Thread: CBTO new projectile

Originally Posted by Moutere

The seating depth tool measures the distance from the base of the case to the lands. This datum's then used to measure OAL/CBTO using a comparator. This distance is specific to the rifle and surely not how the projectile interacts with this point.

The only variable is whether the comparator is the same size as the bore.

The Sinclair tool is more or lees the same as the Hornady tool, but is not calibre specific.

I'm just being lazy cause the gun cabinet is buried behind piles of crap at the moment and I didn't want to repeat the measurements.

Glad you made that point, different projo's are just that, different. To assume they be the same is not in the shooters best interest. Good luck with your tidy up, let us know what the difference was between the bullets.
I load ELDM's and Siera's (both 155 grain) they go to different specs on the comparator.

Please do, I'm interested. VLDs specifically are reputed to have precision issues with seating depth - the single load I've tried with them was 10rd into 0.6MOA at a totally random arbitrary depth & charge

Originally Posted by gimp

Please do, I'm interested. VLDs specifically are reputed to have precision issues with seating depth - the single load I've tried with them was 10rd into 0.6MOA at a totally random arbitrary depth & charge

I found with VLD's if you go to the recomended jump its all good, the biggest improvement to group sizes I got was from driving them hard.
Maybe I lucked in and maybe you did too @gimp, mind you I have always found the .308 easy to load for.

I bought some 105gr 6mm VLDs to test and see if I can identify any difference. I dunno why I keep doing this

Originally Posted by gimp

I bought some 105gr 6mm VLDs to test and see if I can identify any difference. I dunno why I keep doing this

Just admit it, you have an addiction

Originally Posted by johnd

Just admit it, you have an addiction

To building the understanding, not to actually testing loads

Ok @Kelton I loaded & shot some 105gr "hunting" VLDs from my 6mm GT. Granted the 6GT is a modern case specifically designed to be precise. However 1) I have to use the rifles I have and 2) I'm not sure why you'd select a cartridge that isn't known for precision if you want precision.

The hunting VLD was what I could get in stock.

I followed the Berger process https://bergerbullets.com/vld-making-shoot/

Found the lands at 1.980" CBTO

loaded 6rd each at 0.010", 0.050", 0.090", and 0.130" jump, with a random 34gr of 2208.

I also loaded 4 bonus rounds of the 0.050" jump load, as shooting these on the same target as the 2x 3rd groups would be more or less the same as my normal load selection approach.

Shot groups this morning, letting barrel cool (although it makes no difference). I shot 2x 3rd groups of each increment on different targets, with the exception of the 0.050" jump. For this load I shot both 3rd groups on the same target then added the bonus 4rd for a 10rd group.

Here is the results:

All targets


0.050 group 1 & 2



And the table of results


I don't see any obvious difference here. Taking my process of "load 10rd at 0.030-0.050 off, shoot, etc" gives me a predicted ø95 of 27.04mm(+ or - lets say 10%, so 24-30mm) centred about 0.2mrad right. Every single shot from the other seating depths falls comfortably within that circle. By my estimation it's a 0.8 - 1.0 MOA system. Exceptionally good for 8.5LB.


I have fired 28 of my 100x 105gr VLDs, I will take any suggestions and shoot any (reasonable) amount of any suggested load to verify. But what I'm seeing is that with this rifle, cartridge, bullet, powder, shooter combination - there doesn't look to be any meaningfully resolvable difference in precision at different seating depths, following the Berger method.

Originally Posted by gimp

Ok @Kelton I loaded & shot some 105gr "hunting" VLDs from my 6mm GT. Granted the 6GT is a modern case specifically designed to be precise. However 1) I have to use the rifles I have and 2) I'm not sure why you'd select a cartridge that isn't known for precision if you want precision.

The hunting VLD was what I could get in stock.

I followed the Berger process https://bergerbullets.com/vld-making-shoot/

Found the lands at 1.980" CBTO

loaded 6rd each at 0.010", 0.050", 0.090", and 0.130" jump, with a random 34gr of 2208.

I also loaded 4 bonus rounds of the 0.050" jump load, as shooting these on the same target as the 2x 3rd groups would be more or less the same as my normal load selection approach.

Shot groups this morning, letting barrel cool (although it makes no difference). I shot 2x 3rd groups of each increment on different targets, with the exception of the 0.050" jump. For this load I shot both 3rd groups on the same target then added the bonus 4rd for a 10rd group.

Here is the results:

All targets
Attachment 273453

0.050 group 1 & 2
Attachment 273454
Attachment 273455

And the table of results
Attachment 273456

I don't see any obvious difference here. Taking my process of "load 10rd at 0.030-0.050 off, shoot, etc" gives me a predicted ø95 of 27.04mm(+ or - lets say 10%, so 24-30mm) centred about 0.2mrad right. Every single shot from the other seating depths falls comfortably within that circle. By my estimation it's a 0.8 - 1.0 MOA system. Exceptionally good for 8.5LB.


I have fired 28 of my 100x 105gr VLDs, I will take any suggestions and shoot any (reasonable) amount of any suggested load to verify. But what I'm seeing is that with this rifle, cartridge, bullet, powder, shooter combination - there doesn't look to be any meaningfully resolvable difference in precision at different seating depths, following the Berger method.

Note that the "average" group size is not the group size of all 6 rd for each, it's just the mean of the 2x 3rd groups. I'll get a proper overlaid 6rd group for each another day

I bet if I overlaid all 28rd they'd make about a 0.9moa group centred about 0.2mrad right.

And for any combination of these components with my loading technique and gear I would predict an SD of 10, +-2, fps. If measured with enough shots to get a meaningful result.

Also also 34gr of 2208 is probably too hot for this particular bullet in my 6GT, published data is 36.6 max for a vapor trail 103 or 34.0 for a 107 SMK. The 0.236 barrel may not handle quite so much powder as a 0.237.

Cheers @gimp il have a read shortly iv also shot this morning was an educational trip re my 708 also shot saum 10 rounds of a random depth and 10 of what I had considered to be my best tested so far il get back once iv finished my jobs and post findings

Next is seated a lot deeper and this photo is at 5 rounds before the suppressor cooling and removal of the bush

This next one is the last string of 5 with the bush gone into the same target but marked with ballistic x its left me wanting to shoot some more with the bush gone though its level of accuracy hasn’t cost me an animal yet

Not much to see with the 7mm08 but being suppressed I was removing the can after 5 shots more or less to try and cool it quicker to reduce the mirage threw the scope shooting the notoriously fussy Nosler LRAB and when removing the second time I noticed how polished my barrel is from the suppressor bush so I shot the last 5 with the bush out and things took a turn for the better. I never faffed around to much with this rifle got it good enough for hunting which is is and just go hunting it’s left me wanting to do it again with the bush gone and see if it has really helped or if it was luck .


First 10 shots with can removed at 5 for 5 mins


Attachment 273482

Next is seated a lot deeper and this photo is at 5 rounds before the suppressor cooling and removal of the bush Attachment 273485

This next one is the last string of 5 with the bush gone into the same target but marked with ballistic x its left me wanting to shoot some more with the bush gone though its level of accuracy hasn’t cost me an animal yet Attachment 273488

Order jumped around their but I’m sure you’ll make sense of it neither of those were depths I’d shot before one closer to saami and one closer to mag max of 2,955