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Seating depth theory

mikecr said:
Fine tuning, or group shaping, is NOT full seating testing.
Whole different animal, and this is important.

For decades competitors claimed that VLDs had to be in the lands (ITL) to shoot well.
Turned out none of them ever did full seating testing. Not one of them..
They just made it up, and they were dead wrong.
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Any opinion that's published some people will believe it's 100% true and they will repeat it over and over. Sound familiar.
 
Alex Wheeler said:
Doesnt have anything to do with barrel length. I can think of many cartridges I chamber in many barrel lengths and those customers end up in the same place with seating and powder. The load really has to do mostly with the barrel maker and reamer. Keep those two the same and not much will change.
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Agree. I have multiple barrels of different lengths where seating is within a few thousandths of each other. Seating depth to me is number one.
 
Bottom Fodder said:
A lot talk and discussion on seating depth and a lot of theory about what all its doing to help with accuracy. We all agree “I think” that it does help

I would like to hear your thoughts on WHY Over the years I hear many theories from bullet alignment, adjusting case capacity, pressure and others. talking about this could enlighten us all

What’s your thoughts?
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In trying to understand internal ballistics as best I can, it's quite evident that seating depth effects pressure and velocity. But, I had a hard time finding out why and how. A couple years ago I discovered an in depth study from back in 1965 that pretty much nailed it for me. Though there's more to read (see attached PDF file), here's the graph of the data on page 47 that made it clear to me what's going on with seating depth:
Seating Depth vs Pressure graphic.jpg
 

Attachments

Alex Wheeler said:
I feel very fortunate to have been able to live in the pre internet era for a short time. Back then, in all the books and magazines this was very well known because people had to go out and do it for themselves. The precision shooting magazines and such. The idea is doesnt matter or that its not that important is very new and totally wrong. But to answer the question, its definitely a relationship to the lead. When I can chamber 100s or even 1000s of barrels in one cartridge and 90% of the guys end up within a couple thou of seating depth that tells the story. Its not capacity or distance to muzzle. I can use different freeboes and the distance to lead stays the same. The barrels are cut to length with a tape measure, not critical. Doesnt matter. Now why does that relationship matter? My guess is the way the pressure curve forms. The pressure curve is important. Its why some powders shoot and others dont. Things like seating depth, primer, and neck tension all effect that curve.
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While I do agree with the common seating depth, I've also seen where the same bullet in different cartridges shoots best at a similar distance off the lands. But this theory also raises the question, why it doesn't always change with throat wear? For those that don't chase the lands, this theory seems to suggest you should.
 
Fast14riot said:
While I do agree with the common seating depth, I've also seen where the same bullet in different cartridges shoots best at a similar distance off the lands. But this theory also raises the question, why it doesn't always change with throat wear? For those that don't chase the lands, this theory seems to suggest you should.
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Yes sometime they do shoot best off the lands, but in my experience its less common and usually in larger bores like 30s. I have had only 1 barrel that I didnt chase the lands on. It was one of my first br barrels and I have never had another. It was also early in my own knowledge so maybe it would have benefitted from some chasing. There are two games that you win by shooting small groups, long range BR and short range BR. Its very common in long range to have to chase, and in sr the ppc and 30br are so much easier on throats, its less common. So while there may be a lot of guys that dont chase, that doesnt mean they are at the best tune.
 
The more I shoot the less i know. But if change powder by 3-4 gr the target is going to change a hell of a lot more than 3/8 inch. At the distance I tune at anyways.
 
Last edited:
This is very interesting to me.
My accuracy needs are in the 1/2 MOA range.
Do we think that I could arbitrarily choose a powder charge [223] and tune with seating depth to get 1/2 MOA? Assuming match bullet, match barrel and rifle capable of shooting it?
 
jelenko said:
This is very interesting to me.
My accuracy needs are in the 1/2 MOA range.
Do we think that I could arbitrarily choose a powder charge [223] and tune with seating depth to get 1/2 MOA? Assuming match bullet, match barrel and rifle capable of shooting it?
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arbitrarily choose a powder charge '' you could maybe get a tuner to help but to say arbitrarily choose a powder charge I don't like that thinking
 
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