Bullet seat depth changes after setup - why?

[Dr OCD]

Newbie on this forum. I have looked for this topic but couldn’t find anything. Let me set the stage:
I only reload pistol ammo and find that after I have set up bullet seating depth (empty, sized and expanded cases using only the seating die) I lock the dies and start my batches. Invariably the finished rounds are 0.004-0.010” longer than the set length.
Asking around my club members, this is not an uncommon problem though nobody has identifies a cause.
When I run the loaded rounds back though just the seater and crimper (separate dies) they come out spot on the original set OAL.
This is not press specific (I use Hornady LNL, others use Dillons 550, 650 and 1050), although all are turret presses, nor is it die manufacturer specific ( I have experienced it with Lee and Redding dies).
So, it only seems to happen when running a full turret with cases going through the full set of dies simultaneously - size, expand/powder, seat, crimp - but not when run cases through just the seat and crimp dies.
I am interested to see how common this is and if there are any reloaders out there that have figured this out!

 

[243winxb]

Different deck height of the shell plate, if any die is contacting it.

Slop in the press linkage.

Tool head movement.
Seating stem doesn't fit bullet.

Common to have as much as .010" col on a progressive & .005" on single stage press.

From Lee-
Another possible cause for bullet seating depth variation is seating and crimping at the same time when trying to apply a firm crimp to untrimmed cases. Variation in case length also causes variation in the amount of crimp applied. Long cases get a heavier crimp than short ones. When seating and crimping at the same time, the crimp is formed as the bullet is seated into the case. The crimp will form sooner on a long case, and therefore the bullet will not be seated as deeply. The solution is to seat and crimp in a separate step and/or trim cases to a uniform length.

The amount of force required to cycle a progressive press varies with the number of cases in the shell plate. When the shell plate is full, it is harder to lower the lever than when there are one or two cases present. This can lead to variation in cartridge overall length because there are different loads placed on the working parts of the press. When the shell plate is full, seating depth will be slightly long, because the load is higher and all of the clearances are taken up. With the shell plate nearly empty, the load is not great enough to squeeze out these clearances, and the seating depth is short.

A potential solution for this on progressive presses is to turn the sizing die in far enough so that the carrier is stopping on the bottom of the die. This removes clearance problems when no sizing but yet seating / crimping is occurring. Take special care not to turn the die in further than to just touch the shell plate and possibly just a tad more. About 1/4th of turn more is all you want to go, turning the sizing die in too far causes other problems.

https://support.leeprecision.net/en/knowledgebase/article/overall-length-oal-variation

 

[243winxb]

Can you shoot the difference between? A .010" variation compared to Zero? I can't @ 50 yards.
If bullets are touching the rifling on the longest col, but not the short ones, , use a shorter col.

finished rounds are 0.004-0.010” longer than the set length. / Or spot on the original set OAL.

Do measure some factory ammo to compare col. May supprise you.

 

[mgunderson]

This can be a shell plate and tool head deflection issue. The loading with all the stations full is different than just running one shell at a time. I see it on my 550, but others might be able to speak to the bigger presses.

 

[dellet]

The reasons you get different results, is simply because you are using different methods when seating the bullets.

The fully loaded shell plate vs single station being used.
Whether the die is locked down and when you tightened the lock ring
How you arrived at the desired length.
Case prep
Bullet sorting
Time in the press, time under pressure.
Die choice
Lube

Die choice, carbide is very helpful. It helps even out the pressure required to size the case and that pressure effects the opposite side of the shell plate.

Lube, same as above.

If you place a round in the seating die, seat a bullet, measure it, place it back in the press, change the setting, reseat the bullet, change the setting, reseat, call it good. You will get a different length than when you seat in one step. Since your rounds even out the second time through the die, this is a good place to start.

If you set the lock ring of the die or seating stem without a round in the die, it will change your setting.

If you seat at a different speed when measuring than actually loading, it will change your seated depth.
Are you certain that you are bottoming out the lever on the press each time and allowing it to rest the same each time?

Mixed headstamps will change neck tension, as will number of firings.

Those are probably the big things. Basically all the little things that people spend time with on rifle loads, that get ignored with pistol rounds and the speed of a progressive press add up to what you are seeing.

One of the simplest things to try is to set the seating depth with a fully loaded shell plate. Then be really anal about timing when pulling the lever. Both on the working stroke, and the time at bottom. Once you do that, and all rounds measure with a reasonable variance, you will probably have to adjust your die again. Then every time you change your timing, readjust or ignore.

One thing is for certain, depending on the strength of your OCD, loading pistol cartridges on a progressive press, and expecting precision rifle quality loads, will either cure it or drive you insane.

 

[Dr OCD]

Different deck height of the shell plate, if any die is contacting it.

Slop in the press linkage.

Tool head movement.
Seating stem doesn't fit bullet.

Common to have as much as .010" col on a progressive & .005" on single stage press.



https://support.leeprecision.net/en/knowledgebase/article/overall-length-oal-variation

Thanks for this info. I appreciate you taking the time. My problem is not the variation in OAL between rounds, it is the variation between setting the initial OAL then running a batch of ammo. Once running, I am getting very consistent length but, it is a different length to that which I set up on the individual test rounds.
i will, however, check the shell plate height variation through the various steps of reloading cycle.

 

[Dr OCD]

This can be a shell plate and tool head deflection issue. The loading with all the stations full is different than just running one shell at a time. I see it on my 550, but others might be able to speak to the bigger presses.

mgunderson: thanks for the response, this sounds a likely possibility given the shell plate may be pivoting vertically about its central mounting point, I will certainly look at this. If this is the case then it will be easy to determine and overcome.

 

[Dr OCD]

Can you shoot the difference between? A .010" variation compared to Zero? I can't @ 50 yards.
If bullets are touching the rifling on the longest col, but not the short ones, , use a shorter col.

Do measure some factory ammo to compare col. May supprise you.

What you say is probably true. However, for my personal satisfaction this is purely about understanding how this variation occurs not the final result in effecting accuracy. The other potential problem with OAL for a semi-auto pistol is feeding reliability.

 

[Dr OCD]

The reasons you get different results, is simply because you are using different methods when seating the bullets.

The fully loaded shell plate vs single station being used.
Whether the die is locked down and when you tightened the lock ring
How you arrived at the desired length.
Case prep
Bullet sorting
Time in the press, time under pressure.
Die choice
Lube

Die choice, carbide is very helpful. It helps even out the pressure required to size the case and that pressure effects the opposite side of the shell plate.

Lube, same as above.

If you place a round in the seating die, seat a bullet, measure it, place it back in the press, change the setting, reseat the bullet, change the setting, reseat, call it good. You will get a different length than when you seat in one step. Since your rounds even out the second time through the die, this is a good place to start.

If you set the lock ring of the die or seating stem without a round in the die, it will change your setting.

If you seat at a different speed when measuring than actually loading, it will change your seated depth.
Are you certain that you are bottoming out the lever on the press each time and allowing it to rest the same each time?

Mixed headstamps will change neck tension, as will number of firings.

Those are probably the big things. Basically all the little things that people spend time with on rifle loads, that get ignored with pistol rounds and the speed of a progressive press add up to what you are seeing.

One of the simplest things to try is to set the seating depth with a fully loaded shell plate. Then be really anal about timing when pulling the lever. Both on the working stroke, and the time at bottom. Once you do that, and all rounds measure with a reasonable variance, you will probably have to adjust your die again. Then every time you change your timing, readjust or ignore.

One thing is for certain, depending on the strength of your OCD, loading pistol cartridges on a progressive press, and expecting precision rifle quality loads, will either cure it or drive you insane.

Thanks for the detailed response. Having read through all your points I see one in particular which will be my first point to look at: having consistent pressure on both sides of the shellplate when running the reloading cycle. As stated, when I set the OAL initially I do it with only one case fitted. when I run with the shellplate fully populated I get a longer OAL. Very consistent between rounds, but longer than the ‘model’ load.

 

[SSchnd]

What seating die are you using? Pull the seater stem and make certain there are not any cracks at the bottom when the ogive engages the stem. A cracked stem can cause the seating depth inconsistency issues. Easy variable to check. I have run into this with my Forster Ultra Mic Seater

 

[divingin]

This can be a shell plate and tool head deflection issue. The loading with all the stations full is different than just running one shell at a time. I see it on my 550, but others might be able to speak to the bigger presses.

Agree with this.

OTOH, most pistol ammo isn't that sensitive to depth changes. As long as it doesn't cause problems, why worry about it?

 

[Dr OCD]

Agree with this.

OTOH, most pistol ammo isn't that sensitive to depth changes. As long as it doesn't cause problems, why worry about it?

Although for general pistol shooting, small changes in OAL may not be significant, there are actually several problems related to OAL, the main one being reliability. Many pistols are actually sensitive to OAL and will not feed reliably especially if your chosen round happens to be close to either end of the scale.
Another problem is in pistols such as .32 S&W long, shooting ISSF disciplines with wadcutter loads, variations in seating depth here definitely cause accuracy issues.

 

[Dr OCD]

What seating die are you using? Pull the seater stem and make certain there are not any cracks at the bottom when the ogive engages the stem. A cracked stem can cause the seating depth inconsistency issues. Easy variable to check. I have run into this with my Forster Ultra Mic Seater

The problem is not variation between rounds when running a batch of reloads, but between the initial rounds used to set up the OAL seating depth and the rounds consequently run. If I set the seating die to give me 1.245” and that is repeatable for rounds put through individually, it goes to around 1.255” when i run “production”.
This occurs regardless of dies, I have used Lee and Redding, my friends have had similar results using Dillon and RCBS, and on different presses (Hornady for me, Dillon for them).

 

[divingin]

You're seeing press stretch or other load-induced flex. Simple solution would be to set up using real-world conditions (i.e. each press station populated and working.) You'll probably lose a small amount of consumables, but the settings shouldn't change.

If you want to see exactly what the cause is, most force will result from sizing. You can check if sizing is causing your variation by pre-sizing a dozen cases, then run them through the entire process with the sizing die removed. If your seat depth doesn't change, that was it. (Of course, you can also verify most other steps in the same manner.)

I run an LNL, and haven't really noticed a problem (though I do check and adjust on the fly, so may have had the same problem and corrected for it.)

And I do (among other things) shoot ISSF CF Pistol with an old original Pardini HP in .32SWL.

 

[Dr OCD]

You're seeing press stretch or other load-induced flex. Simple solution would be to set up using real-world conditions (i.e. each press station populated and working.) You'll probably lose a small amount of consumables, but the settings shouldn't change.

If you want to see exactly what the cause is, most force will result from sizing. You can check if sizing is causing your variation by pre-sizing a dozen cases, then run them through the entire process with the sizing die removed. If your seat depth doesn't change, that was it. (Of course, you can also verify most other steps in the same manner.)

I run an LNL, and haven't really noticed a problem (though I do check and adjust on the fly, so may have had the same problem and corrected for it.)

And I do (among other things) shoot ISSF CF Pistol with an old original Pardini HP in .32SWL.

Very good ideas, I will look at these points. Interesting that you haven’t seen this but, as you said, if you adjust on the fly that might account for it

 

[Hoot]

I've had this happen countless times. Using one charged case, I intentionally set the seating depth long. I then adjust the stem down a little, re-stroke and remeasure the COL. This can take 5-10 cycles until the bullet COL is precisely what I want it to be. I then lock everything down and go to the next charged case, except, I seat the bullet in one continuous stroke. Lo and behold, its seated too deep and I have to back the stem off a little.

I suspect the culprit is that first round is not benefiting from the gliding effect and/or you have the die body screwed down to where it is applying some crimp at the end of the cycle. I'm sure that there is a better description for what is happening but i can't tell you how many times I've seen this happen. Now, I set up with the COL still .01 or so long and run a one stroke cycle afterward to see the actual result. That amount is not a for sure amount of back-off. It will vary with neck tension and the condition of the inside of the neck. If the cases are immaculate, it seems to be worse. Dipping my case necks in Imperial Dry Lube before charging and seating reduces this tendency considerably. This problem also improves immensely if you anneal before reloading.

This is an anecdotal observation.

Hoot

 

[sdbob]

Fill all your shell plate stations when setting up!!!!