strange possibly over pressure sign

G

georgehwbush

New member
yes i hand load. this is the first time i have ever seen pierced primers.

was trying a new powder in the 243 "hoping for a little more speed".
loaded well within safe starting charge, and first shot; pierced primer.
there were no other visable signs the primer cup is not flattened the case head has no marks... easy eject... i'm stumped.

second shot pierced primer. same thing....

third shot no fire. take the gun apart and remove the primer peaces from the firing pin hole...

could it be the primer cup is brittle ? they were imported from the cheepest sourse in the world...
thoughts ?
 
and please give us the load...
- Actual bullet, it's weight,
- Powder, it's weight
- Overall length when loaded
- The primer manufacturer
 
Check your bench trash can for your primer package.
I don't know for sure that you used pistol primers, but I'll just about guarantee
if you load pistol primers a .243 you will get the same results.

FWIW , the hot, high pressure gas will very quickly erode the firing pin tip and firing pin hole in the bolt face.

I suggest pulling the bullets rather than shooting them up.
 
Recheck brass sizing to make sure there is no excessive head clearance.

Inspect firing pin head profile. It should be smooth hemisphere without any sharp points/edges.

Check firing pin fit in the hole. It should be good slip fit. Any slop there allows room for the brass to flow. My cheap ar-10 had that problem. The bolt has over sized hole. Bought another bolt from a friend and problem solved.

-TL



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NH15-45 i had used one box of them before but these were the first out of this box.

HiBC: the outer container (box of 1000) says large rifle but the inner sleeves (100 count) are just plain white sleeve no writing.

tangolima: yes this is that cheap ar-10, that could be something to check indeed.

as per mehavey: ladder testing, hodgdon hybrid 100V, with SMK-107's,
winchester cases, and these cheap china white box large rifle primers.

charge weights: 38.7 40.1 40.5 40.9 41.1 41.3 41.5

only fired the first batch because the primers were being a pain.
 
I had, and unfortunately still have the majority of, a batch of Winchester primers that had brittle cups.
But it sounds like you have questionable primers in a questionable rifle.

Assess the rifle and try different primers first.
(If those primers are Chinese, they're probably corrosive, btw. Clean your gun as you would for corrosive ammo.)
 
Inertia/weight of the firing pin strike is enough by itself to cause pierced primers. I think you mentioned before you had issues with the carrier set-up on this particular rifle. I recommend you take a look at JP Enterprises enhanced and enhanced high pressure bolts.
 
I have been dealing with this issue on AR-15/ar-10 platform, mostly related to budget parts. The bolt hole is machined oversized, and the bolt is expensive. Have been trying to find firing pins that have thicker tip. But they are stubbornly elusive. Please let me know if there are sources for such firing pins.

I have thought about retipping the firing pin. I have done that many times for old guns with worn firing pin hole. But I need more desperation to kick start the action.

Actually such issue doesn't seem that uncommon. A lot of once fired brass I have picked up have cratered primers.

-TL

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Bushing is certainly an option. But I tend not to put it to the front. Bolt is expensive. It hurts if I screw up. The steel is hardened. It could be difficult to machine. Annealing is not preferable as it requires proper rehardening.

-TL

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Before you do anything ... if the load is not excessive ...
Try some new and better primers ... could be a batch of primers with thin cups or that maker just uses thin metal cups to save money .

Way back in the stone age Alcan sold primers and powder branded S&W ... most of the primers were OK ... but one lot of small pistol primers were bad about piercing primers on firing ... I'm talking a 38 special - 148 gr. WC - 2.7 grs. Bullseye load ... not excessive in the least but the primers would pierce 3 out of 5 ... they were just poor primers with thin cup metal ... they all fired but it just didn't look right !
Changed to CCI and never any problems ... check the primers first !
Gary
 
I took a quick stock of what I have. Here are a few figures to illustrate the point.

AR-15
Bolt A, hole diameter 0.063"
Firing pin 1, tip diameter 0.058"
Firing pin 2, 0.060"

Bolt A + pin 1: shallow crater at mid range loads.

Bolt A + pin 2: ok

I believe the hole is supposed to be 0.060". Bolt A + pin 2 came with a budget complete upper. I managed to find pin 2 to make it work.

AR-10
Bolt B, 0.084"
Bolt C, 0.080"
Pin 3, 0.075"
Pin 4, 0.077"

Bolt B + pin 3 came with a budget complete upper. It craters primer event at minimum loads. Pierced primers when close to max load.

Bolt B + pin 4 is better but still not kosher.

Bolt C is the one I bought from friend. It work well with pin 4.

The hole is probably spec'd to 0.080".

The pin / hole fit must be <0.005", better <0.003", best 0.

-TL

PS. I just keep buying cheap steel firing pins of different brands whenever I order parts. Sometimes I get lucky and get one with thicker tip.



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Do you have a firing pin protrusion gauge? If you have one, do you use it??

I don't know if there is one for the AR 10, but there ought to be, as there is one for the AR 15 and it was part of the small arms repairman's kit. Min/max firing pin protrusion for the M16 rifle series.

Too much firing pin sticking out can cause pierced primers. Not saying this is the cause of you problem, only that it could be, and if you don't measure it, you don't know if it can be ruled out.
 
while we are measuring things anyone know where a full set o specs for the ar-10/15 are posted? i would like to know what i'm looking for on things like firing pen protrusion or diameters ...
 
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