Bullet seating depth

[Morrey]

I recently bought a box of Sierra Match King 155 gr Palma bullets just for a try in my Remington Long Range 30-06. My normal match style bullet in this gun is Sierra MK 168 grain and I get great accuracy at 200 yards, so I wanted to try this Palma 155.

When using my Hornady gauges to check the seating depth I noted the bullet's base is barely in the neck of the brass when the ogive touches the lands. I seated a dummy round 30 thousandths off the lands and the bullet doesn't seat in the neck very far at all. In fact, I can wiggle the bullet in the brass feel it move. Like I said, it is barely in the neck where the boat tail starts forming.

Interesting, it chambers just fine since the ogive is off the lands and the case and shoulder of the bullet is meeting headspace specs. Only thing is this bullet feels like a child's tooth that you can barely wiggle when they are nearing losing a baby tooth.

Since I am single loading this bullet from a bench, is this a concern? I suppose my Forster Ultra seating die is making the bullet seat concentric. I guess I could seat it a bit deeper to maybe 40 thousandths off the lands but my concern will be that accuracy is likely to suffer the further off the lands I go.

Anyone else had this question with the 155 grain Palma from Sierra??

 

[Robert101]

I would be concerned about the seating (or lack of seating depth) you described. I understand that you want the bullet to be a certain distance from the lands but you also need to have sufficient depth in the case mouth. As you stated "the bullet wiggles" is the point reference to my concern.

 

[witchhunter]

It is a common rule of thumb to leave a bullet diameter in the neck for sufficient neck tension. So .308" of the bullet should be inside the neck.

 

[TimSr]

It is a common rule of thumb to leave a bullet diameter in the neck for sufficient neck tension. So .308" of the bullet should be inside the neck.

Yes. This is far more critical for uniformity than distance from the lands.

 

[Wreck-n-Crew]

I recently bought a box of Sierra Match King 155 gr Palma bullets just for a try in my Remington Long Range 30-06. My normal match style bullet in this gun is Sierra MK 168 grain and I get great accuracy at 200 yards, so I wanted to try this Palma 155.

When using my Hornady gauges to check the seating depth I noted the bullet's base is barely in the neck of the brass when the ogive touches the lands. I seated a dummy round 30 thousandths off the lands and the bullet doesn't seat in the neck very far at all. In fact, I can wiggle the bullet in the brass feel it move. Like I said, it is barely in the neck where the boat tail starts forming.

Interesting, it chambers just fine since the ogive is off the lands and the case and shoulder of the bullet is meeting headspace specs. Only thing is this bullet feels like a child's tooth that you can barely wiggle when they are nearing losing a baby tooth.

Since I am single loading this bullet from a bench, is this a concern? I suppose my Forster Ultra seating die is making the bullet seat concentric. I guess I could seat it a bit deeper to maybe 40 thousandths off the lands but my concern will be that accuracy is likely to suffer the further off the lands I go.

Anyone else had this question with the 155 grain Palma from Sierra??

If your seating as shallow as you suggest, another .010 is not going to make enough difference.

Mark a bullet you have seated and pull it. You can get a better visual and it will be measurable enough to get an idea of seating depth. Take some pics and post them. They help a lot.

 

[Morrey]

It is a common rule of thumb to leave a bullet diameter in the neck for sufficient neck tension. So .308" of the bullet should be inside the neck.

I checked the seating depth of the bullet's base to be .225. If my goal is .308 depth, and factoring in I was seating to be .030 off the lands to begin, this new seating depth would have me .1130 off the lands. You know it seems like a lot, but I have measured factory rounds that are further off the lands than this. Of course factory rounds tend to be less accurate than carefully crafted hand loads, so I'm not expecting to get much out of this bullet. Of course you never know until it groups, but I am not inclined to waste a lot of time and powder on this load.

With the bullet only .225 in the neck, I was worried about run out. Even with the Forster Ultra precision seating die, it can only do so much with a shallow seat as this. Honestly, I'll be surprised if this load makes it in my lineup of accurate rounds.

Thanks for the feedback.

 

[witchhunter]

Morrey, don't discount it yet. Each rifle is different, yours may like them. Like I said work up loads and when you get all you can with powder charge, then adjust you seating depth by .002 and keep looking for improvement. The seating depth decides when the barrel harmonics start and end, it is just a crap shoot sometimes.

 

[Morrey]

Morrey, don't discount it yet. Each rifle is different, yours may like them. Like I said work up loads and when you get all you can with powder charge, then adjust you seating depth by .002 and keep looking for improvement. The seating depth decides when the barrel harmonics start and end, it is just a crap shoot sometimes.

Agreed, Witchhunter. Like you said, surprises come in every box! And if this bullet's design characteristics simply don't pan out for good accuracy, I'm only out $36 for a box of bullets that was an experiment to begin anyway.

 

[Bart B.]

I have heard this "bullet diameter = seating depth" stuff every once in a while. But never seen nor known of it's mandate among competitive shooters producing best results.

Federal, Remington, Hornady and Winchester match ammo I've shot all had an OAL of about 2.800 inch. About .250" of their body was inside the case neck. I've shot 30 and 26 caliber bullets into 1/2 MOA with as little as .050 inch seating depths (bullet travel into the case neck from first contact). One of my Palma rifle loads with Sierra 155's in .308 cases have .150" seating depth in cases 2.000" long having a 2.800" OAL that I used to put 20 rounds in 3.25" at 800 yards testing some old WCC60 .308 Win match brass.

If this is far more critical for uniformity than distance from the lands, how come it's not mentioned by people seating bullets a bit long so they set back a few thousandths as the touch the lands winning matches and setting records? There's about .080" advance of the rifling from erosion as a .308 Win barrel wears out. People get excellent accuracy for the life of the barrel at that point in its wear.

I got .100" throat advancement in my .264 Win Mag barrel over 650 rounds. It still shot sub MOA through 1000 yards for 20-shot strings while bullet seating depth changed from .150" to .050" for seated bullets to contact the lands.

Can someone explain the physics why the seating depth decides when the barrel harmonics start? Harmonics are uneven multiples of the barrel's resonant frequency. They change after the bullet's left the bore.

Therefore, I consider this "standard" another myth among dozens for best accuracy. It is not a common rule of thumb to leave a bullet diameter in the neck for sufficient neck tension.