Bullet Seating (lands) help needed please

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darkwing327

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Hi All,

I've got myself totally lost here and looking for some advice.

Have a .308 i built for target shooting that does very well. Nice cloverleafs at 100m with the loads i have worked up. But trying to tweak things now and this is where I seem be hitting a wall.

My understanding is that you just want to seat the bullet off the lands of the rifling and the way to find this is via the dowel down the barrel method or making a dummy round and marking the bullet.

I have done both and both ways are telling me that the bullet is touching the lands at 2.71" with a 155 Sierra Match. But load data has been having me load this particular round with an OAL of 2.775 and my 168's 175's at 2.800". So it seems to me that I am WELL into the lands and may explain why 46.5 grains of Varget behind the 155's give me an occasional tight bolt even though I am not at max load.

Just wondering if anybody can shed any light on this. I've heard of chambers that are too long to be able to be able to get the bullet close to the lands, but I haven't ever heard of one being too short.

Any thoughts are appreciated.

Cheers,
Darren
 
The reamer your chamber was cut with may have a short freebore (the area between the end of the chamber and the rifling of the barrel).

If this is a match chamber then it will vary from SAAMI specs which your load manual is based on.

Find the length to the lands in YOUR chamber using a fired case and putting a light crimp onb the neck with pliers. Put a bullet just slighlty into the case, chamber the round and then carefully remove it from the rifle.
Measure your length and do this 3 or 4 times again and average the length out.

You will probably find that 4 of the 5 times come out the same, this is probably your OAL to the lands.

Load a dummy round to the length you measured, with the same bullet you used for the chambering test, but add .010 to the length.

Chamber the dummy round and see that there are land marks on the bullet, reseat a few thou in and check again for land marks. (Use fine steel wool to polish the bullet between chamberings to be able to see the land marks).

Once you get close to having no marks on the bullet, reseat by .001 until you see no marks from the rifling, add .001 to that measurement and this will be your OAL to the lands.

You can adjust your seating depth based on that measurement.

Another note, to get a proper OAL reading you should be using a bullet comparator of some sort so that you are not measuring off the bullets meplat which can vary the bullet length by as much as .015.
 
Have you tried berger vld's they will allow you to seat your bullets out further. you could chamber one of your sierra reloads then take it out and see if it is pushing the bullets into the lands or if it is seating the bullet deeper into the case.
 
X2 on the comparator.....much more accurate.
And a tip....color your bullet with a black Sharpie and even light touches on the lands will be apparent.
 
155 SMK don't have to touch the lands to shoot well. You are however finding max pressure with the bullets out touching the lands. While you may be getting a stiff bolt with the bullets into the land, that load may be just fine .020" off the lands.

BTHP bullets really start to shine at longer distances. If you are only shooting 100-200 try a flat base bullet.
I shoot 155's with 46.0 of Varget behind them .020" off the land. Your load it right up there but playing with seating depths may be the solution to the smaller groups you are looking for.
 
The tip of the bullet cannot used to make this measurement. You must use a bullet comparator to get the ogive point of contact with the land. You also need an OAL gage to do the job. Hornady is a cheap tool ( $35 about ) to do this or RCBS OAL die ( Cost about $70 ) that is also used to adjust the sizing die. Sinclair has great tools also.

Check this web site for more information - the page is about the 6 mm BR, but the same apply to other caliber. http://www.6mmbr.com/catalog/item/1433308/977259.htm

With your method - you are WELL - into the land.
 
X1000 on the OAL gauge and bullet comparator. These tools are what you need to accurately do the job.

PM mysticplayer and order them.

You will find that match bullets vary somewhat in the measurement from base to tip, but not from base to ogive, which is what touches the lands.

Take a measurement with the OAL gauge, measure with the comparator, and check your loads with the comparator until you dial in your dies just right.

Then be happy!
 
Good advice here, to which I can only add the suggestion that you do your testing at 300yds. 100yd groups aren't telling you the whole story.
 
Also true. 100y is for scope adjustment, not precision load testing IMO. 200y is a useful range, 300 even better.
 
Thanks for all the suggestions guys. I have smoked the bullets; polished the bullets; jiffy marked the bullets and still can't get a positive answer (at least one gives me a confident result). It's possible that I might be going out shooting with mysticplayer this week or next, so I will ask him then.

Thanks again.
 
This is our new Digital Headspace Gauge. Besides measuring your chamber clearance (at the shoulder), it can also measure the "jump to the rifling.

dhsg3pics.jpg

I use a similar method that is being described. Just make a sample round with a slotted case like this:

OAL-3.jpg

This is the quickest and most accurate method I've found yet. It also works on ALL calibers and there's nothing else to buy.

- Innovative
 
I just bought one of these off of another member here on CGN.

I can't wait for it to arrive and give it a try. I will post a review here when I get it.

Richard
 
Well I guess the main issue I am having is probably being confident in what is a rifling mark and what is a scratch from ejecting the round. No matter how carefully I remove the cartridge, there is a scratch from tip to ogive (very slight). I am assuming this is from going in but don't want to be wrong.

Any thoughts?

Darren
 
You need to drop the round into the chamber and close the bolt. Rifling marks will appear on the bullet evenly were the lands touch it. Like I said before SMK bullets are the most forgiving when it comes to seating depth. Even if you jumped them .040 they may still be a accurate as bullets touching the lands. Every rifle is different you may find an accurate load touching the lands and that same load it just as accurate .025" off but doesn't like them .005" off.
The ammo that was issued for competition in Bisley last summer was loaded with 155 SMK's to the OAL of 2.800".
 
darkwing327 said:
Well I guess the main issue I am having is probably being confident in what is a rifling mark and what is a scratch from ejecting the round. No matter how carefully I remove the cartridge, there is a scratch from tip to ogive (very slight). I am assuming this is from going in but don't want to be wrong.

Any thoughts?

Darren
Click to expand...

If you load a dummy round .030-.050 longer than you think is the "to the lands" OAL and chamber it, you should see a definite pattern made by the lands (4 marks if you have a 4 groove, 5 marks for a 5 groove, etc..)

If the bullet pulls out of the case when you remove the round...seat a little deeper and try again so that it will show marks but not grab the bullet enough to yank it out of the case. You can make adjustments then incrementally until you see little or no marking on the bullet.
 
Janeau said:
The tip of the bullet cannot used to make this measurement. You must use a bullet comparator to get the ogive point of contact with the land. You also need an OAL gage to do the job. Hornady is a cheap tool ( $35 about ) to do this or RCBS OAL die ( Cost about $70 ) that is also used to adjust the sizing die. Sinclair has great tools also.
Click to expand...

I see now... I am strictly going by COL, so my reloads have varying freebore?
I am using Lee seater and get frustrated when the COL is about .05 to .1 or so shorter.
Time to get the OAL gauge. In the meantime, once the seating depth on the die is corrected for a dummy round... would it be good not to make other adjustments?
 
Yes...once it is set, it will seat the rest of the bullets the same until you change to a different bullet. Then you do it over again.

Measuring off the bullet tip will give you variances...ignore them. Get a comparator and measure off the ogive.
 
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