quick off the lands question?

[hondaracer408]

alright i got the sinclair chamber gauge
my chamber lenght is 2.047
Then i did the "cheaper way" of measuring the bullet off the lands. I seated a bullet in a case way above what the book says and ran it in in small incurments until my bolt closed easly the number i ended up with was 2.950 so then i should subtract .020 which would leave me with 2.930 so i get .020 off the lands correct?? which from what i read is a good starting point to work around once i determine my powder charge.
If any of the info. doesnt seem right or im doing it the wrong way please let me know I apprepicate any info u guys throw at me.
thanks
Justin Miller

 

[bheadboy]

you should be off the lands but not .020 as you can not feel the first -005-.010,

Bob

 

[hondaracer408]

so what should my coal overal lenght be?

 

[spclark]

Chamber length isn't an indicator of where your bullets should be seated. It's important to know when you're trimming your brass though! Nobody should be chambering cartridges that are too long for their chamber as the case necks will deform & cause unsafe pressures when those rounds are fired.

COAL will vary depending on the OAL variation in the batch of bullets you're working with; bullet meplats (the pointy ends) can be pretty ragged unless you trim each & every one in a separate operation.

Much more reliable to work from the point on the bullet's ogive where it encounters the lands as that dimension, relative to the bearing surface & base, tends not to vary as much in high-quality match bullets.

 

[fdshuster]

Justin: If your chamber measures 2.047", I personally would let them stretch and trim to 2.037" for clearance between the case mouth and the end of the chamber. Except for magazine length critical ammo, like in my AR-15's, I really don't care what the cartridge O.A.L. is: it varies too much anyway to have any meaning. The only dimension I care about, and record, is the length from the case head to the ogive point of land contact, and I arrive at that length with the Stoney Point/ Hornady Chamber O.A.L. gauge.

 

[necchi]

Well ya got the right idea,,
But I was told by trusted loader that when you do it the "cheaper way" it's best to subtract .010 before you do the math, (saftey first)

So your begining # of 2.95 is moved too 2.85,,then do your math.

I gave up trying it that way and bought the Hornady O.A.L. Gauge, it's peice of mind to know for sure.

stay safe man,,good luck, ;D

 

[whiskey08]

cant work off of oal, gotta measure at the ogive to have any hope of consistency, what kind of bullet are you shooting. With sierras i start at .002 of the lands and end up somewhere there. tried some scenars and couldnt figure them out.

big factor of where to start is what kind of bullet your shooting

 

[hondaracer408]

i am using 175 SMK

 

[hondaracer408]

soo what should i set my max O.A.L. at 2.800 or 2.900

 

[whiskey08]

if you think you re touching lands at 2.950, and if you have enough neck and bullet length then id start at 2.945. Problem with that is, if your shooting a remington or something similar, magazine length is around 2.850-2.860.

Cool thing about sierras is there pretty tolerant. so if all i cared about is accuracy id start at 2.945 and try a few loads subtracting .005 -008 at a time. If you need your magazine then 2.860

 

[necchi]

cant work off of oal,

It's kinda hard to tell a new loader that, then tell him to buy an OAL gauge.

And it's, IMHO, a bad idea to give someone a measurment for his bullet having never looked at his gun, nor seen how he reads a mic. Some guy's can sqeeze them things pretty hard.

 

[whiskey08]

I didnt give him anything, I used his gun, his measurements. Nor am I assuming he doesnt know how to read a mic as good as you, or cant assimalate this info.

 

[gilream]

hondaracer408...read your post with some interest and felt the need to respond here. Just this morning I was measuring 5 different bullets for my recently re-barreled 7mm Rem Mag. Your method sounds good in theory but (and there's always a but with this stuff right?) Neck Tension can play a big part in when, or how far that bullet will slide back into the case as you close the bolt. I would not trust my sense of feel with this method if it were me. Most dies with a sizer button will give around .003" (three thousandths) neck tension; with bushing dies you can choose your neck tension by the size of the bushing you use. I prefer this latter method because it allows me to precisely get the neck tension that i desire. I digress...

If you really want to find out PRECISELY at what seating depth your bullet hits the lands you'll need; the Stoney Point OAL guage, which is manufactured by Hornady now; a standard sizing die with the decapping rod/sizer button removed; a fired case with the neck cleaned inside and out and a piece of fine steel wool. Run the case fully into the sizer die with no sizer button involved, this will give you about 5 thousandths neck tension (at least that's what i got with my Redding standard sizing die), which is too much to use in a sporting load but good for this process. Next, get a reading with your OAL gauge and add .025 to .030 to this seating depth. This longer seating will jam the bullet into the lands pretty good and the strong neck tension will enable you to extract this dummy round and see the rifling marks that will be left on the bullet. Ease it out of the chamber very carefully. Hopefully, the bullet will not get stuck in the barrel. If it does get stuck, carefully and slowly (so not to bump the crown or throat) send your cleaning rod through the muzzle and gently pop the bullet out and start over using less length the next time.

Using fine steel wool you can polish the rifling marks out and bring the bullet back to a shiny smooth brilliance so that you can step the length of the dummy round down and do it again. Keep seating the bullet deeper incrementally until the rifling marks disappear altogether. These marks will usually disappear at a point that’s about 10 thousandths longer than the original OAL gauge measurement.

Many benchrest shooters like to use the depth where the rifling marks are SQUARE SHAPED as a reference to work off of. They might start their load development at this point, or -.010 or –.15 etc. Of course do not use a jammed bullet to hunt with. Most manuals recommend starting off of the lands at .010 to .20. Once you find a powder charge you can adjust the seating depth to further refine the accuracy of your load.

This will give you the assurance that you are close to the lands but not jammed into them as you start load development.

Hope this helps. Sorry for the length.

 

[357Mag]

off the lands question?

Honda _

Howdy !
I use a Sinclair " bullet comparator " ( looks like a big 1" Nut, w/ six holes in it of various calibres ). The are basically low-buck, simple to use; and robust.

THe comparator is used along with a vernier caliper, to either sort bullets or set/adjust loaded cartridge OAL; and distance off the lands.

Regards,
357Mag