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jlow
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Posted: 4/1/2011 8:48:44 AM EST
OK, I know that the max length according to SAAMI is 2.015” and recommended trim length is 2.005”. I also know that one reason you trim is to keep within SAAMI spec to avoid possible jamming of the neck into the bullet if my chamber is cut to SAAMI length, so this is a safety reason.

The other reason to trim is to keep the case neck length consistent from round to round i.e. to maintain even neck tension for greater consistency between rounds. So for that standpoint, I measured the case length of 100 of my new 308 Win brass that has already been FLR to see the range in length. You can see them in this Excel graph. So they range from a max of 2.0190” to a min of 2.0000” with an average of 2.0066”.



So now here is the question – if I trim to 0.01” below SAAMI which would be 2.005”, then they would certainly be safe, however, 34% of the cases will be shorter than 2.005”. I imagine that this would make their neck tension also different than the ones trimmed to 2.005”. So the question is what should I do? If I trim everyone to 2.000”, then it is likely that almost everyone of my 308 brass (500 pieces) will likely have the same length, but would the 2.000” length be too short? What would be the disadvantage of trimming them this short?
magnum_99
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Posted: 4/1/2011 8:58:58 AM EST
[Last Edit: 4/1/2011 9:00:36 AM EST by magnum_99]
That's a fancy graph. You obviously put a lot of work into that.

Guess what?

It's not going to matter.

Load them, and shoot them. Trim them to 2.005" when they exceed max length, which will probably happen in 3-5 loadings if you FLR. More if you neck size.

I only trim the cases that are longer than 2.015", and leave the others alone. I still get .5" groups or better out of my stock 700P.
7zero1
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Posted: 4/1/2011 9:04:46 AM EST
Originally Posted By jlow:
OK, I know that the max length according to SAAMI is 2.015” and recommended trim length is 2.005”. I also know that one reason you trim is to keep within SAAMI spec to avoid possible jamming of the neck into the bullet if my chamber is cut to SAAMI length, so this is a safety reason.

The other reason to trim is to keep the case neck length consistent from round to round i.e. to maintain even neck tension for greater consistency between rounds. So for that standpoint, I measured the case length of 100 of my new 308 Win brass that has already been FLR to see the range in length. You can see them in this Excel graph. So they range from a max of 2.0190” to a min of 2.0000” with an average of 2.0066”.

http://www.ijn.dreamhost.com/Photo/308.jpg

So now here is the question – if I trim to 0.01” below SAAMI which would be 2.005”, then they would certainly be safe, however, 34% of the cases will be shorter than 2.005”. I imagine that this would make their neck tension also different than the ones trimmed to 2.005”. So the question is what should I do? If I trim everyone to 2.000”, then it is likely that almost everyone of my 308 brass (500 pieces) will likely have the same length, but would the 2.000” length be too short? What would be the disadvantage of trimming them this short?


Sir, for much the reason you mention, ie: round to round consistancy, I always trim my resized .308 Win. cases to 2.012" which as you know is just under max. The trimmed cases will grow a bit when fired and resized again and I always trim them again after I resize them to reload again. That way I always have cases of the same length. I don't understand why you report a variation in the length of full length resized new unfired brass except to say that something isn't right. I find it difficult to believe you have almost .020" variation of case length. My guess is that you are distorting the brass with the expander ball of your resizing die when it is withdrawn from the interior of the case. 7zero1, out.

7zero1: "High power competition is all about doing your best, everyone else is there for your entertainment".
jhuggans
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Posted: 4/1/2011 9:15:34 AM EST
[Last Edit: 4/1/2011 9:17:17 AM EST by jhuggans]
Without you finding out the exact size of your chamber you'll never know where to trim to achieve maximum accuracy.

This is all pretty far out there though. Trim to specs, load, an move on.

Here is where you start to find that info out:
Cerrosafe Chamber Casting Alloy
jlow
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Posted: 4/1/2011 9:36:34 AM EST
Thanks for the responses.

Magnum_99, nothing fancy about the graph. I just measured, enter the data, sort from low to high and ask Excel to insert a bar graph, only takes a few seconds. Whether it matters all depends on what you are reloading for. For plinking and everyday accuracy, I would agree to trim to 2.005” and shoot them. However, if you are reloading for precision shooting for long distance (which is what I am interested in), then that is different – see 7zero1’s response.

7zero1 – I am not an expert in this area, thus the question. FWIW, I am using a new Forster Ultra 2-Die set and both the case (not shoulder) but also in the inside of the neck were lubed. But let’s just say that I am in fact distorting the brass with the expander ball of my resizing die when it is withdrawn from the interior of the case, would that not only increase the length of the neck and possibly account for the three pieces that turned out to be over 2.0150”? So discounting those, the range would still be between 2.000” to 2.0140”. I guess the question is what should I have found in terms of length distribution? I mean if you trim for the two reasons I mentioned and the length is 2.012”, then all of them must have started out greater or equal to 2.012”, but I am finding 86% of them shorter than that? Do you see why I am confused?

Jhuggans – yes, sizing to chamber length is yet another possibility, but at least for now, I am just happy to have consistent case length…. One step at a time?
jhuggans
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Posted: 4/1/2011 9:58:01 AM EST
If you're doing long range accuracy, then I say go ahead and do it. Not only will it give help you with your trim length but also the next, and possibly more important, piece of information; distance to lands. In the end, the bullet is seated to an COAL where it meets the lands. Trim length has more to do with how easily the cartridge will chamber, chamber pressure stability, easy ejection, etc.

Good info here for match bullets: Match Ammo Prep
jlow
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Posted: 4/1/2011 10:15:58 AM EST
Thanks jhuggans for the info and link! Yes, I am already doing some of this including seated to lands, but as it is with all good OCD reloaders, I am always trying to nip at the variables….
jlow
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Posted: 4/1/2011 1:51:37 PM EST
I would really appreciate some more feedback from the folks here.

From what 7zero1 said, it would appear that the length distribution I found i.e. 2.000” to 2.190” is unexpectedly wide. If that is true, then what is the norm? Without this answer, I cannot begin to figure out what went wrong.

The other thing that I still don’t have an answer to is assuming that I do want to trim all the brass to the same length, it looks like the longer the better (assuming under 2.015” of course). What is the advantage of the longer length? Is it higher neck tension? What would be the disadvantage of trimmer to something like 2.000” where all my brass would be the same length? What is too short?
CCW
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Posted: 4/1/2011 1:54:06 PM EST
[Last Edit: 4/1/2011 2:10:27 PM EST by CCW]
Originally Posted By jlow:
OK, I know that the max length according to SAAMI is 2.015” and recommended trim length is 2.005”. I also know that one reason you trim is to keep within SAAMI spec to avoid possible jamming of the neck into the bullet if my chamber is cut to SAAMI length, so this is a safety reason.

The other reason to trim is to keep the case neck length consistent from round to round i.e. to maintain even neck tension for greater consistency between rounds. So for that standpoint, I measured the case length of 100 of my new 308 Win brass that has already been FLR to see the range in length. You can see them in this Excel graph. So they range from a max of 2.0190” to a min of 2.0000” with an average of 2.0066”.

http://www.ijn.dreamhost.com/Photo/308.jpg

So now here is the question – if I trim to 0.01” below SAAMI which would be 2.005”, then they would certainly be safe, however, 34% of the cases will be shorter than 2.005”. I imagine that this would make their neck tension also different than the ones trimmed to 2.005”. So the question is what should I do? If I trim everyone to 2.000”, then it is likely that almost everyone of my 308 brass (500 pieces) will likely have the same length, but would the 2.000” length be too short? What would be the disadvantage of trimming them this short?


First, that is an excellent set of data. It also looks like a population that can yield a meaningful standard deviation. I hope you have the data arranged in Excel to use the built in Stats operators. For normal distribution (bell curve) you can say that plus or minus 3 STDs around the Avg. describe the 99.7% probability or confidence interval of range.

Anyway, there are only 3 over the 2.015. So, I would work the brass to move the average back to 2.005. That should bring everything back to below 2.015.

[ETA] changed numbers to fit text

As to neck tension, effects of holding bullet bearing length in the neck to a more precise value, will be lost in the noise of other variables that affect neck tension like neck material thickness tolerance, neck material hardness, neck diameter tolerance, bullet diameter tolerance, coefficient of friction between the brass and copper, etc.
" America is at that awkward stage in life. It's too late to work within the system, but too early to shoot the bastards."
ChrisGarrett
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Posted: 4/1/2011 2:52:55 PM EST
I can trim to ~2.018" on my Savage 10FP LE2b, even longer now that it has 3000 rounds down the pipe.

I prefer to go longer, because I find that I get a better gas seal with longer necks, as long as I'm not pinching anything off.

Chris
jlow
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Posted: 4/1/2011 3:37:32 PM EST
Thanks CCW! I was always a biologist who was weak in stats and having professional statisticians on staff at our disposal did not help to strengthen that skill – LOL! So with that caveat in mind, I did some analysis on the data set and here it is using Excel’s build in Stats operations. Does not look too normal a distribution to my untrained eye…. Have you looked at this before and seen anything similar/different?



Thanks for the advice as to going for 2.005”. I made some calculations to see the percent difference in grip length between a cartridge that is 2.000” in length vs. one that is 2.005” in length and this is what I got:

SMK MK175 gr. bullet = 1.25”
COAL = 2.800”
Cartridge = 2.005”
Length of bullet in round = (2.005+1.25)-2.800”=0.455”
Length of SMK that is the boat tail = 0.180” (approx).
Length of SMK in round that can grip =0.455-0.180 = 0.275”
Length of cartridge neck = 0.27” (approx)
Length of actual SMK that grips the neck = 0.27”
Grip length difference between a 2.000” and 2.005” cartridge = (0.005/0.27)x100 = 1.9%

So the grip length difference between a cartridge that is 2.000” and one that is 2.005” i.e. the greatest extreme after my trimming would be around 1.9%. How much difference would that make in total neck tension I am not sure because it depends on how much error can be contributed by the variables you name i.e. neck material thickness, hardness, diameter tolerance etc. All of which I don’t know. I mean the other option which is what I was thinking of would be to trim everything down to 2.000” in which case all the rounds will have a similar if lower grip length?

ChrisGarrett - I would certainly agreed going longer is better (<2.025”), but I am just struggling with the idea that if I go as long as 2.018”, I would basically not be able to use 98% of my brass - at least initially.
CCW
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Posted: 4/1/2011 4:39:17 PM EST
[Last Edit: 4/1/2011 4:55:47 PM EST by CCW]
Originally Posted By jlow:
Thanks CCW! I was always a biologist who was weak in stats and having professional statisticians on staff at our disposal did not help to strengthen that skill – LOL! So with that caveat in mind, I did some analysis on the data set and here it is using Excel’s build in Stats operations. Does not look too normal a distribution to my untrained eye…. Have you looked at this before and seen anything similar/different?

http://www.ijn.dreamhost.com/Photo/308a.jpg

Thanks for the advice as to going for 2.005”. I made some calculations to see the percent difference in grip length between a cartridge that is 2.000” in length vs. one that is 2.005” in length and this is what I got:

SMK MK175 gr. bullet = 1.25”
COAL = 2.800”
Cartridge = 2.005”
Length of bullet in round = (2.005+1.25)-2.800”=0.455”
Length of SMK that is the boat tail = 0.180” (approx).
Length of SMK in round that can grip =0.455-0.180 = 0.275”
Length of cartridge neck = 0.27” (approx)
Length of actual SMK that grips the neck = 0.27”
Grip length difference between a 2.000” and 2.005” cartridge = (0.005/0.27)x100 = 1.9%

So the grip length difference between a cartridge that is 2.000” and one that is 2.005” i.e. the greatest extreme after my trimming would be around 1.9%. How much difference would that make in total neck tension I am not sure because it depends on how much error can be contributed by the variables you name i.e. neck material thickness, hardness, diameter tolerance etc. All of which I don’t know. I mean the other option which is what I was thinking of would be to trim everything down to 2.000” in which case all the rounds will have a similar if lower grip length?

ChrisGarrett - I would certainly agreed going longer is better (<2.025”), but I am just struggling with the idea that if I go as long as 2.018”, I would basically not be able to use 98% of my brass - at least initially.


OK, here for comparison is Quickload Bullet library based data:

SMK 175gn Length = 1.266, COAL 2.800, trim = 2.005, seating depth = 0.471, shank seating depth (bearing) 0.286
–––––––––––––––––––––––––––––––– –trim = 2.006, seating depth = 0.472,––––––––––––––––––––––––––0.287
and so forth.

Also, try changing the granularity of the bars (smallest division) on the horizontal scale of the plot to see if it looks any better. For true test data your distribution is not near as bad as some collections I have called bell curve.

[ETA] OK, so your full population extremes based on your sample will be 2.0178 down to 1.9952. You might want to get a little sharper on the full length sizer operation, like 7Zero1 suggests.
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helotaxi
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Posted: 4/1/2011 4:48:40 PM EST
The trim length is always 0.010" shorter than the max. What no one ever talks about is the SAAMI min case length which is 0.020" shorter than the max. By trimming the cases to 2.000" you're still within SAAMI specs and all the cases are the same.
jlow
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Posted: 4/1/2011 5:00:15 PM EST
CCW - Thanks! Yes, there is going to be some variability measuring off the melpat, and me guessing the boat tail, and neck length (even with a pair of digital calipers), but the actual magnitude of the difference is about the same i.e. slightly less than 2% (1.8% for Quickload vs. 1.9% my Q&D) between 2.000” and 2.005”.

You are right about the granularity, but Excel unfortunately does not give you a choice or at least I have not found one – drives me crazy!

Helotaxi – thanks for the SAAMI min case length – that is indeed good to know! Looks like I might be going that route!
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Posted: 4/1/2011 5:01:33 PM EST
The process of trimming to 2.000 has its own set of tolerances. I have the RCBS trimpro that references off of the case head surface, for trimming. The best I can do for a batch set up is +/-.003. IMO, the SAAMI numbers sometimes tries to anticipate the kind of process variation one is going to generate and sets the number accordingly to keep the operator out of trouble.
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jlow
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Posted: 4/1/2011 5:13:05 PM EST
Originally Posted By CCW:
The process of trimming to 2.000 has its own set of tolerances. I have the RCBS trimpro that references off of the case head surface, for trimming. The best I can do for a batch set up is +/-.003. IMO, the SAAMI numbers sometimes tries to anticipate the kind of process variation one is going to generate and sets the number accordingly to keep the operator out of trouble.


Yea, I can see that is another potential problem. I have the Wilson which is supposed to be pretty good although it’s been a while since I measure its reproducibility. Will start off at the 2.005” length and see what I can get before I run with the rest.

Thanks a lot for the great advice!
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Posted: 4/1/2011 9:05:27 PM EST


: Which of the variables within a reloader's control have the greatest
: impact on rifle accuracy?

Primer uniformity is probably at the top of the list. This is about 60%
of accuracy. But it matters more as the range gets longer. Non-uniform
primers mean a greater velocity spread which means the vertical stringing
at the target will be greater.

Case length doesn't matter much. As long as the mouth is square with
the case axis, case length can vary 10 to 15 thousandths of an inch and
accuracy will still be excellent.


Necks should be reasonably uniform in wall thickness, like no more than
a .0005-in. variance. This helps keep the necks straight when the cases
are resized. And they should not be sized too much. If they are, the
bullet seating pressure will be too high; too much tension will cause a
higher spread in velocity due to the normal variable incountered as each
bullet needs a different amount of force to push it out of the cases. If
neck tension is minimum, the spread of the force to push the bullet out
gets lower resulting in a lower velocity spread.

Case weight variance plays a somewhat important part. Heavier cases have
less volume, hence slightly higher pressures and velocities for the same
set of components. A 1% spread in case weight is typically good enough
for best accuracy. Any more than that doesn't seem to make any difference.

Primer pockets and flash holes should be uniform. Pocket depth needs to
be consistant so each primer has the same pre-load; more uniform ignition.
Flash holes need to be the same diameter so the same flame properties are
transferred to the powder. But these two things only make about a 1/16th
MOA difference in group size.

Case body wall thickness helps too. They shouldn't have a spread of more
than about .003-in. for 30 caliber cartridges; .002-in. for 22 and 24
caliber ones. But again, this only has a small effect, like about 1/8th
MOA or a tad less.

Powder charge weight variance can also cause more velocity spread. But
just as important is powder type and charge weight. It's been my experience
that for a given powder, there's two charge weights that tend to produce
the best accuracy; one at about maximum, and one several grains less. A
chronograph is needed to check the velocity spread to determine this.
Charges with no more than a tenth grain variance is plenty good enough.
Primers typically cause a greater difference in velocity spread than a
tenth of a grain of powder.

Bullet seating depth also has an effect on accuracy. Best accuracy is
usually going to happen when the bullet contacts the lands. A lot of folks
are reluctant to do this as they claim max pressures will be higher. Well,
they're right, but cutting the powder charge a few tenths of a grain will
reduce that pressure.

Bullet concentricity is important, too. In a .308 Win. for example, if
the bullet runout is more than about .003-in., the groups will start to
open up a bit. If it's more than about .007-in., they probably straighten
out as they enter the leade; I've not seen any more accuracy reduction with
such rounds. The more a bullet has to jump to the lands, the straighter it
needs to be. But bullets that are seated out far enough to be pushed back
into the case a few thousandths as the bolt is closed can have a bit more
runout and be accurate as compared to bullets that jump a ways to the lands.
A square case mouth probably does more for letting the bullets seat straight
than most other things.

It's easy to get good cases, bullets, powder and tools to assemble them.
But the hardest thing is getting good, uniform primers. Primers vary
quite a bit across several lots; some much more than others. For ranges
of 200 yards or less, there's not much difference between primers, like
about 1/4 MOA in the groups they can produce for the most part. When
longer ranges are used, primer uniformity becomes more important. A recent
batch of match-grade ammo (about 300,000 rounds) was loaded from the same
lots of cases, bullets and powder. Neck tension was quite uniform. Primer
pockets were not uniformed nor were flash holes drilled to the same size.
Bullet runout peaked at about .004-in. But several lots of primers were
used. Some loaded lots of this ammo would shoot 2.8-in., 20-shot groups
at 600 yards. Other lots would shoot 20-in. 20-shot groups at the same
range. The difference was in the primer lots; some were very uniform,
others were not.

BB


Bottom line: YOU get to spend whatever time YOU want to.......on whatever YOU think is gonna help.

Aloha, Mark



"Guns don't kill people......the Government does."

Dale Dribble
jlow
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Posted: 4/4/2011 2:44:56 PM EST
Sorry for the slow response but pretty much spend all of the last two days working.

The thing that bugs me the most about reloading is that there is so much unknown as to what contributes to accuracy and the worst part is that nothing appears to be nailed down….. Mark, you say the primers contributes 60%, that to me is a startling number, not saying it is true or false but just startling. Is there some study to back those numbers up?

Of the ones you pointed out, I am trying to deal with case length, not dealing with neck thickness (yet), already sort brass by weight, flash hole uniformed, primer pocket depth (not yet done), powder charge weight by hand to 0.04gr accuracy, seating to lands (check), concentricity check/adjusted (check).

I started to trim my Win brass and it is going well. The Wilson trimmer appears to be able to trim reproducibly to within one thousands which I think is really good. The down side is that I have not had too much luck motorizing the process since all my hand drills appears to run with poor concentricity and so they wobble too much. I originally thought that it was the adapter that Wilson sells for this but I found that this problem only exist with my two hand drills but not my drill press. Will have to work to set this puppy up to use the drill press…. I have seen this done before with other trimmers but does anyone have a good design for the Wilson?
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Posted: 4/5/2011 2:14:33 AM EST
[Last Edit: 4/5/2011 2:14:56 AM EST by hrt4me]
Originally Posted By jlow:
Thanks CCW! I was always a biologist who was weak in stats and having professional statisticians on staff at our disposal did not help to strengthen that skill – LOL! So with that caveat in mind, I did some analysis on the data set and here it is using Excel’s build in Stats operations. Does not look too normal a distribution to my untrained eye…. Have you looked at this before and seen anything similar/different?



Looks to me pretty much like a standard bell curve
jlow
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Posted: 4/5/2011 3:43:41 AM EST
fefu23
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max length and only size half of the neck
ma96782
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[Last Edit: 4/8/2011 2:10:40 AM EST by ma96782]
The quote wasn't ME. But, since you asked about the primers............

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Accuracy via microprocessor control ?
Organization: Hewlett-Packard Fort Collins Site

J. Spencer (J.M.Spencer@newcastle.ac.uk) wrote in response to my comments
preceded by : #:

: #In reality, primers are more responsible
: #for velocity variations than powder
: #is.

: How, and why?

Because of the way the priming mixture is prepared and put in pellet moulds
then put in cups, anviled and sealed.

: If the manufacturers can get powder to burn consistently,
: and we can get consistent charges so that their effect is minimal, why
: can't the manufacturers produce consistent primers?

Primer mixture creation and processing is almost a `black magic' operation.
Few folks can uniformly put the putty-like substance in a totally
homogeneous form that's very uniformly mixed.

: And a related question: how do know
: that it *is* the primers, how has it been measured?

Measured by velocity standard deviation, using various primer makes/types
with different powder charges show that primers have the greatest effect
on uniforming velocities.

: That is one variable which we can eliminate, can't we?

Yes. Seat the bullet to where it pushes back into the case when it jams
against the leade as the bolt is closed. That uniforms bullet jump as
leade/throat wear lengthens this part of the barrel. You may need to
increase the powder charge weight by about one-tenth of a grain every
1000 or so rounds to keep velocity at the same level; otherwise it will
drop several fps as the leade/throat dimension gets greater.

: #Some powders tend to cause more muzzle velocity variations than others.
: #Extruded powder tends to be the most uniform; both benchrest and highpower
: #competitors favor this type over ball powder for this reason.

: It's just a bugger that it doesn't meter as well, eh Bart? :-)

Yes, but a charge weight spread of up to two-tenths of a grain doesn't seem
to matter much.

: #When the most mild and uniform primers are used, muzzle velocity standard
: #deviations can be kept to 5 to 7 fps. That's a muzzle velocity spread
: #of about 16 to 22 fps; darn well good enough for even the most demanding
: #shooter.

: Really? I'm genuinely surprised at that (not to imply I'm skeptical,
: just surprised). Which primers do you recommend (for 243 and 30-06 if
: it's relevant)?

If you can afford 'em, use RWS 5341 primers. Otherwise, Remington 9-1/2
standards are also very mild and work very well indeed.

BB


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: [RELOADING] What makes Bench Rest Primers special?
Organization: Hewlett-Packard Fort Collins Site

`Benchrest' primers are typically more uniform in their ignition
characteristics than `standard' primers. The process of mixing the
lead styphnate (the explosive), glass frit (the microscopic glass
particles that act as micro-anvils for the styphnate to compress
against) and a couple of other things is a kind of `black magic.'
About two quarts of this priming mixture is mixed together for each
lot of primers. Getting the mixture homogenous (uniform percentages)
throughout the gooey mixture is difficult. This mixture is spread
on a plate with little recesses in it that are the shape of the
primer pellet. Getting exactly the same amount in each little round,
deep hole is also a type of `black magic.' The mixture is much like
putty and a large putty-knife like tool is used to force the mixture
into each hole where it's left to dry. Then the dried primer pellets
are punched out and put in primer cups, topped with a sealer, and
finally the three-legged anvil is pressed in place.

Interestingly enough, some folks do a better job of mixing and spreading
the mixture than others. Within each lot of several thousand primers,
there's bound to be differences in the ignition characteristics from one
primer to the next. As more care is needed to make `uniform' primers,
they usually cost more.

By uniformity, I mean the consistancy of velocity they produce. Velocity
tests of the bullet is about the best test of primer uniformity. Some
very uniform lots of primers will produce a velocity spread of only 15 fps.
At the other end of the spectrum are primers that produce velocity spreads
of 100 fps, or more. Some folks have tested primer uniformity by shooting
BBs from a primed case (no powder) in a 17 caliber barrel; primers that
produce low velocity spreads with BBs do the same with powder and bullets.
Uniform primers tend to produce more uniform pressure curves, too.

Alas, not all the `benchrest' primers are as good as they're marketed to
be. Many times a standard primer will be more uniform than benchrest ones.
And some makes of benchrest primers aren't as uniform as another make of
standard primer. Even some standard primer brands are more uniform than
any benchrest brand. Some benchrest primers are hotter than their standard
versions for the same make.

In many accuracy situations, a milder, standard primer will produce better
groups than a hotter benchrest primer.

BB


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Accuracy via microprocessor control ?
Organization: Hewlett-Packard Fort Collins Site

Randy Howard (jrh@mustang.us.dell.com) wrote:

: I'm curious what you mean by "mild"?

By mild, I mean primers that produce just enough heat to properly ignite
the powder. As primer brisance (heat/energy) gets higher, it also gets
less repeatable from primer to primer. Competitive shooters have found
that the milder primers give both better velocity uniformity and accuracy.
But they aren't after every last fps of speed nor ft/lb of muzzle energy;
just putting all fired shots in as small a group as possible.

: A lot of reloading articles I have
: read seem to indicate that it's better to use magnum primers in all
: rifle cartridges (starting with a lower powder charge than normal and
: working up of course) because they will result in more consistent ignition.

This is true with most ball powders, the type most folks tend to use in
rifles because they meter very uniform charge weights from measures. But
when accuracy is the objective, extruded powders are used and so are mild
primers such as Federal 205M, RWS small rifle, Rem. 7-1/2 BR small rifle
primers. The mildest large rifle primers are Remington 9-1/2 standards and
RWS5341s and they are also the most uniform of large rifle primers. Some
lots of Federal 210Ms are very uniform and others are not; these are not very
mild primers.

But then virtually all folks writing reloading articles for magazines have
no real knowledge of what they are talking about in the first place. When
you consider that most of 'em don't have what it takes to shoot 1/10th MOA
groups at 100 yards nor 6-in. groups at 1000 yards, how in the heck can one
consider their information worthwhile regarding accuracy. They put
enthusiasm and egos in print; not reality. But they get paid for it in
spite of not having any skill or knowledge in putting together a valid set
of tests to produce statistically significant results, then publish those
results in an unbiased manner to boot.

: It sounds like you feel the opposite is true.

So do hundreds of others who have observed the results of lots of primer
makes and types being used by the hundreds of thousands of rounds fired.

BB


Mind you...........that it's an opinion.

Aloha, Mark


ma96782
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Posted: 4/8/2011 3:22:26 AM EST
[Last Edit: 4/8/2011 3:31:21 AM EST by ma96782]
About that 60% number..........maybe it came from here?



Primers

I have come to the conclusion that primers account for 60% of accuracy. When you think about how a primer shoots up through your case and ignites your powder charge, you can realize how it doesn’t take very much variation in primer flash to change the way it ignites the powder charge.

During the last few years I have found that CCI was by far the worst primer, emphasizing as I said earlier that these are my own personal opinions. I have talked with other people around the country and they seem to confirm what I have observed about CCI’s hang firing. On a scale of one to ten, with ten being the best, I rate Remington 4-8, Federal 5-8, Winchester 4-6 and RWS 5-8, when you can find them. You will occasionally find one lot of primers from any manufacturer that rates a 10. What you must do is buy a 1000 primers and test them. If they work real well at 600 yards keep that lot of primers for 600 yards. If they are not satisfactory at 600, use them at short range or in practice since it doesn’t make as big a difference at short range.

Let me tell you about a test I ran that shows how important primers are. One time I loaded up several lots of primers purchased at different times. I must have had 15 or 20 different lots. I tested them at 100 yards using a bench rest gun. They grouped anywhere from a ¼” to 2”. The same bullet, same case, same powder charge were used, the only thing that varied was the primer. Primers can actually make that much difference.

I have also seen primers that would produce ¼” groups at 100 yards, but they were giving a velocity spread of 75 to 80 fps. on a chronograph. At 100 yards, they appeared to shoot fine, but at 600 yards they wouldn’t hold elevation. So if it is possible, you should also check your primers for velocity variation.

When you load primers in your brass, you should handle the primers in such a way that you don’t rub your fingers or any oily substance over the anvil of the primer. Any foreign substance you put on that primer is not going to help assure uniform ignition. Primers should be seated in the bottom of the primer pocket properly and firmly.

Primers should be stored in airtight containers. Humidity can dramatically change the way a primer functions. I know one shooter who had a bunch of bad primers. When he put them in a can with some desiccant and dried them out and then tried them again they worked real well. When he tried drying them even more, they didn’t work at all. This would indicate that there is a moisture content that is ideal, but I cannot say what the percentage is. Until we have that answer, just try to keep your primer storage as uniform as you can. I think an ammo can is the best place.

In addition, I think you ought to keep your loaded rounds sealed up too. I don’t think you can take a lot of loaded ammunition, place it up on the shelf and expect it to be the same six months from now. Two things are going to happen. The primer can change and if you haven’t washed and cleaned the brass properly a chemical reaction between the bullet and case is going to occur and the bullet may begin to stick to the neck of the case. I have even seen rounds that were loaded and stored over a period of time which, when they were fired, had the whole neck come out with the bullet. That is the reason I believe in cleaning cases.


The quote above was written by: Middleton Tompkins

And...........more of his PEARLS...........

Q: What kind of primer do you recommend?

MT: I think you stand a better chance of getting a good lot of Federal benchrest primers than any other brand. To select primers you have to get a lot of primers and take them out and try them. That's the only way you can be sure.

Q: Do you clean the primer pockets?

MT: I imagine there is some merit in trying to clean primer pockets and gauge the flash hole for uniformity, but I personally don't do anything with the primer pocket or flash hole of my cases. I think the little bit of change you are going to make is not worth spending the time.

So.....maybe some out there are asking, "Who is Middleton Tompkins?"

http://clubs.odcmp.com/cgi-bin/distinguishedStory.cgi?distID=12089

OK....OK....things may have changed and he may have changed his mind about some things since then.

Aloha, Mark
jlow
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Posted: 4/8/2011 3:41:39 AM EST
Thanks Mark for putting this out – very interesting reading.

A few thing in it makes me wonder. One is this idea of how the testing was done to “finger” the primers as candidate for the 60% variability. They say “Measured by velocity standard deviation, using various primer makes/types with different powder charges show that primers have the greatest effect
on uniforming velocities.”

That all sounds find and good but it is all predicated on the assumption that in those tests, the testers have the ability to hold all other variables such as case variability, powder variability, bullet variability all completely constant so that the changes in results can be attributed to the primers. At least as far as I can see from my limited experience in reloading, holding the variability in any one of those three players is incredibly difficult if not impossible unless one is willing to testing with huge number of samples.
jhuggans
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Posted: 4/8/2011 4:36:52 AM EST
What distances are you planning on shooting?
jlow
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Posted: 4/8/2011 5:24:48 AM EST
600 yards