Seating Depth Testing

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tactical_tech

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I have been reloading now for a couple years but never done much to tuning the seating depth. I've usually used manual specs or barring no published specs gone with 0.020" from the lands. When it comes down to testing how far do you guys go off the lands during your testing. I was planning on doing 0.005" increments from just off the lands but didn't know how far to go, 20,40,50,100 thou from the lands? I've also heard a lot of people talk about loading with the bullet jammed to the lands or a 5,10,15 thou jam. Now I know jamming can cause pressure spikes and should be done carefully. When they talk about a 5 thou jam, are they referring to seating the bullet 5 thou past the max COAL?( to OGIVE of course )
 
I have always used .005 of the lands to the ogive, recently i did some (proven @.005) loads .010 off the lands and they went to crap at 200 meters. I haven't gone closer than the .005 but I may try it soon to see if the loads get better.
 
I've loaded 80t off with great consistent results. Load five each from jam to 100 thou off in 20t increments and let us know if you find any trends.
 
I have loaded rounds jammed into the lands on a target rifle, to over .100" jump on a hunting rifle, but it's usually around .010" for cup and core bullets and around .050" for monometals. The micrometer adjustments on my seating dies make for quick and easy testing in .005" increments.
 
I find my 10 thou and then look for my best powder load and then I try 20, 30 and 40 thou jump to see what the differences are.
 
Every rifle has it's own sweet spot with a particular bullet. What works for other may or may not work for you. Best approach is to do your own testing. Load up with a modest powder load and follow the Berger routine.
 
I always find where the lands are when doing any new load development as it is a nice reference.

That being said, your seating depth may be limited by the use of the rifle.

If you have a magazine that you are utilizing it will be not very likely that you will be able to seat to the lands and still use the magazine.In this case I get the bullet to seat as far as I can in the magazine without having any functionality issues.As the seating depth can change pressures you are essentially also doing this with varying powder charges.So, doing proper load development will find the right pressure/sweet spot for that seating depth. One powder charge may have a sweet spot at one seating depth and another seating depth likes a totally different powder charge.

Also if for hunting as many others would recommend to not use a load that is jammed as this may make for hard extraction of an unfired round and even possible pull out of the case and be left in the barrel.

A single feed for target , it does not matter.Then you can play from jump to touch to jam.

Some bullets are less effected by seating depth while others are extremely finicky.I find this the case with SMK's(less fussy) and Bergers VLD's(extremely fussy).

A tangent ogive also seems easier to tune then a secant ogive in my experiences.

I still will go with what is recommended by the manufacturer to start initially , vary my powder charges and find the best load this way , then if I want to fine tune further I can play with seating depth, in small increments as I have already found what I feel my rifles like for a charge, I know that kind of contradicts what I said about varying depths vs loads but this is at the extreme fine tuning stage.

When they talk about a jam it does not refer to the COAL as this can vary with different bullets.I have a 0.023" OAL difference on one rifle between two different bullets and similar jump due to bullet shape.

They are talking about how far into the lands the bullet is sitting.Once you find the lands you can use the COAL as a reference but a better measuring system would entail a bullet comparator measuring the ogive, a bit better as tips on bullets can vary , the ogive stays very constant.

http://www.accurateshooter.com/ballistics/tangent-vs-secant-vs-hybrid-ogive-bullets/

There is a photo there that shows exactly what the jump is , think picture 5, jam , just the other direction into the lands.Photobucket had an issue with the photo.

https://www.google.ca/search?q=bull...24MKHdvRAEw4ChD8BQgGKAE#imgrc=aoSsn5HClt_ABM:

I hope that made sense.
 
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I have a buddy's 6BR that he couldn't get to shoot (3" at 300) - so he asked me to try - i had poor results with every load, 20 in to 20 out - nada.... then for ####s and giggles, tried 30/40/50 out - at 40 out, i zinged two 3/4" 300yd groups, back to back, one 3 shot, one 5 shot... thats with a 107 SMK. Wasn't expecting that, but the proof was there! What we did see before (before the proper seat depth was discovered) was a serious 2-1 groups.
Makes me want to try that with some other loads that should work but didnt't...

I have always wondered 2 things - (1) how the angle of the start of the rifling can affect this topic - is there a relationship between this and jump/jam?? One would think the tangent or secant ogive of the bullet would prefer a different angle when hitting the rifling.
And (2), once you find the proper seat depth that your rifle likes, shouldn't that be used for load development before tweaking powder charge? Sort of a chicken vs egg theory...
 
chrismc said:
I have a buddy's 6BR that he couldn't get to shoot (3" at 300) - so he asked me to try - i had poor results with every load, 20 in to 20 out - nada.... then for ####s and giggles, tried 30/40/50 out - at 40 out, i zinged two 3/4" 300yd groups, back to back, one 3 shot, one 5 shot... thats with a 107 SMK. Wasn't expecting that, but the proof was there! What we did see before (before the proper seat depth was discovered) was a serious 2-1 groups.
Makes me want to try that with some other loads that should work but didnt't...

I have always wondered 2 things - (1) how the angle of the start of the rifling can affect this topic - is there a relationship between this and jump/jam?? One would think the tangent or secant ogive of the bullet would prefer a different angle when hitting the rifling.
And (2), once you find the proper seat depth that your rifle likes, shouldn't that be used for load development before tweaking powder charge? Sort of a chicken vs egg theory...
Click to expand...

And that is the million dollar question, which way does one start?The reason I start with a set seating depth and varying powder loads is where exactly do you start, what do you determine as a load range?Then you wind up just doing it based on charge weights anyways to find a safe charge, so many ways to skin this cat.
 
My .223 has a many sweet spots for different type bullets.I always thought when the bullet is fired the jump or no jump to the lands what ever happens there that is would be rectified when the bullet runs down 26 inch of barrel.Apparently not.
 
Out of curiosiry, what does seating depth actually have to do with anything? Why should or would it have any effect? Not implying that it doesn't matter... but why does it matter at all?
 
max-x said:
Out of curiosiry, what does seating depth actually have to do with anything? Why should or would it have any effect? Not implying that it doesn't matter... but why does it matter at all?
Click to expand...

Alignment and pressure changes.

Seating way out to increase case capacity, more specific for guys doing target and wanting to use VLD type bullets.

Function with semi-auto's.

This is just a few.

All these small changes reloaders will vary in order to improve accuracy.

I am sure there are a few I missed.
 
Agreed on the fact that you are tuning pressure and I believe dwell time in the barrel to resonance within a particular barrel.

With my 10TR I need to take a .308 down to a 2.79 OAL in order to even create a jump. The lands are as tight to the chamber as I've ever seen. That being said it's grouping amazingly well so I can't complain.
 
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