110 FCP 338 LM chamber data

[Ray1953]

Working on my new artillery piece. Doing some chamber data. For my rifle I start getting a sticky bolt at 2.325" shoulder length. I have some multiple fired Lapua brass that is now reading 2.327 or less. As my cases fire form, I start bumping them back when case length gets to 2.325" or better. I bump back to 2.324" - 2.323" so a .001" - .002" shoulder bump. Seems to vary based upon load how fast they stretch which would be as expected.

I started looking at seating depth using a Hornady OAL guage. The modified case is 2.317" but all my brass is 2.323" or so. I determined that to get an accurate seating depth the only apples to apples measurement was the shoulder to ogive measurement. This is what I have determined so far:

300 SMK
Gauge measurement 2.829"
Modified case length 2.317"
Shoulder to Lands .512"

So to seat my bullet length touching the lands I have to add the shoulder to lands measurement to the case length being loaded. So if I am loading a case which measures 2.323 to have a 300 SMK bullet touching the lands I have to have a base to ogive length of 2.323" + .512" or 2.835"

What seems amazing to me is the 300 bergers, the 300 scenars, and the 250 SMK all have a shoulder to ogive measurement of 0.522"
The 285 hornadys have a .538" shoulder to ogive length

[Zero333]

Measure the whole cartridge from cartridge base to bullet ogive with a bullet comparator on the calipers.

You're making this a bit confusing for yourself.

The case length is irrelevant when finding the lands with a bullet, no matter what method you use.

[bearcatrp]

Reloading Hornady 285 ELD-M with H-1000, my coal is 3.766, which is 0.020 of the lands. My rifle is in my signature

[Ray1953]

My factory fresh Lapua brass measures 2.317", just like the modified case. My fire formed brass is anywhere from 2.325" - 2.317" depending on number of firings. If I seat a bullet to .020" off using new brass I get a case length if 2.809" (0.492" shoulder to ogive). If I seat to 2.809" in a case that is 2.325" The bullet will be 0.484" shoulder to ogive. This will seat the bullet .008" farther back into the case. So instead of .020" off I will be 0.28" off. Remember the cartridge is drive forward by the firing pin initially. BUT...if the case sets back onto the bolt face upon firing before the bullet exits the neck, then the distance will be base to ogive. HHHHMMMM....I do tend to over think things some time.

[RC20]

The comparator tends to or does measure shot.

Its great for shoulder setback bumps checks, but for bullets.

While best in an unloaded case, put a bullet into a size case (in my case I would even seat it without using the M die to make sure it stuck good in there. I have not had one move yet but its possible.

Then take your best guess but long, load it in, try to gently close the bolt.

Resistance will be felt. Bullet will probably stick in the lands, use a soft hammer or screw driver and gently tap back open.

Move it back .020 until the bolt closes. You can refine it but you can also guess your land are about .010 forward.

Done deal, then measure the bullet OGIVE and you have your setting.

I do not load into the lands, if its a low level fill I will shoot it from there, if its a higher load I will move it back out another .010 before I shoot it.

As noted, its interesting how common some bullets are to the same dimension.

[Cmgoff]

Are you shooting a 338 LM with a standard 110 fcp? If the action was not one of the larger actions intended for a 338 LM then your problem may be because the bolt lugs or the action are deflecting due to the high bolt thrust forces generated by the lapua magnum.

Assuming that is not the cause, I like to measure the distance to the lands using a fired case that I bump the shoulder back .001". Then remove the firing pin assembly and the ejector from the bolt. With these components removed there is no resistance when closing the bolt. This way you can systematically load shorter and shorter until the bolt closes freely. I find this method more accurate and more repeatable.

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[Ray1953]

I bought my rifle chambered in 338 Lapua Magnum from Savage in March of this year. I find cases that are 2.325" will only chamber if I force the bolt closed. I start "bumping" the case length back by 0.001" when my case length gets to 2.324". A length of 2.323" (or less) chambers easily and more importantly extracts without requiring me to beat the bolt open.

[Ray1953]

The issue with seating bullets a known distance off the lands is how tight a tolerance matters. I know that due to my guns chamber I can have a maximum distance error of 0.008". So if I seat a bullet into new lapua brass my base to ogive length is 2.809". This will put the bullet 0.020" off the lands at the start of bullet travel. If I use that same measurement to seat a bullet in a fire formed case of 2.324" (new lapua brass is 2.317") the bullet will be seated 0.007" deeper into the case neck. Since prior to bullet movement the firing pin drives the case forward to the shoulder this means the bullet is 0.027" off the lands at start of bullet travel. If being 0.027" off the lands instead of 0.020" off the lands changes the group performance then this is an issue. If the group performance is not affected then it is a mute point. Since we DO NOT use COAL to seat bullets due to the ogive to bullet tip varying by about 0.010" even in the same box of bullets, my guts says it matters. Therefore you have to correct bullet seating depth by changes in case length to get a consistent distance off the lands at start of bullet travel.