To get a 140gr Sierra GameKing to sit .020 off the lands of my M700, the bullet will only be held by 2/3rds of the case neck (doesn't include the boat tail portion of bullet). Is this sufficient to securely hold the bullet in place or should I just forget about seating the bullet close to the lands and accept the bullet jump?

TIA

The general rule of thumb is to have 1 caliber of the bullet shank held by the case neck. In the 6.5 Swede you would need ~.26" of bullet gripped by the neck.
I wouldn`t worry too much about getting close to the lands in the Swede. The cartridge was designed with a 160gr RN bullet and most chambers are throated so deep you can`t get anywhere near the rifleing with spitzer bullets anyway.
My 6.5x55 seems to shoot best with the bullet seated quite deep. I don`t have my notes handy but I believe the 140 hornady sp I use is seated at about .065" off the lands. This is in a short throated Shilen barreled Mark X.

Thanks Ol` Joe,

I checked and it looks like I'll be at least .060 off the lands to have .264 held by the neck. I guess I could also try bullets without a boat tail to allow them to be seated further out if the boat tails don't work that far off the lands. I suppose Barnes bullets would also help as they tend to be extra long although those XLC's tend to be cost prohibitive.

My 6.5x55 used to allow me to seat 10thou from the lands with 100gr ballistic tips seated about half a calibre in the case. The throat is now a serious distance further away (about .25 of an inch) and accuracy seemed to improve if anything.

This seemed to make a nonsense of my desire to reach the lands so I shortened COL a tad to get more bullet seated in the case. Accuracy was unaffected.

In my 222 I was faced with your problem with 30gr bullets. I went for a 2/3 calibre seating depth and it is accurate (from the magazine too) as hell.

In all my 3.5x55 I made an OAL of 79/80mm.
No problema at all.
Maybee it is not what you arelooking for, but I always had good groups in a industrial and not prepared rifle.
bye