Seating Depth Frustration

[USAFRet]

So, I am setting up some loads for a 308. I am starting with recommended COL of 2.8 and seating .003 back for 4 different loads for accuracy resting. So, objective is
2.8
2.797
2.794
2.791

However, I will get one cartridge measured and the next will be anywhere from .002 to .003 off. I took this that there might be a little tip deformation. So, I broke out the comparator to double check and I am also getting some cartridges with up to .003 difference. With a difference of up to .003 and me trying to seat a .003 difference, makes me wonder if I just wasted a bunch of time.

Am I doing something wrong? Bullets are 168 and 175 Match King. Non-tipped.

 

[L.Sherm]

Measure from the ogive, like Case Base To Ogive. OAL means nothing other than if it fits in the mag box.
It can depend on how consistent your bullets are manufactured, your seating die, brass prep etc

 

[USAFRet]

Measure from the ogive, like Case Base To Ogive. OAL means nothing other than if it fits in the mag box.
It can depend on how consistent your bullets are manufactured, your seating die, brass prep etc

The comparator tool measures from ogive. I was still getting up to a .003 difference on some cartridges.

 

[acloco]

Is the tip of the bullet contacting the internal stop of the seating stem?

Have you measured a bundle of bullets? Are they withing 0.001" for the lot?

 

[JB10]

Can depend on bullet manafacture. Some are more consistent than others.

 

[USAFRet]

Is the tip of the bullet contacting the internal stop of the seating stem?

Have you measured a bundle of bullets? Are they withing 0.001" for the lot?

Each batch was 5 bullets and I was finding about two per batch that were off.

 

[USAFRet]

Can depend on bullet manafacture. Some are more consistent than others.

That is my thought. I would think Sierra Matchkings would be a more premium bullet.

 

[Ned Ludd]

As noted above, do not use COAL as a measurement/indicator for seating depth testing. Bullet nose length variance can render COAL measurements effectively useless for this purpose. Cartridge base-to-ogive measurements are much better suited to what you're trying to accomplish, which is to identify a distance from the bullet ogive to where it first engages the rifling that is associated with optimal precision.

If you and/or your press setup cannot consistently produce CBTO measurements to a range of .001" or less with the die micrometer held constant at a single setting, you might give the following approach a try. I generally set the die micrometer up such that the majority of loaded rounds will have the [longest] desired CBTO measurement with a single pull of the press handle. For example, let's say my desired target CBTO range is hypothetically 2.500" - 2.499". I will adjust the die micrometer such that most of the loaded rounds will have a CBTO of 2.500" after seating the bullet with a single stroke of the press. The key here is that you don't want to seat a bullet too far down in the neck because the only way to "undo" that is to pull the bullet and start over. Any bullet not seated deep enough can always be given another stroke of the press, either with or without a die micrometer adjustment to achieve the exact seating depth you want.

In the above example, if a small percentage of loaded rounds were to come up with a CBTO of 2.501" (or greater), I would put them back in the press and give them another tap. This is usually good for seating the bullet another .0005" to .001" deeper in the case. If that doesn't work or get you where you want to be, you may have to dial the micrometer down .001" and give the loaded round another tap. By setting the die micrometer carefully so that you're not ever seating any rounds below 2.499" COAL after a single stroke of the press, you can always "finesse" the bullets down to where you want them to be using additional strokes of the press and/or slight adjustments of the die micrometer as described.

The caveat to this approach is that having to use extra strokes of the press or continually adjust the die micrometer and remember to turn it back once the desired seating depth CBTO has been achieved for that loaded round can be a major PITA. To that end, you might also consider length sorting bullets. In my hands, the majority of bullet length variance lies in the nose region. The boattail and bearing surface lengths are generally pretty consistent. The two contact points absolutely critical for consistent seating depth both lie in the nose region; i.e. the point out near the bullet meplat where the seating die stem "pushes" down on the bullet and point at which the caliper insert seats just above the bullet bearing surface when we measure CBTO (see diagram). Any length variance in between these two critical contact points can introduce unwanted variance in CBTO /seating depth measurements. Because the majority of bullet length variance resides in the nose region, one can sort bullets by overall length and do a reasonably good job of minimizing nose length variance. It is not a perfect method, but it can provide a noticeable benefit or improvement in seating depth consistency if nose length variance is a contributing factor. Alternatively, a tool such as BobGreen's Comparator can be used to directly sort bullets between the two critical contact points.



Finally, the use of consistent force on the press handle when seating bullets and having consistent neck tension/interference fit that is not too tight in the brass are also important for generating uniform seating depth. The first may simply require some attention and practice, the second requires good brass prep and attention to detail, which can be verified by taking routine neck diameter measurements.

 

[Straightshooter1]

So, I am setting up some loads for a 308. I am starting with recommended COL of 2.8 and seating .003 back for 4 different loads for accuracy resting. So, objective is
2.8
2.797
2.794
2.791

However, I will get one cartridge measured and the next will be anywhere from .002 to .003 off. I took this that there might be a little tip deformation. So, I broke out the comparator to double check and I am also getting some cartridges with up to .003 difference. With a difference of up to .003 and me trying to seat a .003 difference, makes me wonder if I just wasted a bunch of time.

Am I doing something wrong? Bullets are 168 and 175 Match King. Non-tipped.

There's different things that could be a play for that kind of variance. First, it's VERY common to have that much variance in CBTO's within a lot of bullets; and why many reloaders will sort their bullets. There can be even larger variations from lot to lot.

It could be an issue with your neck tension. Cases can have various work hardening from the sizing process and variation in seating resistance when seating the bullets can be felt that can result in that much seating depth variation.

There could be an issue with your seating stem where it doesn't fit the ogive consistently the same.

When I first started precision reloading, I had the same kind of variance on seating my SMK's. Two things really helped me. The first was I started annealing my brass and that gave me much more consistency with neck tension resulting in more consistent seating resistance. The second thing was that I sort my bullets bullets with a comparator that has the same diameter as my seating stem's contact point on the ogive. It's that contact point that give you seating depth (seating depth being that distance from the stem's contact point to the base of the case). If the bullet has variations of it's base to that contact point, you'll have variations on how deep the base of the bullet is into the case, effecting case volume.

As you look at Ned Ludd's picture above, that distance between where the caliper insert touches the ogive and where the seating stem touches the ogive has variances. This is why when bullets are sorted with a standard caliper insert, one still winds up with variances in seating depth.

Keep in mind, you want to focus on consistent seating depth, not your distance to the lands as measured by a standard caliper insert. That distance to the lands is always going to be changing as your throat erodes.

 

[USAFRet]

So, i am not a precision shooter. I am a hunter. 1" groups are plenty good for what I do. It was suggested that my spreads in seating depth are too low and are withing margin of error with standard equipment. Should I open my gaps in seating depth between cartridges to maybe .010?

 

[WSnyder]

Should I open my gaps in seating depth between cartridges to maybe .010?

How to Load a Hybrid Bullet

Berger Hybrid Bullets were designed to be easy to load and tune to your rifle. Follow these simple steps to get started.

bergerbullets.com

 

[USAFRet]

How to Load a Hybrid Bullet

Berger Hybrid Bullets were designed to be easy to load and tune to your rifle. Follow these simple steps to get started.

bergerbullets.com

And there is my answer. I hate wasting components.

Load 24 rounds at the following Cartridge Base to Ogive lengths.

1. .015″ off the lands (jump) 6 rounds
2. .030″ off the lands (jump) 6 rounds
3. .045″ off the lands (jump) 6 rounds
4. .060″ off the lands (jump) 6 rounds

 

[Ned Ludd]

And there is my answer. I hate wasting components.

Load 24 rounds at the following Cartridge Base to Ogive lengths.

1. .015″ off the lands (jump) 6 rounds
2. .030″ off the lands (jump) 6 rounds
3. .045″ off the lands (jump) 6 rounds
4. .060″ off the lands (jump) 6 rounds

This is an approach used only to identify a rough or coarse seating depth region that might show greater precision than another. It would still be necessary to test finer increments within that region to truly optimize seating depth. There is no definitive answer to your question here. You will need to test until you find a seating depth that provides whatever precision you find acceptable. Just be aware that even a single .003" seating depth increment can make a significant difference in terms of precision. Thus, using a seating depth increment as coarse as .015" could easily miss something good. Then again, it might work just fine for you. The only way to know with any certainty is shoot the test and then decide whether any of the groups show acceptable precision. The optimal intrinsic precision of the rifle setup would be an important factor in making such a decision.

Within reason, using up components to find a load that shoots well is not a waste. What's truly a waste is attempting to carry out load development using a spotty and haphazard approach, hoping to get lucky and hit on something that works, instead of a rigorous and incremental approach that is much more likely to find the sweet spot wherever it may lie. The first approach will usually waste far more valuable components in the long run than the second.

 

[Mark611]

I'm sure some of this has been answered already? but from the last post I see your getting the idea, first using the bullets your going to use, you need to find the jam length, and work back from there, 308win is usually an easy cartridge to get set up, if your reloading technique is sound and you have components that work for your barrel, I shoot the 175gn SMK's they like to be at 10k off the jam length, I also do not load to a max powder charges!!! Because pressures change when seating bullets deeper in the case or closer to the lands, if your using a seating die that seats the bullets off of the Meplat? your seating depths are going to vary quite a bit depending on the bullets your going to use, even quality bullets like Sierra have varying OAL of 10k or more from base to tip! This is more info then your probably going to want for a hunting gun? but it still makes a difference, IMO you need to sort your bullets from base to ojive, and use a seating die that doesn't seat the bullet off the Meplat, this will give a better chance at keeping your seating depths consistent, otherwise your seating depths will be all over the place! I keep my base to ojive measurement 1/2 thousandth or less if I can and nothing over 1k in the batch of bullets I'm loading, if you want to go this far which I doubt? after I sort to the ojive, I sort my bullets by overall length, I find the shortest bullet, I then trim all the Meplats and bullets to the same length, then clean out the burr in the Meplat and retip the bullets! TMI but there is my thoughts!

 

[dgeesaman]

So, i am not a precision shooter. I am a hunter. 1" groups are plenty good for what I do. It was suggested that my spreads in seating depth are too low and are withing margin of error with standard equipment. Should I open my gaps in seating depth between cartridges to maybe .010?

Getting .001 consistently for base to ogive requires really consistent bullets. Sierra Matchkings are good but maybe not quite that good. Hand pulled match bullets are where I get .001” CBTO consistently.

I think you’ll do well working seating depth in .005” or .010” increments. 308 is a forgiving cartridge with wide tune windows.

Just by carefully monitoring your loaded dimensions and developing a load you’re way ahead of most hunters.

 

[USAFRet]

Thank you all for your replies. I see I can really go down a rabbit hole with this. I ended up doing the same with archery. Putting in tons of time and getting very small change in results. I just need to find that balance for the outcome I am looking for. gain, nit 1/2 MOA groups, although that would be nice. 1" groups would be fine as I load for hunting. These match bullets are for a buddy who wants to try them in his AR-10. He just shoots for fun. He is also the main provider of al my good Norma brass. Haha.

 

[Jeff Porter]

A while back I measure HPBT match bullets from Sierra, Hornady, and Nosler. What I found was all of these were held to 0.002" variation from base to ogive, but the total bullet lengths varied as much a 0.012". the ablity to control the draw of the jacket ot the hollow point is more difficult in high speed manufacturing.

Add in the difficulties of having a seating stem that pushes on this part of the bullet that varies the most and you will get the results you are seeing.

For your stated purposes, use the Berger jump test for Hybrids and when you see one group that is smaller and rounder than the others, you can play off either side of that by 0.005"at a time and see where the edge of the cliff is.

 

[Coyotefurharvester]

The easiest way to seat to to caliper error range(without sorting bullets) is a micrometer equipped seating die. Seat about 10 thou long, check length and adjust die for each round. A problem for standard seating die not covered yet, neck lube/ interference fit. Clean brass necks(no firing residue or lube) on the inside and 0.004+ neck interference fit can result in very uneven seating force. The difference in force needed for each bullet often results in depth variations round to round. So batch loading with a standard seating die requires very consistent brass prep for seating depths to run within BULLET ogive and length variations. Yup you can load to a range(middle of say 8-10 thou) and be very happy with field performance.

 

[dellet]

What really sucks is after going through all of the above, sorting bullets, matching the profile of the bullet to the seating stem, annealing the brass and all the other care taken to insure matching components and tools, only to find you still have inconsistent lengths.

Not all load data shows compressed loads, and with compressed loads or even high density loads, how you drop the powder can affect how much pressure is required to seat the bullet. A settled drop vs an unsettled drop where the bullet has to move the powder or not while seating.

Inconsistent pulls on the press handle and time spent with the ram at full extension.

Watching someone use the same equipment and components get a completely different assembled length, with less variation, can be a humbling experience.

 

[USAFRet]

What really sucks is after going through all of the above, sorting bullets, matching the profile of the bullet to the seating stem, annealing the brass and all the other care taken to insure matching components and tools, only to find you still have inconsistent lengths.

Not all load data shows compressed loads, and with compressed loads or even high density loads, how you drop the powder can affect how much pressure is required to seat the bullet. A settled drop vs an unsettled drop where the bullet has to move the powder or not while seating.

Inconsistent pulls on the press handle and time spent with the ram at full extension.

Watching someone use the same equipment and components get a completely different assembled length, with less variation, can be a humbling experience.

That is something I have tried to focus on. Being repeatable, especially on the press handle pull. Rotating each cartridge 1/4 of a turn after partial seating to make sure to make sure the bullet seats straight.

The good thing is, I know the margin of inconsistency. So, anything in there, I will not worry about. I need to expand the difference in seating out of that margin to see any real difference. I almost want to go back and reseat some of them deeper before we shoot tomorrow. I had a set of two 5 round groups that I adjusted seating depth. Measured the first one. Afterwards measured the rest and literally most of them were within .001 to .002 out of both groups, so literally no measurable difference.