Thread: .243 load development part deux

Note on language -

You can't tighten a group. It has already been shot, it isn't getting any tighter than it is. You could put a patch over one of the holes I suppose.


When you make changes in your load specifications, what you hope to do is improve the precision of the system. You hope that you'll shoot smaller groups in future as a proxy for measuring the precision of the system. However with 5-shot samples we actually have basically no idea what the precision of this system is at the moment, and it is impossible to measure any improvement or attribute it to any changes with any evidential basis.



Have a flip through this thread - I spent 15 years following the same handloading approaches and achieved some good results over the years in spite of the process rather than because of it; and with a lot of uncertainty and wasted time/components/effort. Essentially I realised I end up with the same result no matter what I did, the process was actually pointless, just fooling myself fiddling with characteristics that didn't actually change anything.

There is a simpler way - follow the simple process and you'd be in a position now of knowing much more, with less components used. I would prefer if others didn't have to waste their time and components either.


https://www.nzhuntingandshooting.co....opment-106057/



If you're seating the bullets anywhere in the functional window you should be (0.030-0.100 off the lands, or mag length - whichever is shorter) I have yet to see any convincing evidence that tweaking the seating depth makes any difference to precision. I have tested it with a few bullets and I cannot find a difference with valid measurements. Likewise powder charge. But, maybe this is the situation where that doesn't hold true.


However, given the initial results with those massive groups - first step for me now would be immediately dropping the bullet and trying another, or looking at is there something wrong with the rifle/scope mounts. Do you have a bank of previous data from the factory ammo with this bullet?

Originally Posted by gimp

How far off the lands are you seating the bullets?

Short answer....I don't know, what I can tell you IIRC is that I was just under 2mm shy of max OAL, I mounted a projectile to case without powder and cycled that through the action, it cycled nicely and the decision was made to leave OAL as it was with the intention of fine tuning it later, how/what affect does distance to lands have on projectile?

If the bullet has an excessive free run or is poorly supported during that period it may tilt and become asymmetrically engraved as it travels down the bore - principle axis tilt. This imparts an angular velocity as it exits the muzzle - a sideways vector of variable size and direction. I.e. poor precision.

This can be mitigated by seating in that window of up to about .100" off the lands if possible, or at least as close as your mag allows if not possible, and by choosing to use cartridges with more modern chamber designs that have tighter tolerances in the neck/throat area. Most bullets seem to shoot perfectly fine in that window.

A lot of people believe you can make small adjustments to seating depth within that window to "tune" a load. Noone has been willing to demonstrate it with evidence. I believed it for 15 years. When I started trying to test properly, I could not measure a detectable difference.

Seating depth also influences pressure and velocity.

I recommend never seating closer than .020 to the lands, you will see poor results with "just touching" the lands and .020 gives a comfortable margin away to cover for stacking tolerances

One thing I noticed, that may not be readily apparent in the pictures is that the 42gr load had the cleanest holes through the target, the other loads were slightly more "ragged" with the 43gr load being particularly more so, does this indicate that the projectiles are "less stable" than the 42gr load, target mounting boards are faced with a very high density foam?

Originally Posted by gimp

Note on language -

You can't tighten a group. It has already been shot, it isn't getting any tighter than it is. You could put a patch over one of the holes I suppose.


When you make changes in your load specifications, what you hope to do is improve the precision of the system. You hope that you'll shoot smaller groups in future as a proxy for measuring the precision of the system. However with 5-shot samples we actually have basically no idea what the precision of this system is at the moment, and it is impossible to measure any improvement or attribute it to any changes with any evidential basis.



Have a flip through this thread - I spent 15 years following the same handloading approaches and achieved some good results over the years in spite of the process rather than because of it; and with a lot of uncertainty and wasted time/components/effort. Essentially I realised I end up with the same result no matter what I did, the process was actually pointless, just fooling myself fiddling with characteristics that didn't actually change anything.

There is a simpler way - follow the simple process and you'd be in a position now of knowing much more, with less components used. I would prefer if others didn't have to waste their time and components either.


https://www.nzhuntingandshooting.co....opment-106057/



If you're seating the bullets anywhere in the functional window you should be (0.030-0.100 off the lands, or mag length - whichever is shorter) I have yet to see any convincing evidence that tweaking the seating depth makes any difference to precision. I have tested it with a few bullets and I cannot find a difference with valid measurements. Likewise powder charge. But, maybe this is the situation where that doesn't hold true.


However, given the initial results with those massive groups - first step for me now would be immediately dropping the bullet and trying another, or looking at is there something wrong with the rifle/scope mounts. Do you have a bank of previous data from the factory ammo with this bullet?

Thanks for posting that link, I've previously read that and came to the conclusion that I need to read AND understand in order to comprehend although I get the gist, I think, of the points you made but my knowledge needs to increase before I can benefit from those points

Originally Posted by gimp

If the bullet has an excessive free run or is poorly supported during that period it may tilt and become asymmetrically engraved as it travels down the bore - principle axis tilt. This imparts an angular velocity as it exits the muzzle - a sideways vector of variable size and direction. I.e. poor precision.

This can be mitigated by seating in that window of up to about .100" off the lands if possible, or at least as close as your mag allows if not possible, and by choosing to use cartridges with more modern chamber designs that have tighter tolerances in the neck/throat area.

A lot of people believe you can make small adjustments to seating depth within that window to "tune" a load. Noone has been willing to demonstrate it with evidence. I believed it for 15 years. When I started trying to test properly, I could not measure a detectable difference.

Seating depth also influences pressure and velocity.

I recommend never seating closer than .020 to the lands, you will see poor results with "just touching" the lands and .020 gives a comfortable margin away to cover for stacking tolerances

That makes sense and my question then is that if I understand correctly, distance to lands is a direct result of COAL adjustment, if I know my Max COAL (69.8mm) then this measurement puts my projectile just on the lands so my current COAL of 67.5mm puts me within the 0.100" - 0.030" window you mention?

Originally Posted by Zedrex

One thing I noticed, that may not be readily apparent in the pictures is that the 42gr load had the cleanest holes through the target, the other loads were slightly more "ragged" with the 43gr load being particularly more so, does this indicate that the projectiles are "less stable" than the 42gr load, target mounting boards are faced with a very high density foam?

The difference in stability factor at slightly different speeds in the same barrel is essentially nothing. Barrel twist drives stability with velocity only playing a minor part. Your bullet in these loads has an SG of around 1.6 which is well above optimally stable. Once it is stable, more spin doesn't mean better. Until it's drastically overspun, it means nothing

Originally Posted by Zedrex

That makes sense and my question then is that if I understand correctly, distance to lands is a direct result of COAL adjustment, if I know my Max COAL (69.8mm) then this measurement puts my projectile just on the lands so my current COAL of 67.5mm puts me within the 0.100" - 0.030" window you mention?

You need to measure the OAL or CBTO of a cartridge that is touching the lands for your own rifle and bullet.

If you don't have the equipment available to do that, just seat it where it is and don't worry about it.

I am assuming you've taken that max COAL figure from the manual, not obtained it by measuring your chamber and this bullet.

Originally Posted by gimp

You need to measure the OAL or CBTO of a cartridge that is touching the lands for your own rifle and bullet.

If you don't have the equipment available to do that, just seat it where it is and don't worry about it.

Ah but I do worry lol, it seems there is a method to measure CBTO without a gauge by mounting a projectile in a case with a medium to light neck tension and then chambering the round which should have the lands push the projectile back into the case to give me a measurable CBTO, that needs verified by repeating that process a number of times to get a consistent CBTO within 0.001" and then I can with reasonable certainty load within the window?

Reference: https://bergerbullets.com/shoot-bett...coal-and-cbto/

CBTO is case base to ogive; its simply a way of measuring the length of a cartridge to a different reference point than the COAL.

There are a variety of methods to find your cartridge length to the lands, such as the one you mention. I personally find that method unreliable and finicky and prefer to use a Hornady gauge.

Originally Posted by Jaco Goosen

You've picked the one bullet I struggled to get to group in my Musgrave. I could never get the 95SST to group as well as the Noslers would. I went to the 87s in the end.

Maybe I just gave up to soon. But anyway, your 42gr group looks promising.

I would suggest playing around with seating depth to tighten the group.



I take it is a hunting rifle? What make/model?

This is a Franchi Horizon wearing a Burris Fulfield E1 scope and yep there may be room to tweak seating depth, this is an ongoing learning curve! It seems all rifles prefer different projectiles, I've heard lots of people getting good results with the SST and I chose it as it's one of the few projectiles with a flat base, which my .243 seems to prefer over BT's

Originally Posted by gimp

You need to measure the OAL or CBTO of a cartridge that is touching the lands for your own rifle and bullet.

If you don't have the equipment available to do that, just seat it where it is and don't worry about it.

I am assuming you've taken that max COAL figure from the manual, not obtained it by measuring your chamber and this bullet.

MAX COAL was measured rather than referenced but I didn't do the measuring, someone with far more experience and knowledge did

Or cleaning rod method...or my favourite. Forget the measuring stick completely. Set up seating die off existing loaded round and call it good. In theory if projectiles are SIMILAR shape the seating depth will also be similar as the seating stem will enguage at same diameter/ fatness of projectiles olgive/ curvey bit. If it fits in magazine and chambers without pressure or leaving projectiles in rifling( case comes out,powder all through action,air turns blue and more hair gets pulled out) I can call it good and leave it alone.

Beautiful rifle.

Thanks for the reply. Nothing wrong with the 95gr SSTs - they just did not work in my rifle.

Seeing the replies, it seems like you've managed to get a team of knowledgable reloaders involved. You'll be on your way before long.

Originally Posted by Jaco Goosen

Seeing the replies, it seems like you've managed to get a team of knowledgable reloaders involved. You'll be on your way before long.

either that or more confused than ever...lol