The importance of seating pressure

  • I wanted to create another thread so as not to clutter up the .223AI thread. The target immediately below is representative of how my .223AI is presently shooting: (as I said, I made a turret adjustment between the 5 shot group and the individual shots)


    Here is two groups shot immediately before the above target with the exact same load, nothing changed. All except the brass used for these groups below was kept out of the normal process and had varying amounts of imperial wax inside the neck. From none at all to greased up fairly well. This was brass used during setup of the sizing die as well as brass that was actually fired and then sent to whidden to have the sizing die made.

    Same exact load, same exact specs on all the components, but I could feel significant differences between them regarding how much pressure was applied during the bullet seating process. The results are apparent. The brass that was treated with my "normal" process produces extremely predictable results on the target and had very uniform seating pressure across all the rounds. The brass with non-uniform seating pressure produced 3/4moa or marginally better.

    This is a prime example of why shooters that can not shoot better than 1/2moa often have significantly different views on both equipment and processes as compared to shooters that do consistently shoot better than 1/2moa. Getting 1/2 to 3/4MOA is quite easy with TS Customs rifles and quality components offered today. However you must be on top of all the variables to consistently get better than that. Seating pressure is probably one of the most important aspects of this process and likely one of the most overlooked by novice reloaders.

  • Did more or less seating pressure group better or does it not matter as long as it is uniform?

  • Within reason, it doesn't seem to matter as long as it's uniform. However if you are on either extreme, it can definitely cause issues.

  • So for a guy like me who doesn't have custom dies, or even bushing dies, is there other ways to control the neck tension? I have Forster dies now which are way better than the RCBS I had before. I have also now learned that either wipping the necks with Q tips or running the brass through the rice again helps.

  • @norcal_in_az Mainly it is about the process. Good equipment helps, but understanding the process is important, otherwise the good equipment will go to waste.

    For instance, unless you neck turn, the brass will always have some non-uniformity in case thickness up along the neck. Even after turning, it doesn't all come out. So consider the people that do not use expanders in their dies and instead only neck size or FL size without expander. Where does the non-uniformity get pushed to?

    Right... inside, where the bullet goes. If using an expander, it will keep the non-uniformity to the outside, where it doesn't matter nearly as much. So, a nice polished expander on the decapping stem, and having that decapping stem be loose to move around and align itself a bit is important.

    Making sure to use smooth dies will help. I polish my dies with flitz. Both the inside of the die and the expander ball/mandrel. This when combined with the use of imperial wax makes the sizing process effortless. Despite that, the uniform application of wax is paramount to ensuring each piece is sized just as the previous was. A dry case followed by 5 greasy cases and you'd absolutely see a difference in the dry case. The same amount of lube in the same areas is a good practice to get into.

    Deliberate and methodical operation of the press is also critical. You can't expect the same results on a case that is ran into the sizer hard to have the same treatment as a case that is run up super slow and gingerly.

    The lubricity uniformity of the inside of the neck is important. This is why I love the rice method so much. The carbon/fouling deposit inside the case mouth is pretty uniform after firing. The rice smooths out what parts are not uniform, but largely leaves the residue in place. This residue absorbs some uniformity problems between components and also allows a more consistent bullet release than bare metal. With stainless tumbling I had to sort my loaded rounds into much larger and more diverse batches due to the significant difference in pressure during seating. So, anything you can do to keep the surface of the case necks in good shape is a plus.

    Neck turning is another thing that can really help with seating pressure consistency. Those material deformities I was referring to earlier can be largely fixed by proper turning. Uniform thickness will result in a much more uniform behavior from case to case.

    Annealing is another step that helps a ton. Brass of the exact same makup and thickness will still behave differently if it is of a different elasticity from the other pieces. So annealing will significantly help keep them behaving the same.

    Clean bullets is another thing to consider. If not clean, at least uniform in their lubricity. I've worked with bullets that showed up kind of oily before, and it was a disaster. They had to be washed free of it before they would shoot at all. Keeping your hands free of lubrication and contaminants during the seating process is important, for if you deposit some junk on the bullet while you're situating it over the mouth... it will result in non-uniform lubricity from bullet to bullet.

    Keep a good chamfer on the inside of the case mouth. A hard edge there will cause the case to scrape bullet material and bind it up between the bullet and the case neck during seating. Make sure there's a smooth transition.

    I have more thoughts... but if you have any specific questions just ask.

  • @orkan thanks for the detailed reply. That does help a ton.

  • What is your case lube routine?
    I have Imperial wax and just barely touch it every case with my fingertip and work a film all around it.
    Should any go inside the neck?
    I did buy some Flitz just to polish dies and other metal around here.

  • @hypo said:

    I have Imperial wax and just barely touch it every case with my fingertip and work a film all around it.
    Should any go inside the neck?

    I do the same thing, just spin it between my fingers for the outside. I then use a q-tip and put a very very light swab around the ID of the case neck. This helps the expander move smoothly.

  • Thanks. I may be adding a dry tumbler in the future to get the wax off and for reloading after the initial case prep and firing.

    I do like the wet tumbler for giving nasty range pickups the first cleaning.
    Will probably consign all my range pick ups to be blaster ammo for the AR.

    After going through my Lapua 30-06 compared to the Lake City 223, it is a whole lot less work getting it ready to shoot again.

  • @hypo said:

    I do like the wet tumbler for giving nasty range pickups the first cleaning.

    Yup... it's great for cleaning stubborn things. It still has a use, it's just not in my precision rifle process anymore.

  • @orkan said:

    This helps the expander move smoothly.

    Are you using the expander ball on the sizing die, or is this done in a separate operation as with the 21st century mandrel die?

  • @ragnarnar I have expanders in all my FL sizing dies. I have separate expanders that I use for neck turning and various other jobs, but as a matter of course I use a expander on the decapping rod in every FL die I use.


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