Comparator insert vs bullet jump question

[MJY65]

I think I know the answer to this, but would like to call upon the experience of others to solve it definitively.

I typically use a Stoney Point comparator to determine the max COAL (touching) for a particular bullet/rifle combination and then back off .020 for jump. This measurement will vary somewhat depending on bullet style. I'm thinking that this is due to the fact that the comparator insert is measuring on a point that is not exactly the same as the land dimensions (.295 comp vs .300 lands), so any variation in ogive profile ahead or behind that line affects the measurement.

If I had a comparator insert that matched the land diameter, should all of my comparator measurements on that particular rifle be the same regardless of the brand or style of bullet?

Thanks<script type="text/javascript" src="safari-extension://com.ebay.safari.myebaymanager-QYHMMGCMJR/1d20eafd/background/helpers/prefilterHelper.js"></script>

 

[Powermac]

You pretty much answer your own question there , as long as there is a difference in the bullet skape/ ogive you will get different measurements. Adding or subtracting a few thousands will Only change where on the bullet the comparator makes contact.

As for starting load development and seating depth tuning it is best to start with the bullet touching the rifling, as this is the point you will have highest pressure, and work out from there to find what your rifle prefer with each bullet. This is simple for safety respons.
Myself i zero my inline seaters at that point and move in/out the micrometer adjustment from that referanse.

As for comparators i use Bob Greens comparitor and caliper tool to sort bullets and check seating depth, it has made it very easy to achieve consistent seating within . 001 every time.

 

[MJY65]

You pretty much answer your own question there , as long as there is a difference in the bullet skape/ ogive you will get different measurements. Adding or subtracting a few thousands will Only change where on the bullet the comparator makes contact.

Except, if the comparator insert had the same diameter as the lands, it would actually touch each bullet in the same place that the lands do. I think the problem now is that the lands touch in a slightly different spot than the comparator. Ogive shape between those two points is where the differences come in.<script type="text/javascript" src="safari-extension://com.ebay.safari.myebaymanager-QYHMMGCMJR/1d20eafd/background/helpers/prefilterHelper.js"></script><script type="text/javascript" src="safari-extension://com.ebay.safari.myebaymanager-QYHMMGCMJR/1d20eafd/background/helpers/prefilterHelper.js"></script>

 

[Steel head]

I drill out my comparator inserts to more closely match the lands.

 

[gstaylorg]

Because the ogive is different for different bullets, you will probably never get the exact same measurement using a Stoney Point type of tool when combined with calipers and a comparator insert. Generally, the closer the comparator insert actually seats in relation to the ogive/bearing surface junction, the closer your measurements will be when using differently shaped bullets. For example, the aluminum Hornady comparator inserts have a noticeably smaller hole than do the comparable steel inserts from Sinclair. Therefore, they seat further out on the ogive away from the bearing surface junction and will give larger apparent measurement differences between bullets of different ogives.

In practical use, it matters very little if you are using the same comparator insert and the same bullet in the Stoney Point tool as in your load. If you use a different bullet in the Stoney Point tool than you're loading to measure to your lands, then your measurements will be off by however much the ogives of the two bullets differ between where they actually touch the lands and where the comparator insert seats in relation to that point. As long as you measure with the exact same bullet you're loading, it will be very close.

However, if you are simply trying to seat various different bullets at .020" off the lands, you may have bigger issues than the slight variance in measurement due to ogive differences. Although .020" may work well for some bullets, it may not be optimal for others. A seating depth test (typically in .003" increments) using your optimal charge weight will allow you determine what shoots best. As I mentioned above, as long as you determined the distance to the lands with the exact same bullet you're loading/testing, you can generate very reliable and reproducible seating depths in that way. If you're trying to do that using different ogive bullets without using something like the Green comparator, it's not going to give you very satisfying results.