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Varied seating depth. What results should I see? and other questions.

The subject of seating depth comes up and usually my eyes roll back. I realize alot depends on the way the ammo is fed intothe rifle (magazine fed or single loading) so I have some general questions about varing the seating depth if the rifle will allow it (single loaded).

I usually seat bullets off the lands and not really paid attention to the POI results as I dont know if its me, the gun, the load or... the seating depth ( I shoot CMP and NRA HP matches so dime size accuracy at 100 yards is nice but really not needed).

I had a rifle out recently and on a lark varied the seating depth from just touching, .010" off and .020" off the lands. At 250 yds the 10 round grouping of the .20" off appeared to be more "rounder".

It got me thinking that perhaps there is something to this seating depth issue that I should address but.... I really dont know where to go with it.

Question 1). What POI should I see if I seat off the lands? I know shooters will say "better accuracy" but what exactly should I see? "Rounder" groups as I seemed to have observed? Smaller groups? No unexplained fliers? How do I differentiate POI changes due to seating depth changes and that of amount of powder used that might be "reducing group sizes? Or different primers? Or anything else? ( I have a chronograph )

Question 2) Is there a "norm" for varing seating depth when one is changing the depth to get what ever results we're suppose to be getting? Should one vary groups of say... 10 testing rounds..... .010", .020", .030" or more? I find it hard to believe that with all the varibles involved a shooter can see POI results with only .010' or .020" difference between testing groups. I would think I'ld see a change in POI results if I made sizable seating depth changes ie: to the lands, then .020" off then .040" off then .060"....... but make mychanges in multiples of say..... .020"

Question 3) I one finds that seating depth "X" is giving whatever desired results one gets with varing seating depth should you go back and vary powder charges... or any thing else?


Thanks for "educating" me on this topic.
 
All of your questions revolve around "What type ogive bullet are you shooting?". Seating depth has different effects on different ogives.
 
In my experience, it depends on the rifle. I have some that are sensitive (accuracy wise) to seating depths while others (within reason) are relatively insensitive to it. The only way to know is to check.

Because I load primarily for hunting applications and functionality is just as important as accuracy, I start at .020" off the lands and work back. But I don't spend an inordinate amount of time experimenting unless I can't achieve my accuracy goals which are in the 1/2 moa range for my varmint / predator rifles and 1 moa for my big game rifles.

Also, some bullets with different ogives are affected more or less by seating depth. One in particular at least for me, is the 6mm Sierra 85 grain boat tail hollow point. Varying the seating depth can affect pressure so you need to be aware of that if you are loading at the high end of the range.
 
I am by no means an expert here and hopefully more experienced ones will chime in but:

Seating depth is one variable in an equation of many.

Bullet type.

Bullet weight.

Bullet manufacture.

Powder charge.

Powder type.

Powder manufacture.

Primer.

Neck Tension.

Case variables.

To list but a few. Seating depth could rank in there at the top, the bottom, or somewhere in between, you'll never know until you experiment. Like any equation when you change a variable you change the outcome, how much so is up to debate but you change it none the less.
 
mattri: Let me add another factor to your list. Leade angle. Some bullets "like" the standard 1 degree 30 minute angle, and some do not.
 
mattri said:
I am by no means an expert here and hopefully more experienced ones will chime in but:

Seating depth is one variable in an equation of many.

Bullet type.

Bullet weight.

Bullet manufacture.

Powder charge.

Powder type.

Powder manufacture.

Primer.

Neck Tension.

Case variables.

To list but a few. Seating depth could rank in there at the top, the bottom, or somewhere in between, you'll never know until you experiment. Like any equation when you change a variable you change the outcome, how much so is up to debate but you change it none the less.

Although I agree with all the above listed variables, one other variable folks seem to overlook is the rifle itself. I've tested suggested seating depth in my rifles and found that what seemed to work very well in one rifle, doesn't necessarily mean it'll work well in another, even if the same model. make and caliber. IMHO, testing is the ONLY way you'll know for sure even if you follow all the variables listed above closely. Just my thoughts and experiences.
 
Read this thread.

http://forum.accurateshooter.com/index.php?topic=3814361.0

It has helped me get great shooting groups out of 3 of my rifles. Starting with finiding a powder charge and then tuning the load with seating depth.

What i have seen in my testing is that seating depth changes effect group sized just like powder charges and is worth testing and tuning.
 
What rifle are you shooting, as well as bullets and powder? I realize that your question was general, but knowing these things might let someone give you more specific information if they are working with the same components and rifle. Generally, I find that seating depth has a large influence on accuracy, but to a great degree this depends on the inherent accuracy of the rifle, and you may have factors that limit what you can do, like magazine length and throat design.
 

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