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Seating depth variations

KeeblerArmy

KeeblerArmy

Private
Full Member
Minuteman
Aug 26, 2005
92
3
Oregon
I just got done loading 20 rounds and have been having a problem that is bugging me. I'm using a RCBS single stage press with Hornady dies.

For whatever reason, I'm getting a variation in my COL of +/- .004 or so from zero, measured with a comparator. If a cartridge ends up a little long and I fine adjust the die to get it down to zero, more often than not the next cartridge will end up short. If I don't touch it, I'll still end up with different COL's.

Now is a difference of .008 in COL going to actually show up on paper or am I just chasing warm fuzzies?

Where do you think the variables are that are causing this much change in the COL? I've considered getting a precision die insert but really don't think that should be necessary, and kind doubt if it is going to work.

In interest of full disclosure, my press is screwed onto a board which is C clamped to the bench. There is some flex in the way it is set up so you could say it is not securely mounted. Wouldn't what is going on inside the press/dies not really be affected by that though?

 
Re: Seating depth variationso

If you're measuring from the bullet tip, you're chasing your tail. The tips vary that you're going to bet 0.005" variance in the measurement. If you're measuring off the ogive, then you might be experiencing some press or die lockring flex.
 
Re: Seating depth variationso

Found this at another forum and think it might apply here as well. I've been suspicious if the primers have always been flush, sometimes they feel like they aren't:

"Recently, I reloaded some .45 auto without cleaning the primer pockets. Using a dial caliper, I noticed the OAL was different with just about every round. While measuring, it also occurred to me one of the caliper jaws rested against the primer, and primer seating depth was very likely being affected by residue in the primer pocket, causing the wide variance in OAL, so I went back to cleaning primer pockets, and the OAL settled right down!"

http://www.reloadersnest.com/forum/topic.asp?TOPIC_ID=2346
 
Re: Seating depth variationso

Your primers should never be flush. They should seat down a couple thousanths below flush.
As has been said you must measure from the ogive to be consistent. If you are loading compressed loads this can greatly affect your seating depth consistency. I ran into this with a compressed load recently and I realized there is no cure with this particular bullet beyond going to a faster burning powder.
 
Re: Seating depth variationso

You didn't mention brand of projectile you are loading, but I would suggest measuring and sorting your bullets by length, weight etc. What you may be seeing is variation in the shape or arch of the ogive and since the seater die seats the bullet on a fixed dimension, the contact location on the ogive may change. Any variation in the projectile ogive would result in a different seating depth.

I went through this process working up a load for my 7mm STW using Berger 180 gr VLD's. I measured and weighed every bullet in the box and the variation in overall length, and fixed ogive diameter to base was eye opening.
 
Re: Seating depth variationso

Your comparator IS measureing off the ogive so that's fine.

Your extreme spread is either 8 thou or 16 thou. ?? The former is probably okay, the latter may well be excessive. Being precise in all things is very good, up to the point of diminishing returns for more effort. But being consistantly and precisely off the sweet spot by any amount is not good, so it matters how you found your 'best' OAL and where you are seating inrelation to that length.

Unless you're using handmade competition bullets it will be impossible to be precise every time. The ogive shape of mass produced hunting bullets can easily give you an 8 thou spread even if you're doing perfect work. And the potential for ogive variation increases as bullet diameter increases.

Small bullet jump variations are usually meaningless at rational ranges. But, IF you have chosen a seating depth/jump that's right on the ragged edge of the good range your current spread can easily go outside what won't matter. Suggest you shoot 'em and see how they do before you get too wound up over it.
 
Re: Seating depth variationso

Armored Chicken: If it should be a couple thousandths below flush then there might be a problem here because I suspect some of the primers are actually protruding a little bit. I'll see if I can validate that with calipers. The load I'm using isn't a compressed one.

mtang45: They are Sierra 175gr BTHP. Maybe I'll try looking at variations in the bullets too. I thought the whole point of measuring at the O give was that the tips were too inconsistent, and now you are telling me the o gives have variations too??

Fuzzball: I haven't really searched for the perfect OAL with this rifle, I'm just trying to be consistent. I'm not loading X thousands off the rifling or anything. (I'm not good enough of a reloader to do that yet anyway).

With some at +.004 and others -.004 that is where I would get a potential jump of .008 between rounds. I grouped them in my ammo box by similar size to help control variation in group size at least. How would you define a small bullet jump variation and a rational range?
 
Re: Seating depth variationso

A protruding primer will be far more problematic than a .008" spread inseating depth. It can also cause false pressure signs. I do not clean primer pockets very often and I never have protruding primers. I use a press mounted priming system and it works flawlessly in seating primers.
What rifle are you using to shoot these loads? You cannot apply benchrest reloading voodoo to a factory rifle and make it shoot custom rifle groups. Nothing wrong with making the best ammo you can make but sometimes the view is not worth the climb.
 
Re: Seating depth variationso

I'm using a Hornady hand priming tool, which seems to work ok.

"You cannot apply benchrest reloading voodoo to a factory rifle and make it shoot custom rifle groups. Nothing wrong with making the best ammo you can make but sometimes the view is not worth the climb."

I might be guilty of that here since I'm shooting a stock R700 VSS. Is sub MOA really too much to ask?
smile.gif
I'll even settle for 1 MOA consistently.
 
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Re: Seating depth variationso

"I'm not loading X thousands off the rifling or anything. (...With some at +.004 and others -.004 that is where I would get a potential jump of .008 between rounds."

Understand, but wasn't thinking about a specific jump, only the variation. You first mentioned both a +/- .004" and +/- .008". The first may not be an accuracy problem. The second, at a .016" spread, is quite likely to affect accuracy, IME.

It might help us get a feel for what the variation effects may be if we knew the cartrige, bullet and the rifle you're shooting it in. ???
 
Re: Seating depth variationso

Sorry, I guess I wasn't very clear about the size of the range. What I meant to say was, a +/- .004 from zero, with an over all spread potential of .008. It is not going as far as .016. Does that make more sense?

As to what I'm feeding into what, we are talking about a.308 Remington 700 VSS. The cartridge is second hand federal brass with Sierra 175gr BTHP. Remington primers (cause I bought them in 2008-2009 when there was NOTHING available on the shelves) and H4895(again the only thing available) 42.2gr.
 
Re: Seating depth variationso

What they said, plus you really should mount your press up as solid as possible.
 
Re: Seating depth variationso

Okay, when you said +/- .008 I took it literal, you meant the extreme spread.

For questions such as this we need to know the cartridge, bullet and rifle, rest of all that detail matters not. A seating spread of 8 thou with a 250 gr hunting bullet means virtually nothing in a factory .338 W, the same spread in a custom 6PPC rifle with a hand made bullet would be awful!

A thousanth of an inch is not much, even 6-8 times that much really isn't a lot but it's more seating variation than we would prefer.

Lots of things can and do produce small seating variations. Lever pressure being totally consitant is much more important than a lot of people think; even a massive cast iron press has some small degree of spring/flex. Even the amount and vicosity of the oil in the toggle and ram pins is responsive to lever pressure AND operation rythum. And compressed loads will often push bullets up a little bit after ram pressure is released; with your moderately long bullet you may need to take a look at that possibilty.

It's unlikely there is any real springing in the die or seater stem if they are locked down just hand tight.
 
Re: Seating depth variationso

Invoking the dark arts of Necromancy...

I finally got around to mounting that press properly so it is nice and secure. Loaded up some rounds and here were the numbers (all measured at the ogive). The load is the same as mentioned earlier, 175gr sierras. 2.227 was my target length.

2.227
2.226
2.230
2.228
2.226
2.228
2.227
2.225
2.228
2.227
2.223
2.230
2.225
2.226
2.227
2.226

I measured some Federal GMM 168gr. and came up with these numbers (they are sorted).

2.222
2.223
2.224
2.225
2.225
2.225
2.225
2.226
2.226
2.226
2.228
2.228
2.228
2.228
2.228
2.230
2.230
2.230
2.231
2.232

Call it good or try to improve upon my anal retentiveness?
 
Re: Seating depth variationso

No, I wouldn't call it good.
You said your using a comparator, a must with vld style bullets. That RC press should be rock solid.

Try this, I never fully seat the bullet on the first upstroke, get it almost all the way in, let it down a little, rotate the case a 1/4 turn or so in the shellholder, then seat the bullet, let down and repeat a couple of times. I'm positive this works for me.
I'd be upset with a ".001" variance.
Maybe borrow a friends die, set it up in your press???
I just bought a set of Hornady match grade dies, and I'm impressed with the quality of them.
 
Re: Seating depth variationso

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: milo-2</div><div class="ubbcode-body">No, I wouldn't call it good.
You said your using a comparator, a must with vld style bullets. That RC press should be rock solid.

Try this, I never fully seat the bullet on the first upstroke, get it almost all the way in, let it down a little, rotate the case a 1/4 turn or so in the shellholder, then seat the bullet, let down and repeat a couple of times. I'm positive this works for me.
I'd be upset with a ".001" variance.
Maybe borrow a friends die, set it up in your press???
I just bought a set of Hornady match grade dies, and I'm impressed with the quality of them. </div></div>

You know, you are the second person to mention that technique over the night. I have a similar thread going on elsewhere and they said the same thing. I had not heard of that before and will definitely give it a shot.

Thanks for the tip
 
Re: Seating depth variationso

For what it's worth, I measure my bullets from base to ogive with a comparator and sort by length. I've found Sierras to run +/- .005 from mean.

Noslers, on the other hand, have never varied more than +/- .001".
 
Re: Seating depth variationso

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: milo-2</div><div class="ubbcode-body">Try this, I never fully seat the bullet on the first upstroke, get it almost all the way in, let it down a little, rotate the case a 1/4 turn or so in the shellholder, then seat the bullet, let down and repeat a couple of times.</div></div>

I seat my bullets at least 0.100 long and then run them through the seater die (with a different setting). So, for example: I target 3.000 for the first seating, then target 2.943 fro the second seating (0.015 from my lands).

Since ther two seatings have 50-odd other cases run through, there is a low probablility to get the same case rotation twice.
 
Re: Seating depth variationso

If you tune your load by seating the bullets .003" - .005" incriments you should see a sweet spot where one to two seating depth areas which will be very favorable, pick the one that is in the middle so there is still some margin of error.

Many people just do an OCW for the charge weight and then stop on the first seating depth that is favorable. I chose do do the seating depth in the same manner as the charge weight by chosing the the range where the accuracy fall between to seating depths.
 
Re: Seating depth variationso

Hedge,
After you measure the ogive, and sort them, what do you do?

Chase the lands accordingly?

Where the _uck is Baldwin, ND?
 
Re: Seating depth variationso

Yeah, chase the lands, but only with Hornadys because of the secant ogive. They're kinda touchy about seating depth. +/- .003 doesn't seem to affect my groups much, but .005" really does. Go figure. Sierras I quit using. For whatever reason, my rifle spits 'em out cock-eyed.

laugh.gif
A several klicks north of Bismarck. Got a little place where I can snipe coyotes from my back yard when my horses are out of the way.
 
Re: Seating depth variationso

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ballistic308</div><div class="ubbcode-body">If you tune your load by seating the bullets .003" - .005" incriments you should see a sweet spot where one to two seating depth areas which will be very favorable, pick the one that is in the middle so there is still some margin of error.

Many people just do an OCW for the charge weight and then stop on the first seating depth that is favorable. I chose do do the seating depth in the same manner as the charge weight by chosing the the range where the accuracy fall between to seating depths. </div></div>


Excellent idea. I'm one of the guilty ones that only applied OCW to the charge weight. Now I'll try it on the seating length also. Thanks for the tip!
 
Re: Seating depth variationso

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: milo-2</div><div class="ubbcode-body">No, I wouldn't call it good.
You said your using a comparator, a must with vld style bullets. That RC press should be rock solid.

Try this, I never fully seat the bullet on the first upstroke, get it almost all the way in, let it down a little, rotate the case a 1/4 turn or so in the shellholder, then seat the bullet, let down and repeat a couple of times. I'm positive this works for me.
I'd be upset with a ".001" variance...
</div></div>

Updates: I added this technique to my loading process and it indeed tightened up the specs. Numbers are available if anyone is really interested.

I also noticed during that session that the times when the OAL got suddenly larger, the primer was protruding from the bottom of the case just a tad. (Could see light between the bottom of the casing and the caliper)

Just today a Lyman primer pocket uniformer showed up in the mail so hopefully that will address the primers not seating completely.

Will report back with results.

I'm really starting to wish I had one of those motorized case prep stations.
 
Re: Seating depth variationso

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ballistic308</div><div class="ubbcode-body">If you tune your load by seating the bullets .003" - .005" incriments you should see a sweet spot where one to two seating depth areas which will be very favorable, pick the one that is in the middle so there is still some margin of error.

Many people just do an OCW for the charge weight and then stop on the first seating depth that is favorable. I chose do do the seating depth in the same manner as the charge weight by chosing the the range where the accuracy fall between to seating depths.</div></div>

Ballistic, would you please elaborate on the procedure for this? I elsewhere recently that there should be a sweet spot for OAL length that the rifle will like just like you are describing.

Personally, I do not want to have to single load rounds, meaning I'd like to retain the use of the internal magazine. So should I try to seat the bullet as long as will fit comfortably and shrink it from there?

How do I make sure I'm not getting close enough to the lands to create pressure spikes? Given that this is a factory Remington, I'm pretty sure that is unlikely. I understand that they tend to have very long throats.

Thanks
 
Re: Seating depth variationso

Thread Necromancy!

Ok, I have a theory on the seating depth problem that goes beyond variations in O-give which I can't control anyway. Won't be able to confirm this without different equipment however.

For chamfuring/deburring I have been using a cheap little Lee tool to do it. I've been noticing today that this last batch of cases has had a lot of resistance when I initially start seating the bullet. I am also seeing that there is a bit of copper scraped off on the edge of the case mouth.

I had one that seated nice and smooth like butter. I must have been less lazy when cleaning up that case mouth. That bullet in particular also happened to seated a couple thousands deeper than the other ones I have been doing today.

So the theory is that perhaps some of the seating variation comes from inconsistent case mouths and potentially from material getting scraped off the bullet and getting all bunched up between the case and bullet.
 
Re: Seating depth variationso

You are correct, all things being equal, less neck resistance = deeper seating depth. I've pulled and reseated many bullets due to this scenario.
 
Re: Seating depth variations

Bullet length does vary. Measure from the ogive if you want consistent readings. OR find the seating depth that shoots well and go with it.
 
Re: Seating depth variations

Seating based on ogive won't necessarily give you consistency, either, sorry to say. However, I believe it to be a better method than base to tip.

Depending on the quality of the bullets, there can be quite a variation. I make it a practice to measure all my bullets by ogive and have found as much as .015" variation in the same lot of Vmax bullets. Noslers and Sierra and even Berger's show a variation but to a lesser degree.

I segregate them by base to ogive length and adjust the seater to compensate. The critical point is where the bearing surface starts.
 
It took a half a year, but I believe that I have proven that copper scraping off is indeed effecting the seating depths. Recently I invested in a RCBS VLD chamfering tool and used it on my friends case prep center to process this latest batch of brass. The VLD tool cuts a steeper angle into the inside of the case mouth so bullets like the SMK will seat smoother.

Seating the bullet feels completely different, much smoother. And NO copper shavings now. Compare these numbers with the spread posted above. (2.227 was still the target OAL but I ended up with 2.228 on the die. It is a Remington factory throat so close enough.)

2.229
2.230
2.228
2.229
2.228
2.228
2.228
2.228
2.229
2.229
2.230
2.231
2.229
2.228
2.229
2.228
2.229
2.228
2.228
2.229
2.228

Some of that could very well be from variations in bullet shape. Would have to measure the bullets separately and keep them in order to show that correlation.
 
Very cool. Those numbers are doable.
I'm not sure how you actuate your press handle, but I myself let the weight of the handle do the work at the end of the seating stroke. I find this to be very adequate and repeatable to
 
I'm no expert by any means.
I shoot 175 SMK's and the ogive will vary alot 4-12 thou.
I sort my bullets by ogive lengths.
If my rifle shoots best at .005 off lands I get sorted bullets and measure that bullet to the lands and go from there.
When I shoot the sorted bullets up I sort some more and do the process over again.
I have found that A-Max's don't vary as much as SMK's.
Just my .02 worth
 
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