How do you determine seating depth? Do you go by manufacturer recommendations? Can you deviate from these as long as you are under the OAL for the cartridge? Context for the question: I am reloading 7 prc and noticed that hornady recommends 163 eld-x COL of 3.070” and 175 eld-x COL of 3.265”. Seems like quite the difference.
Good question. The reason the case overall lengths are so different is because the bullet is longer from ogive (where the bullet hits the rifling) to the tip.
For this reason, a base to ogive measurement is better than OAL in this case.
You can determine seating depth by first measuring your rifle’s action with a gauge. There’s a video in the course on Backfire to show how.
Generally, I’d try 25, 50, and 75 thou increments off the lands and see which shoots best.
The place you can get into trouble is off you jam the bullet into the lands (touching), which can spike pressures in an unsafe way.
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Went back and watched the video. Very helpful. So if I make the OAL measurement using the hornady’s gauge and then back it off by >25 thou should be fine as far as avoiding spiking the pressure it sounds like. I’ve heard of having to try different OALs to find a “node”. Do you find that to be necessary or helpful? Load development seems tricky bc there are so many variables including having a barrel that ages with every shot.
I don’t think a traditional ladder test of seating depth works. A bigger increment is needed to see any real difference, which is why I generally do the 25, 50, and 75.
Side note, you mentioned OAL’s but we’d be talking about base to ogive in this case because that’s where the bullet will hit rifling.
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Oh yes, thanks for the clarification.
Hey there, where did you find this video? I don’t see it anywhere in the library but maybe I’m looking in the wrong spot.
Thanks in advance!
Jim I hope that this link is OK. It is from a friend of yours that I also follow and it is the easiest way that I have found. It’s from Gavin at Ultimate Reloader https://youtu.be/90DOVa2cFNs?si=QUi4YsMpEoM6-jhR and it really helps
Thanks! Did Jim make a video as well? I tried this method but am not getting consistent measurements. Curious if you’ve been able to have consistent results measuring chamber.
I have used Eric Cortina’s loctite method gotten results that are within a thousandth or so. I usually do it 5 times and take the average…
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Question for you. Are you having inconsistencies with the oal gauge itself? By that I mean do you insert the bullet in the modified case, insert the modified case into the chamber, advance the bullet to it jams, then take a measurement. And then start over from scratch and take another measurement and get different numbers?
Or, are you having inconsistencies with just taking a base to ojive measurement with the comparator tool? By that I mean if you were to take a round of loaded ammo for instance, take a BTO measurement, then take the exact same loaded round and measure a second time, notice a significant inconsistency?
Or some of both?
Thanks guys.
Im having inconsistencies with the OAL gauge itself. My depth isn’t very consistent so my measurements aren’t as consistent as I would like them. I’ve tried to do it 10 different times and then take an average measurement but I wasn’t sure if others are seeing better consistency with this method.
I know the instructions as well as most/all YouTube videos mention using the most minimal amount of pressure needed to “kiss” the lands.
I myself have found that to lead to inconsistencies. I get better results when applying significant pressures, make sure its not hanging up on something else. Not using a hammer or anything, but firm, it doesn’t move anymore pressure. I will occasionally get stuck bullets, but not often.
Thanks, I’ll give that a shot. From there, do you back off 30 thou to begin your load development? Sorry for all the questions…
Depends upon the bullet manufacturer’s recommendations. I typically use Barnes all coppers and they recommend starting off 0.050 and then seating deeper if needed.
I know I recorded a video for the reloading course about seating depth but I’m not seeing it in there. Couldn’t believe it when I checked! I’m creating that video over again tomorrow and will post it in the course.
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Yes sir…its very frustrating
Jim any luck creating this video? Thanks!