Question on seating depth

[kmw1954]

This question relates to adjusting seating depth for improved accuracy not as a starting point. I am asking this because I have never really explored this aspect because with my other 223 Savage changing seating depth seemed to make no difference.

After I installed my new barrel I did a soft jamb with several of my most commonly used bullets. This gave be a measurement of between 2.310" - 2.321" depending on the bullet.Then most all of these bullets the suggested seating length is 2.250" - 2.260"

So the other day I loaded some .224 Hornady 68gr Match which have a different ogive than everything else I load and is a significantly longer bullet much like the VLD I am guessing.

To begin with I mocked up a depth with an empty case and a raw bullet and laid the bullet to where the beginning of the boat tail was even with the bottom of the neck. So the only thing extending into the case was the bottom of the boat tail.

I then seated one to that length and it came to 2.311" so I took that and chambered it into the gun, the bolt closed smoothly and w/o and interference. It also fit into the magazine. So from here I loaded some test rounds to 2.30" and what I found was although they fit the mag they would not feed completely. Upon closing the bolt the bullet would hit low on the barrel but if I pulled the bolt back and pushed down slightly on the case in the mag it would pop into the chamber. But that is a separate issue.

Of the 5 small groups I loaded I found 2 that were very good. as at 100yds they were all touching. One was just 2 holes for a 3 shot group. The other was all center bull just strung horizontally but still touching. Could almost draw a straight line thu the center.

So how much movement in or out do you commonly see before you can see a difference in pressure/speed?

 

[kmw1954]

Wow, not a single comment about how much anyone is moving a bullet shallower or deeper. A fellow shooter at our range loading for a 6BR says he moves deeper in .003" increments.

 

[lordpaxman]

I don’t load for a .223 bolt gun but used Berger’s advice when I did some ‘06 and .243 work ups:
https://bergerbullets.com/shoot-better/shooting-knowledge/how-to-load-a-hybrid-bullet/

 

[kmw1954]

I don’t load for a .223 bolt gun but used Berger’s advice when I did some ‘06 and .243 work ups:
https://bergerbullets.com/shoot-better/shooting-knowledge/how-to-load-a-hybrid-bullet/

Very insightful, thanks.

 

[Walkalong]

A fellow shooter at our range loading for a 6BR says he moves deeper in .003" increments.

A waste of time IMHO, others feel differently. A good bullet/gun/powder combo will shoot so well at a variety of seating depths, so unless your shooting registered Benchrest matches just load some up at at .010 off, .020 off, and .030 off the lands and see if you can tell a difference. If .030 is the best, more jump might be better.

 

[nettlle]

My standard has always been .015" off the lands. I have experimented with as little as .010" and as much as .030". It's not a huge difference in accuracy but when reloading the devil is in the details. Each little thing, bad or good, can add up to something bigger in the overall package.

 

[AJC1]

A waste of time IMHO, others feel differently. A good bullet/gun/powder combo will shoot so well at a variety of seating depths, so unless your shooting registered Benchrest matches just load some up at at .010 off, .020 off, and .030 off the lands and see if you can tell a difference. If .030 is the best, more jump might be better.

It's a small dial like a lot of others. If you have the barrel and the bullet you rule the day...
Decenting opinion it can be important with some vld bullet shapes that I avoid.

 

[JFrank]

This question relates to adjusting seating depth for improved accuracy not as a starting point. I am asking this because I have never really explored this aspect because with my other 223 Savage changing seating depth seemed to make no difference.

After I installed my new barrel I did a soft jamb with several of my most commonly used bullets. This gave be a measurement of between 2.310" - 2.321" depending on the bullet.Then most all of these bullets the suggested seating length is 2.250" - 2.260"

So the other day I loaded some .224 Hornady 68gr Match which have a different ogive than everything else I load and is a significantly longer bullet much like the VLD I am guessing.

To begin with I mocked up a depth with an empty case and a raw bullet and laid the bullet to where the beginning of the boat tail was even with the bottom of the neck. So the only thing extending into the case was the bottom of the boat tail.

I then seated one to that length and it came to 2.311" so I took that and chambered it into the gun, the bolt closed smoothly and w/o and interference. It also fit into the magazine. So from here I loaded some test rounds to 2.30" and what I found was although they fit the mag they would not feed completely. Upon closing the bolt the bullet would hit low on the barrel but if I pulled the bolt back and pushed down slightly on the case in the mag it would pop into the chamber. But that is a separate issue.

Of the 5 small groups I loaded I found 2 that were very good. as at 100yds they were all touching. One was just 2 holes for a 3 shot group. The other was all center bull just strung horizontally but still touching. Could almost draw a straight line thu the center.

So how much movement in or out do you commonly see before you can see a difference in pressure/speed?

You won’t see huge swings in pressure or speed with simple seating adjustments as you would with powder increment's

 

[kmw1954]

So I will reiterate my experience with bullet seating. My old Savage model 10 did not benefit from moving seating depth. So I never pursued it much. Though I do see it make a difference with some of the guys Bench rifles such as 6mm and 308.

I have read and watched enough to understand setback or jamb. have also followed "chasing the lands".

With this Hornady Match bullet by my best measurement I am ruffly .015" off the lands and have found loads between 23.0 and 23.3gr of TAC to give the best groups tho I have not chrono'd them yet as I only have 100 of these left. The first box I shot mostly thru the Model 10 at std. lengths and never did find a load that worked very well. But have have again been told I could probably tighten these up some more by playing with seating depth. So just trying to get a consensus on how much movement at a time.

 

[AJC1]

So I will reiterate my experience with bullet seating. My old Savage model 10 did not benefit from moving seating depth. So I never pursued it much. Though I do see it make a difference with some of the guys Bench rifles such as 6mm and 308.

I have read and watched enough to understand setback or jamb. have also followed "chasing the lands".

With this Hornady Match bullet by my best measurement I am ruffly .015" off the lands and have found loads between 23.0 and 23.3gr of TAC to give the best groups tho I have not chrono'd them yet as I only have 100 of these left. The first box I shot mostly thru the Model 10 at std. lengths and never did find a load that worked very well. But have have again been told I could probably tighten these up some more by playing with seating depth. So just trying to get a consensus on how much movement at a time.

The legit answer is running the berger seating depth test. It's not my opinion but a procedure.

 

[kmw1954]

Practical experience at this is very limited so any and all guidance is welcome!

 

[JFrank]

Seating changes are more of a fine adjustment to group shapes rather than size, notice here that at 300 yards the changes are from vertical to horizontal then erratic. Neck tension is another important part of tuning as you can have very inconsistent groups on paper until you get the bullet hold that the load prefers.

Added: if your not sure how much hold to use.. start with plenty.

 

[JFrank]

Wow, not a single comment about how much anyone is moving a bullet shallower or deeper. A fellow shooter at our range loading for a 6BR says he moves deeper in .003" increments.

Initial VLD seating increments are much more aggressive then Tangent ogive until you find the seating window from there small adjustments are in order.
You’ll probably not get there but when I jam a bullet there isn’t a big difference from .005 -.010 meaning if it likes 5 thou jam it will still like .010 or even .020 in the opposite - jump can be very sensitive.

Confused yet?

 

[243winxb]

223 Rem.

although they fit the mag they would not feed completely.

This can destroy accuracy, if bullets get crooked on loading.

I start with the full diameter of the bullet at the neck shoulder junction. 50 to 69 grs.

To begin with I mocked up a depth with an empty case and a raw bullet and laid the bullet to where the beginning of the boat tail was even with the bottom of the neck. So the only thing extending into the case was the bottom of the boat tail.

Then, if possible, make OAL adjustments of .010" in steps. Longer & shorter. An OAL of 2.320" works in factory Savage Axis 223. Sierra 69 gr hpbt & Nosler 55 gr. I do not like the Sierra 69 plastic tip bullet. To long.

https://www.thehighroad.org/index.php?media/albums/targets.141/

 

[243winxb]

Bottle neck cartridges.-

In gerenal, .010" off rifling for maximum start length. Must fit/work in magazine.

Minimum- The bullet ogive should never go below the case mouth. This mark is where the bullet diameter gets smaller.

 

[kmw1954]

View attachment 1088019 Seating changes are more of a fine adjustment to group shapes rather than size, notice here that at 300 yards the changes are from vertical to horizontal then erratic. Neck tension is another important part of tuning as you can have very inconsistent groups on paper until you get the bullet hold that the load prefers..

Yes this is what I have been instructed upon by the friends at the range. Fine tune for shape. One load was horizontal the next was vertical but still nice and tight with touching from one to the next. So I believe I found a nice power/accuracy node.

Learned the lesson last summer about neck tension and annealing. Paid huge dividends! Also after an unscientific test I found I was seeing the best and most consistent results with Norma and PMC brass over 4 others tested. Have yet to test Hornady or FC brass. Still not ready to invest $1.00+ for Lapua or Peterson brass.

 

[kmw1954]

Now I have also had discussions with guys at the range about ogive shape and jump sensitivity. Until now have not tried long/pointy ones.

These rounds are being fed singly and slowely to where they just touch the barrel, no force. Then in relation to your picture the bullet was seated as you suggest so that just the bottle neck potion of the bullet is below the neck, which is how I arrived at the 2.230 length to start.

Today as the wife is home for the holiday I may try to get to the bench and load one of these to this length and then slowly move it back to where it will feed from the mag and not foul. Just to find out how far that actually is with this bullet.

If I can get this load to repeat I may have to invest in some more.

 

[mdi]

FWIW; for me the very last "tweek" for chasing ultra accuracy is "distance off the lands". My most accurate handloads (rifle) were a Hornady 155 A-Max over a load of IMR 4895, using Hornady manual overall length. 7/8" @ 100 yds...

 

[denton]

The estimable Dr. Floyd Brownell did some work on that, back shortly after mud was invented. The attached data graph may be helpful. Note that there are two horizontal scales, on for seating depth and one for COL. One of those scales seems to run backwards.



For very deep seating, pressure is higher. It drops until the effect of being near the lands takes over, and starts increasing from there.

Trying to explore in increments of .003" looks like a very hard way to get actionable data. This data covers a range of nearly half an inch.

 

[Walkalong]

Trying to explore in increments of .003" looks like a very hard way to get actionable data

Agreed

 

[nettlle]

I have always have adjusted in .005" increments. +/- .003". A good turret (my T7) or a good single stage (my RCBS JR) or a good progressive (my Dillon 550) are not going to hold any tighter tolerance than that.

 

[Kaldor]

I tried a bunch of stuff, and I was just making it too hard, and never got any results I was happy with. I ended up going with Erik Cortina's method. This is an abridged version that pretty close.

Step one: Measure bullet distance from lands

Step two: Set first round 20 thou off lands, or if constrained by mag length, max length in mag, whichever comes first.

Step three: Shoot groups (I shoot a Satterlee at this point, then shoot the best on the velocity curve for groups)

Step four: Fine tune seating depth on best group(s) from step three. I never go closer to the lands, only further away. There is merit in a 3 thou moves for seating depth, but you have to be a pretty good shot with an excellent rifle to see it. I generally back off the lands in 5 thou increments as I am only a slightly above average shooter, with maybe slightly better than average rifles.

 

[Driftertank]

I would say that tuning for jump, as well as how big your steps are, depends on a few things.

A big one is ogive shape; from what I've seen, secant ogives TEND to be more jump-sensitive than tangent ogives. With a secant ogives (like most match or VLD bullets) I would say to make adjustments in small increments, .005" to .010" starting from pretty close.

You may also find there are nodes for jump, just like charge weight, as you back off.

Anecdotally, I've seen where Hornady ELD-Ms group well at relatively short jumps in 6.5 CM, then tend to open up or throw flyers, then settle down again somewhere between .050"-.080" depending on gun and load.

I've also heard that some of the tangent ogives Noslers (BT, PT) can be happiest with a LOT of jump. Like .120"-150" I'm looking at chasing that angle to see if some disappointing loads in my .308 with Accubonds will settle down at shorter lengths. I would probably ladder out at .020" intervals for that experiment, using a baseline charge weight that's far from max.

Couldn't tell you where you need to start tweaking your charge weight. I think you may need to kind of see-saw back and forth a bit between making COAL adjustments and tweaking charge by .1-.2gr....but never at the same time.

 

[kmw1954]

So particulars, right now I am playing with 2 bullets and one powder in a relatively new barrel. The Bullets are the 68gr Hornady Match and the 69gr Nosler Custom Comp..
The powder is Ramshot TAC.

The Nosler are seated to 2.260 wirh the beginning of the BT even with the neck/shoulder. Found a group between 22.8 and 23.4 with the middle 23.1 the best so I will explore that 23.1 higher and lower see if I can find the best part of this node. This one should be easy. The Hornady may be more difficult and I think will come down to more in the way of seating depth than powder charge.

 

[AJC1]

So particulars, right now I am playing with 2 bullets and one powder in a relatively new barrel. The Bullets are the 68gr Hornady Match and the 69gr Nosler Custom Comp..
The powder is Ramshot TAC.

The Nosler are seated to 2.260 wirh the beginning of the BT even with the neck/shoulder. Found a group between 22.8 and 23.4 with the middle 23.1 the best so I will explore that 23.1 higher and lower see if I can find the best part of this node. This one should be easy. The Hornady may be more difficult and I think will come down to more in the way of seating depth than powder charge.

There are ruff tests and fine adjustments. The berger seating depth test is a ruff test. Then fine adjustments to find width of the band can be done. I would focus on the long end of any window as your lands don't grow. I'm not saying chase the lands, I'm saying load the long side of the window and shoot till the load requires adjustment.