XP-100 7mm BR chamber neck diameter and neck turning tradeoff

[Mark26]

I have an XP-100 in 7mm BR and am starting to prep some unfired Remington 7mm BR brass for it.
From what I've read, it seems like the chamber necks on the XP-100's were .309" and most competitors turned the necks on the brass down to .010", leaving zero neck thickness variation. Are both of these correct?
Remington ammo fired from my XP-100 gives brass with necks at ~.3095" after a day or so, suggesting a chamber neck at ~.3105", or maybe .310", instead of .309".
And a .010" neck thickness would give a ~.2835+2(.01)=~.3035"loaded diameter, and thus a relatively large .309-.3035= .0055" diametrical interference (clearance) with the chamber (or ~.0065-.0070" in my case), vs a diametrical interference of ~.309-(.2835+2(~.0118))=~.0019 with no neck turning (or ~.0029-.0034" in my case), based on the 55 cases measured.
This seems to suggest that there is no tradeoff between the neck thickness variation and diametrical interference in this particular situation. Removing ALL of the neck thickness variation is the optimum thing to do. Is that correct?
The neck thickness variation on the Remington brass IS pretty large, e.g. averaging a thickness range of ~.0023", but a decent part of that could be skimmed away while keeping the diametrical interference closer to .004".
Perhaps the newer Peterson 7mm BR brass with thicker necks would be one answer. But what people did back in the day with the Remington brass might be sufficient for my purposes.
Thanks for any help!

 

[Old Navy]

Are you shooting an original center grip with the factory barrel?

 

[wheelgun7360]

Standard neck on an xp 7br is .310. I have a custom built defiance action xp clone that I had built for IHMSA shooting. I had the reamer made for a .308 neck. I use the new Peterson 7br brass. I turn the necks to .306 for .002 clearance!

 

[Mark26]

Are you shooting an original center grip with the factory barrel?

Yes. A Zytel version with a 14" barrel and no sights and a 1985 barrel marking. I think it was called the "silhouette match" version.

 

[LCazador]

That XP is not the most accurate of pistols but it's no slouch as well. With that said if you want to clean up brass with a neck turn of .002" it isn't going to hurt.

 

[dhagerty40]

Factory chambers varied between .310-.312 in the chamber neck. but a factory gun is capable of 1MOA or better without turning necks.

as you have found, remington 7BR brass varies a lot and got worse with newer brass. Brass made after 2010 is the worst. The last lot of 100 I got was junk in that it varied .004" around the neck and I threw 3 away that had holes in the shoulders. I also lost 5 cases after the second firing from neck splits. Keep them annealed if you use Remington brass.

Peterson brass is much higher quality but weighs 10-15grs heavier case depending on the lot.

other than that, it is a fun gun to shoot and not finicky when loading for.