Occasional misfires

[Patch700]

I have 2 dial calipers,1 dial & 1 electronic. I use them to ck. 1 against the other, the measurements are virtually identical. I'm the using the electronic for convience. Firingpin diameter is .066,the protrusion is.075-.077, is, .020-.022 enough to warrant adjustment ? According to the S/N (F24xxxx) shouldn't it have the larger diameter firingpin ? What is it's diameter, I'm wondering if the prior owner had these problems. Paul


Those numbers (0.075-0.077") are your protrusion depths?? Or are they the numbers you got when you did your plunge measurement from the bolt lug face to the top of the firing pin in the fired position?

The reason i ask is if memory serves me correct my measurement from face of bolt lug to the floor (where pin protrudes from) is .105 or maybe .107... Those numbers would make more sense if they were the measurement from face of lug to tip of pin in fired position , thereby making your pin protrusion at somewhere around .032" which may be a bit short.

[thomae]

Is this how you measured your firing pin protrusion?

To measure firing pin protrusion, use the depth measuring rod on the butt end of a set of calipers, put the calipers on the rim of the bolt face, then set your zero on either the bolt face or the protruding firing pin (in the fired/uncocked position), and then, without changing your zero, measure to the firing pin or bolt face (whichever you did not use to set zero). The difference between these two measurements will be your firing pin protrusion.

Did you ever check that your crosspin was aligned correctly? a misaligned crosspin could add friction to the firing pin, inhibiting it's movement (although I don't know if this would be significant enough to prevent primer ignition)

[BillPa]

Firingpin diameter is .066,the protrusion is.075-.077, is, .020-.022 enough to warrant adjustment ? Paul

At .075-.077" its about .040" too long. Reset it to .035", .040" max.
http://i59.tinypic.com/nqcnc5.jpg



Firing pin diameter is .066. According to the S/N (F24xxxx) shouldn't it have the larger diameter firing pin ? What is it's diameter Paul

The difference between the old (.140") and the newer(.095") pins is the portion that passes through the bolthead retaining pin and the bolthead shaft to the vent. Pass that that they're same size.


I'm wondering if the prior owner had these problems.

Could be. It might be why is was on the used rack.

Bil

[joeb33050]

Well, I understand the firing pin/cup/anvil theory, but I never heard it before and am skeptical. I find it hard to believe that that little brass 3 legged anvil hitting the primer pocket can stop that firing pin. But-it doesn't matter.
I shoot almost only cast low velocity bullets. After installing a 22-250 barrel on a M10, got a few no-fires. 3 never went off, another half dozen fired on the 2nd try. I increased the firing pin protrusion from ~ .035"/.040" recommended to ~ .062", shot the same loads yesterday with no = zero misfires. More protrusion fixed misfires for me, yesterday.
joe b.

[thomae]

I am glad you cleared up the symptoms, however, I still would worry that something is not quite right if you need that much protrusion.
Here are some thoughts:

Have you checked the brass you are using with a comparator both before and after you fired?
Perhaps you need to adjust your sizing dies.


I've seen instances where too much head-space will cause this. You should set your F/L sizing die so that it only bumps the shoulder back 2 thousandths. Your brass will last longer too.

Were these cartridges loaded specifically for this rifle? If they were loaded for (and previously fired in) a different rifle, differences in the amount of headspace from one to another might be your problem.

If they were already shot in this particular rifle, could the brass is work hardened? If the brass is too hard, it might not take the shape of the chamber. This problem would be solved by annealing the brass.

[jonbearman]

How are you measuring for shoulder bump? You cant really measure bump correctly without a hornady kit which attaches to one blade of your caliper and uses a specific bushing to measure off the shoulder to compare cases. You simply can not eyeball it.

[scpaul]

Remeasured the firing pin protrusion,it's a little over the spec. that Steve @ Shooters Supply gave me.(.055 vs. .069)I compared new full length resized brass to one time fired brass (same lot of Winchester brass)found very minor case body length difference.Notes outside in shop,measured w/digital caliper. If the headspace were off by much I'd have a noticeable differance in base to shoulder length.If memory serves the measured differance was .007 to.010,new F/L sized vs. fired. Can't prove it but I'm starting to get a gut feeling about the primers.I haven't had any problems with them before,but there's always a 1st. time. I've had this batch a while,they're Rem.9 1/2.They have been stored the same as the rest of my stock,several brands&batchs.Some older than these by 2 yrs.,and I'm still thinking about the bind on the bbl. nut I found when I bedded the stock. Guess I'll find out next range session.I'm in S.C., we've been having ice/snow/freezing rain. It's supposed to be over now ,so look out range here I come. Let ya' know how it turns out,THANKS all,Paul

[scpaul]

Believe prob. is headspace. Shot today,had 3 misfires. Took 2 and w/ a pair/pliers and pulled the bullets out slightly, approx. 1mm. Before I pulled the bullets out I painted the bullet/case junction w/a sharpie so I could see the movement.Tried to fire them a 2nd time. The impact o0f the pin reset the bullets to the orig. O.A.L. I'm going to load a few more at a lower pressure and seat the bullet touching the rifling.There shouldn't be any slack movement,headspace prob. or not. At this point unless I have a bad f-pin spring the prob. is not the in the bolt. I don't believe the spring is the prob.,I can't see the pin impact changing that much nomatter where the ctg. happens to wind up with the bolt closed. Increasing the O.A.L. will position the ctg against the bolt face,and I plan to use a Lee crimp die to make sure it can't move when the f-pin impacts. F.Y.I. all tests have used the same batch of Rem. 9 & 1/2 primers. Thinking about that I'm going to load a few of the previously misfired cases w/CCI l.rifle primers just to be absolutely sure no primer prob. exists. Thinking about it I used my RCBS case checker to ck. for case streaching ,looking for the thin ring ahead of the the cases belt . The cases I ck'ed had been fired 3X. That should have been enough to detect case streaching if I had a headspace prob. I think in a.m. I'm going to disassemble the bolt again. Thomae, I think that you will find that a spring like a f-pin spring will loose strength from being left compressed for long periods of time or being exposed to high temps.(don't believe temp. has caused any problems here,it would need to be much higher than inside the rear window of a truck.(gun rack) Can't do any range work until next week, I'll let you know what happens. Glad I"m getting to work this out before it's rechambered or rebarreled. Thanks everyone,Wish me luck Paul

[sharpshooter]

"Thomae, I think that you will find that a spring like a f-pin spring will loose strength from being left compressed for long periods of time or being exposed to high temps."

Lots of people want to believe that, but since the early 60's, firing pin springs have been made from "rocket" wire. Rocket wire as it is known, was developed by NASA and soon replaced music wire springs which were known to take a set. Even in the fired stage, the firing pin spring is still compressed @20 lbs. For heat to damage the temper, it would have to be in excess of 350 degrees. I check every main spring when I rebuild actions with a spring scale and have yet to find one that is below specs.

[scpaul]

Sorry it's taken so long to get back with ya'll. I've been fighting compuker problems, one after another, think we finally found it. After numerous things I finally streched the firing pin spring +- 1/2 in., that got it, no more misfires even with the batch of cases that were causing the problems. I haven't changed anything else, dies,primers,seating depth, nothing. Maybe this spring wasn't up to spec. or who knows what the prior owner did. Guess I'll be ordering a new f-pin spring soon. Thanks everybody for the help, Paul