consistent base to ogive measurement

[Martin52]

Seeking more consistent base to ogive measurements - is it the die or my own technique?

Currently using .308 Forster BR seater die, have replaced the spring and the seating stem. Out of a typical batch of 25 reloads the base to ogive variance can be 0.003" with 155 gr Sierra 2156's. Measurements taken with Hornady comparator and Mitutoya caliper.

Maintain consistent ram pressure, rotate the projectiles through 180 degrees when seating, neck tension is consistent at abt 0.0015, concentricity is generally around 0.001, necks brushed after being annealed and the Forster FLS die has been custom honed. No lube inside the neck. So all seems basically OK except the seating depth variance.

Anyone using a Forster BR seater die - what variance are you getting.
Anyone using a Wilson seater with arbor press - variance ?
I use a Lee Cast press (the heavy duty version) which works fine when full length resizing, holds shoulder bump with minimal variance - <0.001. Just doesn;t hold same when seating.

Thanks

Martin

 

[michaeljp]

Are you measuring the projectiles? The variation might be in them.

 

[Martin52]

Yes, I have given that some thought but if the ogive to base length varies, the seater stem still makes contact at the same point, the ogive. The variable would be amount the projectile is pressed into the case, the longer the base to ogive distance then the more bearing surface is in the case neck, the less the base to ogive distance then the less bearing surface is in the case neck - the ogive to cartridge base would remain the same in both examples because the seater stem always contacts the ogive at the same point and that is what determines base to ogive distance.

i stand to be corrected....that's my own theory !

Thanks
Martin

 

[mikecr]

You may have some ogive radius variance, which directly affects the datum your tool is taking.
But if not, how are you ensuring the press slop is removed from the process?
Same way as with bumping?

You ask about using Wilson, I do with micrometer tops. I also use a Sinclair 'nut 'comparator.
I've never seen variance so much as 1thou with this combo.

 

[kelbro]

You're certain that the seater stem is contacting the ogive and not the tip of the bullet?

 

[nra-for-life]

Seeking more consistent base to ogive measurements - is it the die or my own technique?

Currently using .308 Forster BR seater die, have replaced the spring and the seating stem. Out of a typical batch of 25 reloads the base to ogive variance can be 0.003" with 155 gr Sierra 2156's. Measurements taken with Hornady comparator and Mitutoya caliper.

Maintain consistent ram pressure, rotate the projectiles through 180 degrees when seating, neck tension is consistent at abt 0.0015, concentricity is generally around 0.001, necks brushed after being annealed and the Forster FLS die has been custom honed. No lube inside the neck. So all seems basically OK except the seating depth variance.

Anyone using a Forster BR seater die - what variance are you getting.
Anyone using a Wilson seater with arbor press - variance ?
I use a Lee Cast press (the heavy duty version) which works fine when full length resizing, holds shoulder bump with minimal variance - <0.001. Just doesn;t hold same when seating.

Thanks

Martin

hey Martin...

I have been using almost the exact same setup... forster seater, mitutoyo caliper, hornady comparitor,. i am also using sierra bullets, I also rotate the bullets 180 etc etc....i use a different press but our process is very similar and historically i have had similar results...

I recently switched to an arbor press and a Wilson die, with the arbor press you are really able to feel the bullet seating tension (in my case i get a measurement) and i have done a lot of experimenting to come to some conclusions.

In my case I believe that the bullet seating depth varies due to neck tension. IN every case i have documented, the more neck tension, the longer the length and visa-versa. Your cases are likely varying due to neck tension differences. I believe with more neck tension the brass has more springback and tends to push the bullet back up a little bit after being seated. we are talking minor amounts, in the thousandths (my theory anyway).

Try to focus your efforts on uniforming your neck tension... this may be difficult as it has almost no way of being measured. IN my case in particular I believe now that my neck tension problems are being caused by differences in the case neck thickness...time will tell on my next batch i am going to really focus in on this.

I hope this might help you some...good luck. - Justin

 

[mikecr]

Justin's right. Regardless of equipment your seating forces need to be close to one another.
I also measure seating forces and uniform them, but before seating bullets. I should have mentioned this qualifier about my results.
I also measure/cull bullets by ogive radius way before using any. There, Think that covers it.
Well, one more, I lead dip stress relieve the cases once in a while. With annealing, first seating forces go way up which affects seating results. With this the tension is less(until restored through cycling), but seating forces are higher initially.

 

[Bob3700]

Martin,

In order to uniform neck tension, you might try running a mandrel into the necks before bullet seating.

Lyman used to make an "M" die for just such tasks.

I made one up and have turned several mandrels with different ODs so that as the case gets more firings on it, I can run the mandrel into the case and uniform the ID of the neck and keep the neck tension the same. You can feel the difference when neck ID's change, the case drags differently on the mandrel.

Bob

 

[in2deep]

You often hear that neck tension variation effects bullet seating depth but can't see how unless you have so much tension that the brass is yielding at the neck then springing back (which I have seen and done). but otherwise it seems that some bullets would necessarily have to back themselves out somehow as it can't happen the other way around and bullets can't drop farther into the case.

But I have wondered if the trapped air in the case can push bullets back out and maybe that's why some guys give a double-tap with the seating press to release any trapped air?

 

[nra-for-life]

..... I have wondered if the trapped air in the case can push bullets back out and maybe that's why some guys give a double-tap with the seating press to release any trapped air?

i had the same thought, but after thinking it over i came to the conclusion that it is counter-intuitive. the overall length is longer when the tension is higher. my train of thought is that if the trapped air in the case was compressing and forcing the bullet back, then the cases with less tension would be the longer ones, as there would be less resistance to the compression allowing the air to push the bullet back further. (come to think of it i dont know if handloaded cases are air tight..?)

 

[mikecr]

No, no. Seating is affected by tension because of wedging of the seater stem about the ogive curvature. You can do it yourself with the caliper comparators through more or less force.

Put another way:
When seating force is high, the stem wedges further up onto the bullet nose, causing reduced seating depths(let's say 1.5thou less). Then with a lighter tension, the stem holds at touching, causing increased seating depths(another 1.5thou the from baseline), leaving OP with 3thou of variance. -If tension is the cause-
It's like the difference between 'touching' lands, and 'jammed' into lands.
Were only talking a couple thou here

 

[lpreddick]

THANK YOU mikecr! i have racked my elderly brain trying to figure out why light seating bullets almost always seat deeper than tight seating ones. i'v removed the spring in my redding die thinking it was at fault..realized later the spring has no effect on seater stem tension, etc. one thing i've noted and measured...bullets with .015 thous or more difference in base to ogive, assuming the boattail is the same length, have longer bearing surfaces. this increases barrel drag and pressure and muzzel velocity and accuracy. if the difference is .025 thous plus(a recent batch of sierra 100 gr .25 cal matchkings) it's almost like shooting different brands of bullets. thanks again.

 

[nra-for-life]

No, no. Seating is affected by tension because of wedging of the seater stem about the ogive curvature. You can do it yourself with the caliper comparators through more or less force.

Put another way:
When seating force is high, the stem wedges further up onto the bullet nose, causing reduced seating depths(let's say 1.5thou less). Then with a lighter tension, the stem holds at touching, causing increased seating depths(another 1.5thou the from baseline), leaving OP with 3thou of variance. -If tension is the cause-
It's like the difference between 'touching' lands, and 'jammed' into lands.
Were only talking a couple thou here

great explanation. that makes sense, particularly with the caliper reference i could see how that would happen....

so now if i could just get someone to custom make a slip proof seater stem to match the o-give of my bullets id be golden!!!

 

[mikegaiz]

I use Forster ultra seater and Redding comp seater and have the same issue. I now use a Redding instant comparator to see what is going on and make adjustments.

 

[normmatzen]

You may want to take a close look at the new spring. Or, just take the die and try pushing the sleeve up into the die proper. It should go all the way in. If it is inhibited from going all the way into the die body, the spring is coil binding.

I and a friend had the same problem. we both ground the spring down to make it shorter and make the end of the coils flat instead of stepped. Problem went away, from results like you claim to barely measurable variation.
We also complained to Forster and they sent us new springs that were not only shorter, but weaker. Now, we have accurate seating as well as a weaker spring so we can feel the seating force.

 

[Martin52]

Thanks guys, there's a lot of good comments there. Mikecr's comment about the seater stem being forced deeper on the bullet is interesting, I always assumed that would be a constant but it makes a lot of sense, more force pushes the stem lower on the bullet, or higher with less force. If you can't get a constant relationship between the cap on the seater stem and the ogive the seating depths will definitely vary.
Better seater stems ? I hear Wilson make a VLD stem.
Martin

 

[fguffey]

I make transfers, the tool determines the distance from the head of the case to the ojive contact with the rifling, after adjusting the bullet out to make contact I move the transfer tool to the seater die, adjust for bullet ‘running start’, then start seating bullet

F. Guffey

 

[noload]

I use a wilson seater and arbor press. I found that the seater stem will stick onto the bullet and cause a groove. if a hard press (tight neck) hence the case will not drop out of the seater body because it is being held by the crimp line on the ogive. I solved this by spinning a bullet coated with fine grinding compound or Floss. in the seat er stem just enough to break the sharp corner that causes it to dig into the bullet ogive. It is important to spin the bullet straight in line with the stem. Using a drill press seems to work. This has eliminated the bullet stick problem and reduced the crimp line around the ogive. Especially with VLD secant bullets, Pat