Major Factor in Primer Seating Depth Variability

[Clearlight]

“But wait there’s more” um, why are you presenting this as if this is some tv shopping commercial for some cheap gimmick? Is this some kind of page outta the Primal Rights advertising scheme or something?

Na, just sharing empirical evidence of a relatively meaningless statistical sample of one unique combination of components that happens to work. You watch TV?

 

[Dolomite]

How much is 1/10 MOA worth?

 

[Tokay444]

.1

 

[Sniper King 2020]

Na, just sharing empirical evidence of a relatively meaningless statistical sample of one unique combination of components that happens to work. You watch TV?

I try to stay away from the TV. I like your message…never underestimate any combination of things that could pleasantly surprise you. This is why I write down the load for fouler loads because rest assured, an odd combo of something that you thought wouldn’t shoot and just be useful for fouling all of a sudden dots right up on target. I don’t know why I get surprised by it anymore

 

[Sniper King 2020]

I have been following this for a while with primers and seating ect and I wondered the same thing. @Bryan Zolnikov , did you say it was norma brass you used? Also I guess number of firings would have some effect too or maybe not? Lapua vs ADG vs Norma will probably provide some variation due to the rim thickness and variation among each lot.

That's kind of the issue though right? Anything that uses a shell holder yo keep the case from moving when the primer is pushed in will have the variation of the rim of that lot of brass. Spacing measured off the head of the case seems to be a more consistent way to do though probably a lot harder way to actually hold the brass in place and get good results. It see.s the Lee system with a hold down rod does do it well though so.......

Just my 2 cents

Couple things: yes, it was a lot of Norma brass from ~6 years ago. I tried their newer lots and they do not have much variance in rim thickness so I think I just got a “bad lot.”

Yes, a tool that does not introduce rim thickness as a variable does much better than the ones that do. I just posted results from the old Sinclair hand priming tool and it showed the same minimal variance as the Lee ACP.

 

[Sniper King 2020]

I’ve been following Bench Addict on Patreon and he is putting out data on primer and cup height for certain primers and brass. Seems like the allegedly higher quality and more expensive primers have minimal height variation (this includes anvil protrusion from the cup). With that data and mine, seems like a reasonable method to remove a whole lot of variance in primer seating is to:
1. Ream the primer pockets to uniform depths. This operation could also shave off any large variation in pocket width;
2. Use primers with minimal height variance;
3. Calculate pocket depth, primer size, and assume cup size is uniform to get your desired depth/anvil compression when seating; and then
4. Use a priming system that seats to the depth you want with minimal variance. I have found that tools that are not brass rim thickness dependent are the most consistent. Or, alternatively, you could measure rim thickness and cull out piece that vary by whatever tolerance you are willing to have.

This is a “current state” practice that should yield great consistency. Bench Addict is introducing ideas like sorting primers for height, etc that may yield more consistency but I’m not sure by how much given the already low variance in overall height. That would be a test to put in target. Anecdotally, I’ve found the method I described in this post to yield great results and I’m not sure how much more precision can be had with say sorting primer heights by the .0005”. We will see though.

 

[secondofangle2]

The only setting tool I've ever seen that uses the bottom of the case as a datum is the M2 Precision fore 50 cases.

Alan, I use that M2 Precision seater for my 50 BMG and it’s design definitely eliminates the variability everyone is talking about in this thread. I was hoping someone would bring it up.

It works just like the Sinclair hand priming tool in Brian‘s one video. You have to spin it down, so it pushes the case head against the bottom of the priming die, making rim thickness irrelevant. When I get home tomorrow from my 35 hour New Year’s shift, I’ll post pictures of how it works.