Thread: what causes differences in OAL with a comparator ?

Eg. kist loaded up 83 rounds of 7mm saum, all brass was resaized the same, annealed etc. loaded to 57.86mm with the 7mm comparator, and half of them went between 57.78 and 57.9 mm, the other half were bang on.

what would cause this ? Seems to happen with whatever cartridge im reloading. could it be my hornady calipers ? Additionally, if you were aiming for 57.86mm, what tolerance would you call safe ? I can hit a tartet at 460 with this, 2 rounds less that 13mm apart centre to centre.

Projectiles consistent in length?

havent actually checked those. Id imagine that would cause a small discrepency ? berger projectiles, or hornady though.. im assuming that they are all different lengths to a degree, but seating them pushes down on the ogive also ?

Seating stem doesn't contact the bullet ogive. It contacts somewhere above it. Any variation in projectile shape means the seating stem isn't contacting in the same place each time. This is further complicated by the fact your Hornady comparator isn't measuring to the ogive either.

I now also use a Short Action Customs comparator which is the correct diameter for the given projectile diameter and all the variances I used to experience is eliminated (for Bergers).

interesting.... might have to look into the SACC ,

I’ve measured several boxes of Hornady and Sierra with a comparator. A box of Hornady projectiles have a variance of 0.13mm and Sierra 0.08mm. As for what’s safe for seating depth tolerance it would be beat to test it.

As said, the seating stem doesn't contact the ogive, it pushes not far below the plastic tip on my dies.
I have noticed a difference in projectile length between batches of Hornady ELD-X, but haven't noticed it within a box.

I literally spend the time, pulling and seating them all to the perfect depth. But that would definatly cause my discrepancy
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Everything mentioned above including Neck tension variances

There is a fix regardless of the cause

Don’t load to final length first time

Load 5 or 10 thou short on them all

Then measure and micrometer adjust the seating stem for the last measured thou for each one

IE. this one only needs 2 thou, this one needs 4 thou, this one needs 8 thou and this one needs 2 thou

Problem solved

@Larskramer ....you need a good comparator which measures in a similar spot to where the seating stem contacts, then you can measure from base to ojive on your bullets. You will see a difference in length even with the bullets from the same batch.

Never mix different batches as they will be streets apart at that point on the ojive.

You might also consider lapping the projectile to the seating stem and your comparator if you want to be really fussy.....the witness mark should be at least 0.040" wide....a narrow ring contact tends to dig in and give erratic performance as you are experiencing.

The measurements you are quoting are not relevant when measuring with a comparator....they are designed to provide a comparison between the items you are measuring. You should be finding at what point the bullet touches the lands then determine where you want your projectile to sit compared to that datum...ie either jammed or jumped......!

Originally Posted by Larskramer

interesting.... might have to look into the SACC ,

Get yourself a kit, comes with two bodies and your choice of inserts for headspace or base to ogive.
https://ozarkoutdoorsnz.co.nz/reload...omparator-kit/

Originally Posted by 7mmsaum

Everything mentioned above including Neck tension variances

There is a fix regardless of the cause

Don’t load to final length first time

Load 5 or 10 thou short on them all

Then measure and micrometer adjust the seating stem for the last measured thou for each one

IE. this one only needs 2 thou, this one needs 4 thou, this one needs 8 thou and this one needs 2 thou

Problem solved

That's hugely tedious. Best for the OP to find the cause and go from there. If I got a variation of 2 to 8 thou I'd be mortified.

Originally Posted by gqhoon

Get yourself a kit, comes with two bodies and your choice of inserts for headspace or base to ogive.
https://ozarkoutdoorsnz.co.nz/reload...omparator-kit/

Sac make a very nice product but you don't need to spend those sort of dollars.
I've got the original Stoney Point set (Now Hornady) and have added to it Sinclair shoulder bushes and ogive bushes which do a slightly better job of measuring than the Hornady.

Originally Posted by zimmer

Sac make a very nice product but you don't need to spend those sort of dollars.
I've got the original Stoney Point set (Now Hornady) and have added to it Sinclair shoulder bushes and ogive bushes which do a slightly better job of measuring than the Hornady.

Where could one obtain said Sinclair ogive inserts ? sorry can't google from work

Loading ELDMs in 7mm and the projectile length is different from what hornady states, then there is variation of up to +/- 2-3 thou. Annoying but you can batch them for group shooting.