Seating depth of short .243 projectiles (70 grain Sierras)

[on_one_wheel]

So I thought I'd try out something lighter in my .243

I've been using 100 gn Sierra SPBT's which I was able to seat just off the lands, but when I set out to find the JTL of my new projectiles ( 70 gn Sierra Blitz King ) I found that at JTL the projectiles are seated about 1mm into the neck.

Obviously this isn't nearly enough seating depth even after I add my .2 mm jump , so my question is
What is the general rule of thumb for minium seating depth to allow enough bearing surface.

Interestingly my Nick Harvey 5 th addition reloading manual makes no mention of seating short projectiles for use in a chamber with a long throat.

[Oldbloke]

NFI, but will follow this with interest.

[Strikey]

Seat them into the cases where you think they should be and try them, you may find that jumping them won't affect anything but you won't know if you don't try, in my old Omark .308 I could not find the lands with 155SMK's but that rifle would shoot .25moa all day, long throats are not necessarily a bad thing.

[Wm.Traynor]

I read years ago that it should be at least equal to the calibre, so that the concentricity etc won't be spoiled by feeding from a magazine for instance. If you are going to single-load them, they should come to no harm.

[Apollo]

Minimum seating depth is just enough so the bullet doesn't fall out of the neck.

Don't know what "JTL" is, not a term I have heard used but I'll take a guess and say "Just Touching Lands" maybe. If that is so, the measurement found will differ as to the means used and force used to make the measurement and different people making the same measurement will likely come up with a different result.

That said, is this for hunting or target shooting, single shot feed or magazine feed.

Regardless, if I was testing a new bullet in my .243W I would start with a measurement I make with my OAL Gauge of a bullet "On the Lands" without applying any pressure to the bullet. I then start with my load development / powder charge range at that seating depth. When I find the most accurate of those tests I then start seating the bullet further back into the neck to find the most accurate seating depth. For hunting that must now also fit for length into the magazine, if not I need to go shorter and find the ideal accuracy that fits into a magazine.

For target use it doesn't matter as long as the bullet doesn't fall out. I have tested some that I can actually pull the bullet out with my fingers easily but that's not where the best accuracy was so they ended up deeper into the neck. I also use adjustable neck tension and have had a starting point where the bullet will virtually slide further into the neck if touched, not ideal so I tighten the tension in steps until it does really take a little pressure to move the bullet.

In another calibre (6.5x47L) I have some bullets seated about 1mm (0.040") which came about by the bullet maker (Berger) shortening the bullets in a production change. Not good for my long throated rifle and not good for transporting especially over rough roads. They are no longer as accurate either so I changed to a lighter and longer bearing surface bullet.

If you are only using these for target then test and see what happens, likely you will be seating them deeper (further off the lands) to improve accuracy. If for hunting then 0.040" is probably not enough by a fair margin.

Alternative is to use longer bodied bullets if you want the weight change.

I've used 55gr 6mm bullets and from memory they were a fair distance off the lands to maximise accuracy.

Edit.

Most all my benchrest target rounds (not all) are "soft seated". That is they are seated say 0.040" (1mm) longer than on the lands and when the bolt is closed it pushes the bullet back into the case neck. There is no force required as neck tension is minimul.

[Mick280]

At least a caliber in the neck is what I was always taught!!!

[Apollo]

At least a caliber in the neck is what I was always taught!!!

That was a very old and basic starting point. I doubt anyone looking for accuracy these days even in hunting would not start there. I remember that story from more than 40 years ago and for one Hornady in their reloading manuals sort of pushed that idea to relieve the danger from creating over pressure loads. Times do move on.

The problem is if you start a certain distance back, how do you decide to go longer or shorter to improve things.

The more modern approach is either start with bullets on the lands (even slightly longer with light starting loads) or at maximum magazine length then work backwards from there.

Each to their own though.

[on_one_wheel]

Minimum seating depth is just enough so the bullet doesn't fall out of the neck.

Don't know what "JTL" is, not a term I have heard used but I'll take a guess and say "Just Touching Lands" maybe. If that is so, the measurement found will differ as to the means used and force used to make the measurement and different people making the same measurement will likely come up with a different result.

That said, is this for hunting or target shooting, single shot feed or magazine feed.

Regardless, if I was testing a new bullet in my .243W I would start with a measurement I make with my OAL Gauge of a bullet "On the Lands" without applying any pressure to the bullet. I then start with my load development / powder charge range at that seating depth. When I find the most accurate of those tests I then start seating the bullet further back into the neck to find the most accurate seating depth. For hunting that must now also fit for length into the magazine, if not I need to go shorter and find the ideal accuracy that fits into a magazine.

For target use it doesn't matter as long as the bullet doesn't fall out. I have tested some that I can actually pull the bullet out with my fingers easily but that's not where the best accuracy was so they ended up deeper into the neck. I also use adjustable neck tension and have had a starting point where the bullet will virtually slide further into the neck if touched, not ideal so I tighten the tension in steps until it does really take a little pressure to move the bullet.

In another calibre (6.5x47L) I have some bullets seated about 1mm (0.040") which came about by the bullet maker (Berger) shortening the bullets in a production change. Not good for my long throated rifle and not good for transporting especially over rough roads. They are no longer as accurate either so I changed to a lighter and longer bearing surface bullet.

If you are only using these for target then test and see what happens, likely you will be seating them deeper (further off the lands) to improve accuracy. If for hunting then 0.040" is probably not enough by a fair margin.

Alternative is to use longer bodied bullets if you want the weight change.

I've used 55gr 6mm bullets and from memory they were a fair distance off the lands to maximise accuracy.

Edit.

Most all my benchrest target rounds (not all) are "soft seated". That is they are seated say 0.040" (1mm) longer than on the lands and when the bolt is closed it pushes the bullet back into the case neck. There is no force required as neck tension is minimul.

Your right , JTL Just touching lands. For every new projectile I use, I record this measurement to ensure I'm not hard up against the lands. I record it as COAL @ JTL , I'm probably using the wrong terms but I know what it means I'm my notes.

Perhaps reloaders like myself could benefit from a glossary of terms and abbreviations section somewhere in the forum.

I'm going to try these 70 gn blitzing's for varminting in my Remington 700 bdl with internal mag so length isn't an issue as she fits the long ones just fine but fragility might be a issue, I'm happy to single load them but like to retain the option to fill the mag without worrying about the affects of recoil on my loaded cartridges.
I'm going to see if I can turn rabbits into red mist and fur from 200 meters and beyond ( thanks to that bloke who's been showing off with his long range varmint videos I'm keen ) as such I was hoping for minimal jump because that's where my accuracy has been so far, all be it with totally different projectiles.

I guess for now I'll just seat them 6mm into the neck as suggested in the formula above and see how it goes.

Perhaps in the long term I'm going to need a more suitable varmint rifle.

[Homer]

G'Day Fella's,

O_O-W, as Strikey said!
I always seated my bullets out to within 0.020" to 0.030" of the rifling, because I could, then I rebarreled an old "War Horse", with a cheap and new screw out barrel.
I found that if I seated to bullets to function thru the magazine, the bullets were 0.190" off the rifling! Bugger said I, then I spent a day at the range................................. see attached image (and I'm no BR shooter)!

390.JPG (486.56 KiB) Viewed 4487 times

Doh!
Homer

[Turtleburp]

Minimum seating depth is just enough so the bullet doesn't fall out of the neck.

Don't know what "JTL" is, not a term I have heard used but I'll take a guess and say "Just Touching Lands" maybe. If that is so, the measurement found will differ as to the means used and force used to make the measurement and different people making the same measurement will likely come up with a different result.

That said, is this for hunting or target shooting, single shot feed or magazine feed.

Regardless, if I was testing a new bullet in my .243W I would start with a measurement I make with my OAL Gauge of a bullet "On the Lands" without applying any pressure to the bullet. I then start with my load development / powder charge range at that seating depth. When I find the most accurate of those tests I then start seating the bullet further back into the neck to find the most accurate seating depth. For hunting that must now also fit for length into the magazine, if not I need to go shorter and find the ideal accuracy that fits into a magazine.

For target use it doesn't matter as long as the bullet doesn't fall out. I have tested some that I can actually pull the bullet out with my fingers easily but that's not where the best accuracy was so they ended up deeper into the neck. I also use adjustable neck tension and have had a starting point where the bullet will virtually slide further into the neck if touched, not ideal so I tighten the tension in steps until it does really take a little pressure to move the bullet.

In another calibre (6.5x47L) I have some bullets seated about 1mm (0.040") which came about by the bullet maker (Berger) shortening the bullets in a production change. Not good for my long throated rifle and not good for transporting especially over rough roads. They are no longer as accurate either so I changed to a lighter and longer bearing surface bullet.

If you are only using these for target then test and see what happens, likely you will be seating them deeper (further off the lands) to improve accuracy. If for hunting then 0.040" is probably not enough by a fair margin.

Alternative is to use longer bodied bullets if you want the weight change.

I've used 55gr 6mm bullets and from memory they were a fair distance off the lands to maximise accuracy.

Edit.

Most all my benchrest target rounds (not all) are "soft seated". That is they are seated say 0.040" (1mm) longer than on the lands and when the bolt is closed it pushes the bullet back into the case neck. There is no force required as neck tension is minimul.

thanks for taking the time to draft that! - we need some credit system for genuinely useful feedback

It was helpful to me too... I was loading some round noses recently and sweating the jump (actually envisaging bullets camming in the neck) when a more experienced friend gave similar feedback. Pointed out to me that COAL was minimum (rather than max) to avoid compression and that their rifle (you got it, another Omark) would shoot lights out with a jump.
Its nice to have help when your putting explosive compounds in thin brass cases that you intend to detonate not far from your face

[Apollo]

Another little tip, perhaps something to ponder if one is worried about the amount of depth a bullet has in the neck if it's a rather small amount is to add a "crimp" to the case neck to tighten slightly.

Lee make "Factory Crimp Dies" that will allow this to be done in degrees of the amount of crimp applied.

I have several and have tried a couple to see if it improved accuracy / consistancy at all. Not much happened to most so I gave up the experiment as I usually have enough bullet seating depth to hold bullets. Much needed with the likes of the 30-30 Tube Feed Lever as I did confirm that bullets will move under recoil so all 30-30 reloading gets a Lee Factory Crimp.

The biggest advantage I found of adding a crimp came when I was chasing accuracy with a .22 Hornet. The accuracy improved greatly when I crimped the bullets and I account for this being that the Hornet Cases are so thin they provide not much neck tension and / or the crimp provided a little more pressure build up before releasing the bullet from the case. As far as the Hornet goes a lot of time was spent getting it to be at least 0.5 MOA or better accuracy and it all paid off. Not only with mine but a few other different rifles.

Oh what fun reloading for accuracy brings.