cartridge overall le ngth

[sandyn]

I notice in some posts and write-ups people state that they
load the bullet say ".0l5" into the lands...how do you know its
that much jammed into the lands? I would think you would
press the bullet back down the neck rather than up the barrel.
I'm confused as to what they mean..I always thought the starting
point would be touching the lands. I read where people then back off from the lands in .005 increments then check groupings. I'd appreciate some clarity on this

 

[billmo]

sandyn, "Into the lands" is kind of term use more or less. What is being done here is the COL measurement to touch the lands is found from the ogive back to the case head with a variety of tools and then the bullet is seated "Into the lands" whatever amount you would chose whether it be .005, .010, or .015, etc. by leaving the COL that amount longer than your first "found" measurement mentioned above. Basically, you are just letting the bolt finish seating your bullet by your chosen amount. Due to some inconsistancy in the different tools verses the actual chamber,rifling-lands starting point diameter) these tools don't always tell the complete truth. But, at least you have a method of obtaining a starting point. A fairly common practice used when checking for bullet seating depth accuracy is to start with a powder charge under MAX. and seat maybe five bullets, .015, .010, and .005 into the lands and then the same increments out or away from the lands and shoot the six 5 shot groups to see what distance the rifle will like best. CAUTION - YOU WOULD NOT WANT TO START WITH A MAX POWDER CHARGE AND JAM TO LANDS ESPECIALLY WITH TIGHT NECK TENSION. And that is another subject entirely. I hope this helps. Bill

 

[billmo]

gunamonth, Do you start with a mild load when you seat .020 into the lands? Thanks, Bill

 

[MSwickard]

I notice in some posts and write-ups people state that they
load the bullet say ".0l5" into the lands...how do you know its
that much jammed into the lands? I would think you would
press the bullet back down the neck rather than up the barrel.
I'm confused as to what they mean..I always thought the starting
point would be touching the lands. I read where people then back off from the lands in .005 increments then check groupings. I'd appreciate some clarity on this

The easiest way to understand bullet seating is to first look at the bullet JAM. JAM is the point in which the bullet just makes contact with the lands. At this point, you can set your seating die up and call the JAM, zero. From there you can adjust the seating depth to either seat a bullet long or short the desired length, be it 0.010" 0.020" 0.060" etc.

As for seating into the lands, this is really difficult to determine. One can seat a bullet +0.015 of the JAM, but that is not to say the bullet is actually 0.015" into the lands. A bullet can only be pushed so much. At some point the neck tension will give and the bullet will be pushed back into the case. So essentially you are reallty only hard JAMing the bullet into the lands.

Is there an advnatage to seating into the lands. Yes and no? My Bench Rest shooting experience has told me that it is better to jump. Granted I have shot great groups seated into the lands, but I would always at some point get an unexplained bullet out of the group. Once I started jumping the fliers went away. I believe that the pressure curve sometimes spikes with JAMMed bullets and that increase in P causes a flier.

Another plus to seat off the lands is the fact the bolt is easier to close and if you have to remove the bolt with a round in the chamber the bullet will not stick in the lands and you won't have a chamber full of powder.

Anyway, that's my 2 cents.

Mike

 

[sandyn]

thanks to everyone for the info...it will come in handy
Sandy

 

[jb1000br]

Personally I think it makes more sense to define JAM as:

"The longest you can seat a bullet without the chamber seating the bullet deeper upon chambering the round."

A lot of times you can get 0.035" or more INTO the lands before chambering the round shoves the bullet back.

Recently I have preferred to start with this MAX OAL "JAM" as it is the only length you really know for sure.

IMO, you really can't tell within a couple thou if you are actually JUST contacting the lands.

My "JAM" length is a more concrete point to base measurements from IMO.

YMMV,
JB