Bullet Seating Force

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   I discovered something today while seating bullets for my .308/7.62 NATO chambered No. 4 DCRA. 
For a few years now, I’ve been using Wilson In-Line Bullet Seating Dies for long range match loads.  They have given me very little bullet runout measured with my RCBS Case Master runout gage, particularly when using the long profile bullets with secant ogives, such as the 168 gr Tipped MatchKing. 
The in-line seating die works with an arbor press, the bullet is pushed into the die with the case fully supported rather than the case pushed over the bullet in a standard seating die. The standard bullet seating dies we’re giving me bullet runouts of more than 0.010, some as bad as 0.020 inches. 

But, what I noticed today was the significant difference in bullet seating force and consistency when the case necks are brushed. I typically have brushed the insides of the case necks before loading, but today I forgot this step.  Bullet seating forces seemed much higher than I remembered:

Without Brushing Neck ID   90 to 140 lbs, 50 lb variation
With Brushing Neck ID.        45 to 50 lbs, 5 lb variation

I use a nylon .30 Cal bore brush, just give it a few turns, that’s it. Much more consistent neck tension.

Will it make any difference in accuracy?  I don’t know yet…

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britrifles Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: February 03 2018 Location: Georgia, USA Status: Online Points: 8404	Post Options Post Reply Quote britrifles Report Post Thanks(0) Quote Reply Topic: Bullet Seating Force Posted: April 06 2025 at 11:24am
	I discovered something today while seating bullets for my .308/7.62 NATO chambered No. 4 DCRA. For a few years now, I’ve been using Wilson In-Line Bullet Seating Dies for long range match loads. They have given me very little bullet runout measured with my RCBS Case Master runout gage, particularly when using the long profile bullets with secant ogives, such as the 168 gr Tipped MatchKing. The in-line seating die works with an arbor press, the bullet is pushed into the die with the case fully supported rather than the case pushed over the bullet in a standard seating die. The standard bullet seating dies we’re giving me bullet runouts of more than 0.010, some as bad as 0.020 inches. But, what I noticed today was the significant difference in bullet seating force and consistency when the case necks are brushed. I typically have brushed the insides of the case necks before loading, but today I forgot this step. Bullet seating forces seemed much higher than I remembered: Without Brushing Neck ID 90 to 140 lbs, 50 lb variation With Brushing Neck ID. 45 to 50 lbs, 5 lb variation I use a nylon .30 Cal bore brush, just give it a few turns, that’s it. Much more consistent neck tension. Will it make any difference in accuracy? I don’t know yet…

Strangely Brown Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: April 05 2022 Location: Wiltshire Status: Online Points: 645	Post Options Post Reply Quote Strangely Brown Report Post Thanks(0) Quote Reply Posted: April 06 2025 at 12:09pm
	Brushed? Geoff by brushed, do you mean using a dry lubricant on the internal neck?
	Mick

britrifles Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: February 03 2018 Location: Georgia, USA Status: Online Points: 8404	Post Options Post Reply Quote britrifles Report Post Thanks(0) Quote Reply Posted: April 06 2025 at 12:28pm
	Mick, just a plain nylon bore brush, no lube. The cases were wet tumbled for about 1 1/2 hours, no steel pins. That doesn’t get them all that clean on the inside. I suspect the brush smooths out the carbon layer in the neck. It really lowers the seating force, and makes it much more consistent. I wish Wilson made a .303 inline seating die. Using this die, the bullet runout on the .308/7.62 loads with TMKs are typically less than 0.002 inches. it did seem to improve accuracy at long range (800-1000 yds).

Strangely Brown Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: April 05 2022 Location: Wiltshire Status: Online Points: 645	Post Options Post Reply Quote Strangely Brown Report Post Thanks(0) Quote Reply Posted: April 06 2025 at 12:31pm
	Understood!
	Mick

Shamu Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Logo Designer / Donating Member Joined: April 25 2007 Location: MD, USA. Status: Offline Points: 20510	Post Options Post Reply Quote Shamu Report Post Thanks(0) Quote Reply Posted: April 06 2025 at 1:18pm
	I actually chuck a bronze bore brush in m y electric screwdriver, start it turning then pass fully in & back out still turning. Then I use the little Midway "thingus" to dip the neck in the dry lube well & slide it over the brush of the correct diameter from the set in it. I also polish my expander balls. Seating is light & smooth for me. Runout is about 3 thou & seating depth is very consistent.
	Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)

britrifles Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: February 03 2018 Location: Georgia, USA Status: Online Points: 8404	Post Options Post Reply Quote britrifles Report Post Thanks(0) Quote Reply Posted: April 06 2025 at 1:57pm
	I’ll try that Shamu. I don’t can’t really tell what the seating forces are with a regular press. The arbor press with the force pack dial gage allows you to measure the seating force to within one pound. There is some thought that the bullets are actually “released” from the case necks which first expand under the rapidly increasing chamber pressure before they are pushed out by said pressure. There is no way to know for sure, but my best guess is that the pressure builds up so quickly that the case neck expands to release the bullet before the bullet begins to move (inertia resistance to forward motion is slow compared to how quickly the case expands from internal chamber pressures acting to expand the case neck). As far as I know, no one has seen exactly what goes on inside the chamber when the powder ignites!