Seating Depth Informative Thread

[Shortywy]

For rifles where I can't work close to the lands because of some constraints, I usually try a few different bullets that are supposed to be more jump tolerant. Berger Hybrids and full bore have tended to work well for me. The Berger VLDs are generally more sensitive. The Elite Hunters are supposed to be more tolerant but haven't worked too well for me yet.

Hornady bullets are more economical and many report good results with ELD-M or ELD-X. I haven't generally been able to get as good of groups with the Hornady bullets with most of my rifles, but my 308 does well with SSTs which are being jumped in an AR platform.

Having a good chronograph, even if you have to borrow one, also helps in providing critical information during load development and in controlling variables.

Thank you I will try the Berger's. So far it has been Hornady and Sierra.

 

[aushunter1]

I have tried the same test may times with my various competition rifles, I usually start at .010" jam and move backwards with 3 shot groups. When I find the best OAL, I write it down and begin a new sequence with another powder and primer.

PS - I rely on marks on the bullet in my dummy round. The bullet comparators are not consistent.

Personally I don't think 3 shots groups tell you enough, should be 4 minimum but 5 is ideal.
If you shoot 3 & have 2 touching & 1 flyer then the result is inconclusive imo, shoot 4 with 3 touching & 1 flyer then its worth following.

Also I dont get the statement in red, do you mean you cannot get a consistent result by using a comparator or the comparator's themselves are not consistent??
How do you then know what measurement you are at??
I have been using Hornady comparators for 12 years & never had a problem with them!!
I use the anvil which I find gives a better result as it keeps the base of the case more level.
You wont get marks on the projectile at 10 thou anyway!!

Anyway each to their own, reloading is about whatever works for you!

So my process is-

Firstly I obtain my lands measurement for the projectile I am using with a Hornady OAL gauge, the modified case I use is a case that is fireformed to my chamber & then reamed to fit the OAL gauge, measure CTBO 5 times to get an average.

I start all my LD @ 10 thou off lands, load 4 or 5 rounds per powder increment, sometimes 1gr intervals if the min/max range is 5gr or 1/2gr loads if there is only say 3gr min-max load.

I then choose the best group from charge range.
My next step is to change the CBTO to 5thou, 15thou & 20thou with 4 each.

Find the best from that & then if I want to try & bring it in more or didn't quite get the result I was looking for I will then do some smaller 1/2gr powder increments either side of that charge with the best performing CBTO.

By that stage I have fired 40 rounds or less, if I am still not happy I will go through the same process with a different powder.

 

[Canhunter35]

<.05" jump I've found seating depth finicky, greater than .1" jump and powder charge affects groups. Look at saami spec 308, there will be an optimal seating depth, but when ur jumping .15"-.18" powder charge makes such a big difference, much the same with wby freebore too. At least that's my experience

 

[Oddbod]

My latest (factory new) rifle has highlighted the importance of checking seating depth: .270 win should have a COL of 3.34" but it is at 3.278 - 3.286 with the three bullets I've tried so far.
I'm actually OK with this, as both the 100gr BTHP & 130/150gr spire points I intend using will actually seat nicely without being 0.100 & more off the lands.
IF it doesn't shoot, I can then take it back & bitch about the chambering not being to SAAMI spec...

 

[Oddbod]

[snip]

PS - I rely on marks on the bullet in my dummy round. The bullet comparators are not consistent.

I've always found them to be 100% consistent, with differing lengths actually highlighting variations in the accuracy of bullet shape/dimensions. It's not the comparator that's out - it's the bullet.

 

[Clem Bronkoski]

Now I have to start all over?

Not really. You have a load that shoots well? Just tinker with the OAL. Move .005" and .010"in and/or out from there and see if there is any improvement.

 

[Tulsa Reiner]

The COAL in a loading manual is typically the SAAMI recommended length for that particular cartridge. That means if you load ammo to that overall length it will fit, feed, function, and be safe in all guns chambered in that caliber. You really don't want to go below their set length because you could run into premature pressure issues and other problems. Typically, you have room to seat the bullet out before you hit the rifling. You will normally find your best accuracy somewhere closer to the rifling than with what the manual recommends, in most cases. You can still find good accuracy at the book listed COAL with some bullets, but others, particularly long, heavy, VLD bullets like to be seating closer to the lands. If you want to start experimenting with seating depth, I recommend finding your lands with a Hornady OAL tool or by seating a bullet into a sized case extra long and slowly seat it deeper with your die until you stop feeling resistance when closing the bolt. If you use the later method, you have to remove your firing pin assembly and plunger ejector, if your bolt has that style ejector. This will allow the bolt to drop closed effortlessly when the chamber is empty. You want it to get to the point when chambering the dummy round where you can just start to feel it close easily. That will be where your rifling is, with that particular bullet. Every different bullet will touch the rifling at a different spot. So you have to do this every time you change bullet types, if you want to find your lands. This is the best method I have found and it sure beats any guessing or confusion.

Using the Hornady Bullet Comparator is SOOOO much easier, and a very accurate way to find the seating depth at which each bullet you load touches the lands. And the kit doesn't cost very much ($30-40), plus a few bucks for a modified case in each caliber you want to load.

 

[Jud96]

Using the Hornady Bullet Comparator is SOOOO much easier, and a very accurate way to find the seating depth at which each bullet you load touches the lands. And the kit doesn't cost very much ($30-40), plus a few bucks for a modified case in each caliber you want to load.

I find the other method with seating a bullet to be more accurate and consistent for me. I also can't get modified cases for some of my cartridges, and I don't like ruing a good piece of brass to make one haha. So I just use the other method

 

[eric1115]

Those of you that do seating depth first, do you do a new seating depth test when switching to a different powder, or do you find that your rifle likes a certain jump for a given bullet regardless of powder?

If you do a new seating depth test when switching powders, is it typically pretty close, or can a bullet prefer big differences in jump for the same bullet for different powders?

 

[Canhunter35]

Those of you that do seating depth first, do you do a new seating depth test when switching to a different powder, or do you find that your rifle likes a certain jump for a given bullet regardless of powder?

If you do a new seating depth test when switching powders, is it typically pretty close, or can a bullet prefer big differences in jump for the same bullet for different powders?

I haven't noticed changing powders affect seating depth preference, at least not by a great margin. I've found seating depth preferences move in and out of preference much like nodes from powder adjustment. Ex. If a bullet likes .01" jump is might also like .13" jump and nothing between. Hard to know until you test though.
Ex: 208eldms liked .01" jump in my 308, I got tired of single feeding them so I pushed them as deep as I seat the 168s for magazine length and they shot just as well

 

[Muddyboots]

I mirror pretty much what most are doing to measure CBTO and starting 0.010 BUTTTT, I've begun to alter some of my preconceived opinions on how far off the lands I should start. Two good examples are Berger and Nosler. We all know the Berger CBTO recommendations but I recently noticed a statement from Nosler on their ABLR that caught my eye. I've been shooting the .308 168 ABLR with decent results out of 300WSM and 30-06 0.020 off lands. On the Nosler web page for the ABLR there is a statement:
TECHNICAL NOTE
*When loading the AccuBond®-LR bullet, Nosler ballisticians have found that loading to the maximum SAAMI cartridge overall length tends to provide best accuracy."

Link: Nosler Accubond Long Range

So I tried back to the SAAMI and yes both rifles improved quite a bit on their accuracy. I estimate I shaved at least 1/4" off groups at 200 yards and the final hunting load for both rifles is at SAAMI for the 168 ABLR. So this was a more direct comment from Nosler for best accuracy for this specific bullet that is not in the manual that I know so far. My comment here is more along the lines be open minded on how far off the lands will be best accuracy.