Author Topic: Correct bullet seating depth (Read 669 times)

Buckskin · « **on:** April 09, 2006, 06:57:28 AM »

I am just beginning reloading and have a question about determining COL.
I'm in the process of reloading a batch of 204s for my encore and am trying to figure when I am off the lands. I seated a half dozen loads about .015" longer than factory loads. It looks like a big difference. I use my wifes mascara to see if I was in the rifling. I'm getting a smudge on the bottom of the bullet but no rifling marks. Is > .015" a typical difference between factory loads and hand loads or am I missing something?
Thanks for any help

ricciardelli · « **Reply #1 on:** April 09, 2006, 12:37:39 PM »

OAL totally depends on the bullet you are using and the chamber of your firearm...

:?

Gregory · « **Reply #2 on:** April 09, 2006, 01:21:44 PM »

Every gun is different as to the max OAL. You can determine what it is for your 204 barrel very easily:

You'll need a cleaning rod, a bullet, calipers, and a magic marker.
Drop the bullet down in the empty chamber and hold it against the rifling with a pencil. Insert the cleaning rod till it contacts the bullet and then mark the rod even with the muzzle. Push out the bullet, close the action with the chamber empty, and insert the rod again, mark it again, even with the end of the muzzle. Measure the distance between the marks and that's the max OAL for your gun and for that particular bullet.
Try 1/32 to 1/16 inch less than the max OAL for your starting loads.

Grumulkin · « **Reply #3 on:** April 09, 2006, 04:43:44 PM »

With the Encore, you can seat the bullet just a little and then try to chamber it. Chances are you will get resistance. Seat the bullet progressively deeper until the action just barely closes easily with no excessive resistance. The bullet should be just off the lands.

PaulS · « **Reply #4 on:** April 09, 2006, 05:07:51 PM »

I always start with the OAL listed in the manual - that way the pressure is a known quantity. After I work the load up I can play with seating depth to fine tune the load. It usually takes a bit more powder as you place the bullet out farther (in my experience) so I am better off working the load up first. The manuals list an OAL for a given load that produces the advertized pressure. As you place the bullet deeper into the chamber the pressure will drop slightly and if your accuracy begins to fall you can make it up with a slight increase in powder charge (.1 or .2 grains).
With that said I will tell you that some rifles have such a long throat that you can't set the bullets in far enough to be close to the rifling without them losing contact with the shell casing. My 3006 is such a gun but when loaded to the manual listed OAL it shoots sub MOA groups - no change or deviation needed.

Dusty Miller · « **Reply #5 on:** April 09, 2006, 06:56:32 PM »

Does the RCBS "Precision Mic" Micrometer Headspace and Bullet Seating Depth Gauge solve this problem or is it just a gimmick that is more trouble than its worth?

PaulS · « **Reply #6 on:** April 09, 2006, 07:52:29 PM »

I don't have one so I can't speak to what it does or doesn't do. There are many tools that measure from the base of a loaded round to the point on the ogive that will contact the rifling. If you know how far from the lands you want your bullet to be they can be a valuable tool. If you want to experiment with different depths they give you a good maximum length but measuring tools don't give you any idea where you will get the best accuracy from your rifle. They are designed to make it easier to duplicate a known seating depth with new rounds. You can make most any rifle shoot sub-MOA groups without seating the bullets close to the lands just by finding the right load of the right powder for your gun and bullet. There are certain "rules of thumb" that simplify the process. The most important is to find a powder that comes close to filling your cartridge while providing close to the maximum pressure for your gun. The next is to be sure that your powder selection is ignited uniformly from round to round. Some powders require a magnum primer to do this while others (normally single base powders) do not need magnum primers. Sometimes compressed charges give very good results and in other guns they don't - find a powder that gives you what you need to have and works in your gun. I choose double base powders whenever I can. I have always had better luck with them than with single base powders. I can almost predict the load that will work in MY guns before I ever load a single round. I usually get my accuracy load at very close to the maximum loading. That means that my velocity is also very close to the maximum. Some of my guns have a short throat and others have throats that are so long that even with a heavy bullet I could not seat them out far enough to remain close to the rifling and stay in the shell.
The tools that measure to the ogive of a loaded round are just a tool - like a 12 pound sledge hammer. If you need it, and know how to use it the job is easier with it than it is without it. If you don't need it then it just takes up space because it is too light for a good anchor and too big for a paper-weight. If you can get 1/2" groups without the tool then it is just a gimmic but if you need it to get those 1/2" groups then it is a tool. Only you can decide if you need it or not. I don't need it - my groups prove it.

Buckskin · « **Reply #7 on:** April 10, 2006, 08:42:15 AM »

Thanks for the Help!

Glanceblamm · « **Reply #8 on:** April 10, 2006, 10:59:01 AM »

Gregory took the words right out of my mouth.

Seems like the 30 cal class likes the bullet seated so that the rifling would scrape soot off a bullet without leaving any mark on it.
My .22 Centerfire's seem to prefer that the bullet be seated .010 behind the rifling.
Some say the bullet should be seated at least to the depth of it's overall circumferance.