Does seating depth truely matter?

[ricco1949]

Start with conservative powder load and increase in 1% increments until you hit pressure. I choose a preliminary load in the middle of a group trending together in the ladder.

 

[wright brothers]

ricco how do you measure the pressure?

I promise no more dumba questions today.

 

[AlNyhus]

#1: Yes, seating depth matters for accuracy.
#2: If you're not testing over wind flags, forget #1
#3: If the answer to #2 is 'no', any conclusions are suspect.

Good shootin' -Al

 

[ricco1949]

ricco how do you measure the pressure?

I promise no more dumba questions today.

Heavier bolt lift.

 

[wright brothers]

Thanks I never thought of that for a "gauge".

 

[searcher]

ricco how do you measure the pressure?

I promise no more dumba questions today.

There are no dumb questions in respect to safety - and pressure is what gets most people into accidents. Aside from noticing heavier force required to lift your bolt handle, there are other ways of spotting pressure signs. Images of some will likely be in your reloading manual. If you don't have such a manual - get one.

Other methods people use to spot pressure are to measure across the brass case, just above the "web", (usually around 3/4" from the bottom of the brass) Measure before firing, then again after firing. If the firing expands that measurement .001" or more from the unfired measurement, that may be the first sign you are a bit over in pressure.

Increased pressure warning signs continue, with flattened primers, pierced primers, split necks on newer brass, a primer being blown out of the case, splits up the side of a case (rupture), are all signs of too much pressure, starting from milder to worse.

 

[jackieschmidt]

In one Chambering where seating depth is paramount is the 30BR.
Once you find what your bullet/barrel/powder combo likes, you will know it.

Seating Depth can turn a .250 30 BR into a sub .200 30 BR.

And once you find that seating depth, avoid changing it at just about all cost.

 

[boltfluter]

Used this approach to tune a 222 for an egg/pool chalk match in ND:

1. Pressure ladder at hard jam
2. Pick a preliminary powder load based on the ladder
3. Shoot two shot seating depth ladder moving back from hard jam
4. Shoot another two shot group powder sequence with the chosen seating depth to finalize the load.

Worked well enough to win with some noteable LRBR competitors in attendance.

This is a very good approach that has worked for me as well. Years ago, with my old .22BR, I was getting ready for my first ever benchrest match. This was a hunting rifle with a plate on the front for tracking. I was shooting in modified class which was basically varmint hunting rifles. Most of the rifles were Remington based actions. I was running moly bullets at the time. Still do. So, before the match, a buddy and I were messing with seating depths trying to get an advantage, group wise, to be more competitive with some really nice varmint rifles that were on the line. On a whim I decided to lengthen my seating depth by .050 and let the rifling seat the bullets when I closed the bolt. And then the magic happened! Groups went from around .550 avg down to a shocking .325 avg!! Thinking this must be a fluke the next group measured .350 or so. I handily won the match, but that was anticlimactic as to what I had just learned. The lights came on and off to the races we went. Fun times, to say the least. And the local coyotes and rockchucks were not very happy, to say the least. All this with a run of the mill Douglas barrel purchased second hand for $150.00. Fun times. So yes, seating depth can be very important at times.
Carry on and small groups guys.
Paul

 

[Doom]

There is a lot of anecdotal evidence that seating depth does matter and specifically in the neighborhood of the lands. But whether ot not this is actually true or not is very hard to prove. I have not seen very much extensive testing and one thing that isn't done is proving that the indicated "bad" depths are truly bad. One of the better recent "tests" is documented on the Precision Rifle Blog (multiple articles).

Bullet Jump: Is Less Always Better?

About 2 years ago, Mark Gordon shared some preliminary research he’d conducted with the Applied Bal...

precisionrifleblog.com

Jeff Siewet address the issue in his book Ammunition Demystified.

 

[barefooter56]

Good Day all
I recently performed a seating depth test on my 308 Win from 80 thou Jump to 150 thou
The reason for such large jumps are mag length constraints and a large freebore
The results are in the Hi Vis target
This was shot at 300m (327 yard) from shot 17 to 24 i did change my wind hold as the shots were getting difficult to spot
The total vertical was around 2.7 inches for 24 shots
I then loaded up 21 of the same charge and seating depth (CBTO = 2.205) and shot a group at 300m which measured around 4 inches , note the powder used here was a collection of the left over powder in the powder measure Yet the SD of both strings were 7.5 and velocity avg was within 1fps of each other
I don't know what do make of this data?
I've tried a few statistical analysis options
Such as levenes test , welches anova and a few post hoc tests (not a statistician)
I great deal of variation could very well be shooter error
Any insights would be appreciated

Moe,
I suggest you do your load development at 100 yards to reduce the " mother nature factor" = wind etc. And use a separate target marked for each bullet seating depth so you can see what is happening at each change. You can just put "dots" on a large cardboard sheet with each CBTO (CARTRIDGE BASE TO OGIVE) measurement listed under the dot.

 

[precision1]

Factory rifle
max mag length is
a long ways from the lands.

Can anyone answer WHY a rifle manufacturer does this?
Or what am I missing as advantage for this?

They have to accommodate 200 gr to 150 gr pills and more free bore equals less pressure in say 308 I'd guess

But then you have Ruger in my m77 260 very short throat barely enough for my 260 to shoot 140gr bullets with any powder to book without pressure.

Idk maybe difference in thinking on handling a variety of bullets vs accuracy with factory ammo idk I find it odd also

 

[precision1]

Repeat at .002 off lands and redo test.
Single feed and do that test and see what happens