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Can you seat primers too deep? Without even trying


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Before anyone says anything, I did search on the subject. Rather than revive one of the several ancient threads, I decided to start a new one.

I just lightened the hammer on my 625JM. Since, I've fired 150 rounds with one light hit. Trigger looks to be breaking at 6 lbs. The light hit appeared to be from a primer seated too deeply. I do have an Apex competition firing pin installed, and I am using Federal primers.

I got on here and did a search. It seems that .007"-.012" below flush is ideal. I've just been leaning on the handle of my 650 to seat. I measured a bunch of primers and they're mostly around .014" below flush, with a few up to .018. Most people seem to be having more trouble with getting them deep enough, and I seem to have the opposite problem.

Anyway, I'm setting up to load my Nationals ammo, and got out my new Starline brass and some Federal Match primers, and decided to give the old Lee hand primer a try. With no extra pressure at all, just to feel the primer bottom, the hand tool is seating primers .015 below flush. If I squeeze it'll go .020.

Is any of this worth worrying about, or is it enough just to be sure the primers are seated solidly without considering depth?

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Yeah, you're overseating them. And yeah, you do have to worry about depth.

Don't lean on the handle. Give it this stroke: forward until you feel the primer start to engage, then a firm, medium-fast shove, like you're messing with a friend and mock-fighting, shoving his shoulder without any real ill intent. You should bounce away from it a bit, but not flex the reloader at all. When I get a good rhythm going I lean forward a few inches then shove off a few inches, over and over. My failures start at .004 and below and .014 and above.

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Thanks Matt. Maybe "lean" was too strong a word, I wouldn't say I'm flexing the loader at all. And the issue remains, with the hand primer I'm at .015-.017 just to feel it bottom with light pressure.

I'm going to go back and prime on the 650 but try to use less pressure, then shoot a bunch to test.

My ammo's always worked in my 1911s! :)

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I went through the same * learning * issues. You are over seating them, from what I've read .008 - .010 is ideal for a lightened action on a revolver. I had some issues with light strikes when I got to the .014 depth, no good.

Loading both 38 spl and 45 acp, It's definitely easier to over seat small pistol primers over large from what I've seen on my dillon 650.

I cant comment on your equipment, but on my progressive dillon I just give it a firm push forward, just a little tiny bit of muscle when seating. It'll take some trial and error and muscle memory of some test runs, measure the prime depth, adjust your *push* as necessary, and get into a groove. After a while you stop thinking about it and just do.

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If you have several brands of primers around, measure the depth of the cup on all - different brands, not individual primers - and see if there is any variance in the primer cup depths. If so, use the deepest cup brand and see how that works.

Also you might check the depth of the primer pocket on several brands of brass and see if there is any variance there.

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If you have several brands of primers around, measure the depth of the cup on all - different brands, not individual primers - and see if there is any variance in the primer cup depths. If so, use the deepest cup brand and see how that works.

Also you might check the depth of the primer pocket on several brands of brass and see if there is any variance there.

Steve, most of the revolver shooters are using Federal primers because they are easier to set off, so were kind of stuck with that dimension.

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Ok, makes sense. How about the primer cup depth on different brands of brass ??

Sure, probably a good idea. Most of the revolver shooters are probably using Federal, Starline or Winchester brass, not sure how much they vary in primer pocket depth. Alecmc has some good pics of flat well seated primers.

Good shooting with that Taurus at 25yrds, don't imagine you could shoot better with good vision.

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Thanks, getting new glasses - actually, new lenses with new prescription - next week. I'll give it another try. Unfortunately the range we usually shoot at can't shoot anything over .30 caliber on 50 or 100 due to a law suit so I can't shoot at any more than 25 yards with a .45.

This was in an agreement at court, so you can shoot a 7mm Weatherby mag or such, but not a .30 carbine. Typical. :surprise:

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Took some measurements. New Starline brass pocket depth is .129", and Federal LP match primers are .117-.118. So, with zero crushing, I'm at .011" deep already. Looks like Starline put Large Rifle pockets in this batch of brass for some reason. I'll have to measure other brands later.

On another note: Happy Easter everybody! Also it's my daughter's 10th birthday, so she's old enough to shoot at the local indoor range.

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Congratulations on your daughter being able to shoot at the range, also 10th birthday.

Maybe you could use LRPs in the brass, don't have any idea about the toughness of various brands of primer cups so might not work.

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Rifle primers would be too hard.

More data: it appears SAAMI spec is .118-.122 for pistol primer pocket depth, and .128-.132 for LR. I grabbed a handful of my well-used range brass, and pockets are as follows: Federal .127, WCC .123, Win .128, R-P .126. So while Starline's .129 seems to be out of spec, by no means is it alone.

The only other LP primer brand I have is CCI, and it measures .120, but that's not cup depth because the legs of the anvil protrude slightly.

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Well seated Federal Primers anyone having problems when using extended firing pins. Just bought a Lee Primer seater to push the primers a little deaper and using Apex long firing pin. Not having problems now just don't want to open a can of worms that doesn't need opening.

My 650 will easily seat .004 -.006 deep maybe I should stop there?

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Think you'll have better luck with the primers seated properly, anvil against bottom of primer pocket and let extended FP take care of the deeply seated primer. Otherwide you would be using some of the hammer force to fully seat the primer, which isn't conducive to proper ignition.

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I'm no technician but its seems to me that you've covered all the technical aspects of your problem thoroughly. To me, if you think the main problem is that your giving it to much "muscle" when seeting the primers, maybe you should just do it by hand vs. using the 650. Yes, you could get the job done with both, but I'm guessing you'd be less likely to "give it to much muscle" doing it by hand. Its just a thought anyway, take it for what its worth.

Edited by Dragon11
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The C&S XL firings are about .510-.511" as compaired to the Apex one you are using .495 from their web site. I have a C&S in my gun, load on a 650 and use Win brass for practice and R&P for match. I seat the primer on the first push after I fell the primer start to go into the cup. I let off the handle to neutral and push forward again more firmly at the end of the stroke. The onlly time I've had light stirkes is when the strain screw got loose. My primer look llike the pics that have been posted here several times.

My question is, If the primer is NOT at the bottom of the cup, Won't the hammer lose some momentum driving the primer to the bottom before it will ignite? If this is the case, would it not look like a light hit? Try running the cylinder around agin to the light hit and see if it goes off. I would think that if it does go off, the primer wasn't down far enough.

What to y'all think?

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Ok, makes sense. How about the primer cup depth on different brands of brass ??

Sure, probably a good idea. Most of the revolver shooters are probably using Federal, Starline or Winchester brass, not sure how much they vary in primer pocket depth. Alecmc has some good pics of flat well seated primers.

Good shooting with that Taurus at 25yrds, don't imagine you could shoot better with good vision.

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I dont have any issues with starline brass, in fact - I havent had any issues with any brass with federal primer depths.

More importantly then how hard you push are these points

  • Make sure your shell plate on your dillon is as low as it will go and still be able to spin.
  • Make sure your primer punch is screwed all the way in.
  • Make sure the the primer punch arm thinger that the punch hits to activate is adjusted all the way upward

Edited by alecmc
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Is any of this worth worrying about, or is it enough just to be sure the primers are seated solidly without considering depth?

I think it is. With Federal primers I can easily "overseat" using MFS, R-P and Starline 38 special brass using my 550. I can induce misfires almost at will using my Carmoized 67-6 with a factory firing pin. I segregate these headstamps and load everything else normally.

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My question is, If the primer is NOT at the bottom of the cup, Won't the hammer lose some momentum driving the primer to the bottom before it will ignite? If this is the case, would it not look like a light hit? Try running the cylinder around agin to the light hit and see if it goes off. I would think that if it does go off, the primer wasn't down far enough.

What to y'all think?

I think that's exactly correct. Measuring the depth of the primer won't mean much--unless you're using all identical brass with exactly consistent primer pocket depth from one piece to the next.

What really matters is consistently seating the primers against the bottom of the cup.

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I agree with Carmoney on the seating to the bottom of the cup. I make sure that I have a slight witness mark on the primer. With the practice I have been doing, not one misfire in 2,000 reloaded mixed cases. And I do mean mixed.

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Well, I loaded some of my deep-pocket Starline brass. This is all new brass, with pockets uniform in depth. I was careful not to crush the primers too much, and duplicated the gentle hand-seated depth of .015". Test firing yielded a dismal 30% light hits, FAR worse than my mixed range brass with its slightly shallower pockets. This was supposed to be my Nationals ammo. If I increase mainspring tension, will it compensate for too-deep primers? Should I try shortening the FP spring? I doubt I can get a new batch of brass at this point.

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I have had good luck seating primers using an old RCBS bench mounted priming tool. It gives me a better feel than even a hand held priming tool. Of course this means extra work in that you need to use you press to deprime and then add the step of priming offline from the rest of the reloading operation, so I save this method of priming for my match ammunition. I have never gone so far as to measure the depth of the seated primers, but may consider doing so just to get an idea as to how consistent my primers are seated. It will also be helpful to have a base to use for comparing those rounds that don't go bang.

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