Finding the Lands

[heytonyman]

I've read of at least half a dozen ways to find the lands when starting load up on a new rifle. Loading up for my Surgeon .308 I used the barely-sized case neck of a fired Lapua case and a 178 A-Max sticking way out. The round slid with light resistance in the case but not so much I couldn't easily move it by finger. I chambered the round and come up with a reading of 2.180" at the ogive. Repeated this process a dozen or so times and readings stayed fairly consistent to within +-.002". This puts my COAL right at 2.800" with a 178 A-Max. Cool. All my testing to date has shown great groups when backing off about .015" and seating them at 2.165" ogive. 300+ rounds down range thru ladder / pressure tests with no issues. No stuck bullets, no over pressures (that I didn't self-induce), etc.

Last week I decided to try the cleaning rod and tape method just for shits and giggles and came up with 2.150" ogive. Odd yes, but in my mind eyeballing a piece of tape to the rod at the crown was hardly a precise measurement but it was fairly repeatable to within +-.005".

Scratched my head for a few days and decided to pick up the Sinclair tool. I initially found the included bushing to be a bit small for my Surgeon 591R action but thru refining my technique I found the measurements I've taken were again fairly repeatable to within +-.002". The Sinclair gauge shows 2.150" ogive.

So, two methods show 2.150" repeatably and one showing 2.180" repeatably.

To add, when I first picked up this rifle I was function-testing some 168 FGMM thru it and had one bullet stick in the lands and made a mess. That has not happened since.

I seated a bullet at my usual 2.165" and smoked it with a candle and found it is indeed touching the lands. Backed off little at a time and finally found at 2.150" I was not seeing any markings on the smoke. Interesting enough that a 178 A-Max is seated to 2.150" ogive gives a COAL of 2.718". Well below SAAMI spec. I know that most custom rifles are going to have a "tight" chamber but damn...

Thoughts?

 

[Break Bad]

If you use a case that is not trimmed evenly or enough then you won't be engaging the headspace correctly...that and your distance to lands will never decrease obviously. I would venture a guess that your 'barely-sized" lapua case was not properly trimmed.

Offtopic: The one thing I have been interested in trying is a chamber molding...CERROSAFE® CHAMBER CASTING ALLOY | Brownells. Of course, your lands will move every 500 firings or so, which is probably why this is more of a bench rest item.

 

[JGorski]

For my 6 creed I pretty much use your first method, take a fireformed 22-250 case and run it thru a 269 bushing, that gives me about <.001" neck tension, shove a bullet in till it stops, then chamber it, pull it out and measure to the ogive, this morning I came up with 2.219", then I seated my 105AMP Hornadys .010" less. There's just enough tension where I have get my bullet puller out but cant pull it out with my fingers.