Bullet off lands?

[vcinri]

I am finalizing a load for my 338 Lapua. I have never played with the bullet off the lands. I have been going by the case O.A.L. recommended in the load data.
Do you see a big difference in the velocity and accuracy adjusting the distance? What distance would you generally start?
Thanks,
VC

 

[BallisticsGuy]

Before the pedants jump on you, seating depth isn't to do with headspace. Headspace has to do with distance from breech face to a datum point forward of that.

In my experience there's no real difference in velocity from one jumped distance to another, that ignores jamming entirely. Seating depth can affect chamber pressures and group size a lot. I've found a heck of a lot of luck using .040" off the lands to get my powder charge figured out and then running a set at whatever charge weight comes of that at each of .010, .040, .080 and .120 jump. There's usually a distinct trend in resulting group size. Sometimes the trend in results toward trying a set touching or jammed is enough for me to do that but I don't like to go there. Running jammed it just causes a lot of practical problems.

 

[ar10ar15man]

actually one of the best tuning tools for accuracy is seating depth( as was pointed out headspace is a characteristic of your rifles chamber from bolt face to a point on the shoulder).
is your rifle mag fed or single shot ?
for a single shot i would start at the lands, and work up a load, then fine tune with length.
for a magazine fed max mag length and shorter.
let some 338ln guys guide your load development.

 

[Howland]

Every rifle/bullet combination likes a particular amount of jump. Some combinations are very forgiving, some very finicky. Some bullets have a reputation for being forgiving, some like to be jammed. Loading to mag length in my .338LM RPR gives me about 0.080" off the lands. I've got accuracy to low .6 MOA. Maybe I could tighten that up with less jump but that would mean single loading. I choose not to go there. If my game was competition off the bench, I'd suck it up and single load if it meant shrinking that.

The first step is to determine what seating depth touches the lands. Measuring cartridge base (head) to ogive (CBTO) will be more precise than OAL. The last lot of 285gr. ELD-M have 0.003" variation from ogive to tip. If you're loading VLD bullets, use a VLD seating stem.

Seating depth differences will have only small effects on pressure and velocity unless you're touching or jamming. A stout but safe load jumping can go over the limit jamming the lands. Finding the optimal seating depth will be more accurate than a one size fits all OAL. Sometimes it's a little, sometimes it's significant.

 

[vcinri]

Thank you for the responses.
I apologize, I should have rephrased the question and thread title. I was referring to the distance of the head off the lands as the head space and adjusting the seating depth of the bullet to get it.
I have a magazine fed rifle.
Thanks again!
VC

 

[BallisticsGuy]

that's called CBTO (case base to ogive) and that's the definition of seating depth.

 

[vcinri]

I used to reload years ago but we never got as technical as we should have. I got back into it for this rifle only. Still a bit ole school I guess but you can certainly learn a lot here.
Thanks.
VC

 

[ronstone09]

I am finalizing a load for my 338 Lapua. I have never played with the head space off the lands. I have been going by the case O.A.L. recommended in the load data.
Do you see a big difference in the velocity and accuracy adjusting the space? What distance would you generally start and what distance is the cut off point?
Thanks,
VC

The load books usually list SAAMI depth which is conservative ! depending if youve got a magazine that limits your OAL! i would get the hornady oal gage and tahe a reading in the lands and then back off 50 thousands and go out from there until you reach the limit of your magazine or find a depth that shoots well !

 

[Capt Kurt]

You got good information for your question. 2 areas to be aware of. Do not extend your bullet passed the maximum length of your magazine if you are magazine fed and do not extend your bullet passed the point that you can not eject the entire round

 

[ar10ar15man]

I THINK WE HAVE A FAILURE TO COMMUNICATE
define "head"
there are companies like berger bullets, sierra bullets hornady bullets..
there are no head companies that i know of in the shooting world.

Thank you for the responses.
I apologize, I should have rephrased the question and thread title. I was referring to the distance of the head off the lands as the head space and adjusting the seating depth of the bullet to get it.
I have a magazine fed rifle.
Thanks again!
VC

 

[Alibiiv]

Thank you for the responses.
I apologize, I should have rephrased the question and thread title. I was referring to the distance of the head off the lands as the head space and adjusting the seating depth of the bullet to get it.
I have a magazine fed rifle.
Thanks again!
VC

VCINRI, I too am in RI. Based upon what you have written, the headspace that the amount of jump off the lands are two different things. Your headspace is determined by the distance between the 20 degree shoulder and the base of your case. The distance for jump is determined first by finding out the exact distance at which the "particular" bullet that you are reloading touches the lands. For determining that amount of "bump" when setting your .002-003 bump on the headspace I use a Hornady Lock-and Load head space gauge. To determine the distance between the base of your cartridge and the junction point of where your bullet touches the lands I use a Hornady Lock-and-Load OAL bullet comparator, along with a Hornady Chamber bullet comparator; and you will need a good set of dial calipers to use these tools. I am sure that there are manufacturer's tools that will make the measurements that you are looking for also, I have found Hornady to do what I need them to do for my particular needs. To help understanding what we are writing about, if you Google the names of the measuring tools that I have written about and click on the "videos" menu underneath the search you will find plenty of You Tube videos demonstrating how to use the tools. I hope that this helps. PM me with a phone number if you would like, I'll get back to you.

 

[misterc01]

Pu get to load so the magazine feeds. Usually ends up a ways off the lands. Second - IMHO a little more research will help get the terminology standardized. For seating depth, you need tool that lets you use the case you will be using (usually a fire formed once-fired case) and the bullet you are going to shoot and used the tool to push a bullet lightly inside the case mouth and getting the bullet seated lightly up to and against the lands which is your max seating depth (also your highest seated bullet pressure point) and then back the bullet off (seated further in the case) in selected increments in five-ten round groups and then shooting them to see what the rifle likes (best group.)
Example: Five seated one thousandths, five a two thousandths, five at three thousandths and so on. Some shooters get their best performance 10 or more thousandths off the lands. IT is tedious, but that is what you do to get the n best accuracy. (Clarifications or corrections welcomed!!)

 

[DUSTY NOGGIN]

your jump measurement should always be greater than the head clearance measurement

 

[rugers]

If you dont have all that fancy stuff, take bolt out of rifle put the bullet you are going to use in barrel and gently seat it with a piece of dowel rod insert a cleaning rod into barrel from muzzle mark rod when it stops on bullet, remove bullet, put bolt back in and close it reinsert rod until it is on bolt face put another mark on rod, remove rod and measure the Mark's , it will get you a starting point, back it off a bit and work up. Sinclair makes a col gauge that is relatively cheap and can be used on any cartridge. I will state that the above method is not the most accurate and would really suggest you invest in any one of the mentioned col gauges they all work real well