Starting seating depth

J

jaybic

Guest
Hello all,

I am looking for seating depth advice for my new rifle. It is a .308 as per my other thread with a new Krieger tube on it and I am working on getting a depth and keep coming up with 2 different measurements.

Method #1.
The bullets are 168 SMKs and my first measurement using a
Stoney Point Chamber-All tool and bullet comparitor gives me a measurement to touching the rifling of 2.293 +/- .001(tried 3 times to get an average). Is it cosidered "jam" when you touch the rifling?

Method#2
I took a brand new resized Hornady case and seated a bullet in it and then pulled the bullet back out and reseated it to lighten up neck tension and then chambered it in the rifle and let the rifle seat it by closing the bolt(just a bit stiffer than it closes when on an empty chamber). I took it out and measured it on the same bullet comparitor and the length to ogive is 2.308. Is this considered "Jam"?

I dont know which is which I guess. I think Method #2 is Jam but that still has my bullet 15 thou into the rifling doesnt it?

If #2 is really jam and I am that far into the rifling, is it even safe or maybe I have just done this all wrong?

Help!!!!!!!

Jamie
 
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Some guns like a little jump. Try seating at 2.815"oal to begin with.

size the case with a neck sizer or fl so that just enough tension to seat by hand and hold the bullet place in chamber close the bolt. Use cleaning rod to remove and caliper or micrometer the Overall length.
 
Seems like method one may be what I would call a JTL dimension (just touching lands) you can get a good idea as to the relationship of where your bullet just touches the lands by coloring your bullet with a sharpie marker or polish your bullet with 0000 steel wool. Chamber the round, preferably a case sized and with out a primer or if the case is primed make sure your firing pin is removed from the bolt body. Chamber round close bolt, open bolt remove cartridge if a wide land print appears around the circumfrence of your bullet your probably in the lands too far. Repeat the process a couple times to make sure you aquire consistant reads on your bullet and then adjust your seating die accordingly. You will find your JTL dim, I use magnification this helps if your over 40. I don't think there is any one seating beyond .010 into the lands unless their fireforming.
 
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I use the same method as speedpro does in the previous post. The only thing I will add is that after you remove the case with the bullet, adjust your die to set this length as zero, and re-seat the bullet .005 deeper and rechamber. I repeat this until the contact marks are gone.

I did this on my 30BR and had to move the seating stem in .030 before the marks were gone.

I find that using .001-.002 neck tension, seated .010 into the lands is a good place to start. Actually, that is where I finish, as I tune the powder and charge as well as the primer to get it to shoot.
 
On seating depth

I split the neck of a sized case with a junior hacksaw and make up a dummy round. Next light a candle and rotate the projectile in the flame untill it is nice and black. Next I close the bolt on the dummy round and extract. The slightly greasy candle soot gives a very clear indication of where the lands are. Some rifles and loads shoot close to the lands but if you strictly follow that policy you waste half of your load development. A lot of rifles and loads shoot best anything up to 1/4" off and give poor accuracy close to the lands.:D
 
jaybic said:
Hello all,

I am looking for seating depth advice for my new rifle. It is a .308 as per my other thread with a new Krieger tube on it and I am working on getting a depth and keep coming up with 2 different measurements.

Method#2
I took a brand new resized Hornady case and seated a bullet in it and then pulled the bullet back out and reseated it to lighten up neck tension and then chambered it in the rifle and let the rifle seat it by closing the bolt(just a bit stiffer than it closes when on an empty chamber). I took it out and measured it on the same bullet comparitor and the length to ogive is 2.308. Is this considered "Jam"?

If #2 is really jam and I am that far into the rifling, is it even safe or maybe I have just done this all wrong?

Help!!!!!!!

Jamie
Click to expand...

I've used your method 2 for years in every rifle I reload for whether competition or hunting and it's always worked best for me. It's simple and yes; that's "jam". This method takes one of the variables out of reloading and it always at least in my case...has been where I leave the bullet seated (from 15-20 thousands into the rifling).
 
Thanks fellas,

This helps alot.

I just finished loading up some 168smk and Varget. 5 rounds @42grains, 5 @ 43gr and 5 at 44gr to start with while I am doing barrel break in.

The distance to the rifling measured by my Stoney Point OAL tool and the comparator say that the distance is 2.293 which is the length that I loaded all 15 rounds so they should be in contact (just touching) the rifling. I guess I will start there and just see what happens. If I dont see what I like, I will try loading at Jam and working away from it I guess.

I dont know, maybe I should just be breaking in the barrel and not worry about accuracy right yet?

Jamie
 
One additional suggestion.

When experimenting with bullets just touching the lands -- certainly not jammed in! -- I kind of watch my charges.

If a range of charges is provided in my loading manual from 32 to 36 grains of powder, and I am experimenting with just touching the lands -- maybe I will set the charge at 33. For shooting holes in paper, a person does not need the very hottest loads, and so?

I experiment by closing the bolt on a round. Sometimes there will be very faint marks, which suggests I'm just barely touching the lands.

People say that some rifles like to be away from the lands. Maybe they are right. I do suspect -- can't prove -- that MOST rifles like to be barely touching or just a couple of thousands off.
 
To Montana Pete and others.

A lot of people equate accuracy with concentricity so they reason that a bullet seated close to the lands, will have the best chance of being concentric and therefore give decent accuracy. Sometimes it happens and we think great, look at that it works but it is just luck. What really happens is this. Rifle barrels vibrate mostly in the vertical plane,they yield most in the central part of their amplitude and if your bullet exits the muzzle here we get poor accuracy. The barrel steel gets progressively stiffer at the top and bottom of the amplitude untill it overcomes the barrel vibration force and heads the other way. If a bullet exits in the stiff slowdown stage we get good accuracy. When we do powder step or seating depth alterations we alter the moment that our bullet exits the muzzle. To follow what my bullets are doing in that nodal maze I do a graph of all my load developmemt, with seating depth 40 times actual size and group size twice actual size. Suddenly where your accuracy is trending becomes very clear and close to the lands is only the right place to be sometimes. Hope I haven't made the situation worse but you did want to know about seating depth. Reguards Murphy.:D
 
I'm confused here. I too am running a Krieger barrel on a .308 with a 95 Palma chamber and just measured the distance to the lands using the same gauges this weekend. My measurements were the following:

175 SMK
3.202 comparator

168 SMK
3.215 comparator

With that said, how are you measuring to get 2.293? I'm measuring with calipers with the Stoney Point chamber all attached to one side of the caliper and am measuring from base of shell to ogive. I guess what I'm saying is that my measurements account for the length of the chamber all gauge attached to the caliper. What am I doing wrong here?

jaybic said:
Hello all,

Method #1.
The bullets are 168 SMKs and my first measurement using a
Stoney Point Chamber-All tool and bullet comparitor gives me a measurement to touching the rifling of 2.293 +/- .001(tried 3 times to get an average).

Jamie
Click to expand...
 
stoney point

Robertb
I think jaybic is miss reading his stoney point. The comparator adds 1 inch to the reading of the micromreter, and if he is using a digital, and rezeroed, he might be taking this inch out by mistake, if standard caliper, he is still reading something wrong as he is 1.160 inches short of the standard 308 depth 0f 3.800. I know ya lose a little going to the ogive, but have never seen that much.

Jaybic recheck your figures and if not using a digital mike, get one and use it for your stoney point, rezero, then measure again, I really do believe you are an inch off.

Good luck
DR
 
DR4NRA,

Yeah, I am subtracting the 1 inch for the length of the comparator and my caliper is not a digital. That is where my measurement comes from. To compare apples to apples, just add that inch back in and it would be 3.293. It sounds like I am measuring just the same as robertb, from ogive to base of the case otherwise.

My setup routine is this. I clamp the comparator onto the fixed end of the caliper and close the jaws and then reset the dial to zero and all the measurements are based of that set up. I guess I thought that is how is was supposed to be set up anyway. It that right? IDK, maybe I got it all wrong!!!!!

My reloading manuals say that the book COL is 2.800 and is case head to bullet meplat. I am trying to get case head to ogive readings and these numbers are what I come up with assuming I am doing it correctly.

Is is normally accepted that when talking about these types of measurements that that 1 inch for the comparator is factored in? I just want to be sure I am speaking the same language as every one else and I apologize for the confusion.

Let me know what you guys think and see if this makes more sense.

Thanks

Jamie
 
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No problem!!!! I just thought I was goofy for a second.

Thanks again,:)

Jamie
 
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