When trying to determine exact chamber dimensions to set C.O.L. could you seat a bullet in a case ( unprimed and no powder of course ) and gently chamber this , then remove and measure oal? You could then do it a few times to see that the dimensions repeat. Once you came up with a dimension from bolt face to lands , how far off the lands , would you start when first developing the load. I am looking to begin trying to develop a load for a .223 and thought this method might work. Thanks.

Yes. Maybe .020 to start, then .015, .010, .005 checking for accuracy at each setting with the same bullet/load. COL is much easier to determine, and more accurate, with some type of comparator like RCBS or Sinclair.

That's just how I've done it before. The bullet comparator will make this process easier. Then I discovered the stoney point "over all length gauge". Personally I start .050" off the lands. You need to start somewhere.

I use a method very similar to what you describe to determine my chambers over all length. I have one case for each caliber that I have split the neck to the shoulder with a Dremal and cut off wheel. Deburr the cut edges on the brass, then you can barely start a bullet by hand then close your bolt to seat the bullet precisely on the lands. With the spli, the bullet seats with less force and is easy to pull back out to repeat the process a couple times to verify the correct OAL. If the bullet moves too freely in the brass, simply pinch the neck shut a little with your fingers. The modified case can be stored in the box with your dies and used over and over if you change bullet profiles or guns.

Mike

Thanks for the replies and tips. Just to make sure I am reading things correctly you guys are suggesting to start off the lands from 2 to 5 HUNDREDTHS , not thousandths . Is that correct?

Jim,
I seat my bullets right on the lands if mag length permits it, the bullet is centered in the bore better and usually provides top accuracy this way, but work up loads gradually. Pressure is not generally too much higher but could be in some cases.

I suggest the method that MBK uses too, I used this before I got my Stoney Point OAL guage and it works the same, the added benefit of the SP is that the measurementt can be taken from a consistant point on the bullet at the ogive rather than the tip which is not always consistant.

Use plenty of tension on the bullet or the bullet will stick in the lands and leave it there when pulled out or leave marks on the bullet indicating it was pulled out a little.

The Barnes XLCs are the hardest to keep from pulling loose with the slit neck method. I sized the case before using the cutoff wheel to split the neck. Using this mmethod I was .005" longer than the Stoney Point method accross the board so it seats them a little more into the lands is all, but is very consistant, much more than any other method I've used.

I would start at the lands and find a powder charge that works good then back off .005" at a time until your groups prove what length the gun likes best. .005 deeper into the lands is a place to start too. Good luck. Your magazine box may dictate a much shorter OAL and then your screwed, most of my factory chambers have absurdly long throats and leave me with sometimes over .100" jump or more if seated at the max allowable length anyway.

Slight variation:

Take a fired case, and gently squeeze down the neck so that a bullet can slip in the opening, but will feel some friction. Put some Krazy Glue inside the neck. Slip a bullet part way in, and chamber the bullet and case. Count to 60. Remove the bullet and case, and the bullet will be glued in the position where it contacted the lands.

If you don't use glue, the bullet can be slightly extracted from the case as you eject it.