Does powder charge change with seating depth?

[DngBat7]

As my throat is eroding, And the bullet needs to be seated farther out, does powder charge need to change seeing there are most likely pressure changes happening due to slightly increased case volume?

 

[BradY]

Do the testing. Chronograph and target will tell you.

 

[tom]

Not very much in the scheme of just chasing your lands. The noise of changing enviromentals, and or chronograph limitations will outweigh it. Now a big change however will usually be a completely different powder load.

Tom

 

[Mickey D]

Not very much in the scheme of just chasing your lands. The noise of changing enviromentals, and or chronograph limitations will outweigh it. Now a big change however will usually be a completely different powder load.

Tom

An old timer once told me any time you change anything when reloading a round, you change everything. What you are asking will probably not be much. But I would run a couple through a crony just to see what if any change took place.

 

[std7mag]

And it obviously depend on how much the change is vs the case capacity.

0.010" in a 300 Win Mag isn't going to matter as much vs a 204 Ruger.

 

[K22]

It can depending the case capacity and the amount of change.

I've found that in some rifles that they shoot more precisely with a longer jump which is counter intuitive but I've experienced it never the less. The "longer" jump to the lands means that the bullet is seated deeper in the case which often changes pressure. Also a deeper seated bullet tends to have less run out.

My Rem 700 Varmint has a lot of free bore yet this is one of the most accurate rifle I have shooting in the sub 1/2 moa range with tailored reloads w/ the bullet well off the lands.

One of my Tikka 223's is like this also. It's shoots tighter at COL of 2.275 rather than at a longer length at 2.300, the latter which is about .020" from the lands. Yet my Douglas match barrels like a short jump.

In your case does your target tell you that you have to seat the bullet out further or are you just assuming it does because of the throat erosion?

 

[ronemus]

I find that in .223 with heavy (75 gr) bullets I need to go up ~1 gr (RL-15 & N-550) after a few hundred rounds to maintain velocity (~2930 fps in a 28" barrel), and another 0.5 gr as throat erosion goes to ~0.1"; I keep the jump constant (0.020" for the Hornady 75 gr BTHP & 0.030" for the 75 gr A-max). I use DPMS VLD magazines, so I start with the shank just above the neck/shoulder junction and when the erosion gets to ~0.1" I don't have much shank in the case; if the throat erodes further the accuracy goes south in a big way. This pattern has held true for several barrels (Krieger, Bartlein; 4-groove and 5R).

I've just worn out my first .284 barrel (4-groove Hart) and the same pattern applies.

 

[46and2]

I find that in .223 with heavy (75 gr) bullets I need to go up ~1 gr (RL-15 & N-550) after a few hundred rounds to maintain velocity (~2930 fps in a 28" barrel), and another 0.5 gr as throat erosion goes to ~0.1"; I keep the jump constant (0.020" for the Hornady 75 gr BTHP & 0.030" for the 75 gr A-max). I use DPMS VLD magazines, so I start with the shank just above the neck/shoulder junction and when the erosion gets to ~0.1" I don't have much shank in the case; if the throat erodes further the accuracy goes south in a big way. This pattern has held true for several barrels (Krieger, Bartlein; 4-groove and 5R).

I've just worn out my first .284 barrel (4-groove Hart) and the same pattern applies.

Where can I get DPMS VLD magazines??

 

[ronemus]

Where can I get DPMS VLD magazines??

No longer in production - you'd have to find them used.

 

[46and2]

No longer in production - you'd have to find them used.

What a shame!

 

[David Christian]

As my throat is eroding, And the bullet needs to be seated farther out, does powder charge need to change seeing there are most likely pressure changes happening due to slightly increased case volume?

Tested this many times. No, throat erosion and chasing the lands has a negligible affect on velocity.

 

[cem]

Notice that as a general rule the slightly increased case volume has a negligible effect. The dominant pressure change with a seating depth change is the other way, seating deeper and so reducing powder capacity will reduce pressure because giving the bullet a running start at the throat will reduce pressure. Jamming the lands for maximum powder capacity also tends to raise pressures enough to notice.

It has been suggested that wider than usual variation in pressure with the 7mm Remington Magnum is due to more throat changes faster than most cartridges.

Then again Neal Knox did some testing with a rail gun in .220 Swift a long long time ago and suggested first that the Swift would shoot but not very long and second that the rail gun was still shooting pretty well when the throat was long gone and the barrel sectioned for direct observation and pictures for the magazine.

Sadly it doesn't seem possible to generalize (see e.g. Brownell's Pressure Factors and some military studies) throat wear and pressure as the throat may get bigger but also rougher. I do think that in extreme cases a little abrasive smoothing of a rough throat helps consistency.

My own answer to the initial question is that I do believe the change in seating depth has little effect on powder charge but combined with all the possible effects, such as having the the powder storage exposed to atmospheric changes and so to humidity changes and so to temperature change effects over time, there may be a reason to change powder charge but probably not - or not much. Then again I know folks who load at the range for short range bench rest and who often go up or down by clicks according to rules of their own or perhaps by gut feel.

For long range bench rest I have no idea. I suspect there would be more benefit from slight or even large changes but given the vagaries of testing at extreme range I wouldn't know how to make adjustments.