How much does seating depth effect pressure?

[Tenntrapper]

Just as this title asks??

I'm loading 243 win. I'm using Norma load data, brass, bullets, and powder. Only thing different, I'm seating bullet .070" longer than their specs (still .030 off the lands). Ive been working on my ladder loads. Usually work up to max (or signs of over pressure), then back off a bit. Nearly everything I've loaded, I'm usually showing...or starting to show, signs of pressure...at or before max. With this combo, I'm at max, and not even the slightest signs of pressure (a good thing). Just curious if seating .070 longer would have that effect?
Any advice?
Thanks

 

[DaveB]

Nope. Following DA's mantra
1. Get the FPS you want
2. Modify length to achieve accuracy.

For example, Our 243 Rem 700 ADL has a very long throat and modifying COL is easy to get inside MOA.
If I set the bullet at SAAMI specs no accuracy (1.6 inch groups is not accurate)

Matter of fact, just my own bias, I do not like long jumps and .030 is long. I try to get under .010

Long jumps is where you will get flyers (my bias). Most of the time the reason is inconsistent neck pressure so the bullet leaves the brass ever so slightly angled before becoming completely engaged in lands. ever notice how Mr. Big jams some rounds into the rifling? He doesn't do that because he can't figure out .007.

 

[infoman jr.]

This is an interesting case. On one hand, by extending your OAL, you are increasing the case capacity. An increase in initial volume would reduce pressure. However, SAAMI .243 chambers have such a long jump to reduce pressure, and you're working against that by getting closer to the lands. I guess case volume wins this round.

 

[Remi]

will bullet seating depth affect pressures?

This is a 257 Roberts and the 115g NBT COL seems to be around 2.775 and my lands hit about 2.97, so i'm trying about 2.91 COL my question is : will the same charge at 2.775 be a different pressure than the 2.91 cartridge? thanks

www.24hourcampfire.com

There is a good read on seating depth and pressure.

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precisionrifleblog.com

There is a link with more depth data. My own stuff settles down .050-.070" off the lands. My loads aren't as sensitive to small variations in seating depth in the .050-.070" range.