Mikecr
Well-Known Member
That is UNSAT right there..
There are some things leading to easy accurate seating(not close, but dead nuts) that lead to other good things as well. Let's break it down.
Seating force variance: when you create excess seating forces, you create excess seating force variances. A higher/lower seating force changes stem wedging at it's contact datum.
-To mitigate this, stop oversizing necks to cause excess interference fit. This does nothing more than over work necks, and using your bullets as neck expanders. Bullets are not neck expanders.
-Stop cleaning the carbon layer out of necks. Carbon is the perfect seating lube. If it wasn't provided with firing, someone would be selling it to you.
-Either minimally size necks with minimum chamber clearances, or plan to anneal very accurately & often.
The better your friction and force control, the better your neck tension correlations and matching from this.
Ogive radius variance: To begin, the entire nose is the ogive. It's shape affects both stem contact datum and land contact datum (which are separate points). So where you want your land contact datum consistent, to provide same CBTO as tested best, the ogive shape needs to match across every bullet seated.
This is accomplished using an ogive radius comparator, which measures the distance between the two seating/land datums. You can do it manually with separate tools, or use a Bob Green Comparator (BGC), and cull out offenders from each lot of bullets. This variance affects BC as well, and it's measure is far more valuable than base-to-ogive (BTO) comparisons. https://greensrifles.com/new-product-page
Seating stem issues: Just run the smallest drill bit into the stem that will clear interfere of bullet tips. Then lap, per the before mentioned process. Never had to do this with Wilson stems. They just work for all bullets.
Measurement: Don't set & forget your dies, ever. Measure CBTO result of every bullet seated.
It helps to have micrometer adjustable seating, so that you can creep into perfect with every one. As far as comparator tool used for this, any work as well -unless the company went out of their way to get fancy & screw it up.
So the simpler, the better.
I use a Sinclair 'nut', hard to get it wrong, but I gotta say this Forster upgrade looks really good: https://www.forsterproducts.com/product-category/inspection-measurement/datum-dial/
Don't go over-bored: Test for best CBTO early and reproduce it, but you will have a seating window to work with. This window will get wider as the lands erode, and you do not have to chase this. Just keep on with what you originally tested as best for the accurate life of the barrel. Eventually, you may be tempted to adjust this, when the gun step changes away from what you're used to. That's where you've past accurate life. Unscrew the darn barrel and screw another on, right there. Don't waste your efforts otherwise. It sucks, but barrels live & die.
