Would appreciate a bit more help on finding distance to lands...tried a bunch of stuff

[want2learn]

Hi, tried a bunch of ways to figure out distance to lands. This is for a 6.5x47 Lapua and a Berger 130 VLD Target projectile.

For reference a standard C.O.A.L. is listed as 2.8 inch for what ever that’s worth.

I attempted countless times with the OAL gauge but got widely varying values, this despite reading tutorials and viewing videos etc.

I couldn’t figure out how to dissemble my Sig SSG3000 bolt to remove the extractor so couldn’t really try the naked bolt in receiver technique, though it seemed like a great way to go. The bolt looks a lot different than the Remington type bolts i often see.

I then read about using a fire formed case and coating the projectile with a marker. In so doing i very slowly closed the bolt and it sure left a rim of uniform marks in the color coating which was very promising.

I then measured the distance from the base to the mark. This measured 2.18 inch.

I also used a Forster tool to measure case length to datum which yielded 2.24 inch.

The case length itself is 1.85 inch.

Length of projectile is 1.32 inch.

Not sure how to proceed? I'd sure appreciate any help.

Should i have just measured the C.O.A.L. of the marked projectile in the fire formed case and used that as the maximum length and subtract .01 inch to allow an appropriate jump? (of course i didn't do that...i already took that set up apart but i guess i can do that again).

Thanks.

 

[Sheldon N]

I attempted countless times with the OAL gauge but got widely varying values, this despite reading tutorials and viewing videos etc.

Is this with the hornady OAL tool? If so, jam that bullet into the lands hard, knock the bullet out of the lands with a cleaning rod, then take that measurement. I just write that number as "hard jam" and then back off 30 thousandths from it. In my experience the difference between max/hard jam and "touching" is around 10 thou or so, depending on the rifle and bullet. No need for an exact number, just a starting point from which you can load test rounds for accuracy.

If you want an exact number for touching, look up the video "Find your lands exactly" by Wheeler Accuracy on youtube. That's a bit more involved though and requires getting a properly sized piece of brass, stripping your bolt, etc.

 

[want2learn]

thanks....i appreciate it and will try again using your technique.

The Wheeler technique sounds great but i can't figure out how to strip my bolt and replacement parts are impossible to find in case i bugger it up.

 

[ditter]

You said you used an OAL gauge. What was the problem with those measurements? If you have Hornaday OAL gauge, a fired case and it was tapped, you should have pretty consistent readings. You can get a good idea of the measurements if you just average 10 or so CBTO measurements. Sounds like you aren't using the OAL gauge correctly.

 

[want2learn]

ditter....thanks.....i'm not sure what to say, i cleaned the bore and chamber, i read the instructions several time, i saw a bunch of videos, it seems really easy to do but the Extreme Spread of values i'm obtaining are too broad to accurately secure a number to .01 inch.

I think i'll try to measure the Jam C.O.A.L. and subtract .02 inch from that and go from there.

 

[2aBaC̶a̶]

Curious on what tools your using. How are you measuring the case base to bullet ogive?

My Hornady comparator tool measurements are pretty consistent with the stripped bolt chamber test.

 

[want2learn]

i'm using a Forster tool that seems to work quite well.
Here's a link to the Datum tool:

Datum Dial™ Kit – Forster Products

Datum Dial™ Kit $ 192.00 Original price was: $192.00. $ 144.00 Current price is: $144.00. Datum Dial™ Kit quantity Add to cart SKU: DDKIT Cate

www.forsterproducts.com

 

[lash]

...
I then measured the distance from the base to the mark. This measured 2.18 inch.

I also used a Forster tool to measure case length to datum which yielded 2.24 inch.

The case length itself is 1.85 inch.

Length of projectile is 1.32 inch.

Not sure how to proceed?

You're getting lost in the numbers, but your answer is right in your first post. using your forsters gage, you measured 2.24”, so that’s your base to gage length that you need to replicate for your load testing, minus 0.020”. 2.220” gage length should put your near 0.020” off the lands. After your initial load development, you can work with 0.005”-0.010” longer or shorter to see what dials in your load. It’s really not more difficult than that.

 

[nn8734]

Acquire these tools and follow the procedure for use.

Step 1. Thread Hornady modified case onto oal gauge until tight then insert a bullet into the case
Step 2. Remove bolt and insert assembled oal gauge fully into chamber pushing the bullet into the lands using the gray plunger.
Step 3. Tighten the plunger rod screw
Step 4. Remove assembled gauge Using a cleaning rod to prevent bullet from sticking in lands
Step 5. Using bullet comparator and dial caliper, measure base-ogive length and record it.
Step 6. Adjust seating die based on desired jump

Note: not sure how anal you are about consistency in jump from round to round but I ogive sort all my bullets and follow the above procedure for each sub-population.

 

[2aBaC̶a̶]

Looks like a nice tool. Are you also using the Hornady coal with a modified case as mentioned above?

When you say Datum I think headspace measurements.

Ogive is on the bullet measurement.

i'm using a Forster tool that seems to work quite well.
Here's a link to the Datum tool:

Datum Dial™ Kit – Forster Products

Datum Dial™ Kit $ 192.00 Original price was: $192.00. $ 144.00 Current price is: $144.00. Datum Dial™ Kit quantity Add to cart SKU: DDKIT Cate

www.forsterproducts.com

?

 

[want2learn]

Hornady doesn't make a 6.5x47L case for the OAL gauge so i had to purchase a custom one.

thank you all so very much. I think i'm set.

 

[spife7980]

When you say Datum I think headspace measurements.

Ogive is on the bullet measurement.



?

Datum is just a reference plane. It can be anything.

Ogive is a curve. Anything with a curve has an ogive.

We use a datum to measure the ogive. We use a datum to measure a cone.

 

[2aBaC̶a̶]

Datum is just a reference plane. It can be anything.

Ogive is a curve. Anything with a curve has an ogive.

We use a datum to measure the ogive. We use a datum to measure a cone.

Semantics. Yes, technically you are correct.

Thank you

 

[John Glidewell]

I use a cleaning rod in conjunction with OAL gauge. I use the cleaning rod to help work the bullet back and forth, you can feel it touch much easier and I get very consistent #s. You have to use both hands. Holding the gauge in place/all the way forward in the chamber and using my pinky on the back of the plunger while the other hand works the cleaning rod.

 

[ditter]

+1 on the method above with the cleaning rod and pushing the bullet back and forth into the lands. You'll feel a definite hit when you get to the lands. If you do ten or so measurements, you'll get a good sense of the measurement.

P.S. You dont have to buy a modified case for your caliber. If you send a fired case to Hornady, they will tap it for you so it will work with the OAL gauge. it costs about 15 bucks or so and takes about a week to get back to you.

 

[Rlandry]

All I can add is that when using the Hornady Comparator, use just enough finger force to feel when the bullet hits the lands. It's possible to jam the bullet into the lands enough to affect your measurement. It will take some practice. Do a half dozen or so "practice runs" and write down your measurement. You will gradually see the measurements get closer.

 

[want2learn]

thanks will do.....appreciate all the help

 

[Deleted member 113831]

Easiest way is to take a sacrificial sized case, use a dremel with a cutting wheel to cut a slit in the neck that goes right to the neck/shoulder junction.

Finger seat a bullet in the neck and chamber the round a few times turning it so the lands hit different spots. The bullet will seat back into the case upon contact with the lands, but the neck will still have enough tension to keep the bullet.

Measure and you are done.