Measuring Primer Depth with Calipers

[243winxb]

My RCBS has same to measure depth.

 

[243winxb]

How do you know you're seating to the bottom of the pocket when seating by feel?

RCBS Ram Prime on a Rock Chucker works well, by feel.

 

[Webster]

How do you know you're seating to the bottom of the pocket when seating by feel? OK, that you're getting very good results with the way you're setting them, but . . . you really don't know you're seating to the bottom, huh?

I question this because, a couple years ago I read a study that actually tested how seating by feel got primers to the bottom. . . or not. It looked at several different people using different tools seating their primers by feel. As it turned out, sometimes the primers were indeed seated to the bottom and lots of times they were not near as close as thought. It was inconsistent in terms of being on the bottom or not. This was done by taking detailed measurements. The study did not try to determine the effectiveness on velocity, accuracy or precision, just about how far primers were actually being seated. I found it a fascinating report.

What's fascinating about a test that has nothing to do with accuracy. It just shows that measuring things isn’t an exact process. The study didn't prove that measuring and achieving a very small variation has anything to do with how the rifle performs. Personal skills are far more important than a 1 or 2 thou variation in primer seating depth. How do you measure or determine personal skills. Are you even aware of bench techniques you need to work on?

 

[Straightshooter1]

Good question, I’ve had several seaters that I could not tell exactly what was going on. I had to use a lot of force and hope it was good, but with the 21st century I can feel the anvil touch followed by the primer making full contact, and that’s what is IMO the most important factor.
My K&M was not that sensitive nor was any of the bench/ ram seaters I’ve owned.

I think ideally, the pic shows where it's thought where seating at the "bottom" is. When the primer cup height is .118" (like CCI-200's) and the large primer pocket is .127" deep, the primer is going to be .009" below flush when seated that way. Or even .010" below flush if using Fed 200's. Take SRP's pockets that are .120" deep using primers with cups that are .109" tall, that would be .011" below flush. Do people really seat their primers that deep when seating by feel? And, isn't that a lot of crush going from a primer with an over all height of .121" to .109" when at the bottom of pocket (e.g. your illustration) an awful lot of crush?

It's been my understanding that .003 to .004" of crush is recommended (crush being the amount the anvil is pushed into the primer cup). And to do that, is the bottom of the pocket that's pushing the anvil into the primer cup. Or have I misunderstood something all this time?

When I seat my primers, it's been my objective to seat my primers with .003 to .004" of crush. My 21st Century seater, being adjustable, does are decent job of doing that for me as I use its ability for a hard stop. My ACP does a better job and more consistent (it's adjustable too).

When I used to seat by feel I noticed something in the fired primer pockets. Most of the primer pocket bottoms were completely covered by the black carbon, but some of them would have parts of the bottom not covered in carbon. This indicated some kind of inconsistency to me. It appeared to me that those with pieces of the bottom not covered in carbon was due to the anvil sitting firmly at the bottom during ignition. I thought, maybe it's just the primer itself not moving in the pocket as much as the others. I wonder if you or anyone else around here have taken noticed of that kind of thing?

I decided to do a little experiment, and that's when I got the 21st Century primer seater (besides, I liked the idea of it being a lot easier on my old hands). So, I measured everything and seated at batch of cartridges with the primers having .003" - .004" of crush. After firing the cartridges and inspecting the bottom of the primer pockets, non of pocket bottoms were completely covered in carbon, which indicated to me that the anvils were definitely up against the pocket's bottom. Here's some fired cases from last weekend that show you what I'm referring to (and yeah, I do clean my primer pockets of any carbon when I process them):



BTW: I'm not trying to convince anyone that seating by feel is a bad thing or that it inherently doesn't work well. Obviously, it works just fine for many or most people. I guess my point is to know and understand what you're actually doing rather than just guessing. . . . much like I used to do when annealing.

 

[Steel Mover]

Sinclair made a primer depth dial type guage. I tested it for the IHMSA News and decided a better solution for me was the CH chamber style trimmer to square the new brass base, then to cut the primer pockets uniform with a CH pocket uniformer cutter, to make all pockets the same size and same depth.