Consistant seating depth...

[6Creed73]

In my experience varying neck tension does have an affect on seating depth consistency.

Yep, a big affect. I can demonstrate this by setting neck tension on two different pieces of brass using two different size mandrels. Seating bullets with the same seating die setting and same bullet will produce different CBTO measurements every time.

 

[JFrank]

This has nothing to do with measuring loaded rounds using COAL. I completely agree with you that CBTO is the measurement with the greater meaning in the context of consistency and serious reloading.

Regardless, look again at the illustration I posted above. Any length variation between the critical contact points will show up as seating depth inconsistency. The seating die stem pushes against the bullet at a point farther out on the ogive toward the bullet meplat. The caliper insert seats at a point on the bullet ogive closer to the top of the bearing surface. If the nose length of bullets between those two critical contact points is not uniform (which it generally won't be unless they have been length sorted), the result will be seating depth variance consistent with the length variance between the critical contact points. It has to be that way, as the distance between the point where the seating die stem contacts and pushes the bullet into the case and the point at which we measure is fixed for a single bullet. If two different bullets have a difference distance between the critical contact points, the resultant seating depth as measured by CBTO will not be the same.

This is why I qualify the nose geometry first when sorting bullets.

 

[20PPC]

Got another stem to try for grins? I've had a redding stem to crack and do that but not a wilson.

@gunsandgunsmithing yes Mike I did try another VLD stem, nothing changed.
I've got some Berger 108 targets I'm going to try.

 

[David Christian]

@20PPC I have not read all 4 pages of comments, my bad. Has anyone asked what neck tension you are running? What is the neck diameter of a loaded round? What size bushing or sizing die are you using? Do you use an expander mandrel?

 

[William Vogel]

@gunsandgunsmithing yes Mike I did try another VLD stem, nothing changed.
I've got some Berger 108 targets I'm going to try.

Are you running a mandrel through the necks after sizing and using a FL bushing die for sizing?
My process is to decap, clean exterior carbon from neck, clean primer pocket, anneal, trim, FL bushing resize, lube neck with lockeze, mandrel neck, tumble, store or load after identification with length and date.

 

[Fire Dog]

Consistent seating depth almost always comes down to brass prep in my experience. I don't sort my bullets and my seating depth is rarely more than .0005 variance. If your brass necks aren't consistent, there will be variations in drag/pressure as the bullet seats which will cause inconsistent seating depth. This is something I've spent a lot of time working on. In my experience, these are the things that help with consistent seating depth.

1. Anealing
2. Consistent chamfer with slight bevel
3. Graphite or Neolube inside of neck
4. Mandrel as last step before seating. Use the mandrel just before seating

I was about to load some up so decided to record it and put my money where my mouth is....I can do this all day and get an extreme spread of .0005. I can't express enough how much difference it makes to use the mandrel right before seating.

What brand of comparator are you using on the vernier? I like the flat surface for the base of the cartridge.

 

[Fire Dog]

This has been more help in seating depth consistency than anything I've tried so far. Pressure on the press handle and no bounce at the bottom of the stroke is key at least with my Rockchucker.

Same for my Co-Ax

 

[6Creed73]

What brand of comparator are you using on the vernier? I like the flat surface for the base of the cartridge.

The comparator is Short Action Customs. That base is actually from a guy on this site...I got it from the classifieds here. I'll try to find the ad.

Edit: @Fire Dog here is where I got the base.

SELLING - Caliper Bases - $22.00 Shipped

Updated - 12.31.2024 - Current time from purchase to received - 3-4 days. Ensures consistent and repeatable measurements during the bullet seating process. See forum comments, reviews and feedback. PM me for additional information. 6061 Aluminum - Hard Anodized Black. Use in conjunction with...

forum.accurateshooter.com

 

[J_idaho]

In my experience varying neck tension does have an affect on seating depth consistency.

What Bill said:

 

[wkdickinson]

Nomex underwear on so I can throw in my pre inflation $ 0.02.

My experience with a load shooting well as the throat erodes ( not chasing the lands ) has led me to sort bullets by BTO (base to comparator touch point ) and then control the CBTO of the loaded rounds under 0.002”. This keeps the base of the bullet at the same location in the case neck and this seating depth control has shown to be more indicative of controlling a loads tune than jump to touch point.

YMMV but this seems to be working for me.

I have wondered for a long time whether when we tune using "jump" if we aren't really tuning with the depth of the bullet base in the case.

 

[William Vogel]

I have wondered for a long time whether when we tune using "jump" if we aren't really tuning with the depth of the bullet base in the case.

I think you’re on to something but I’m also thinking it’s about the pressure “knock” that forms every time an obstruction is overcome. What I mean is there’s a pressure rise and fall when the bullet first moves in the case, the neck is expanding and the bullet reaches the lands. Pressure rises again as the bullet is forming into the bore/grooves. Of course this pressure rise is much greater but it’s a succession of events. I’m continuing to imagine the pressure events and bullet accelerations in the barrel along with the barrel deformation with travel and the release of pressure at bullet exit.

 

[Fire Dog]

I started off with finding the sweet spot of my new barrel and have never changed the COAL over the life of the barrel.
Seem to be working for me and I have read other items written saying Do Not chase the lands...
A bit along the lines of "If it ain't broke.... Don't fix it"

 

[20PPC]

@20PPC I have not read all 4 pages of comments, my bad. Has anyone asked what neck tension you are running? What is the neck diameter of a loaded round? What size bushing or sizing die are you using? Do you use an expander mandrel?

@David Christian I am not running a mandrel, my necks are turned to .112 with a .262 bushing in a .268 chamber .
My loaded rounds measure .2650 - 265, I'm sure all my neck thickness have some variance to them.
I'm using a Harrels fl bushing die and haven't been able to anneal because my Annie is in for repair.
I'm sure a set of mandrels would be of benefit.

 

[JFrank]

@David Christian I am not running a mandrel, my necks are turned to .112 with a .262 bushing in a .268 chamber .
My loaded rounds measure .2650 - 265, I'm sure all my neck thickness have some variance to them.
I'm using a Harrels fl bushing die and haven't been able to anneal because my Annie is in for repair.
I'm sure a set of mandrels would be of benefit.

Yours sounds like a very similar set up to my own, I don’t use mandrels or anneal.

Q) Curious as to your seating depth and the neck ID prep prior to seating ?
What size bushing are you running ? ( I see the .262 ) disregard this Q

 

[jelenko]

seater stem makes contact any where on the ogive a very slight change in the diameter at the point of contact

I asked Forster about whether their seater 'compensated' in any way for small changes in the shape of the ogive.

Their response:

If using a bullet comparator measuring O-give to base you should find your bullets to be extremely consistent. It is important for bullet manufacturers to maintain this distance as being consistent as this will determine how consistent your bullet encounters the lands of your rifle. By keeping this profile extremely consistent, even with your comparator hitting at one spot, your seating stem hitting at a slightly different spot, and your rifling hitting a slightly different spot, we should see this stay consistent.​

​

My take => The variation in the shape of the ogive is consistent enough that variations in base to ogive measurements are small enough to ignore.

 

[jelenko]

bullet nose length can have a significant impact on consistent seating depth because the two contact points critical for maintaining consistent seating depth are located on the bullet ogive.

Ned - I asked Hornady if sorting bullets from the same lot would improve the consistency of the base to ogive measurements. Here's their response:

The base to ogive measurement is a more consistent method for comparing bullets than overall length, as the ogive is the most consistent place to measure. Variations in the bullet tips can lead to differences in overall length, but the base to ogive measurement tends to remain more uniform. Sorting bullets by overall length may not necessarily result in more consistent base to ogive measurements within a sorted group, as variations can still occur due to manufacturing processes and material differences. It is recommended to use a bullet comparator to measure from the base to the ogive for more consistent results. If you are experiencing significant variances and it is affecting your accuracy, it may be worth examining the bullets more closely or contacting the manufacturer for further assistance.​

My understanding is that the length of the tip is essentially independent of the process that forms the ogive.

What do you think?

 

[Bill Norris]

jelenko​

My take => The variation in the shape of the ogive is consistent enough that base to ogive measurements are small enough to ignore.

On most bullets I believe this is true but there are some exceptions where the ogive is not consistent enough to ignore.

 

[jelenko]

jelenko​

My take => The variation in the shape of the ogive is consistent enough that base to ogive measurements are small enough to ignore.

On most bullets I believe this is true but there are some exceptions where the ogive is not consistent enough to ignore.

Bill - Do the exceptions come from certain manufacturers?

 

[barefooter56]

I just started shooting mid range 600 yards and am experiencing problems getting consistant seating depth in the case.
I'm shooting a 6BRA chambered by Ronnie Long, Lapua brass, Varget, Federal primers and 105 Berger Hybrids.
I cannot get 2 bullets in a row to seat the same depth, I sent the Wilson seater stem to Ronnie because it was was not making the consistant proper contact on the bullet.
He opened it up a slight amount and polished it to what now appears to be perfect contact with the tip of the bullet.
I've measured BTO on the bullets and all of them appear to be within + - .0015 yet when seating I'll get .004 - .010. difference.
Needless to say 2 1/2 hrs later " actually longer " and only 75 rounds loaded is getting to the point the hassle of loading is outwaying the enjoyment of shooting.
Any advise would be appreciated.
Dave

Dave,
You don't want to seat rifle bullets off the tip of the bullet. The seating stem should 'cup" or make contact somewhere on or close to the ogive of the bullet. The two dimensions we track in A LOT OF BULLETS. Are the bullet base to ogive and weight. Thats all. You should have had the stem drilled DEEPER instead.

 

[Straightshooter1]

Ned - I asked Hornady if sorting bullets from the same lot would improve the consistency of the base to ogive measurements. Here's their response:

The base to ogive measurement is a more consistent method for comparing bullets than overall length, as the ogive is the most consistent place to measure. Variations in the bullet tips can lead to differences in overall length, but the base to ogive measurement tends to remain more uniform. Sorting bullets by overall length may not necessarily result in more consistent base to ogive measurements within a sorted group, as variations can still occur due to manufacturing processes and material differences. It is recommended to use a bullet comparator to measure from the base to the ogive for more consistent results. If you are experiencing significant variances and it is affecting your accuracy, it may be worth examining the bullets more closely or contacting the manufacturer for further assistance.​

My understanding is that the length of the tip is essentially independent of the process that forms the ogive.

What do you think?

I've been sorting my bullets by base to the seating stem contact point on the ogive and it gives me very consistent seating, even when the seating is measured by a typical caliper insert (seldom seeing any significant variation between the two contact points). When comparing those sorted by seating stem contact point with their OAL, I find a significant variance in OAL's. That distance from seating stem contact point to the meplat varies quite a bit. These bullets I've measured are the Bergers and SMK's. The most consistent bullets I've measured this way are my 6.5 Hornady A-Tips, where these measurements hardly varied at all. Since I've sorted based on seating stem contact point, I get VERY consistent seating depths . . . and with the annealing, the consistent seating resistance helps.