Bullet Seating Depth

[mike hall]

I have some general questions regarding bullet seating and I thought this would be the best place to ask them. I am trying to figure out how a bench rest shooter gets all of his loads to seat at the same depth. I am currently using Hornady custom dies but i get two to three thousands difference in the length measurements using a Hornady digital caliper and a Hornady comparator set. I even checked some custom factory ammo I purchased and it too has variations similar to my reloads. Am I being to picky? I am assuming that this is a problem with the seating die but there is no micrometer adjustment so what should I do?

Any help or advice would be greatly appreciated.

 

[cajun]

They use benchrest seating dies like the redding,forster or the wilson and an arbor press. But they also sort bullets by ogive length. I would check the bullets you are using.

 

[Barrelnut]

Hornady makes a micrometer for their dies. It works but is harder to read than the black ones from Redding, etc.

For best consistency when seating the bullets, first sort the bullets by bearing surface, second make sure the case necks all have the same tension. I keep my brass together in lots based on how many times they have been fired. This helps keep the neck tension the same.

If that doesn't work, try making a mark on the seater stem adjuster and the die body. Then turn the stem counter clockwise 1/8 turn or so. Seat the bullet, measure, turn some more measure, until the seating depth is perfect.

 

[mike hall]

Thanks for the information. I really appreciate it!

 

[mike hall]

OK after some more testing and some help from a friend I learned you have to be smarter than the equipment that you trying to operate. In having a friend, who loads a considerable amount more than I do, come over and inspect my situation he determined that I was reading the dial caliper wrong. My bullets were 2-4 hundred thousandths off not thousands.
Thanks for the information that you guys have provided. Nice to see that others will take the time to help someone else out!

 

[AZShooter]

Wow .200-.400"???? That is how hundred thousandths is written numerically. Think your friend isn't good at measurement or someone made a mistake in describing the measurement. Now if you said
2 or 4 ten thousandths written .0002" - .0004" that would be very small. .003" (three thousandths) is the thickness of most human hair. .0003" would be 1/10th the thickness of that measurement.

On to the issue you discovered....different over all length of loaded ammo. OAL (overall length) is mentioned in loading books as a length that SAMMI adopted. Nosler's book talks about this seating depth as not set in stone it is simply a reference. Many magazines are longer or shorter and have to have their OAL altered from the suggested one.

As for measuring OAL it is only an approximation of length. Ammo length will vary some because the tips on the bullets are not always the exact same length.

The way handloaders measure the loaded round is from the base of the cartridge to the ogive of the bullet. The ogive is the widest part of the bullet where it meets the taper of the tip. The seating stem inside the seating die is hollow and will generally sit on the ogive or close to it as you seat the bullet. To see if your bullets are all seated the same you will use the caliper and one of several types of tools that sit on the ogive.



One tool that is used with a caliper is a comparator:

SINCLAIR INSERT STYLE BULLET COMPARATOR | Sinclair Intl


video on using a comparator:

[ame=http://www.youtube.com/watch?v=M92w4YoxbEM]Reloading 101: Measuring Cartridges With A Bullet Comparator - YouTube[/ame]

 

[Barrelnut]

Wow .200-.400"???? That is how hundred thousandths is written numerically. Think your friend isn't good at measurement or someone made a mistake in describing the measurement. Now if you said
2 or 4 ten thousandths written .0002" - .0004" that would be very small. .003" (three thousandths) is the thickness of most human hair. .0003" would be 1/10th the thickness of that measurement.

On to the issue you discovered....different over all length of loaded ammo. OAL (overall length) is mentioned in loading books as a length that SAMMI adopted. Nosler's book talks about this seating depth as not set in stone it is simply a reference. Many magazines are longer or shorter and have to have their OAL altered from the suggested one.

As for measuring OAL it is only an approximation of length. Ammo length will vary some because the tips on the bullets are not always the exact same length.

The way handloaders measure the loaded round is from the base of the cartridge to the ogive of the bullet. The ogive is the widest part of the bullet where it meets the taper of the tip. The seating stem inside the seating die is hollow and will generally sit on the ogive or close to it as you seat the bullet. To see if your bullets are all seated the same you will use the caliper and one of several types of tools that sit on the ogive.



One tool that is used with a caliper is a comparator:

SINCLAIR INSERT STYLE BULLET COMPARATOR | Sinclair Intl


video on using a comparator:

Reloading 101: Measuring Cartridges With A Bullet Comparator - YouTube

OP does mention that he is using a Hornady comparator set...

 

[boomtube]

"... i get two to three thousands difference in the length measurements ..."

That's nothing. Your rig isn't a BR rifle and you aren't a BR shooter and you aren't loading handmade bullets and you don't have any seating variation that you will ever see on targets. Develop a good load and tiny variations in OAL - or powder charges - won't matter.

Micrometer seater heads are user adjustment aids, they don't make a bit of difference for OAL or concentricity of the ammo. Any die can/may be out of tolerance but it's rare. Most common seaters (and sizers) are capable of making much better ammo than their users can produce.

 

[foggybottombob]

The biggest variable affecting seating depth is neck tension of the case. There is some flexibility in your entire press/seating die system. With variances in neck tension you will get variances in bullet seating depth. The press linkages have some flex and the seating die plug does too. We are only talking thousandths of an inch here. There is a post in the middle of this page that covers the neck tension idea thoroughly.

Reloader's Nest Forum - How much does neck tension affect MV?

 

[260VLD]

Measuring/ batching base to ogive will get you half way there , now if you want to get real picky , you need to consider where the seater stem contacts the projectile as the bullet is seated, for not all ogive to bullet tips are the same. Therefore if the seater stem contacts the bullet .002" further off than the previous bullet then you will still have a ogive jump variance , will you not ?
So you will batch base to ogive and then batch that batch into sub lots, the ogive to where the seater stem contacts the bullet tip.The only way to do that is to use a Bob Green Comparator which is sort of like a barrel chamber , you insert a projectile into it, the other end has a machined seater stem on top of which there is a dial indicator , the chamber has a throat reamed into it so the projectile as it is pushed in contacts the lands and the indicator gives you a read out thereby creating your sub lots.

Hope this makes sense but search Bob Greens Comparator for a better explanation.

Mike.

 

[Shootin4fun]

Measuring/ batching base to ogive will get you half way there , now if you want to get real picky , you need to consider where the seater stem contacts the projectile as the bullet is seated, for not all ogive to bullet tips are the same. Therefore if the seater stem contacts the bullet .002" further off than the previous bullet then you will still have a ogive jump variance , will you not?

Ah ha! This is what I have just discovered. I have never compared the ogive measurement between bullets of the same make/model before until today when I was loading up a batch of 130gr SSTs for my 270win. I found an accurate load a few weeks ago and am confirming and trying to replicate it. This batch was about to bridge 2 boxes of SSTs so for the heck of it I started measuring ogive to bullet base to see if there is a difference. INDEED there is. (Great, another variable to measure and sort!)

Lo and behold, there were 3 basic base to ogive lengths each: ~1.280,
~1.285, and ~1.290". Holy smokes that's an extreme spread of .010! 50% were at the longest end. (Also, the shorter ogive bullets were shorter end to end by approximately the same amount.) This means that the longest could potentially be seated .010 deeper into the case than the shortest ones since the die always contacts the bullet at the same circumference. Now I'm assuming for a moment that the jump to the lands remains the same because presumably the seating die hits the bullet at the same point on the ogive each time (just to keep considerations simple). There was no correlation in weight differences to length differences.

So my big question is, how much will the variation of .010" into the case affect pressure/burn, considering we are changing the case capacity?

Does this count more than a variation in jump of .010?? My guess is no, but it still matters.

If I found an accurate length/charge for the longest ones, how should I compensate for the difference when loading up the shorter ones. Should I seat the shorter ones .010 shallower? Conversely if the accurate load is with shorter ones, should I seat the longer ones deeper?

BTW, this is a hunting gun (Browning BAR) not a BR gun, and my best loads often give me 3 of 4 in a clover leaf, and 1 flier .2 - .8" away @ 100. I have never figured out if the flier is me or the load. But as mentioned above, I want to develop the tightest load possible so variance in the field is due to me and external factors.

Thanks in advance for any sage advice y'all have to offer.

 

[Shootin4fun]

...Oops, sorry, the dimensions I listed are wrong. Didn't have my notes when I wrote that.

Ogives measured:
.682"
.690"
.695.

The OAL of the bullets were close to correspondingly different at approx:
1.234
1.241
1.245

So the bullets are proportionately scaled but different sizes. This means that the jump is within a few thousandths, but the seating depth is .013" different at the extremes.

I loaded 24 of 2 different powder weights using a sorted set of all the same dimension SSTs. It will be interesting to see if the velocity ES and SD are lower. I have records of previous outings of everything the same, but unsorted.

 

[260VLD]

The only time I bother getting real picky about batching bullets is for 1000 yards Palma Matches . Elevation Elevation Elevation ! The best wind reader on the planet will suffer if the vertical dispersion of his ammo is BIG !
Now as you are aware there are various gadget gimmicks and paraphernalia that allows hand loaders to tweak cases , projectiles , measure this and measure that BUT there will be a point of diminished returns.
Example : bullet pointing and meplat trimming works , how much , is always a question for debate and can reduce vertical dispersion by as little as 1/10 MOA and some say better than 1/2MOA @ 1000 yards. The bull measures approx 20 inches the X ring 10.
Personally , I know I can't hold better than 1 MOA on a good day , so pointing and trimming meplats for me is a time waster OR a diminished return.
As far as seating depth goes , I use a Redding instant indicator , I have a dummy round set up to the seating depth using Berger 155.5 projectiles. I set the dummy up and zero the dial indicator , I then nominally seat my bullets and then one by one check the length in the indicator and re seat each projectile accordingly. Therefore I now have 25 rounds for match all with a jump of thirty thou , the seating depth of the base of those projectiles will and do vary but I am looking for consistent jump length. Important to note that the Redding Indicator takes measurement from an internal bush which makes contact pretty near the ogive so one needs to be mindful that when seating the bullet, the seater stem WILL NOT contact every projectile in the exact same place , and it takes a bit of practise to know how much to rotate the micrometer seater. I know with mine , a 1 thou increase on the dial will give me nearly 2 thou extra depth, so I compensate for this error.
I have yet to see any effect on my scores caused by the increase of 2 or 3 thou or more in base depth. For the short ranges 300-700 yards I don't even bother with the above procedure, I just load them straight out of the box , and for some big meets I will do the seating procedure for my 800 900 yard ammo.
For hunting ammo , I seat to mag length and don't batch projectiles at all , even for one of my single shot rifles where I can control seat depth, I don't bother.
I have a buddy that tweaks , cleans , bends, shapes anything he can with his ammo,he is an accountant so is anal by profession. Sometimes he eats the bear , sometimes the bear eats him , I guess what I am trying to say is , one has to decide to what lengths and expense one is prepared to go to before the returns are diminished.But if you shoot BR then you better be anal if you wish to compete.

regards
Mike.

 

[Shootin4fun]

Thanks for your input Mike. I too think that the jump distance has a more critical effect on grouping than the amount of case volume change when changing the seating depth.