Thread: Using comparator tool when seating projectiles.

Originally Posted by Micky Duck

understood.....what Im saying is that if you already have a load that shoots well in your rifle..eg in my case factory 130grn old school silver tip in .270

when I set up seating die using that for other spitzer projectiles the difference in olgive shape /how curvey the front bit of projectile is, isnt a huge deal as the ring that contacts..be it 4.5mm or what ever will be same distance from base of case and same distance from start of rifling..so the only difference in rounds over all length or distance to rifling is going to be tiny...that 4.5mm might be at worst 1mm either way on different projectile.... you multi ladder testing types will be reworking load after changing component anyway so point is moot..if your using the SAME projectile that 4.5mm ring will be in the same place....

It’s quite common for rifles to have a CBTO tune window (node) of 0.006” (1.5mm). So using your example above, the 1mm variance either way equates to 0.008” between shortest and longest CBTO for a given projectile. So while you consider it to be tiny, it’s is enough to put you well out of a previously good performing node.

You really need to understand that the slightest difference in shape or profile of the ogive, will give a massive difference in CBTO measurement.

Originally Posted by gqhoon

It’s quite common for rifles to have a CBTO tune window (node) of 0.006” (1.5mm). So using your example above, the 1mm variance either way equates to 0.008” between shortest and longest CBTO for a given projectile. So while you consider it to be tiny, it’s is enough to put you well out of a previously good performing node.

You really need to understand that the slightest difference in shape or profile of the ogive, will give a massive difference in CBTO measurement.

That’s 6 thou and a lot smaller than 1.5mm. Most people tune in the 3 - 5 thou window. 0.07mm - 0.12mm

Originally Posted by McNotty

That’s 6 thou and a lot smaller than 1.5mm. Most people tune in the 3 - 5 thou window. 0.07mm - 0.12mm

You’re right, my maths sucks. But the point remains, +/- 1mm difference in seating depth makes a massive difference.

Originally Posted by gqhoon

It’s quite common for rifles to have a CBTO tune window (node) of 0.006” (1.5mm). So using your example above, the 1mm variance either way equates to 0.008” between shortest and longest CBTO for a given projectile. So while you consider it to be tiny, it’s is enough to put you well out of a previously good performing node.

You really need to understand that the slightest difference in shape or profile of the ogive, will give a massive difference in CBTO measurement.

if the projectiles are not the same at that given point on curve of tip...they wont be the same at fattest point either..so point is moot.. either they are the same projectiles with same shaped jacket or they are not..agree the cartridge overall length will vary because of tip shape..but he point the seater pushes..for want of better word,should be the same for all your projectiles in that batch,it will be same fatness,so no different than seating from your olgive point.... the fattest part closest to the tip.

Originally Posted by Micky Duck

if the projectiles are not the same at that given point on curve of tip...they wont be the same at fattest point either..so point is moot.. either they are the same projectiles with same shaped jacket or they are not..agree the cartridge overall length will vary because of tip shape..but he point the seater pushes..for want of better word,should be the same for all your projectiles in that batch,it will be same fatness,so no different than seating from your olgive point.... the fattest part closest to the tip.

It’s not a moot point. The tip to ogive variance is exactly what you need to be aware of when seating projectiles, as any variance in ogive shape will absolutely give different case base to ogive dimension and therefore different jump to the lands.

That is one of the reasons that people modify seating stems to better match the ogive shape of their favourite VLD projectile. The point of contact is then over a longer length of the ogive radius, which is likely to be more consistent over the longer length than just a single, thin point of contact of a standard stem.