I was reading this article last night and found it informative and thought that I would share. It is a couple of years old but I think it is still relevant. It is an American article and talks about their powders etc.
Based on an article by John Barsness - GUNS magazine pg 26 May 2009. [JB, formerly of Handloader is one of the most qualified gunwriters when it comes to primers and reloading in general]
Information from the Speer #14, Hornady #7, Nosler#6, and Lyman #49 reloading manuals, Alliant and Accurate Arms data.
Additional Information from James Calhoon - “Primers and Pressure” Varmint Hunter Magazine, October, 1995
Hopefully this explains a bit more about, not only primers in general, but specific characteristics that can aid a reloader in choosing the optimum sparkplug. Pertinent information will be added to this section when more information becomes available.
Primers come in different strengths, technically known as “brisance,” a word defined as “the shattering effect of a high explosive.”
Primer brisance mostly depends on the length of the flame that leaps out of the flash-hole after the firing pin whacks the primer cup. This flame can also be manipulated to last a little longer, by adding tiny particles of other flammable material to the priming compound. These differences really can effect not just accuracy but pressure.
For instance, in a very small rifle cartridge such as the .22 Hornet, a “hotter” primer might start to dislodge the bullet before the powder really gets going. Instead of a relatively gentle, slowly accelerating push, the bullet gets cruelly hit hard. This is why some Hornet fans use small pistol primers, with much milder brisance than small rifle primers.
Really huge rifle cases such as the biggest Weatherbys, Remington Ultra Mags, and older British African cartridges require a lot of very slow-burning powder to operate at all. Slower-burning powders are normally more difficult to ignite, and a bigger flame of longer duration helps, especially in cooler weather. The first “magnum” primer, the Federal 215 was designed for this very purpose. Many handloaders think the 215 is still the hottest commercial rifle primer, but the CCI and Winchester magnum rifle primers are just as hot, if not a little hotter.
Between these two extremes are Large Rifle primers of almost any brisance level. Remington and CCI primers tend to be the mildest “standard” primers and Winchesters the hottest (the reason that Winchester never had a magnum rifle LR primer until recently), with Federals somewhere between. Deciding which to use depends not only on the size of the case but the powder.
How fast a powder burns depends not only on granule size (bigger granules have more relative surface area) but on exterior coatings. Extruded powders, such as relatively small-grained 4895 or large-grained H-4831 depend mostly on granule size to control burning rate. Ball powders don’t vary much in granule size, so depend mostly on relatively flame-resistant exterior coatings to control burning rate. By definition, these coatings make ball powders harder to ignite.
For example, in the 30-06, IMR 4895 is very easy to ignite, one reason it’s often suggested for reduced loads down to 2/3 of a case’s capacity. We’ll probably get the very best accuracy from a mild primer such as the CCI 200.
To make the 30-06 zip however, we might try Ramshot Big Game. The Ramshot ball powders burn cleaner than most ball powders, but they also require more flame. Winchester Large Rifle primers are the hottest “standard” rifle primer and often perform very well with Ramshot powders, but if they don’t definitely try a magnum primer. This can often result in smaller groups.
Something else to remember is that competition rifle shooters often favor mild primers i.e. primers that produce just enough heat to properly ignite the powder. They feel that as primer brisance gets higher, it also gets less repeatable from primer to primer. Another train of thought is that the powder is ignited a tad more gently. When this happens, the front slope of the pressure curve is less steep. Which means the bullet is pushed a tad more gently into the rifling which tends to deform it less. Whatever the scientific reason, competitive rifle shooters seem to feel that the milder primers give both better velocity uniformity and accuracy.
The same principles also applies to handgun cases. You might find that magnum primers aren’t good for milder loads, especially with cast bullets for some reason or another (Elmer Keith claimed that the hot flame tended to slightly melt the base of the bullet - no way of knowing if that is true.) Whatever the case, often using a standard pistol primer can reduce group size with milder or cast loads.
On the other hand, magnum primers are almost always recommended for magnum loads, especially if hard-to-ignite ball powders like W296, or its H-110 twin, are used. In fact, magnum pistol primers were developed for the large case revolver magnums like the .357, .41, and .44 Magnums. They seldom are needed for standard autoloader rounds or standards like the .38 Special.
Some powder manufacturers recommend standard pistol primers with certain of their powders even in magnum pistol loads. Alliant 2400 is one where the use of magnum primers is strongly discouraged, and another is Accurate Arms, which recommends standard pistol primers with their handgun powders, including #9, unless “they provide better accuracy in your firearm.”
There also is an unusual situation that should be considered when deciding whether to use standard or magnum primers with ball powders that is pointed out in the Speer manual: Powder manufacturers may state that their propellents do not require magnum primers. This is generally true at maximum safe pressure levels. But Speer’s ballistic testing fully explores propellent behavior over the usable range of charge weights. They often found that a particular propellent works fine with standard CCI primers at the maximum safe pressure. However it may not consistently ignite with lower charge weights. In the lower pressure regimes typical of “starting loads” they commonly saw increased extremes of pressure and velocity. Some ball powders ignited by standard CCI primers will even produce short hang-fires–called “click-bangs” for obvious reasons–at start load levels but not at maximum safe pressure. In those cases the use of magnum CCI primers to insure performance over the range of charge weights is recommended (or perhaps a switch to a hotter standard primer such as the Winchester WLR).
So as you can see, picking the right primer brisance can be very important and can give you optimum accuracy and consistent performance. Fortunately for us there are primers of every brisance level in every category of primer, whether it be standard or magnum.
Different primers have different cup thicknesses. You can see the importance of cup thickness when primers are considered for semiautomatic rifles that have free-floating firing pins. This topic is discussed in greater detail in the post “MILSPEC PRIMERS FOR SEMI-AUTOS FAQ AND INFO” that follows the primer chart.
Handgun primers have thinner cups than rifle primers, making them easier to ignite with the typically weaker firing pin fall of handguns. Small Pistol primer cups are .017" thick, while Large Pistol primer cups are .020" thick. This is the reason using handgun primers in .22 Hornet rifle loads sometimes results in pierced primers in some guns. Obviously their substitution in the high pressure .223 Remington would not be a good idea.
Even the same type of primers from different manufacturers can have different cup thickness. Federal primers tend to have thinner cups than Winchester, Remington and CCI primers. On occasion this can be handy. Some revolver trigger and action lightening jobs may result in a lighter hammer fall that results in not all the primers going off. A switch to Federal pistol primers can make the load 100% again. The same thing can happen in cold weather with some “modern” bolt actions with light, fast firing pins. These are supposed to whack primers with the same approximate energy as an old-fashioned 98 Mauser strike, but under some adverse conditions they can occasionally use a little help. Federal primers can provide that help.
With Remington small rifle primers, the 6 ½ primer has a thin cup and is not recommended for higher pressure rounds like the common .223 Remington. It was intended for the .22 Hornet. When Remington introduced their .17 Remington round in 1971 they found that the 6 ½ primer was not suitable to the high-pressure .17. The 7 ½ BR primer was developed for this reason. According to Remington, the 7 ½ has a 25% greater cup thickness and they state on their web site: “In rifle cartridges, the 6-1/2 small rifle primer should not be used in the 17 Remington, 222 Remington or the 223 Remington. The 7-1/2 BR is the proper small rifle primer for these rounds.”
CCI/Speer Technical Services says: “The CCI 400 primer does have a thinner cup bottom than CCI 450, #41 or BR4 primers… [with] the CCI #41 primer… there is more ‘distance’ between the tip of the anvil and the bottom of the cup.” so that is their AR15 recommendation, although it seems like there are no complaints with using the BR4 and 450 primers by AR15 shooters and reloaders, in general. The #41 just gives you a little more safety margin for free-floating firing pins and would be the best choice for commercial reloaders who have no control over the rifles their .223 ammo is used in.
Another factor which determines the strength of a primer cup is the work hardened state of the brass used to make the primer cup. They are made with cartridge brass (70% copper, 30% zinc), which can vary from 46,000 psi, soft, to 76,000 psi tensile strength when fully hardened. Manufacturers specify to their brass suppliers the hardness of brass desired. It is possible that a primer manufacturer could choose a harder brass in order to keep material thickness down and reduce costs. Winchester WSR primers are somewhat thin, yet seem to be resistant to slam-fires and this is likely due to this hardness factor.
Large rifle primers all appear to have the same cup thickness of .027", no matter what the type.
This also affects pressure tolerance. Cases that utilize small rifle primers and operate at moderate pressures(40,000 psi) should use CCI 400, Federal 200, Rem 6 1/2, or Win WSR. Such cases include 22 CCM, 22 Hornet and the 218 Bee. These primers can also used in handguns such as the 9mm., 357, etc. Other cases that use the small rifle primer can use the above primers only if moderate loads are used. Keep to the lower end of reloading recommendations.
Cases that utilize Small Rifle primers and operate at higher pressures (55,000 psi) should use CCI 450, CCI BR4, Fed 205 and Rem 7 1/2 etc.
MATCH or BENCH REST PRIMERS
The difference between match primers and standard primers is the degree of testing and quality control used in their making. Hornady reports that in their research that match-grade primers performed very, very consistently from load to load as measured in their pressure tests. CCI states that Benchrest cups and anvils are selected for exceptional uniformity. During the assembly operation, the operator who meters the primer mix into the cups (or “charger”) is chosen from the most experienced workers with an outstanding record of consistency. The BR line runs at a little slower pace to provide time for extra inspection.
STORING YOUR PRIMERS
Primers can be damaged by extreme heat, cold, and humidity. Therefore proper storage is necessary. We have seen primer shortages and therefore runs on primers by people stocking up for the future. What would be the use of having 20k primers if you don’t store them properly and they deteriorate?
Heat dries out the priming compound making it brittle and subject to disintegration during the seating process, causing a misfire. Further, the primer can still detonate if you try to disassemble misfired rounds and punch out the “bad” primer. That is one reason that de-priming “live” primers is discouraged. High humidity can cause the priming compound to be too wet to detonate properly as well. Therefore you should take pains to store primers in a cool, dry place. No garages, attics, sheds, or damp basements. Desiccant in the larger container that holds your primer boxes is probably a good idea if it is humid where you live.
Metal ammo cans are popular for storing various items like ammo and brass among reloaders. However they should not be used to store your primers in (or your powder as well). If anything sets off those primers (or lights off the powder), the metal can just adds shrapnel. Of course you shouldn’t store primers and powder together for obvious reason.
There are watertight plastic ammo cans like MTM’s Sportsman’s Dry Box [#SDB-0] or their military-sized (AC30C & AC50C caliber) O-ring sealed plastic ammo cans available, or you could use some type of wooden box etc. that would be a better choice than the usual G.I. steel ammo can for your primer storage.
PRIMER CHART & REFERENCE GUIDE
Small Handgun Standard .017" cup thickness
Federal 100 - Has a soft cup - good to use if hammer strike is light.
Federal 100M - Match version of above
Magtech PR-SPC - Lead-free “Clean Range” primer for indoor ranges etc.
Remington 1 ½
Wolf Small Pistol SP - brass cup
Small Handgun Magnum .017" cup thickness
CCI 550 See Note 1 at the bottom of page
Federal 200M - Match version of above
Remington 5 ½
Wolf Small Pistol Magnum SPM - brass cup
Large Handgun Standard .020" cup thickness
Federal 150 - Has a thinner cup
Remington 2 ½
Wolf Large Pistol LP - brass cup
Large Handgun Magnum .020" cup thickness
Wolf Large Pistol Magnum LPM - brass cup
Small Rifle Standard
CCI 400 -thin .020" cup, not recommended for AR15 use by CCI/Speer. Good for .22 Hornet, .30 Carbine. See Note 1 at the bottom of the page
CCI BR4 - match primer with a thicker .025" cup.
Federal 205 - Mil-Spec cup thickness according to Federal - okay for 5.56mm. .0225" cup thickness.
Federal 205M - same as the 205 but the match version.
Magtech PR-SR - .025" cup thickness (not much feedback yet on this new primer as to AR15 suitability but with the same cup thickness as the Rem 7 1/2 it looks good so far)
Remington 6 ½ - thin .020" cup, intended for older, lower pressure rounds Remington says do not use for the .223 Rem or other similar pressure rounds. Good for .22 Hornet, .30 Carbine.
Remington 7 ½ BR - A match or “bench rest” primer. Lyman & Nosler classify this primer as a Standard. Remington says the compound is the same as the 6 1/2 but with a thicker .025" cup.
Winchester WSR - some piercing issues noted when changed from silver to brass cup. Cup thickness is a bit thinner at .021". Most say they are good to go for the AR15 despite that, probably because of the hardness of the cup. Some feel they are less resistant to higher pressures.
Wolf Small Rifle SR - soft, sensitive copper cup, not recommended for AR15/military rifle use or high pressure rounds.
Small Rifle Magnum
CCI 450 - same thicker .025" cup as the BR4 and #41.
CCI #41 - commercial version of the fully-qualified DOD primer for use in U.S. military ammo. With this primer there is more ‘distance’ between the tip of the anvil and the bottom of the cup than with other CCI SR primers. .025" thick cup. Same primer mix as CCI 450.
Remington 7 ½ BR - A match or “bench rest” primer. Hornady, Handloads.com, and Chuck Hawks classify this primer as a Magnum, differing from other sources that classify it as a Standard. .025" cup thickness.
Wolf Small Rifle Magnum SRM - hard, less sensitive brass cup intended for AR15/military rifle and high pressure rounds.
Wolf Small Rifle 223 SR223 - “This is the newest primer available in the Wolf line. It is ever so slightly hotter than the small rifle magnum primer and it comes with a brass colored thick cup. This primer can be used in place of the SRM primer or used when a different powder is used that is hard to ignite.”
Large Rifle Standard
CCI 200 - mild in brisance. Hard enough for use in semi-automatics.
CCI BR2 - same as the 200 but the match version. Hard enough for use in semi-automatics.
Federal 210 - medium brisance between CCI/Remington & Winchester. Do not use in semi-automatics.
Federal 210M - match version of the above primer. Do not use in semi-automatics.
Remington 9 ½ - mild in brisance.
Winchester WLR - the hottest standard primer. Hard enough for use in semi-automatics.
Wolf Large Rifle LR - all brass - Used by noted match shooter David Tubbs who says: “Be sure they are seated into the case - if not they can be hard to ignite. Russian primers use a different sinoxide compound (closer to the European type), which, in my testing, consistently delivers better extreme spreads over Federal…” Hard enough for use in semi-automatics.
Large Rifle Magnum
CCI #34 - commercial version of the fully-qualified DOD primer for use in U.S. military ammo.
Federal 215 - original magnum primer
Remington 9 ½ M - mildest magnum primer.
Wolf Large Rifle Magnum LRM - all brass
CCI #35 - commercial version of the fully-qualified DOD primer for use in U.S. military ammo.
Primers recommended for use in .223 Rem/5.56 semiautomatic rifle loads:
CCI #41, 450, BR4 (#41 & 450 good with ball powder)
Federal 205, 205M
Remington 7 1/2 BR (good with ball powder)
Winchester WSR (good with ball powder)
Wolf SRM (good with ball powder)
Wolf SR223 (hotter than SRM - great with ball powder)
Primers recommended for use in .308 Win/7.62x51/7.62x39 semiautomatic rifle loads:
CCI #34, 200, BR2, CCI 250
Winchester WLR, WLRM (good with ball powder)
NOTE 1: According to Speer/CCI Technical Services - Both the CCI 550 Small Pistol Magnum and CCI 400 Small Rifle primers are identical in size. Both primers use the same cup metal and share the same cup thickness. Both primers use the same primer compound formula and same amount of primer compound. They can be used interchangeably.
MILSPEC PRIMERS FOR SEMI-AUTOS FAQ AND INFO
THERE IS A RE-OCCURING QUESTION AS TO WHICH PRIMER TO USE FOR RELOADING THE SKS, AK, AND OTHER MILITARY SEMI-AUTOS WITH FREE-FLOATING FIRING PINS.
THE FOLLOWING HAS BEEN REPRODUCED AS A SAFETY GUIDE.
Some rifles are much more susceptible to slam-fires than others. The SKS/AK are more susceptible than the AR15 and M1 Garand and M1A/M14, for example. Therefore, there is more ‘forgiveness’ built in to them as to primer selection. Another factor is rifle condition, parts tolerances, and cleanliness. A clean in-spec rifle is much more tolerant than one that isn’t.
While one, with luck, may shoot a lifetime with standard commercial primers and a free-floating FP - IT IS STRONGLY RECOMMENDED THAT YOU HEED THE ADVICE OF EXPERTS IN CHOOSING YOUR PRIMERS AND THEN SEAT THEM PROPERLY BELOW THE SURFACE OF THE CASE BASE.
Another possibility is to have a MURRAY’S GUNSMITHING www.murraysguns.com spring-loaded firing pin installed in your SKS. This frees up your primer and ammunition choices.
The SPEER reloading manual is an excellent source of expert advice and states the following:
A slam-fire is the discharging of a cartridge in a firearm by the closing of the bolt without a pull of the trigger. In most cases this is a phenomenon associated with military-style semi-automatic rifles and handloaded ammunition. The slam-fire can be caused by a high primer or by a heavy, unsprung firing pin. High primers contribute to slam-fires because the closing bolt drives the high primer cup against the anvil. All handloads must be checked for high primers; this caution is even more important when shooting military-style semi-auto rifles.
Slam-fires have been reported even when primers were properly seated. Many semi-auto service rifles have no firing pin spring and the firing pin itself is quite heavy. The inertia of the firing pin may cause it to snap forward as the bolt stops, firing the cartridge. If the bolt is not yet fully locked, the result can be a ruptured case with the potential for gun damage and injury to the shooter. Military primers are less sensitive than commercial primers to minimize this hazard.
In 1994, CCI introduced the No. 34 [large rifle] and No. 41 [small rifle] primers for military semi-auto rifles… No. 34 primers are recommended for reloading 7.62mm NATO, 30-06 and 7.62x39 ammo for military semi-auto firearms.
No. 34 and No. 41 primers feature mil-spec sensitivity to minimize slam-fires. They are both fully DOD-qualified primers for use in U.S. military ammunition. However, no primer can provide 100% protection against slam-fires if the loader doesn’t seat the primers deeply enough, or the rifle has a headspace problem or an out-of-spec firing pin.
PETER G. KOKALIS, noted military firearm author and expert, especially on select fire weapons, former Special Forces operator and combat veteran stated in the “Fighting Firearms” article on “Kalashniklones” the following:
I have fired tens of thousands of rounds through several hundred Kalashnikovs of every make and configuration [and one can assume extensive SKS experience as well]… Military issue Kalashnikovs and their semi-auto equivalents [and the SKS] do not have spring-loaded firing pins. If commercial or reloaded ammunition - usually with primers more sensitive than milspec because of a thinner cup and sometimes a difference in the primer mixture - is fired in rifles of this type, the free-floating firing pin can, and eventually will, result in a slam fire with ignition out of battery. The resulting detonation can lead to self-destruction of the firearm and anatomical damage of varying severity to the shooter… [going on to speak of the then-loaded Black Hills 7.62x39 ammo] Aware of this primer-sensitivity problem, Black Hills is using the CCI No. 34 milspec primer…
CMP U.S. RIFLE, CALIBER .30, M1 MANUAL
Manual delivered with a CMP Garand, Ammunition section paragraph 3:
…In most military semi-automatic rifles including the M1, the firing pin will lightly mark (“dimple”) the primer of a cartridge as it is chambered when the bolt closes. Military ammunition has harder (less sensitive) primers than are usually found in commercial ammunition or available to handloaders [the CCI #34 excepted], and such dimpling is normally insufficient to fire a primer provided the receiver, bolt, firing pin and chamber conform to prescribed design dimensions. However, the use of non-military ammuntion with softer (more sensitive) primers reduces the margin of safety and requires the shooter to exercise greater caution. Conditions arising from excessive wear, out-of-specification parts or heavy chamber fouling that might pose no hazard with military cartridges could be dangerous with other ammunition.
RELOADING FOR THE M1 GARAND by KEN MARSH www.charm.net/~kmarsh/m1reload.html
- Use a CCI mil-spec primer. These use primer cups that are harder than standard and help prevent slam-fires. Very important and often overlooked.
Avoid high primers, which cause slam-fires. Store ammo nose-down and look across the case heads, that allows you to quickly inspect 50 or more cartridges at once. Also run your fingertip over all primers as they come out of the press or priming tool.
Loading bench slam fire cures are primarily primers. First is choice. LC ammunition has a tough primer. The only commercially available primer I know of that’s similar in construction is the tough skinned WW®. CCI® is hard aplenty too. There is greater insurance against a slam fire using either of these primers. The one that, I say (as well as did every single gunsmith I’ve asked) not to use is Federal ®. It’s “touchier.” Remington® is okay, but not a positive step (in this direction). That’s too bad because the Federal® can work well with other .308 W. loads. Honestly, it’s a risk on an M14.
Primers recommended for use in .308 Win/7.62x51/7.62x39 semiautomatic rifle loads:
CCI #34, 200, BR2, CCI 250
Winchester WLR, WLRM
SMALL RIFLE (.223/5.56) PRIMERS?
The .223 Remington or 5.56mm NATO round is commonly found in semiautomatic rifles and also has special primer considerations using Small Rifle-size primers. Some recommendations follow:
Primers used for .223 Rem. loads should have heavy cups to resist perforation at the high pressures normal for this round. Military 5.56mm primers have a cup thickness of about 0.24", compared to .020" or so that was traditional for the standard small rifle primers. Federal 205, 205M, Remington 7 1/2 BR, Winchester WSR, and CCI BR4, 450, #41, and Wolf SRM (QQQSRM) primers have cups of about the same thickness as military primers, and are the best to use when reloading the .223.
The Remington 6 1/2 and 7 1/2 are essentially the same. The 7 1/2 cup metal is thicker so that the primer can stand up to higher pressures… cup thickness is 25 percent greater… BRIAN PEARCE (quoting Remington), Pg. 14, HANDLOADER, October 2006.
The Remington 7 1/2 BR primer was developed for the hot, high-pressure 4100 fps. .17 Remington round and also used in .223 loads. When Freedom Arms transitioned the .454 Casull case to use the small primer, they picked the Rem. 7 1/2 BR because it gave reliable ignition and easily withstood the 65,000 psi generated by the hot pistol round. It is highly recommended for .223 AR15-type loads.
CCI states: “The CCI 400 primer does have a thinner cup bottom than CCI 450, #41 or BR4 primers. The appropriate primer for an AR15 platform is the CCI #41 primer, which helps to prevent slamfires. With this primer there is more ‘distance’ between the tip of the anvil and the bottom of the cup.” [as per: Linda Olin - CCI/Speer Technical Services]. Despite this, it seems that most AR15 reloaders have experienced no problems using the BR4 and 450 thicker cupped primers in rifles in good condition. The #41 gives the greatest safety margin however.
The experts at 6mmBR.com have this to say about AR15 primer choice:
For use in semi-automatics and AR15s, we advise that you stick to CCI and Remington primers. These brands have harder cups and are much less likely to pierce primers. Also, the AR15 has a free-floating firing pin that dents the primer on loading. This creates a risk of slam fires. So you want hard primer cups. The latest generation of Winchester primers, with brass-colored cups, should be avoided for AR15 use. The old silver Winchester primers worked fine, but the current WSRs are soft and can be pierced more easily than CCI or Rem primers. A poll of Highpower competitors (mostly shooting ARs) showed that Rem 7 1/2 primers are the most popular (33.23%), followed by CCIs (25.78%). The majority of CCI users favored the CCI BR4s, but both CCI 400s (small rifle standard) and CCI 450s (small rifle magnum) were also popular. Only 10.25% of Highpower shooters polled used Federal primers (either 205M or 205). At the time of the poll, many shooters reported using WSRs, but this was the older version with silver cups.
Wolf also makes two small rifle primers that are suitable for 5.56 loading. First is their Small Rifle Magnum SRM primer (not the Standard). They have this to say: “If you are loading for an AR15 or Military Style semi auto rifle, or are loading high pressure cartridges in any other type of rifle ,we recommend you use the Magnum Small rifle primers. Both primers use the same amount of compound. The only difference is in the cup hardness. The WOLF Standard Small Rifle Primers have an all COPPER CUP, which is a little more sensitive than the brass cup magnum primers.” Second is their newer Wolf Small Rifle 223 SR223 “This is the newest primer available in the Wolf line. It is ever so slightly hotter than the small rifle magnum primer and it comes with a brass colored thick cup. This primer can be used in place of the SRM primer or used when a different powder is used that is hard to ignite.” There is no mention, as far as I can find, about how hard their Large Rifle primers are.
Primers recommended for use in .223 Rem/5.56 semiautomatic rifle loads:
CCI #41, 450, BR4
Federal 205, 205M
Remington 7 1/2 BR
PRIMER SEATING DEPTH AIDS
Uniforming primer pockets about guarantees no primer sitting flush with or above the plane of the case head, which won’t guarantee no chance of a slam fire, but it won’t hurt. A uniformed pocket is assurance of consistent and adequate depth to get the primer the necessary 0.004 or more under the plane of the case head (0.008 isn’t too much). Use a primer pocket uniforming tool in place of a primer pocket cleaner. Next step is making sure they’re under the head. Run a finger across them; don’t just look. Primers have a beveled edge so can look (around the edges) like they’re seated below flush when the center of the primer is not. Believe it or not, your finger is extremely sensitive and accurate for feeling that the primer is below flush and is as accurate as a mechanical measure for the issue.
If proper primer seating depth is an issue with the batch of cases that you are using, SINCLAIR INTERNATIONAL carries Primer Pocket Uniformers that can be chucked in a drill and used to uniform the primer pocket to a standard SAAMI depth and flat bottom for optimum primer seating or match prepping cases. I personally use them and consider these tough carbide-steel tools to be one of the better gadgets on my reloading bench. http://www.sinclairintl.com/product/...r-Pocket-Tools
Large Primer 8000 Uniformer - Item UN-8002
I hope the above information helps?
Have a great one