Bullet Seating Depth

[Stan Malinky]

The Rifle: Browning Titanium Mountain in 300 WSM
Tool used: Hornady OAL Gage, with the Hornady modified case
Current conditions: I tripped over the current load and I have not changed it for 10 years, it shoots .3 MOA. I know that somebody will say "Why mess with a good thing", but what If I can make it better.
Experience: Reloading for 30 plus years measured multiple rifles using this method including the Hells Canyon model and I have received good repeatable results.
The Problem: When using this method on this gun I get varying results in the range of 3 Hundredths and I have never run into this before.

My next step will be to make a dummy case for the Hornady tool.

If this is a known problem with this rifle I will use the trial and error method with the bolt drop.

 

[Carlos88]

Here is my WAG. The case neck, shoulder or body is not of sufficient diameter causing it to be "seated" in a different place each time you measure.

 

[Shane Lindsey]

The modified case is the one that is virgin/saami. You probably would get better consistency with a fire formed case.

I tried a similar method with virgin cases. Totally different than a fired case...

 

[QuietTexan]

I use the Hornady tool to jam a bullet pretty darn hard into the lands and the modified case hard forward onto the shoulder. Use a headspace comparator to measure the difference between the modified case and a fired case, add that to CBTO using the modified case, and that's the maximum "hard stop" length allowing the bolt to close on a case with seated bullet. Then work shorter from there.

All the measurement is telling you where the starting line is for the interactions between several variables (including irregularities in the case and the chamber), it's meaningless other than as a reference point.

 

[Mikecr]

Have you considered shifting focus from land touch point, and focusing instead on seating testing for results?

 

[Stan Malinky]

Have you considered shifting focus from land touch point, and focusing instead on seating testing for results?

Yes, and that is probably what I will end up doing. However, now that I am running into this problem I have a hard time letting it go.

 

[parshal]

As Mikecr is alluding to, the actual number does not matter even if not repeatable. Pick one of those numbers and do seating depths from there.

 

[30378wbymag]

I use one of these https://bullettipping.com/products/seating-depth-comparator/ All my seating depth woes are gone!!!! This tool measures off the shoulder, more accurate than the Hornady off the base tool...

 

[jdyoung]

Yes , create a modified case for the Hornady system using a fired case that positively fits your chamber. ALSO, check the chamber/lands for excessive build-up that could give mixed readings. One of the new bore scopes is excellent for this. They are a great aid !!

 

[Stan Malinky]

Yes , create a modified case for the Hornady system using a fired case that positively fits your chamber. ALSO, check the chamber/lands for excessive build-up that could give mixed readings. One of the new bore scopes is excellent for this. They are a great aid !!

I would have taken my bore scope immediately after running into the problem and looked at the throat, BUT my hunting buddy has it and he is off in the boonies riding his Razor. My next step is to wait for him to get back before before taking ant further action. In the mean time I will make a modified case from fire formed brass.

 

[Mikecr]

People go entirely over-bored with land relationship measure.
But that never mattered to optimum seating depth.
It never mattered whether you take seating datum from case head or shoulders to ogive either, as you set headspace with reloading.
ALL that matters is testing and repeating best CBTO as the target tells you.

This, while off the lands. Just stay off the lands

 

[FEENIX]

People go entirely over-bored with land relationship measure.
But that never mattered to optimum seating depth.
It never mattered whether you take seating datum from case head or shoulders to ogive either, as you set headspace with reloading.
ALL that matters is testing and repeating best CBTO as the target tells you.

This, while off the lands. Just stay off the lands

^^^This!^^^

 

[Stan Malinky]

People go entirely over-bored with land relationship measure.
But that never mattered to optimum seating depth.
It never mattered whether you take seating datum from case head or shoulders to ogive either, as you set headspace with reloading.
ALL that matters is testing and repeating best CBTO as the target tells you.

This, while off the lands. Just stay off the lands

I agree 100%. However, a good dimension allows the tracking of throat wear.

 

[Mikecr]

Why care about tracking throat erosion?
This serves no function for hunting capacity cartridges.
Optimum seating depth is a matter of best bullet-bore interface. It's window widens as lands retreat, and there is only narrow circumstances with which to adjust from initially tested optimum CBTO -for the accurate life of a barrel.

The occasion where this is different is only when you're shooting an underbore for benchrest competition(like a 6PPC, or 30br).
In that case your TUNE would rely on a starting pressure setup by an ITL relationship. This is where it's appropriate to chase lands.
Hunting capacity cartridges cannot go where underbores go. It is not viable to run anywhere near those pressures (achieved with ITL relationships, and very fast powders in tiny cases for bore, & breech support).