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Seating primers

 
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  #1  
Old 07-25-2006, 02:42 AM
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Seating primers

I have 2 queries:
1) A lot of reloaders use a device (either hand held or table mounted) to seat primers.With some hand held tools people say they seat primers to a depth that they recognise by "feel". In the other types the seating depth of the primers may be adjusted to a specific depth.These devices mostly retain the rim of the cartridge either in a shell holder or jaw system so the primer may be seated with pressure being applied by the seating plunger to the primer, the rim acting as resistance. Thus the rim is a sort of a base line.
In some makes of brass I have measured the rim thickness and it seems to vary quite a lot in thickness in a case lot of brass.
Since the "base line" varies in thickness, this would indicate that the primer seating depth also varies. How do you guys remedy this? Turn the ctg rims in a lathe to similar thickness?
My co-ax press has a primer seater which eliminates the seating depth problem, but it is much slower without a primer feed, so I prefer something with a primer feed.
Is seating a primer by "feel" good enough?
2)The primer pockets in brass grows larger with time and shots, requiring less pressure to seat the primers. Does this play a role in loading really accurate rounds? I've read on this forum of reloaders who keep on using their brass till the primers "fall out"
Is consistent primer seating pressure a prerequisite for an accurate round, assuming that the rifle is capable of delivering?
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  #2  
Old 07-26-2006, 08:51 AM
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Re: Seating primers

I too have pointed out the problem of placing a stop on a priming device... even when using uniformed primerpockets, due to the fact that the measurements we are controlling in most cases is the face of the primer to the front of the rim, not the critical dimension, anvil to bottom of the primer pocket. I think feel is the way to go when seating primers due simply to the variances in primer height, primer pocket depth (if not uniformed) and rim thicknesses. However, I firmly believe that you should gauge primer pocket expansion with a measuring tool, not a primer.

As to consistancy of primer seating tension mattering to a load... When I develop a load, I load 3-5 cases to neck splits, untill I see that there is too much primerpocket expansion at a given level, or I decide that the load will be mild enough on brass to last a long time AKA I get bored. I do this for several reasons. It lets me see if the load likes FL sizing or neck sizing, I can see how much the brass grows through firing and sizing, I can get a feel for what pressure im at by primer pocket expansion, and what the pressure is doing to the brass in general. In doing this, I can relate both precision, and POI of the load with both used brass, and new. At different times, and different loads in different rifles, ive seen some that don't change at all, some that shoot better with many times fired brass, and some that are at their best the first go round. That being said, ive batched some of the many fired cases with my regular brass after they survived enough loadings in instances that the poi stays the same, and ive never notticed that tight primer pockets shoot to a different POI than fresh brass. Thats kinda a round-about way to answer your question, but no, I haven't found it to matter. Seat the primer to the bottom of the pocket, measure expansion on a few cases each time you load a batch, and be happy!
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  #3  
Old 07-26-2006, 10:06 PM
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Re: Seating primers

I use a K&M primer tool w/dial indicator. With it I can get the recommended crush of .002"
It does this by doing a simultaneous measure of pocket depth to primer thickness(To Zero indicator). Then you can seat to .004 past this zero, and I've found that the primer will usually back out .002 within 10 minutes or so.
With every shell I set this crush as measured. I've looked away to see how close I can get by feel, and surprisingly I get pretty close. Especially w/Lapua brass and plenty of practice.
It's nice reading the number though and knowing my primers are seated as accurately as my bullets.

Primers are so strong, and such a random element, that it probably doesn't even matter. I've fired 20 primed cases at a mirror in the dark to somewhat see whats going on. Many shots were clearly different than others. But all more than needed to ignite confined powder(overkill). I think thats whats going on. [img]/ubbthreads/images/graemlins/smirk.gif[/img]
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Old 07-26-2006, 11:14 PM
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Re: Seating primers

Thomas,
I am with ab. I use a hand held primer insert tool. There is a feel with it, and if you pass the "feel stop" you will have gone too far. I have loaded like this and never had any problems.
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Old 07-27-2006, 12:48 AM
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Re: Seating primers

Thanks guys, it's nice to be able to bounce queries of you lot and get decent answers, I appreciate it a lot.
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  #6  
Old 07-27-2006, 08:57 AM
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Re: Seating primers

Ken's tool is no doubt the best, superior even to the sinclair model... but its price is a bit higher than most would be willing to spend... at least for their initial tool. I definately agree on getting very close on seating by feel, and thats why I suggest it. Just like everything else, theres the best way (K&M) the really good way (sinclair or lee tool by feel) and the best we can afford given that this is a hobby for most of us, and thats usually either a lee tool, or a modified RCBS tool seating by feel.
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