How far offcenter can a primer get hit and still work?

[theperfessor]

Does anybody know of any tests that have been conducted to see how off center a firing pin strike can be and still set off a primer? Couldn't find anything during a web search. Lots of stuff about how to fix it, nothing to quantify how far off is too far.

Thanks for any help.

[Outpost75]

US government specifications for the M4 carbine and M9 pistol permit the strike to be off-center, notto exceed 1/2 diameter of the indent.

The same parameters were used for the M14 rifle and M60 and later M240 machineguns, however, the striker point diameter is greater for the large vs. the small primer.

Hope this helps.

[theperfessor]

Thank you, that's a start.

[Artful]

It's going to depend upon a lot of variables - in 1911's you can find a fair amount of offset and still set them off.
http://i942.photobucket.com/albums/ad264/45fmjoe/Firearms/brass2.jpg
http://i54.photobucket.com/albums/g112/usmcbob/handguns/taurus2.jpg
It's going to depend upon the amount of energy the firing pin is carrying and how sensitive the primer itself is.
Worst case I know of was the rod & gun used to sell reloads in styrofoam trays - boolit down primer up.
Dufus bought two trays, set one on the table and then proceeded to dump the other tray onto of the first.
the edge of a loaded cartridge actually set off a loaded round in the tray.

[theperfessor]

A while back a poster with a Charter .44 that blew up was searching for a reason. I had an identical gun that went out of time after about a thousand rounds. Most likely the cause was a reloading error, but it made me curious about how far off a primer strike could be. I realize there are a number of variables involved, but I was curious to see if there had ever been a test performed to generate a graph that would plot the eccentricity as the independent variable vs % of successful ignitions as the dependent variable. In other words if the primer hit was centered you would have 100% ignition; if the strike was one radius distance away from center (on the edge of the primer) you would (most likely) have 0% ignition. At what distance away from center does the % of hits drop below 100? And how rapidly does it drop off?

Outpost75 mentioned the military specs so obviously somebody has done some testing.

[Outpost75]

On revolvers you have different issues with timing and cylinder rotation, then with autopistols you can have differences in vertical position of the bore axis, relative to barrel locking position.

The 1/2 diameter of striker indent is useful and agrees with experience.

[theperfessor]

No argument about that the utility of that spec; sometimes curious minds just want to know more. Thanks for sharing that info.

[Mk42gunner]

In my experience, it kind of depends on the primer.

For instance, I had a 16 gauge single shot when I was a teenager that hit off-center enough that misfires were common; but they weren't as far off proportionately as the 9mm that Artful shows in his picture. That gun was a love/hate relationship; I liked the way it shot when it went off (the first time I ever fired it I dropped a fox squirrel DRT at fifty yards), but it also taught me to flinch.

My No. 2 Remington Rolling Block in .32 Long Colt hits small pistol primers almost on the edge, but so far has fired every time.

1911A1's in .45ACP can hit a large pistol primer pretty much anywhere and work okay.

Sorry I can't give a definitive answer,

Robert

[theperfessor]

Sorry I can't give a definitive answer.

Yeah, that is one of the reasons I asked the question. Sometimes us engineer types want those...

[Idaho Mule]

perffesser, a good and honest question, and I do not know the answer but am looking forward to the replies, thanks. JW

[Blacksmith]

I would suspect the answer would be only applicable to a very specific set of components and hardware because of variations in materials and manufacturing tolerances.

A primer fires because an explosive compound is detonated by the mechanical force applied to the compound by crushing it between the containing cup and the anvil. When one starts considering the number of variables that could effect this action then meaningful data would probably only be representative of a specific brand and type of primer in a specific brand and caliber cartridge case fired in a specific make and modle of firearm.

Top of my head list of potential variables each having its own manufacturing tolerance.
The primer cup - type alloy, metal thickness, metal hardness.
The compound - composition, amount, placement, drying
The anvil - type alloy, metal thickness, metal hardness, size, shape
The cartridge case - diameter of pocket, depth of pocket, size of flash hole, dimension of headspace to surface of primer, concentricity of case and pocket, diameter of case
Assembly - primer seating depth, pre stressing the compound
Firearm Chamber - diameter of chamber vs diameter of case
Firing pin - type, shape, size, protrusion, spring strength

I am certain you get the idea. So you might be able to say that in a Goloudenboomer semi auto model XYZ with Unobtainum .45 ACP cartridges with Magic Fireworks type 3 primers your primer strike miss-alignment of XXX will result in a 99% probability of ignition within a two sigma confidence level. But in a different gun or with a different cartridge the number may change.

I think you should write a grant proposal to study the problem. Submit it to all the most liberal funding sources just to upset them. You could start a collection of reject letters.

[theperfessor]

Blacksmith -

Understand completely the number of variables involved. But sometimes any data is better than no data, and the number of variables can be reduced to a few manageable inputs.

Love the grant proposal idea. Actually, the Engineering Department where I work collaborates with the folks at Crane Naval Depot. I might submit a grant request to them for the funding to do the work. I thought it might make an interesting student capstone project for one of my kids this Fall.

[country gent]

I would also suspect that performance is affested by off center hits. The farther away from the center of primer aanvil the less consistent ignition performance will be, meaning less consistent ignition and higher extreme spreads standard deviations in velocity. An intresting line on this was a few 22 that hit the rim 2 at 180 degrees apart claiming better more consistent ignition and less cartridge offset in the chamber than the one side ( lopsided hit). Would be an interesting test. Maybe a case with primer and pellet ( no powder) and a means of accurately offsetting the firing pin. Would have to be adjustable so when testing could adjust from center to farthest position with each primer tested.

[theperfessor]

Yeah, that was kind of my idea. Build a test fixture to eliminate the type of firearm as a variable. Use some sort of micrometer adjusting mechanism to offset the hit by a controlled amount. Determine the minimum impact energy needed to reliably set off a primer with a perfect dead center strike and then increase that by 50 to 100%. Select one brand and caliber of cartridge - I have some brand new Starline .44 Special cases I would lend for the experiments. (Can't imagine it would hurt them for any other later use.) Test 10 strikes at each location. Plot the results.

I think that testing for the effect on internal ballistics would be neat, but I have to give my kids a goal they can accomplish. Building a test fixture and testing two or three brands of primers would be about all I could reasonably expect. Besides, the University will let us pop primers on campus but forbids firing off live rounds even in a lab. I'd have to use up a lot of atttaboys to make that happen, and I'm kind of saving those for when I REALLY need to use them.

[Outpost75]

Additional factors to consider in your experimental design are:

driven protrusion of the striker point (M4 is 0.028-0.032")
striker energy, via copper indent as measured on the government gage, and
vector effect of varied angles of obliquity of striker impact.

While M4s and autopistols hit the primer parallel to the bore axis, break-open guns, revolvers and most falling blocks do not.

Light strikes affect more than reliability of ignition.

That's why the government measures copper indent. Unfortunately since the industry went to piezoelectric pressure measurement there is little demand for coppers and they are both expen sive and hard to get. The only users are the government labs and contractors who must meet the indent specs, and coppers are purpose-built in small lots for the specific contract.

The "holders" are easy enough to get, these resemble a headspace gage with a blind hole to accept the "C" size .225x400 crusher, with a hole for a knockout pin. You can use each copper twice, one whack on each end. Measure the indent on a surface plate with a dial indicator.

Minimum Cu indent for .38 Special revolvers is 0.010", for .357s and 9mm 0.012", for M4 carbine 0.020"

But good luck in getting the coppers. Last time I bought them Olin was the sole source. They won't sell them to the gunsmith trade, you have to have a contract number to order against. The darned things cost $1 each and you had to buy them in 1000 increments! So, if you have government money, go for it!

[Blacksmith]

Some other primer tests that might be done by a student that would be helpful. I can imagine fairly simple precision test rigs that could be made to preform the tests.

Minimum strike energy by brand and type of primer. We all know some primers are harder than others and I have seen some lists. I have not seen a good database showing this information in a format that would be useful for selecting the primer to suit the existing firearm or selecting springs to suit the primer. A series of tests to establish minimums and minium reliable would be interesting.

Good data on primer brissance for the average reloader. I have seen some tests showing the amount of flame produced but done with uncalibrated photographs. I could see a test rig with a primer pocket and flash hole that would fire the primer with a consistent force. The resulting flame photographed against a scale or grid and results plotted by brand and type. Maximum flame could be captured by an open shutter in a light proof box but progress of flame front would also be interesting if high speed equipment was available.

Then one could combine the two to see if impact force effects brissance.

Just thought of another. The angle of the firing pin strike in relation to primer reliability.

[Bullshop]

Because I have a revolver that was converted to CF from RF and the pin strike is enough off center to cause misfires I had to do quite a bit of test shooting to find a primer that was dependable with this gun.
The only primer of the many types tried that I found to be 100% dependable with this gun is CCI. An interesting point is that it matters not whether it is for SR or SP the CCI is the only brand of primer that does not misfire in this revolver.
I know this doesn't answer your question but may be helpful for someone with the problem.

[Dennis Eugene]

I'm thinking you've asked a question that can't be answered. In other words the answer will be different each and every time for each and every unit. But then what do I know, my .22's hit way off to the side and still go off. :kidding: Dennis

[theperfessor]

Our department does have a high speed video camera available. When another faculty member asked our Dean for the funds his comment was "Don't let Keith have it, he'll take it out to photograph his bullets". After he got it, my colleague told me this and asked me when we were going to the range...

I'm bookmarking this thread for my kids to reference. Lot's of good comments here.

Edit to add: I'm curious about the results for the reasons I indicated in post #5, but I'm more interested in my kids learning to set up a test protocol, design and build the necessary equipment, and conduct an experiment in the proper way.

[Outpost75]

The lead-free primer mixes are less sensitive than the usual basic lead styphnate.
There are also differences in anvil point geometry between government and commercial primers.

Base metal thickness of the primer cup may vary between brands, and some imported primers may have plated steel cups rather than brass.

[fecmech]

The differences in primers can be dramatic. I have a Beretta 390 12 ga shotgun that I used in Sporting Clays for years. I kept track of every round fired and for almost 50K rds my reloads used Winchester 209 primers and never had 1 fail to fire. I bought 10 cases of Estate shotshells and immediately experienced a 2-3% FTF rate and that's when I discovered the hole for the firing pin in my breech bolt was drilled off center. A friend bought the remaining shells so no problem there. Sometime later I then ran into the same thing using Fiocchi 209 primers and had to install a heavier hammer spring in the gun to to use the Fiocchi's.

[44Vaquero]

Professor, diameter of the firing pin is also a variable, correct? My Webley has an absolutely gigantic firing pin in comparison to the small pistol primer it strikes and it goes deep too!

I understand the Schools reluctance to sign off on live fire experiments. You could do this instead, build a pressure chamber with a internal sensor and plot the variation of the pressures generated in a given space of a known size. Once you have established a base line for on center strikes then the real experimenting starts.

I should think a pressure chamber of this type would be easy enough to construct and relatively safe to operate.

[theperfessor]

I've been a member of the NRA book club for years. One of the books in my collection is "Gunsmithing" by Roy Dunlap. IIRC it has information on the shape and size of firing pins for various guns. That is a good place to start, and it would be a good exercise for my kids to measure the size of various pins on the handguns in my possession. And I can always contact some of the folks at Crane ND to see what the government specs are for small arms (handguns).

Our British cousins have their own way of doing things, don't they!? Even as a kid I thought it was hilarious when Ian Fleming wrote about James Bond "sharpening the firing pin" of his gun. And putting a .32 ACP up against a .45 Colt SA is almost as funny.

[higgins]

I believe primer quality and Berdan or Boxer may be a factor. I once got a few dud rounds of Pakistani .303 surplus that had been well struck on the edge of the larger milspec primer by a firing pin that was very off-center, but the entire pin struck the primer. They fired without hesitation in my Enfield that has a good centered pin.

I should note that Pakistani surplus .303 has a reputation for being hangfire ammo, probably because of poor storage conditions. Most of it fires just fine but quite a bit of it doesn't. It's not just Pakistani ammo either; .303 loaded in Britain is prone to the occasional hangfire if it gets old under the wrong conditions. Not an indictment of the British primer as much as the variety of conditions under which it was stored all over the globe. Again, no data or specs., just opinions based on my experience with milsurp ammo and what I've read of others experience.

[beagle]

I did pick up a handful of .45 Colt once and the firing pin strike was actually hitting the edge of the primer pocket and skidding in to the primer. Left small peens on the edge of the primer pocket. Gun fired in was unknown but I suspect a SA Colt as it was before Rugers came out. This alignment must not be too critical as these cases were fired. Had to be hard on the firing pin too./beagle

[Silver Eagle]

There might be a difference in the anvil type as well. 3 lobe or 4 lobe and the position of the lobes relative to the firing pin strike.
Many experiments were done to improve consistency of 22 rimfire ignition by the Olympic class arm and ammunition manufacturers. End result was the single edge strike is the most reliable. Also, no definable changes were found during testing of multiple simultaneous hits on the rim.
Not to mention the fact that if they did find a method that was better, it would be used (or have been used) on production arms.

[km101]

Our department does have a high speed video camera available. When another faculty member asked our Dean for the funds his comment was "Don't let Keith have it, he'll take it out to photograph his bullets". After he got it, my colleague told me this and asked me when we were going to the range.

Keith, remember that one "aw****" cancels out ALL "attaboys" so don't take the camera out before you get the OK to do your testing!! Sounds like a very interesting project, keep us up to date!

[Chev. William]

While reading this thread, I got an idea for part of a possible test rig. If the firing pin were mounted in eccentric drilled bushing that was then mounted in a eccentric drilled body such that the amounts of the offsets were equal and opposite when the firing pin were centered over the primer and when rotated 180 degrees the two offsets summed to place the center of the firing pin on the exact edge of the primer pocket, that would give a measurable and repeatable offset distance versus rotation angle.
A Replaceable firing pin tip, like the two part 'striker' firing pin of a M1903A3 Rifle, would reasonable ability to change tip contour in a repeatable manor.
Just some thought in suggestion of possible designs for the test rig.
Best Regards,
Chev. William

[sagamore-one]

Ever look at the firing pin strikes on the 9mm conversion barrels for Glock and Sig pistols with 40 or 357Sig slides ? The hit is way, way off center. They seem to work well.

[Reg]

Not to hi jack the thread but rather to add to it. If the firing pin strike is badly off center will it give inconsistent ignition and thus affect accuracy ??

[theperfessor]

There are two students working on this right now as their Capstone (Senior) Project. They are just getting started but I have reviewed their plans. (I am not the advisor for this project by the way.) They are doing fine and as things continue I will try to update this thread.

Edit to add: Reg, this won't test the difference in ballistics resulting from an off center hit, but I think it is reasonable to assume that at some point if you are only setting off let's say 60% - 70% of the primers you hit there has got to be some effect on the ballistics of the ones that do go bang.

[Blacksmith]

Hopefully they will publish their findings, along with photographs. Perhaps they will consider posting at least a summary on Cast Boolits. Eagerly awaiting updates.

[Reg]

Edit to add: Reg, this won't test the difference in ballistics resulting from an off center hit, but I think it is reasonable to assume that at some point if you are only setting off let's say 60% - 70% of the primers you hit there has got to be some effect on the ballistics of the ones that do go bang.[/QUOTE]

This has been my thought for years but have never seen mention of it anywhere.

[williamwaco]

It's going to depend upon a lot of variables - in 1911's you can find a fair amount of offset and still set them off.
http://i942.photobucket.com/albums/ad264/45fmjoe/Firearms/brass2.jpg
http://i54.photobucket.com/albums/g112/usmcbob/handguns/taurus2.jpg
It's going to depend upon the amount of energy the firing pin is carrying and how sensitive the primer itself is.
Worst case I know of was the rod & gun used to sell reloads in styrofoam trays - boolit down primer up.
Dufus bought two trays, set one on the table and then proceeded to dump the other tray onto of the first.
the edge of a loaded cartridge actually set off a loaded round in the tray.


Terrific answer.

11 pix = 11,000 words!

[felix]

Interesting history. See 1989 for thread relevance. ... felix


1951 – CCI established
1951 – Dick Speer hired Dr. Victor Jasaitis to develop new processes and chemicals needed for primer manufacturing. Dr. Jasaitis was a refugee scientist from Lithuania who specialized in explosive chemistry.
1957 – CCI added shotshells to the line.
1959 – Began making industrial power loads for powder-actuated fastener systems.
1962 – Expanded into rimfire ammunition with Mini-Mag (CCI's most popular rimfire product).
1967 – Oregon firm, Omark Industries, bought CCI from Dick Speer. Omark Industries seeked an in-house source of loads for the powder-actuated tools they manufactured. Seeing the profitability of sporting ammo and components, they wisely elected to let CCI continue to grow in this area. New products such as Stinger, the world's first hypervelocity 22 Long Rifle ammo, rolled out of the CCI facility.
1986 – CCI's development engineers set out on a comprehensive primer improvement program to meet the requirements of progressive loading equipment that was starting to dominate the reloading market.
1989 – The three-year program wrapped up with the introduction of all-new primers. Features included: smooth feeding through automated equipment, reduced residue in non-magnum primers, improved primer seating, and better sensitivity that included a larger "sweet spot" for firearms that produced off-center firing pin strikes.
1990 – CCI perfected the first hypervelocity 22 Magnum Rimfire cartridge.
1991 – CCI opened a new, state-of-the-art primer manufacturing facility to insure that we could supply all our customers' needs.
1993-94 – During the so-called "primer shortage," CCI was the only US primer manufacture to continuously ship primers to commercial account, largely due to the increased capacity afforded by this new facility. CCI is also a major supplier of military cannon primers.
Today – We've continued to add new rimfire products like Mini-Mag™ Silhouette, Segmented Hollow Point, and Velocitor™, the fastest 40-grain .22 Long Rifle load on the market.