Minimum depth bullet should sit in neck?

[Kyle Schultz]

I'm aware of the need to get the boat tail-bearing surface junction of the bullet at or above the neck-shoulder junction of the case. Moving to the other limit, are there any rules of thumb as to how much of the case needs needs to be filled by bullet in order for the bullet to be safely held in place? I've heard 1 bullet diameter but that doesn't leave much "wiggle room" on a 6.5x47 Lapua case with its 0.299" neck. I'm playing with dummy rounds to setup a reamer.

Thanks in advance for your thoughts.

 

[RonAKA]

I think it depends a lot on your application. If your gun has a magazine, or the cartridges are to be used for hunting and will be subject to a lot of handling, you want more bullet in the neck and a larger interference fit. The last thing you need is to have the bullets fall out in your magazine from recoil, and dump powder everywhere.

For target shooting with a single shot, I see some report bullet seating as little as 0.100", much less than a bullet diameter.

 

[camac]

I agree with Ron 100%. I have seated as low as 0.100 and achieved excellent accuracy but would never load these in a magazine. Single shot target shooting only. There are some disadvantages though. First is runout. With little support in the neck you can have fairly crooked bullets unless you watch it very carefully. Also neck tension as such is basically non existent so you rely on the lands (jam or close) to get good consistent initiation.
Sometimes it is best to just set reamer for your longest bullet (allow a little for rifling edging forward after a few hundred rounds). The 6.5 * 47 is a little tricky in most want to try and get the 139-142 class bullet going but need to ensure the 123 and 130's shoot well too just in case. All my reamers were set for the longer bullets and still shoot the 123's better thand the 139-142's. (6.5*284)

 

[Kyle Schultz]

This is a single-feed F-Class rifle.

Camac nailed exactly what I'm trying to do. Right now my gun only has a 0.118" freebore. Fine for the Scenar 123s but just a smidge short for even the Berger 130 VLD. I'd really like to make the Berger 140 VLD fly but I don't want to ream the throat and slam the door on the lighter class bullets.

Looks like I need somthing in the 0.16 to 0.17 range to properly seat the Scenar 139 and Berger 140 VLD. If I can live with about a 60% neck fill, about 0.179" of shank in neck, I can still touch the lands with the Scenar 123 all the way out to a 0.177" freebore if necessary.

Based on comments above, seems like I'd be okay. Thanks!

 

[Rust]

Kyle - As long as you are reasonably sure you have enough bearing surface in the neck so a little rough handling of ammo during transport won't knock the bullet seating out of alignment or change the seating depth it shouldn't matter. Maybe 1/2 bullet diameter of bearing surface would seem prudent for most match only ammo.

One of the short range benchresters made up a 30 BR that had the shoulder blown so far forward there was virtually no neck and it shot pretty well.

 

[camac]

I Reckon you would be quite safe with what you are suggesting. I don't have any scenar 139's or Berger 140's here at the moment but using my home made bullet comparator the bearing surface length difference between 142 sierra and 123 scenars is around 50 thou. Not much really, so if you compromised and set it halfway and had .280 seating depth for the 142/139 class and .230 seating depth for 123's you would have plenty of room to move as the rifling extends out. But if you want less neck filled then you could go down from there. I think anywhere from Rust's suggestion of .130 seated out to .230 would be OK and your suggestion sounds right in the middle. mine is much less seating depth than this and I have a shorter neck in the 6.5*284 and all barrels shoot the 123's fine. (as I said better with the 123's than 142's).
A couple of interesting points looking back through my load development though. The Berger 140's liked a 90 thou jump in my first barrel and so did the sierra 120's. This left a nice chunk of projectile in the neck even with long freebore - That kind of throws another spanner in the works when trying to guess how much freebore will be best.