension increases pressure; does it? And by how much? Asking that because I pulled down some old 8mm Mauser ammo from Yugoslavia, and it was soo difficult I had to break the seal (due to the asphalt looking stuff) with a seater first, before any of the bullets would pull. Are those rounds experiencing a massive pressure spike because of that?

It depends... if we are talking starting pressure, then yes that sealant, crimp, and neck tension makes anywhere from zero to roughly 8 kpsi difference in the starting pressure. But keep in mind, peak pressure and integrated pressure are just as important. Your recipe must include all of it and the start and peak are just part of the whole result. None of those individual issues can be ignored, but that also means start pressure cannot be considered in isolation of the total pressure pulse or the max.

Changes in starting pressure will have a direct effect on the peak pressure and the total. The system has to balance.
For example, if you use sealant or jam the bullets, you typically back off the charge compared to a similar recipe without jam or sealant. When you balance the system, you can get an identical muzzle velocity, but the total shape of those two would have different pressure pulses.

 

[Basic user]

Gotcha

 

[Rocketmandb]

When you balance the system, you can get an identical muzzle velocity, but the total shape of those two would have different pressure pulses.

It amazes me how many people will refute this statement--and much of what you wrote. EDITL What you wrote is spot-on, btw.

@Basic user - the video below explains this somewhat.

 

[Basic user]

LOVE this stuff. Less guessing/theory, more science. Thanks for this!