Proper Primer Seating

[Baer45]

Is the proper way to seat a primer by “feel” to stop when the primer hits bottom or after it hits bottom and there is a slight “crush”?

 

[jimcasey01]

My understanding is a very slight crush.

 

[243winxb]

http://forum.accurateshooter.com/threads/primer-seating-depth.3936969/page-5

A RCBS Ram prime unit is the best way to fully seat primers for me.

After primer fully seats, a little extra pressure will not hurt. But the seating plunger should never mark or indent the primer.

A crushed primer, like in photo, will still fire.

Photo from link. post 82 at link.

 

[6MMsteve]

I quit depth reaming my pockets a few yrs ago..I went a little extreme because of ignorance on my part...until I joined Acc Shooter I done a lot of backwards stuff..I seen the light...I seat mine till they stop with a smidgen more that's it

 

[243winxb]

SAAMI

 

[jepp2]

it hits bottom and there is a slight “crush”?

What you are trying to do, is to have the anvil compress the priming mixture pellet. This makes it more sensitive to the impact from the firing pin strike. So you want to "compress" the compound, not "crush" the body.

You don't mention what you are using to seat your primers with.

I uniform all my primer pockets when I am preparing the brass the first time. You don't know how bad some are until you start cutting them to a consistent depth with a square corner at the bottom. Once they are uniform, I seat the primers with a hand priming tool (have used Lee for many years, but converted to the 21'st Century tool about 2 years ago). A hand priming tool gives you very good feel when seating the primers. And you can measure the depth past flush with your calipers.

 

[garandman]

My method... Hand seat primers using a handtool not a bench press (too much leverage. Exception: my Dillon 550C for pistol / 300BLK) just till they bottom out (no "crush") Crushing detonates primers. Any crush *might* deform the primer anvil and *might* cause malfunction. Primer face s/b seated slightly below the face of the case head.

I've just never seen any value seating beyond the full length of the primer pocket.

 

[Baer45]

Thanks for all of the tips and info..I think I have it down now...after loading for so many years on a 1050/550 this art is lost on me!

 

[Straightshooter1]

I uniform primer pockets on all my brass (even after each firing not only to clean the pockets) and I uniform them to .130. My primers measure .128. I use my Forser CoAx press to seat my primers as it sets the primers in at a consistent depth where they sit at .004 below the base giving me .002 of crush. This is just one part of "precision" loading and may not be necessary for various types of shooting.

I don't really know how much benefit this gives me, if any, but at least by having it so consistent, I feel I can ignore this part of reloading as contributing to any of my adverse shooting results.

 

[Pawnee Bill]

Too much pressure = Bang!! Scares hell out of you. Ask me how I know this.

 

[mikecr]

I set 2thou crush for Feds/Wins/Rems, 4thou for CCIs.
This into cut pockets, using the indicated K&M, which accounts for both pocket depth and primer height simultaneously.

 

[fyrewall]

The K&M tool.

The depth of primer pockets can be reasonably controlled, probably to .001 (+-) but what about the primers that might be pushed into place by a priming tool set for a predetermined depth?

Would variations in primer height affect the degree of primer crushing if a certain tool was adjusted/programmed to shove the primer into the primer pocket at a predetermined depth.

How much variation could be expected in a brick of 1,000 primers.

I played around with this and came up with:

13 Federal Premium AR Small Rifle Match Primers were measured from cup top to lowest anvil protrusion. The average (not rounded) was .1228, extreme spread was .0050. Messing around with numbers I think 95 % of some 1,000 primers could measure a high average of .124 and a low average of .122.

At his point I get real confused - should I seat the primers at a certain depth hoping the desired crush fit will occur or should I seat them by feel knowing that height variations might be in the order of .005 with an expected high average of .124 and a low average of .122. Would the K&M tool indicate when a determined crush was achieved taking into consideration the depth of the primer pocket and primer height (length from top of cup to bottom of anvil(s)? Would individual inspections of primers be warranted to look for crooked or uncentered anvils or any other defects?

I think careful case prep including uniform primer pocket depth would be important but would stop short of machining a conical shape at the bottom of the primer pocket. I did not measure any other primers (yet).

 

[dmoran]

@fyrewall
The K&M Primer Gage takes into account the height of each primer and its measured relationship to the amount it's then seated.
Here's a YouTube on how they work and are used:

Also, only using a sample size of 13 primers (1.3% of 1000) is a very small sample for probability and to base estimations from.
Even the measurements from say 50 primers (5% of 1000) would be a small sample - IMO, but a lot more probable then only from 13.
Just saying.....

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[fyrewall]

@ Donovan Moran

Yes 13/1000 = 1.3 % but that tiny sample has shown a .005 X spread in primer height. I am making an assumption that the height values (like columns in .001 increments) would fit under a bell shaped curve with 95% of the height values between .122 and .124. Increasing the sample size from 13 to 50 will slightly change these values but not much if the standard deviation (square root of variance) remains about the same as expected because Federal makes good primers. Going up from 13 to 50 samples would decrease the distribution from the mean from 2.179 to 2.009, each times the estimated standard deviation of the sampled means, plus or minus- like from directly under the top of the curve left & right.

I only have 40 Fed ARM primers but I have 150 Rem 7 1/2's and 1,000's of others and I could do 50. Measuring 50 is nothing.

Thank you for your speedy response - learning new stuff every day.

 

[dmoran]

..... Measuring 50 is nothing.....

Totally agree.... hence, why I wondered making statistical assessments to 1000 primers from only 13 measured.

Personally I weigh and measure segregate every primer.
On a note: while not spot on correlation, the weights and heights often trend fairly linearly.

PS... corrected my 1.3% typo (my bad).

 

[STOMP442]

I used to use the lee hand priming tool for years and wore more than one of them out. I have since switched to the Bald Eagle priming press and I will never go back to anything else. It gives you the ability to adjust seating depth on your primers in .002" increments and makes things very consistent. Its a small press so it still gives you plenty of feel when seating a primer so you can set it up however you like. The only thing I don't like about it is that you have to feed it one at a time. Over time I have developed a pretty good rhythm and can prime fairly quickly with it. It's one of those pieces of equipment that if it ever breaks I will immediately order a new one.

 

[fyrewall]

Totally agree.... hence, why I wondered making statistical assessments to 1000 primers from only 13 measured.

Personally I weigh and measure segregate every primer.
On a note: while not spot on correlation, the weights and heights often trend fairly linearly.

PS... corrected my 1.3% typo (my bad).

I just had to measure 50 but I looked at CCI 41's because I use them in my .20P, .204R, 5.56 AR and 6.5X47 Lapua. Then I went onto the same box of 100 and measured another 13.

Sample size 50, SD .0011, Estimated true high mean .122, estimated true low mean .122, mean .1219
Sample size 13, SD .0015, Estimated true high mean .123, estimated true low mean .121, mean .1217
The X Spread for both 50 & 13 count samples was .005 - in future priming I will measure 5 out of every 50 I load looking for primers shorter than .119 and longer than .124.
Stuff for both was real close.

I use a press mounted Lee priming tool, like one at a time. With these consistent measurements I don't anticipate any problems using the cheap Lee priming tool to seat primers by feel - it only allows the primer to be pushed into the pocket a limited depth. For my needs, priming right from the box should work out as these primers are very consistent. But I had to play around with the data. The bigger file is the 50 sample size.

Thank you for looking at this.

 

[dmoran]

@fyrewall
I'm a LR-BR guy, and the occasional "odd ducks" is why I will always measure, weigh, and depth seat my primers.
Culprit primers have proven to create flyer's (scenario's tested by many). One errant shot at a BR match can take you right out of it, and hurt your finish. And is also why, statistics and trends to components, have little value to me (every single one matters).

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[fyrewall]

@fyrewall
I'm a LR-BR guy, and the occasional "odd ducks" is why I will always measure, weigh, and depth seat my primers.
Culprit primers have proven to create flyer's (scenario's tested by many). One errant shot at a BR match can take you right out of it, and hurt your finish. And is also why, statistics and trends to components, have little value to me (everyone single one matters).

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I would agree, because running a bunch of stats does not eliminate that bad round that could screw up a success.

What I like and use the stats for, is to provide guidance on component selection and assembly. The stat stuff is a start to selection. Should I be considering a buy of a certain component I would run some stats on it to see what I could expect on a buy of 1,000 more of some item - like how many could be out of spec. Should I dig into a box of 100 and find 18 wako, I might assume the probability of serious problems in a big amount of like 1,000. Weighing and measuring would result in many culls. I would also match my assembly methods to the use of the component.

No argument from here (varmint guy, me) about anybody finding the 4 or 5 bad ones out of several hundred that could screw your day up.

 

[Shoebox]

Too much pressure = Bang!! Scares hell out of you. Ask me how I know this.

I usually firm press after bottom out, might rethink that now !!
Frightening thought !!