how to measure length to lands consistently

[ericnord]

Hey everyone,

I spent an hour this morning trying different methods to measure the length to the lands on my Rem 700 in .308. I tried the method where you cut 1-3 notches in a case, set a bullet and close the bolt. After 15 attempts using different notches and neck tension I couldn't get anything consistent. It was varying 3.5x" to 3.8x". I then took a fired case and put a bullet in it and slammed the bolt a couple times. It was hard to close at first, but then it was smooth. That measurement w/ a 175 Sierra SMK was 3.97" from the bottom of case to tip of bullet.

Since I'm looking to come off the lands .02" I need a way to accurately measure the distance to the 100ths. Anyone found a good method or does 3.97" sound right, seems long to me since the longest I've loaded is 3.85".

thanks

 

[284driver]

measuring to the tip of the bullet is probably where your inconsistancy is coming from, as the tips are not very uniform at all. Get a bullet comparator to get more consistant results,it measures off the bullet ogive instead of tip.
Good Luck,

 

[rayjay]

One slit on a neck sized case has always worked for me.

Casting your chamber will NOT tell you the seating depth of different bullets.

 

[mikecr]

Seriously Rock, a cast won't help at all. It doesn't reflect or account for the actual bullets,their radiused noses).
For example, a reamer print shows you the throat to head distance. But you could not derive from this where a bullet would contact, or how far a bullet would be seated at this point of contact. The same holds for a cast of the chamber.

'Seating depth' is a common term defining 'distance to the lands' in reloading. A bullet is said to be seated .005"off or jammed for example. This only holds true for that barrel and bullet, and is in that sense dimensionless.

There are variables and some assumptions made. It also takes some practice to work out a reliable system of measurement here. I know that I've screwed it up before, even with specialized tools..

 

[rayjay]

Since I'm looking to come off the lands .02" I need a way to accurately measure the distance to the 100ths. thanks

Hey dipstick ROCKJAG4, ericnord is looking for the seating depth of his bullets. He wants to be .020" off the lands. He needs a proper slit case and a Stoney Point tool to measure the OAL to the ogive, not some dipstick trying [ and failing ] to look intelligent.

But hey, great post. Go pat yerself on the back. You really put me in my place

 

[ericnord]

Hey guys,

Thanks for the replies. I'll go ahead and get the Stoney Point tool since everyone seems to have good luck with it.

 

[rayjay]

eric,
Measure a handful of your bullets from base to tip. You will see that the bullets have quite a bit of variation in their length. This is probably the variation you are seeing. It doesn't hurt the accuracy but it does drive you crazy until you start measuring off the ogive.

Next you need to make or acquire a little bushing to measure the case from shoulder to base. Then you can adjust your sizing die to just bump back the shoulder a thou or 2.

 

[ericnord]

Your killing me rayjay! I finally got the whole neck sizing thing down so that my tension is 2 thousandths. Now I gotta go off and read about bumping shoulders...

Thanks

 

[Obtunded]

I have a Sinclair seating depth tool and What that tool did was confirm that the following method is *exactly* the same in terms of accuracy for finding your depth to lands.

Take a fired case and gently squeeze the sides of the neck to a barely perceptible out-of-round shape.

Stick a bullet on the end of the case and chamber the case/bullet combo.

Measure using a comparator.

Viola. Depth to lands.

---===++OR++==----

Measure your COAL to the tip of the bullet from the base of the case after the steps above...

Use the **same bullet**,after measuring seating depth) and seat it in a de-primed, neck sized case. Make the COAL the same as the COAL from your test above.

Put that dummy round in your press and tighten down the seating die until it contacts the bullets and your press is not set to seat bullets to the lands... Make adjustments from there. The die acts like a bit of a comparator in that it does not grip the tip, it grips closer to the Ogive.

 

[AlNyhus]

- Remove the firing pin. assy. from the bolt.
- In an empty new or f.l. sized case, seat the bullet long.
- Polish the bullet with some 0000 steel wool.
- Close the bolt
- Open the bolt and remove the case. If the bullet sticks in in the bore, tap it out from the muzzle end with an 1/8" wooden dowel.
-Look at the bullet and note the rifling marks.
-Lengthen the seating stem .010 and repeat.
-You'll see the rifling marks on the bullet get shorter as you get to the leading edge of the rifling.
-When the rifling marks just disappear, you're just off the lands. This can be the reference point for future seating adjustments and for monitoring throat wear. Record this seating stem figure for each bullet you want to use.

A lot of neck tension works best with this method as it keeps the bullet from sticking in the lands. With a bushing neck die, .004 neck tension works good. When measuring the o.a.l. for seating depth, the only dimension you're concerned about is the distance from the base of the case to the point on the bullet that contacts the lands. The Stoney Point Comparator tool,for measuring the base-of-case-to-ogive) works great..plus, you can get the headspace inserts so you can accurately set the shoulder bump. Make sure you use an unprimed case to measure from as the primers may add a few thou. to your measurements.

This takes less time to do than it does to write this. Once you do it a few times, you'll see how simple it really is.

Hope this helps. -Al

 

[expiper]

Al and Donnovan are givin you the strait "poop"....but I tend to keep it even simpler....Once you get it rite ...the dim. doesnt matter...just record the stem length on your Wilson bullet seater and monitor that from then on....and keep a record of the ammount of shims,or shim stock) under the seater top and watch the bullet engraving marks....keep just enuff pressure on the bullet so that you can barely feel it when you roll the bolt closed ....any more and you will be upsetting the gun...try to keep it there or just a "liddle" more and the gun whuld-shuld be shooting at its best....Roger
PS...with most of my chambers I can use a long universal length on the seater stem and as I need less bullet jam,like an 80 gr vs. 105 gr seating depth) I can add the appropriate ammount of shims and in a few seconds I am loading that particular bullet...I keep a chart of all the bullets I load for a particular cal...or rifle ...and at a glance I can add or subtract shims and load any bullet...

 

[ericnord]

Very good advice guys, thanks. I have a lot of work to do!

 

[AlNyhus]

As Roger mentioned, it's slick when you're using a Wilson seater. I just make a note for each barrels seating depth with a particular bullet on a small adhesive label and stick it to the side of the Wlson seater box. This measurement is the 'just to the lands' figure, so all I need to do to establish a seating depth is to look at that figure, then adjust the length of the seating stem to place the bullet wherever I'd like to. It's also an easy way to follow the throat out and adjust the seating depth accordingly.

For example, my latest 30BR barrel has a seating stem length of 1.730 to 'just touching' with a Dakota B1 117 gr. bullet. This is as measured with the method I outlined above and the Stoney Point base-to-ogive .30 cal. comparator insert. To get .025 'jam'*, I simply adjust the seating stem length to 1.705.

Good shootin'. -Al

* They don't actually go into the rifling .025...but that's a whole 'nother topic.