Thread: Using comparator tool when seating projectiles.

Firstly I've trawled through this forum back to '12 looking for a definitive answer, might be there but couldn't find it. Hence the question.
I load for two rifles, a .308 and a 7x57. Both quite capable of MOA with specific loads, but not always. I have a resonable understanding of the variables involved but at the moment I'm trying to get my projectile seating sorted. I use a Forster Micrometer Bullet Seating die but find my COAL's for same projectile can vary 10 thou easily. Research indicates that's quite common and can vary 25 thou at times, making the COAL as a measurement very unreliable.
So I'll start using BTO as the measurement, when the comparator and OAL gauge arrive. I understand the comparator doesn't sit on the ogive but it will sit at the same place for every projectile of same type.

Say the BTO measurement I'm looking for is 2.752. Do I back out the seating die allowing plenty of room to seat the projectile then measure with the comparator, calculate how many thou I'm out and then screw the micrometer on the die down the correct measurement in thou and reseat? Do it for every cartridge?

That was suggested some years ago by a member.A bloke, Zimmer, said that would be very tedious.

So what is the correct method?

Both rifles are hunting rifles but I can't think of a good reason why they shouldn't shoot to their full potential. One in particular will be used out to 400 and beyond. Same rifle will be used in NZDA comp shooting, but nothing serious.

Cheers RM77

Zimmers method is perfect

Seat 10 thou too long them measure with the comparator

Write that number down if you need to

Then adjust the micrometer seating stem down for the last amount

Sometimes to get your eye in do another 5 thou then measure again, then you might only have to adjust another three thou after that

If you don’t graphite powder your necks and projectiles the “ stiction” in the neck between projectile and brass makes for jumpy grabby seating

But once lubed the projectile smoothly slides any thou that you adjust
You will get the hang of it quickly

Yes it’s onerous but fun

It’s a good idea to be lubing ammo to assemble it anyway, to prevent galvanic corrosion, which increases the case pressure the tighter the neck and projectile corrodes together.

Ammo that’s been assembled for a long time often has weird large ES over ammo that’s just been made, lubing on assembly fixes that

@7mmsaum. Thanks for the advice. No I hadn't been lubing, but black fingers it now is.

I find that even though it's marked in thousandths that sometimes the bullet doesn't move incrementally. I would also say that for 600 yards and under especially in a hunting situation the one gain benefit will be in your confidence the rest would be unmeasurable on dead animals.

Use cotton buds to wipe graphite powder on the inside of case necks and on projectiles

Fingers stay clean then

Originally Posted by 7mmsaum

Use cotton buds to wipe graphite powder on the inside of case necks and on projectiles

Fingers stay clean then

Speaking of graphite powder where is the best place to get some without costing a small fortune?
Cheers

Originally Posted by 7mmsaum

Use cotton buds to wipe graphite powder on the inside of case necks and on projectiles

Fingers stay clean then

Good tip there 7mmsaum..

Originally Posted by Kiwilad2021

Speaking of graphite powder where is the best place to get some without costing a small fortune?
Cheers

Get from Mitre 10, also at a locksmith.

Originally Posted by Kiwilad2021

Speaking of graphite powder where is the best place to get some without costing a small fortune?
Cheers

https://www.gunworks.co.nz/shop/item...-dry-neck-lube

Sent from my SM-S916B using Tapatalk

It lasts forever. I was given a small tobacco tin full, 40 plus years ago. Only ever dipped case necks in it, tins about half full now. If I remember correctly it was from a bloke on this thread.

Come see me at work some time, @Kiwilad2021. We’ve got mechanical pencil sharpeners full of the stuff all around the office 😁

Have a look at the Short Action Customs bullet comparators….the insert matches the leade angle dimensions of your barrel / chamber. So BTO measurements you take relate to where the projectile actually contacts the rifling.

You will still need to contend with the variability of projectile dimensions, particularly in the tip to ogive length where the seating stem contacts.

Originally Posted by tetawa

Get from Mitre 10, also at a locksmith.

Yeah don't go buying it from a gunshop, any gunshop...Bunnings or Mitre10 cheaper by far

Neck tension will give you variances in your seating depth as well. Also how much pressure you put on your press handle at the bottom. I just kiss the bottom of the stroke but if I give a bit of pressure and lean on it a bit, it can change by a couple thou.
Pretty amazing the difference sometimes just by moving a projectile 3-5 thou, can quite often shrink from acceptable to tack driver.

I have another approach to this. It can also be done prior to sizing. Especially if you are just bumping the shoulder with a bushing die and mandrel.

https://youtu.be/02xWd-vBtFM