Interesting COAL/O-Give #'s in my .300 PRC

[rockchalk06]

Working towards finding a starting COAL for these 230 grain Hornady A-Tips.

Loaded to mag length with enough room to get reliable feeding, COAL is @3.750". These will not allow the bolt to close and after running a marker all over the bullet, I am 100% in the lands. Jam test was next. Seated them out to 3.900" and sent the bolt home. 3 times, I got 3.720.5", 3.720" and 3.720.5". Lets call that 3.720" to jam.

Hornady is calling for 3.685" for a COAL on the 230 A-Tip. Using their data on their bullet, I'm only jumping .035" to jam. That seems shorter that I'm used to with Bergara barrels. I know in my .308 Premier, I had over .070" jump to jam and .060"ish in my 6.5 HMR from what Hornady or Berger was calling for.

I'm going to run with 3.700" COAL and 2.817" off the O-Give.

 

[swampratt]

When you jam and remove the markered case how long are the Jam marks ?

For my rifles the marks are usually .030" long.
So seating the bullet .030" deeper leaves ZERO marks on a colored bullet.
If I seat .025" from jam I just touch the rifling and get marks on the bullet of course about .005" long.

.005" off the lands has worked well for me and many rifles but then there are those bullets that like to jump .060" or more. I had some Bergers that did not group well until I set them to jump a long ways like that.

Just boils down to experimenting.
I assume a lot of that bullet bearing surface is in the case.

Sometimes I can find a sweet spot when the boat tail is just past the bottom of the neck.

Still it boils down try and see what your rifle likes.

 

[rockchalk06]

I'll have to do it again and measure them. I neglected to do so.

 

[rockchalk06]

My .308 loves a big jump. .060" on a 168 grain ELDM @2672 out of a 20".

My 6.5 was about as liberal as it can be. I tested the 140 VLD Target from .020" and stoped at .074". To be able to feed out of the mag, I settled at .057" jump. Single digits SD's up and down. Once that bullet passes 2650 FPS it tightens up like a boss.

 

[diggler1833]

Interesting read, thanks for sharing. I like seeing how other people are doing it.

That initial "rough seating depth" test is a lot like a game of Battleship. Each barrel will have multiple depths for each bullet where it will shoot lights out...or like garbage. We take shots in the dark until we land on something that is right.

I try to visualize it like a wavelength; over the course of .150" you might have four peaks and four valleys (or more, or less)...and multiple points in between where accuracy is average.

I've found that the really tight node depths usually run about .005 - .010 long, and that's it. I've since gone to trying to find depths where I can erode .005 and still have an excellent load without having to work up again.

That's all assuming you don't mess with the powder charge weight too .