Why doesnt factory ammo have to chamfer the necks?

Basic user · Jan 8, 2025

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 · Jan 8, 2025

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RegionRat · Jan 8, 2025

Basic user said:
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.

Basic user said:
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.

Basic user said:
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 · Jan 8, 2025

Gotcha

Rocketmandb · Jan 9, 2025

RegionRat said:
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 · Jan 9, 2025

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

Basic user · Jan 12, 2025

RegionRat said:
Flare and crimp.

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.

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.

Question on that flare and crimp; that's on rifle ammo? If so, doesn't crimping the neck to the point where you still get like 4 thou of neck tension WITH springback, not deform those bullets bearing surfaces?

memilanuk · Jan 12, 2025

You can experiment with exactly that using a 'taper' (not 'roll') crimp die.

I knew a guy (10-15 yrs ago) who had their 650 set up to size, trim with the Dillon RT1200/1500, and then expand/flare with a Lyman M die. Next tool head was charge, seat and a light taper crimp. Apparently worked well for mass quantities of NRA Service Rifle ammo; not sure about modern 'precision' rifle.

Basic user · Jan 12, 2025

I guess I could experiment with that... Maybe I should look into that...

memilanuk · Jan 12, 2025

In my experience, you want to get most of your interference fit aka 'neck tension' from the sizing die & expander - the taper crimp is just there to smooth out the tiny flare from what ever you use to do that operation. It's not really 'crimping' in the way most people think.

Rich04 · Jan 12, 2025

The newer Lee collet dies have been shortened to create a perceptible flare, started a bit of a drama in fclass here when it was noticed, hatred flowed but I think it’s actually a good thing when combined with their collet crimp to reclose the neck, saves an operation after trimming

RegionRat · Jan 12, 2025

Lee should have left one of their best ideas alone, or offered that new version in addition. They screwed the folks who used their collet dies to iron out brass before trim/chamfer. Worst move they have made in a long time.

RegionRat · Jan 12, 2025

Basic user said:
I guess I could experiment with that... Maybe I should look into that...

Memilanuk answered your basic question. Here is a context story so you understand why folks who load bulk ammo do this.

Prairie dog ammo needs to be pretty good, and there needs to be a lot of it. Roughly speaking we are talking about stuff like 223 (or 204R) with 40 VMax or along those lines.

Roughly speaking, it may be used in bolt or AR rigs, and will be roughly 1/2 MOA level stuff at distances up to about 350 to 450 yards or less. The majority of shots are roughly 100 to 300 yards. The targets are small and there is almost always wind.

This means the ES/SD can be achieved with careful priming and thrown charges because the trajectory doesn't go out far enough for those issues to ruin the performance. An SD of 15 - 20 works fine.

When I tool up to make 2000 prairie dog loads, I don't touch them one at a time. It is automated or it ain't practical.

So for example, you can break up loading with a 650/750 to some degree using multiple tool heads to avoid the need to handle each case individually.

I even auto-feed the cases to the annealer without handling them individually. Case prep is completely separated operations from the sessions where ammo is assembled (loaded).

The Dillon power trimmer uses a type of FL sizing die (trim die) to "hold" the brass from spinning while the cutting tool spins and cuts the neck, but this is a straight cut only - no chamfer. That straight cut is too sharp and would scrape and damage bullets.

Even if I tumble prior to using a different tool-head for loading the trimmed and prepped brass, those necks are not chamfered and way too sharp as-is.

We use a flare tool to slightly open the necks to be able to place the bullet for seating, then after the seating die there is a taper crimp just to close that flare.

I hope that makes sense, and I realize it isn't something most folks talk about in detail on forums. There are more labor intensive ways to chamfer and do a nicer job, but that isn't practical for prairie dog loads that you make 2000 at a time.

We have made custom flares, used the Lee as-is, or modified the Lyman M dies to be able to run the whole process on a Dillon without the need to handle each case to chamfer. Most seater dies will remove the flare without drama, even without actual crimping. If you are picky, you can use a Redding Taper Crimp die as well. YMMV

memilanuk · Jan 12, 2025

A counterpoint to what I said earlier about getting most of the neck tension from the sizing die, not from crimping:

Years ago, Black Hills was selling a reman load with the 75 BTHP and processed LC brass. Relatively inexpensive, and shot *very* well, at least by the standards of NRA XTC short-yard line ammo. Lots of people tried duplicating that stuff, myself included. Rumor was that it had 24.2gn what looked like TAC.

So... I worked up a load with that bullet, and that powder, in LC brass. Nada. Shot like absolute crap. Ran the charges up *way* past what was in the factory ammo, and all I had to show for it was some wrecked brass. $hite groups, and not nearly as much speed. I grabbed another box from the store, and figured I'd pull down a few rounds to see what was in there, really. Yeah... no. I basically destroyed a hammer-type (kinetic) bullet puller, and never got those bullets to even budge. Finally I broke down and got an RCBS press-mounted bullet puller. Even then, I had to deform those bullets to the point of destruction to get them out. And inside... was 24.2 gn of what looked exactly like TAC. Yes, I know manufacturers often use cannister grade powders that aren't exactly 1:1 equivalent to what consumers can find on the shelves. But still...

Since I'd already tried replicating all the other aspects of this load, I figured why not try replicating the ungodly neck tension - or whatever it was - that made those bullets so hard to move. The bullets I had, and the bullets I pulled, had no cannelure. That's when I got a taper crimp die, and started experimenting. I started testing in steps - taper crimp die just touching the neck, then increasing in half turn increments. I don't recall exactly how much it was - I didn't think to measure it in any meaningful way - but it made an eye-opening difference.

It's not something I normally resort to, that sort of extreme... but if you're trying to make something work, cranking up the neck tension might be an option.

biggershooter · Jan 13, 2025

Rich04 said:
The newer Lee collet dies have been shortened to create a perceptible flare, started a bit of a drama in fclass here when it was noticed, hatred flowed but I think it’s actually a good thing when combined with their collet crimp to reclose the neck, saves an operation after trimming

Lee will make a custom collet die that sizes all the way to the case mouth on request. Still low-cost.

Rich04 · Thursday at 5:38 PM

They will definitely, just need to wait for it, my appreciation for the new ones is this, anneal-full length size-trim and decap- clean.
Pass around a progressive with the collet die to straighten the neck and no chamfer required, powder from a measure or AutoTrickler, chamber seater, Lee factory crimp to close neck.
Almost like cheating for big volumes

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Why doesnt factory ammo have to chamfer the necks?

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