Seating Depth Dangers?

[HK Dave]

Hey Guys

Just finished a ladder test with a 308 bolt action and 175 smk... seems the best node occurred between 43.5 to 44.5 grains of Varget. By 25 grains my bolt got sticky.

OAL 2.80

I'm thinking the next step is to load out 5 rounds of 43.5, 44, 44.5 and group.

Then after that, perhaps play with seating depth? Are there any dangers in increasing the overall length while keeping the same powder charge?

Thanks!

[mark501w]

Pulling the bullet out shouldn't be a problem unless you encounter the lands & grooves. . Pushing it in could produce a problem by increasing the loading density.

[J-cat]

U mean 43.5 to 44.5 grains of Varget, right?

[HK Dave]

Lol yes 43.5 to 44.5 of varget. Was so focused on the Zimmernan verdict.

[LynnJr]

Dave
When you started your testing you should have seated your bullets as long as is possible for your particular set-up.This allows you to find your accuracy node and eliminates the possibility of seating depth based pressure signs.

I would try and find the center of the node or sweetspot then move the seating in 0.005 increments until you locate best accuracy.At that point go in and out in 0.001 increments until you eliminate any flyers from your groups.Eight groups of 3 shots each will find you the exact center of your seating depth sweetspot.

You absolutely have to use a comparator that measures off of the bullets ogive in order to make accurate seating depth readings.They run $20 but as seating depth is the single biggest factor in lowering group size it is money well spent.

[J-cat]

Advising him to go in .001" increments necessitates bullet sorting by base to nose and base to ogjive length.

[LynnJr]

It would be better for his accuracy to sort his bullets but he can still seat them all to within 0.001 of the same length and most manufacturers bullets will shoot better doing that.
I loaded up some Lapua bullets this morning and on the first pass through the seater die I had 80% within 0.003 and 20% were off by more than 0.010
I seated them all to 2.510 and they shot very well.
I have seen 0.023 variance on seating depth with mass produced bullets like Bergers.

[ar15barrels]

Just finished a ladder test with a 308 bolt action and 175 smk... seems the best node occurred between 43.5 to 44.5 grains of Varget. By 25 grains my bolt got sticky.

OAL 2.80

I'm thinking the next step is to load out 5 rounds of 43.5, 44, 44.5 and group.

Then after that, perhaps play with seating depth? Are there any dangers in increasing the overall length while keeping the same powder charge?

You do the ladder test LAST, after you have tweaked the seating depth.

Honestly, just load 43.5gr of varget under 175SMK's between 2.800" and 2.820" and call it done...

[LynnJr]

Never heard of a "Ladder Test" were the seating was done first.

[Whiterabbit]

Nor I. documentation all states that POWDER CHARGE is #1 for accuracy. That seating depth comes in at #2.

[nubrun]

There is also the OCW method which advocates powder first and seating depth second. I have had good luck with it.

[BLR81]

Very few if any load data books, show data for loads loaded to the lands. Saami data as far as OAL is concerned is short enough to be valid for most standard manufacturers barrels. So, if you start out with the bullet seating depth set into the lands, your load data from min to max will not be valid.

Seating the bullet long increases the space in the cartridge and therefore decreases pressure and velocity over stated load data. On the other hand seating into the lands creates a higher pressure not experienced when seated .020" short of the lands which can lower your max stated load data considerably.

Also, most rifles with magazines won't allow bullets long enough to touch the lands, to be fired out of the magazine. Also, if bullets loaded to land length need to be unchambered, you run the risk of unseating the bullet and having it stuck in the lands. That can pretty much ruin a hunt or a match.

That's why I find the COAL to touch the lands, then back off .020". Then I run my ladder test and find the preferred bullet and powder charge. If I'm not satisfied or wish to find the last bit of accuracy out of the load, I'll vary the seating depth deeper in .010" increments out to as much as .100" from the lands. I'll also try in .005" closer to the lands but never into them. To me that's the realm of the benchrest shooter with thousands of dollars in equipment, looking for the 5 shot single hole group. For tactical, silhouette, long-range matches, and for hunting, consistency and reasonable accuracy is more important than one hole groups.

[ar15barrels]

Never heard of a "Ladder Test" were the seating was done first.

His barrel is going to need a seating length approaching 3" to touch the lands.
His magazine is going to limit him to around 2.85"
He can tweak the length all he wants.
It won't matter.
That's why I said he should tweak his length first, because it won't matter.
Then run the ladder test and call it done.

Or, go ahead and run the ladder test, then he can keep tweaking the seating length until he finally figures out that the seating length still does not matter.

Or, just load 43.5gr of varget at 2.82" and go learn about wind...

[Whiterabbit]

both my bolt rifles REALLY prefer a large jump to the lands. In both cases though, I am shooting copper solids. One from Barnes, one from Nosler. So I've heard the stories of Bergers for example preferring to be close to the lands, I just don't know.

Also, I'm just shooting man sized targets to 700+ yards. If I were shooting for groups above 1000 yards, maybe it would make more difference?

[mark501w]

If single loading I'll touch the lands& grooves then, give my bullet seating stem 1/2 turn or a little less for about .0015 . I load to mag length so my rifle is a repeater & go shooting.