…would you put through a new rifle before beginning to develop a load specifically for it? I have plenty of bullets loaded for another .223 to use for initial sighting and break in. How many rounds should I give it before starting on the same bullet weight but loaded just for the new rifle?
We start right out of the gate… knowing that a barrel may need to settle in. The only dramatic change in groupings was Pappabear’s new Faxon QPQ pencil barrel. It went from 4-5 MOA to 1.5 MOA in a few range trips.
WOW- thats dramatic. Wonder why? Tight spot maybe?
It’s just a squirrely barrel.
Mine is a Faxon 20" gunner profile 1:8 twist. Using the 55 gr FMJ handloads I have loaded up for my other rifle it is getting about 1.5 - 2 MOA after its first 120 rounds. I just don’t want to go through an entire load work up knowing that the barrel will settle down some more and possibly throw the work up results out the window.
The majority of a barrel’s throat erosion occurs in the first few hundred rounds. I have watched this occur on several of my rifles, some moving out as much as 0.015” or more in as little as 200 rounds. It slows dramatically after that (but it does continue), and the net result is that the distance from your projectile to the lands is changing quickly early in the gun’s life. This can make nailing down an OAL tricky in some guns in the early stages of break in. I suspect this is less so in a barrel that’s been Melanited, but I can’t prove it.
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Throat erosion occurs during the entire life of the barrel not just the first few 100 rounds. Thats why they make throat and muzzle wear erosion gauges.
Read the link below.
https://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/
Bottom line, heat causes throat and bore erosion and the peak flame temperature of the powder as chamber pressure increases is what causes the wear.
Example a .222 at 46,000 cup or 50,000 psi max pressure will have less throat erosion than a .223 at 50,000 cup or 55,000 psi.
As I said…”it continues.” It does not, however, continue at the same rate.
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My measurements seem to match what you’re saying. I checked my 308 bolt gun not too long ago… expecting a lot more erosion. But it wasn’t nearly as dramatic as the first few years of firing.