In the previous post, we covered why groups suddenly open up — even when your load and process look solid.
Now we’re getting into something most people have heard of, but don’t really understand:
what people refer to as neck tension.
What neck tension actually is
Neck tension is simply the force required for the bullet to release from the case.
That’s it.
It sounds simple — but small differences here are enough to move your point of impact.
Why it matters
If neck tension isn’t consistent:
— bullets don’t release the same way
— velocities change
— impact changes
That’s how you end up with:
— vertical spread
— occasional flyers
— shots that don’t behave like the others
How people usually set it
Assuming you’re using bushings, there are a couple of common approaches.
One way:
— measure the outside neck diameter of a loaded round
— subtract about 0.002″
Another way:
— measure neck wall thickness at multiple points
— take the average
— choose a bushing about 0.002″ under the difference between bullet diameter and neck thickness
Both approaches work — as long as your brass is consistent.
How I approach it
I don’t use standard expanders.
I use:
— separate mandrels
— dedicated sizing setup
And I pay attention to seating force.
Over time, you can develop a feel for it — but most people won’t reliably detect small differences by hand.
There are, however, simple and budget-friendly ways to measure seating force if you want to remove the guesswork.
What matters is this:
— if seating force varies, release force varies
— and that shows up on target sooner or later
What works in practice
From experience:
For target shooting (single feed):
— around 0.001″ to 0.002″
For hunting:
— around 0.003″ to 0.004″
You don’t want bullets moving under recoil or while moving in the field.
These aren’t fixed numbers — but they’re reliable working ranges.
Where things start to drift
Even if you set neck tension correctly:
— it doesn’t stay the same
After multiple firings:
— brass hardens
— behavior changes
— tension becomes inconsistent
So even though your setup didn’t change —
your ammo did.
Real-world example
In controlled conditions, during training:
— the rifle consistently shoots 0.2–0.3 MOA
In competition:
— that same setup often opens up to 0.5–0.7 MOA
Not because the load suddenly changed —
but because real-world factors start stacking up:
— pressure
— anticipation
— timing
— environmental conditions
All of it adds up.
And when you already have that kind of variability,
the last thing you want is additional inconsistency coming from your ammo.
Neck tension inconsistency is one of those variables —
but it’s one you can actually control.
What this means in hunting
With a 0.5 MOA rifle and consistent ammo:
You can reliably hit the vital zone — even with some margin for error.
But that only works if your ammo behaves the same every time.
Otherwise, you’re guessing.
What most people miss
People focus on:
— bushings
— measurements
— setup
But overlook how brass changes over time.
That’s where problems start.
Where annealing fits in
Annealing keeps brass behavior consistent across multiple firings.
Which means:
— more consistent neck tension
— more consistent release
— more consistent results
Bottom line
You can set neck tension correctly.
But if your brass isn’t consistent —
it won’t stay that way.
Next
In the next post:
— how many times you can reload brass before performance drops
— why “it didn’t crack yet” doesn’t mean it’s still good
