Bullet Seating Depth

[Willem .243 musgrave]

Hey guys!

I was just wondering about the most accurate way to determine my bullet seating depth?
I've got a 243win rifle with a 1:10" twist on a 24" barrel, is there data on what is the most accurate distance that the bullet should be lying off of the lands?
Should the bullet be lying just on the lands(know this might cause excessive pressure) or about 2 thousands of an inch off of the lands?
Should I do tests on the seating depth like on finding the correct load, and should these tests be done before I do my load tests or after I have found a load that works best for my rifle?

Please this is something that has been bothering me for a whilst, I am an engineering student so I do not have too much time on my hands to load a lot of ammo and go out to the range to do a lot of different tests, but if that is the only way I will find time, after all shooting is a lot more fun than studying!!!

 

[Rem6br]

The sweet spot off the lands is different for each rifle. that is something you have to find for a particular rifle, you could start at .020 off and then go more
or less if you don't get the results you need

 

[Shynloco]

The sweet spot off the lands is different for each rifle. that is something you have to find for a particular rifle, you could start at .020 off and then go more
or less if you don't get the results you need

BIG +1. No such thing as a "recommended" seating depth for best accuracy. Each particular rifle will tell you what she wants by the groups she puts together on a target. Personally, I start with Saami spec (manual recommendation which is for any rifle and has a jump), then go to .020 off and get closer by .005 each time until I get to jam. You could reverse the process and if you see a gradual fall off, stop and go back.

 

[savageshooter86]

I use the Hornady comparator to measure to the lands. And I use the Berger method at finding best seating depth. This has worked great so far for me and my rifle. There is no way around load testing if you really want it to shoot the best it possibly can

 

[sbranden]

I started out trying just "book COL", whatever the manuals recommended - and shorter.
Then I bought a hornady OAL guage with modified case for my particular caliber.
Now I use the hornady tool, plus a round that I make myself, AND a hornady comparator body w/correct caliber "insert".

You can partially neck size a once fired piece of brass, then manually begin to seat a bullet yourself by hand.
The neck just needs to be tight enough to hold the bullet after it makes contact with the lands and you go to eject it then.
But I'll chamber one fo these, then close the bolt ever so slowly, then eject slowly, and then measure with both the comparator/insert on my calipers, as well as without (for a more standard base to tip of the bullet measurement also).

I always seat then to the comparator (base of case to bullet ogive) measurement then, where the COLs may vary slightly but the jump to where the bullet engages the rifling, no matter how much or how little that may be, should be consistent.

 

[jefats]

To get a true measurement of any seating depth you must first separate bullets according to where the ogive is located on each bullet. Finding where the ogive engages the lands is the "zero" spot, and unless you know exactly where it is you are guessing as to seating depths. It may sound like it's a lot of work to measure each bullet but it really isn't. Measure a few of your favorite bullet and you'll see. Find this measurement and then you will be able to determine seating depth.

 

[gotcha]

Hi Willem! Are you loading for hunting, varminting or competition accuracy? There's a BIG difference in the number of doodads/extra tools necessary to accomplish the various above tasks. I'm considering the extra time & money necessary to accomplish your goal. What kind of optics do you have? Match bbl or factory? Front & rear rest type? Shooting experience? All factors in the accuracy you can achieve even before load developement.

 

[NorCalMikie]

I first measure the chamber length (to the lands) with the Hornady (Stoneypoint) comparator.
From there I measure each bullet by make and style. Write it down for future reference. From then on, I know how long to seat each bullet to reach the lands.
I start off with all my loads with the bullets "jammed" .010 into the lands. I can adjust from there. Everything I shoot is from the bench.
If you are hunting I would suggest that you work up your loads with a jump to the lands. If the time ever comes up that you have to unload a loaded round, you don't want to take the chance of the bullet sticking in the lands and you end up dumping powder in the action. JMHO and what works for me, Mike.

 

[boltgunluvr]

FACT .....all rifles will prefer something different. WE all have our different methods of madness. I've never had a rifle that liked anything closer than a .005-.007 jump. My Rem 700 243s prefer a .020 jump using 100gr Sierra Pro Hunter and a .065 jump using the 95gr SMK. What weight are you trying with your 1 in 10 twist??

 

[Willem .243 musgrave]

I mostly use the rifle for hunting (head shots on deer sized game) and varminting. But I would like to start shooting at longer distances at varmint type animals at ranges like 600 yards +.
It is a factory barrel (24") that was a blank and I had it chambered by a gunsmith. I like to shoot the hornady V-Max bullets. Get good groups with the 87gr, also have a few 65gr. (I have a redfield revenge 6-18x44 varmint reticle scope, I also have a suppressor fitted, when I do load tests and trying to shoot groups I shoot off a bench with a sandbag in front and rear of the rifle, but when I'm varminting I shoot lying prone with a bi-pod)

My case prep: neck size(after cases have been fire formed to my chamber's dimensions)
Tumble so there clean inside out
Trim to correct length(de-burr and chamfer)
Flash hole de-burr and uniform
Primer Pocket uniform
Neck turning

With these cases and a bit of load test I got about a 0.4 MOA consistent group @ 100 yards.

The way I determined my bullet seating depth was to remove the insides of my bolt so there would be no tension caused by the fire pin spring, then I started off seating a bullet in one of my prepped cases (without a primer or powder in) that was very long and tried it in my chamber, kept seating it a bit deeper until the bolt just closed where I could feel there was no resistance (caused by the bullet jamming into the lands). I measured that and just set the bullet about 0.02 inches deeper, I guess that's about the distance it is lying off of the lands. (When I reload I measure every bullet"s OAL, don't have the tools to measure at the ogive of the bullet)

Any advice on anything I'm doing wrong? Will it help to try different seating depth's with the current load that I developed?

 

[gotcha]

Willem, Looks like you're doing very well w/ load developement. Especially w/ a factory BBL There's a very good chance you could improve groups by varying seating depth. Start w/ the depth you're presently using & make 6ea. rounds at .005" shorter increments out to a max of .025" off the lands. You know what your present load does so no need to duplicate that one. Fire 3 shot groups of each loaded depth starting w/ the shortest OAL. One of these groups will probably be smaller than the rest & hopefully smaller than your present best group. The 2nd set of three shot groups will serve to confirm that the smallest group wasn't a fluke. You can then make minor tweeks to your best seating depth (.002" to.003" + or -) to see if you can further improve accuracy. Can't guarantee better groups but its worth a try.