seating depth varying by 1/100th

[MikeInUtah]

I have just started getting seating depths on my last loading varying +/- 1/100th. I am on my 4th firing of the same brass. I am alternating between neck sizing and FL sizing every other firing. I noticed this on the last time I loaded this lot and had to keep tweaking the seating depth across the lot to get them consistent. I am using FGMM brass. I have tried using different bullets from 168 SMKs/ 168 nosler match/ 168 hornady amaxes with the same results. I anneal each time I load. I have tried both my Widden competition seating die and also my rcbs seating die with the same results. I have the Hornady lock and load press.

Talking with one of the reloading guys at my local gun shop he thinks it maybe the ram or links on my press getting loose but seating new brass isnt causing this.

I have a Mituyo caliper with the hornady bullet comparator for measuring seating depth at the ogive.

The only constant where this is evident is the brass but not sure what could be causing this. I do notice that some bullets tend to seat easier than others in this brass now so maybe neck tension is causing this?

 

[HumbleEinstein]

Is there any crud on the inside of your hornaday comparator? The other day, my rcbs mic suddenly started giving erratic readings. I cleaned some buildup out of the inside and the readings settled back to within a thousandths of each other.

 

[wchartz]

20 thousandts of an inch extreme variation is really bad. You have something major wrong or you misstated your measurements.

 

[bigedp51]

Most of the time seating depth problems are caused by a ill fitting seater plug.

Even the photo above is not very correct, many of my seaters hold the bullet at the mouth of the seater plug. I slightly bevel the mouth because it can be sharp and grip the bullet tight enough sometimes to pull the bullet upward.
Having said that most of the time the problem is the bullet tip hitting the top of the seater cone and being compressed. The solution is custom made seater plugs that contact the entire tip of the bullet.

 

[ShtrRdy]

Are you dealing with a compressed load of powder? This will mess with OAL as well.

 

[MikeInUtah]

No compressed loads used. I tried cleaning the comparator and it didnt resolve the issue. I am seating to 2.20 and I am getting between 2.210 and 2.190. I have been backing it off so my lowest seating depth is 2.20 and ~2.21 and then tweak each down so I am consistently at 2.20. I havent noticed any difference in grouping. Big Ed I think you are on to something. I have noticed a few of the longer seated bullets sometimes have a slight stick when lowering the ram. Strange since two different dies are causing this same issue.

 

[scatterbrains]

Have you measured the bullets themselves? Its possible they may be the difference your seeing.

 

[milo 2.0]

I'd say it's inconsistent neck tension, some seat hard, some drop in? Your brass is getting work hardened, and needs annealing. The only other option is a bushing die, and keep reducing bushing size to control neck spring back. My last batch of Lapua 6.5x47 brass gave up the ghost after one firing, unfortunately I failed to notice it before I processed and primed them.
Another big factor in seat depth is press stroke, all the same, all the time, fast erratic strokes will mess seat depth up quicker than anything.

 

[MikeInUtah]

I'd say it's inconsistent neck tension, some seat hard, some drop in? Your brass is getting work hardened, and needs annealing. The only other option is a bushing die, and keep reducing bushing size to control neck spring back. My last batch of Lapua 6.5x47 brass gave up the ghost after one firing, unfortunately I failed to notice it before I processed and primed them.
Another big factor in seat depth is press stroke, all the same, all the time, fast erratic strokes will mess seat depth up quicker than anything.

Hi Milo, My press operation from round-to-round is consistent. I am thinking that my annealing process is suspect. I am annealing by hand with tempilac (750 degrees) but maybe my temps are not consistent enough to be annealing properly.

In my op, i was also thinking it was neck tension related but what I am still puzzled with is, if it is neck tension, how that could be affecting seating depth? Yes, it may require slightly more pressure to seat some but shouldn't each still be seated to the same depth? Maybe, the hardness differences are somehow causing the bullet to spring up or down just after seating? I have noticed slightly different MVs with the last load which would also point to work hardened necks.

 

[MikeInUtah]

Have you measured the bullets themselves? Its possible they may be the difference your seeing.

Bullet length from ogive to base of the bullet wouldn't make a difference as the seating depth is from ogive to base of the case. Bullet diameters are consistent.

 

[AIdog]

those dies are fine, ur press is fine but inconsistent neck tension is a big contributing factor... varying neck thickness will mess up ur tension turn necks to solve that. also try a little dry lube inside neck prior to loading this can assist bullets when seating. if its too much trouble for u to get ur seating depth perfect (not worth your time) those bullets u mentioned are not very sensitive to seating depth and should all shoot fine. if ur chasing a low es and sd consistent neck tension will be more significant and you will need to address that so maybe it is worth your time

 

[SWRichmond]

Bullet length from ogive to base of the bullet wouldn't make a difference as the seating depth is from ogive to base of the case. Bullet diameters are consistent.

FWIW: I also used to notice some significant difference in the length of my loaded rounds. I am now sorting bullets by base-to-ogive in order to increase the consistency of the ogive-to-lands dimension of the loaded round when it is in the chamber. After sorting the bullets I stick the bullet tips into a meplat trimmer to uniform the meplats, and I noticed that some bullets have a lot more material removed by the meplat uniforming tool. In other words, some of the bullets are longer tipped, literally "pointier". If you are measuring the length of your loaded rounds from the base of the cartridge to the tip of the bullet, you are including this variation in tip length of the bullets. I have noticed oddballs being longer than most by 0.015" or more, in very high quality target bullets. This is your difference. These bullets, also being pointier, will fly differently at distance, hence the meplat uniforming.

The bullets, as illustrated above, are being seated by pushing on the leading edge of the ogive; the tip doesn't matter to this process. Once I started uniforming the tip (meplat), and within a batch where I have sorted by base-to-ogive, my loaded rounds are all now within 0.001" of each other.

 

[dmike]

I have a forster mic seating die and I tend to have about .008 spread, but my cheap Lee seater only has about .003. Wondering if there is something out of whack with the forster?

 

[SWRichmond]

I have a forster mic seating die and I tend to have about .008 spread, but my cheap Lee seater only has about .003. Wondering if there is something out of whack with the forster?

Maybe I misread the OP. Are you measuring loaded round length to ogive, or bullet base-to-ogive? My own experience is that once I have sorted bullets by base-to-ogive, and uniformed the meplats and repointed, I get no variation in overall length of loaded rounds. None. And since I know the ogives are also uniform, I know that ogive-to-lands is uniform for rounds in the chamber.

Unless I am missing something...?

 

[dmike]

Maybe I misread the OP. Are you measuring loaded round length to ogive, or bullet base-to-ogive? My own experience is that once I have sorted bullets by base-to-ogive, and uniformed the meplats and repointed, I get no variation in overall length of loaded rounds. None. And since I know the ogives are also uniform, I know that ogive-to-lands is uniform for rounds in the chamber.

Unless I am missing something...?

SWRichmond, I'm measuring loaded round/case base to ogive with an RCBS mic. My point was just that the forster seems to be less consistent than the lee for some reason. The Forster is producing the same kind of variances the OP is seeing with his Whidden and RCBS seating dies.

 

[pawprint2]

Most of the time seating depth problems are caused by a ill fitting seater plug.

Even the photo above is not very correct, many of my seaters hold the bullet at the mouth of the seater plug. I slightly bevel the mouth because it can be sharp and grip the bullet tight enough sometimes to pull the bullet upward.
Having said that most of the time the problem is the bullet tip hitting the top of the seater cone and being compressed. The solution is custom made seater plugs that contact the entire tip of the bullet.

This is very good advice-a local machine shop can easily "fix" your seating die (and the rest of your seating dies while they're at it), you'll be glad you did. It not only solves your current problem, but almost always results in less run out.