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Seating depth
Posted: Mon Feb 20, 2012 5:47 pm
by simong
Evening chaps,
This may be a bit of a bone question but.....am I correct in thinking that there is a direct relationship between seating depth and pressure ? (i.e.: seat deeper = increased pressure). If so then any guesses as to a rough percentage increase for 0.02" would be using a 308 case ?
I understand that any advice, comments, mickey taking finger waggles ect... are acted on at my own discretion. fingers crossed
Thanxs in advance
Simong
Re: Seating depth
Posted: Mon Feb 20, 2012 6:03 pm
by ovenpaa
Do you know how far you are jumping the bullet at the moment? If you are still .015" -.0012" off the lands then I would not be unduly concerned however if you are .002" of the lands and running a very hot load....
Some more information would be handy, bullet weight, powder type and load, primer etc.
Re: Seating depth
Posted: Mon Feb 20, 2012 6:13 pm
by simong
Hi Ovenpaa,
Rifle is a howa 1500, case ruag, powder N140, fast shiny things are sierra 155 palma match and primers cc1 200.
I don't think i am anywhere near ( relatively) the lands, but not sure.
All I'm after is something fairly accurate out to a max of 600 ( the rifle is a bit of an self indulgent plinkster, although a bit special
)
Any pointers gratefull recived sign85
simong
Re: Seating depth
Posted: Mon Feb 20, 2012 6:15 pm
by ovenpaa
How much powder and what is your OAL?
Re: Seating depth
Posted: Tue Feb 21, 2012 7:11 am
by simong
Hi Ovenpaa,
Sorry about the delay in coming back but the connection here I am is a bit iffy :cool2:
At present I am using 42 gr n140 and the oal is 2.795
The sierra book list 43.1 and 2.775 as an "accuracy load" and I was thinking about working up to this...
simong
Re: Seating depth
Posted: Tue Feb 21, 2012 8:53 am
by ovenpaa
I would say you were perfectly safe to advance .002" with that load and OAL however why just the .002"? Your next step has to be to check your maximum OAL for your chamber, once you have that figure you know exactly how much you can safely increase the OAL by.
An OAL gauge is handy at this stage however you can improvise. A case with a couple of lengthways slits hacksawed in the neck to allow the bullet to be gripped but slide under pressure is one way. Chamber the test bullet carefully and open the bolt with a hand in the way to catch the bullet as it comes out. Measure and repeat five times, this should give you an average OAL.
My first ever OAL gauge was improvised by drilling a hole in the back of the case, soldering some copper tube in and then using a piece of wire coat hanger with a kink in it to act as a pusher and friction stop, it worked well and gave me the results I needed.
Or you can buy a dedicated OAL gauge.
)