Handloading the z-grom bullet

[Axxxel]

I've read several threads on how the z-grom factory ammo is decent and affordable, but I've never actually seen any feedback from somebody who has successfully loaded it.

I've got a couple of hundred of these bullets, looking for a decent recipe for .308 Winchester.

Judging by the Vihtavuori recipe for the 170 gr Naturalis N558, with a max of 42,7 grains of N150, I'm thinking of going to the range with a load of 42,0 and one with 42,5.

Other recipes include 44,8 grains N150 max for the TTSX 168 GR, and 43,7 gr N150 max for the 175 gr LRX.

Has anybody here loaded the z-grom?

 

[Brave Echo Niner]

As with any reloading, the general rule is to work up from low to high.
I would be starting at the low load of the Naturalis, then working up in 0.3 gn increments, watching for pressure signs to establish the safe charge range.

From that, if you record the velocity data of this incremental increase, you see flat spots in the velocity between two or more charges, which is where you have a velocity node. This is where variations in charge weight between these charges will not cause large fluctuations in velocity.

Example: 150 Grain in .308, the higher velocity node appears more stable, as the results are incredibly similar despite the change in charge weight.


I would then load a group of a charge inside each velocity node and test them, as often these tend to also correspond with good grouping.
Subsequently if you then want to further improve grouping, varying the seating depth will allow you to further refine the load.


This method I have found works universally regardless of bullet type, material, calibre etc.

Ben

 

[cooperjb1308]

I have just reloaded some this week after getting some from Krank.
They seem to be accurate, haven’t had them out on any game yet, I’m going off the nosler 168gr E-Tip load data as it’s a longer bullet in a comparable weight.
41.5Gr of Lovex D073.4 seems to be a sweet spot. 2.785 COAL.
This worked in my rifle and there was a fairly accurate node at around 38Gr of powder but wanted a bit of extra speed as I wasn’t sure on how the expansion worked on these bullets.

 

[sauer]

So Ben
….
Your graph above you would load at 44.3grns say ( between 44.1 & 44.4 ish ) on flat spot ?

Then if groups go for refine on seating depth ?
Paul

 

[Brave Echo Niner]

So Ben
….
Your graph above you would load at 44.3grns say ( between 44.1 & 44.4 ish ) on flat spot ?

Then if groups go for refine on seating depth ?
Paul

Yes exactly - the load I went with was indeed 44.3 grains, it gave acceptable ES/SD, but not optimal accuracy (~0.75-1MOA).
I then rough tweaked seating depth (0 thou, 10 thou and 20 thou deeper) and that load will now quite happily shoot 1/2MOA.

As that rifle is a close range woodland rifle I didn’t go much further to be honest, if I wanted to squeeze a bit more of out it I would have done more testing around optimal seating depth.

 

[Axxxel]

I'm not going to do a very elaborate load process with this bullet. It's supposed to be an economy load, as I said. Might try 2-3 charge weights and switch out thepowder for a second set of tries if I'm underperforming on my first try. Seating depth is prettymuch set as I'm going to be shooting this cartridge from a variety of rifles, including a semi auto with a tight magazine.

The E-tip might be a good starter, as it does not have those cuts around the cylinder of the bullet, that the Barnes bullets do.

 

[Feugh]

So Ben
….
Your graph above you would load at 44.3grns say ( between 44.1 & 44.4 ish ) on flat spot ?

Then if groups go for refine on seating depth ?
Paul

I’ve used this exact methodology and came out with a recipe which produced a very good group. However, I have since listened to a Hornady podcast and watched a YouTube video by Winning in the Wind which shook my faith in the method. Apparently if one repeats the initial velocity test another few times then the average is a straight line, where velocity increases with powder charge. No flat spots.
Where does that leave me? Well, it leaves me unsure how I would work up a load in the future. Some top ballisticians have simplified to the extent that they they increase the charge until they see signs of pressure, back off by 0.5gn to 1.0gn and leave it at that! Seems disappointingly easy to me.

 

[nun_hunter]

I’ve used this exact methodology and came out with a recipe which produced a very good group. However, I have since listened to a Hornady podcast and watched a YouTube video by Winning in the Wind which shook my faith in the method. Apparently if one repeats the initial velocity test another few times then the average is a straight line, where velocity increases with powder charge. No flat spots.
Where does that leave me? Well, it leaves me unsure how I would work up a load in the future. Some top ballisticians have simplified to the extent that they they increase the charge until they see signs of pressure, back off by 0.5gn to 1.0gn and leave it at that! Seems disappointingly easy to me.

I usually shoot going up the ladder then wait and come back down then plot both ladders and look for flat spots. This has usually given me pretty consistent flat spots to start from.

I can see that if you did it enough times then it would average out to be a pretty straight line though

 

[kenbro]

I’ve used this exact methodology and came out with a recipe which produced a very good group. However, I have since listened to a Hornady podcast and watched a YouTube video by Winning in the Wind which shook my faith in the method. Apparently if one repeats the initial velocity test another few times then the average is a straight line, where velocity increases with powder charge. No flat spots.
Where does that leave me? Well, it leaves me unsure how I would work up a load in the future. Some top ballisticians have simplified to the extent that they they increase the charge until they see signs of pressure, back off by 0.5gn to 1.0gn and leave it at that! Seems disappointingly easy

I’ve used this exact methodology and came out with a recipe which produced a very good group. However, I have since listened to a Hornady podcast and watched a YouTube video by Winning in the Wind which shook my faith in the method. Apparently if one repeats the initial velocity test another few times then the average is a straight line, where velocity increases with powder charge. No flat spots.
Where does that leave me? Well, it leaves me unsure how I would work up a load in the future. Some top ballisticians have simplified to the extent that they they increase the charge until they see signs of pressure, back off by 0.5gn to 1.0gn and leave it at that! Seems disappointingly easy to me.

In the past when developing loads I’ve found that I reached diminishing returns (Velocity wise) before finding any signs of too high a pressure.
Ken.

 

[Axxxel]

I also think it is a lot harder to dependably identify pressure signs, than it is sometimes described.

I'm pretty sure that when you've picked a bullet and a powder, you've done most of the choosing that you can do as far as finding a load that is good for accuracy. Oh I must add that both case brand and seating depth seem to have made a significant difference for me. Lapua brass is better than mixed batches of GGG. When it comes to charge weight, I usually keep some margin to what I consider safe but try to maximize my load within that limit.

With the z-grom I just don't know what to go off. I read the vihtahuori load data, and for example the max load for 168 gr MTAC is 42,0 while for the 168 gr TTSX it's 44,8. Thats a decent difference!

In addition, the Vv data is regarded as somewhat on the light side. I think I'll start with a set of 42,0 and a set of 42,5. I don't think I'll be able to detect any difference in the fired cases.