Clarification on "distance from lands"

[PJ1]

I fought this battle for my first year or so as well, and it can be confusing.

Using the same equipment as you, (presumably), a Hornady OAL gauge and and a Hornady Bullet Comparator, I have developed the following method.

Using a Hornady Modified Case I insert the bullet of choice and push firmly. After locking I use the bullet comparator to find distance to ogive. BTW all measurements are taken from the ogive in my world - I learned that distance to tip is far too variable. I will perform the measurement as many as 10 but never less than 5 times. I average the result and that becomes my new "zero" distance for that bullet in that rifle. I will record that measurement and until a new bullet development comes along that will remain my "zero" for that rifle using that bullet.

Now that that is established I will start seating deeper in increments of .005" and shooting groups of 5 to determine optimum seating depth. The "sweet spot" for me in .264 with heavy-for-caliber (above 130gr) bullets tends to be about 0.20" to 0.30" and again around .050" to .060". Because components are getting so hard to find I will often start at .020" and/or .050" of jump and work in from there instead of running a full series from the lands.

You didn't mention if you are shooting from a magazine. If you are, the "zero" distance is the magazine - often 2.280" OAL, and measuring the ogive distance from there. That being the longest distance you can load and still use the magazine - it makes no difference the distance to the lands. Now the tuning window for seating depth begins with the magazine maximum OAL.

As the lands erode there may be very small changes to optimal seating depth, (my experience has been that as the lands erode it may be necessary to adjust outwards to "chase" the lands).

Once I started working from a "zero", all of my problems pretty much dried up. The best advice came from folks on this forum and from the Berger Tech line. Walt is gone, but Phil and Cory are still giving great advice.

Good luck!

The Wheeler method will not work for me due to the construction of the bolt and polymer housing.

You're correct in that I'm using a magazine and I do measure from base to ogive.

Been trying to use the OAL, for well over a year, and frankly, I have found Eric's method to be repeatable and groups well under MOA.

The part I still have not mastered is the es/sd game. I figure this is the reason I'm not getting repeatable hits at 1000 yards. That's my goal, as I'm not a competition shooter. Just like to hear the steel sing to me.

Thanks to all as I now have a better understanding of what you guy's are referencing as distance to the lands. The way I employ is "touching" the lands without being at hard jam.

 

[pipe]

Years ago i 'smoked' my bullets when finding the lands with a candle or Zippo lighter flame. This works pretty good but after about 4 or 5 tries the lands have pushed down the perimeter of the bullet. You need more bullets to do a good job. This is an easy way if you have more time than money.

 

[thestoicmarcusaurelius]

the es and sd numbers are in the 30's and that concerns me.

I’m not a statistician by any means, but I’ve noticed that the ES tends to be around four times the SD when I have a sample size of 30 or more shots

so, you likely have a very, very large es (>100) if you have an sd in the 30’s

 

[BoydAllen]

Maybe my newbie status to reloading (<2years), but when you fellows refer to 0.xx" from the lands, I'm a little confused. Here's what I am presently doing to determine my distance from the lands:

I follow what Eric Cortina has done in one of his videos. I take a fired 6.5C case f.l. size and then mandrel the neck to give me 0.002" of neck tension. I then seat the bullet out to about 2.3" long(cbto) in the case, lube the ogive area, then chamber the dummy round. Jam comes out to be 2.293" and is very repeatable for Hornady 140g hpbt. Next I subtract 0.020" to give me 2.273" as my starting point. I have found that 2.270 to 2.267" from jam to be the sweet spot.

I have tried the o.a.l gauge method for touching the lands and I end up with varying results. Usually around 2.213" This ends up giving me lousy and non-repeatable groups.

So I am curious as to how you folks are doing this. Please forgive my ignorance.

The Cortina method you mentioned gives you .020 off jam, jam being the length the bullet was pushed back to when chambered. As mentioned, the Wheeler method for finding touch is probably the best. It will be interesting to find out where your .020 off jam puts you relative to touch, keeping in mind that this will vary with the shape of the ogive, and neck friction.

 

[RegionRat]

I’m not a statistician by any means, but I’ve noticed that the ES tends to be around four times the SD when I have a sample size of 30 or more shots

so, you likely have a very, very large es (>100) if you have an sd in the 30’s

Look at enough normal Gaussian Distributions and you will see that ES is approximately 6 X SD.
When it isn't, you have to start asking more questions.

 

[PJ1]

I’m not a statistician by any means, but I’ve noticed that the ES tends to be around four times the SD when I have a sample size of 30 or more shots

so, you likely have a very, very large es (>100) if you have an sd in the 30’s

Yeah I messed up and should have not lumped in the sd. Thanks for noting that.

 

[Longtrain]

What does it really matter? As long as you have a start point for reference, who cares if its +020 or -.140 or whatever. Find a start point, run your seating tests and go. Your rifle and your target will tell you what is best.

+1 For years, I have cleaned a dummy round with 0000 steel wool, seated it with the firing pin removed, checked the marks made by the lands. Clean the bullet again and seat it another .005, repeat until the land marks are hardly visible.
From there I’ll do my seating depth testing.

 

[Ccrider]

There is certainly more than one way to skin this cat. It matters if you want to speak the same language as some of the better shooters and be able to compare what you are doing with what they are doing. If someone tells me that a particular bullet/load shoots well for them .10 into the lands, I know exactly what they are talking about if they use the Wheeler method. It matters once you figure out that some loads and bullets shoot better when touching the lands and some shoot better jumping (not touching).

How far do you have to set a bullet back from jamming the bullet as far into the lands as possible, before there is no contact with the lands? No way to know this just jamming them in and then backing off.

I am pretty confident that most of my guns will shoot well somewhere between .25 off (not touching) and .20 into the lands. I like to watch the trend of the groups as I move into or away from the lands.

In the end, the Wheeler method gives me more information about what effect engagement into the lands is having on the groups.