large vs. small primers problem?

M

msalm

Member
Has anyone ever run into a problem shooting small rifle primers out of a standard action w/ a larger diameter firing pin. Reason I ask is I recently started shooting a 6X47 Lapua I built on an FN SPR action (308/WSM action). Using the lapua brass and Rem 7 1/2 primers (for the harder cup) I'm having issues blanking primers. Even on mild loads where there is no flattening of the primers around the edge I'll get a very raised protrusion around the firing pin dent and half of them will shear around that raised area and blank out a little disk of primer. I'm thinking the firing pin is just too large for the primer???? or ???? Firing pin protrusion is .054" and fits the firing pin hole perfectly, there is no 'slop'. I was considering turning the pin shorter and polishing, only thing else I can come up with is bush the bolt face and turn the fp to a smaller diameter.... Also the firing pin end is a full half sphere and I was thinking of altering the shape to a flatter profile...not sure if that would do it though.

Any thoughts? and thanks for any help.
 
Your problem is the diameter of the hole and possibly the fit of the firing pin. I have that same action in the shop and it has .085" hole and a .082" firing pin so the fit isn't bad. Just to large.

Firing pin tip should be flat with a radius on the edges.

Dave
 
Is this just to do with the small rifle primer though??? Fit of the firing pin is very good on this one, I looked at a couple other ones (I have another action here along with 4 other rifles built on them, 308, 25-284, 284 Win, and 243) and have shot the others a good bit more than this one and have never had any problem with those at all. I did just turn the face of the firing pin shorter (about .015") and rounded the edge, and it's still doing the same thing, only not every time and there's basically a flush 'circle' where the primer indented, but pushed back out flat.... I hate to say this but could excessive headspace cause this? Fired cases are not swelled or anything, but I suppose I should double check...maybe I didn't carry a one and I'm .010" deep....although that certainly hasn't happened before. I guess I'll double check and after that bush the bolt face and turn the fp smaller diameter I suppose....
 
Forget that the firing pin exists, or that it's a "good fit," the pin itself is immaterial. What you've got is a hole in your boltface, a hole that's too large to support against primer cup deformation. The mechanism behind the smaller pin allowing higher working pressures is that the smaller firing pin uses a smaller hole leaving more support for the primer cup.

As far as headspace and "swelled cases" are concerned, you've lost me there.... I can't make a connection, nor even figure out where you're going with your ideas. I will say though that if you've trouble establishing your headspace tolerance you need to come up with something to measure it with, not rely on possibly faulty math based on ...... what???? ...... Use tape, check your headspace using your real components, no math involved.

Also, is there any chance those cases have been altered? Like someone bunging open the flashholes?? The flashholes should be somewhere around .062-.064, if they're opened up to .080 using a reaming tool that'll add to your problem.

hth

al
 
Al,
As far as headspace, I was just brainstorming possible causes, one possibly being too much space between the bolt face and cartridge head upon firing. No, I don't have any problem getting headspace correct to w/in half thou, but when measuring an action for turning tenon and reaming chamber chit can happen. I don't think that was the case, just posting too many thoughts I guess.

As for the hole, yes, needs to be smaller and I'll correct that, just won't be this week or in time for a little prairie dog trip next weekend.

Thanks for the help.
 
msalm said:
Al,
As far as headspace, I was just brainstorming possible causes, one possibly being too much space between the bolt face and cartridge head upon firing. No, I don't have any problem getting headspace correct to w/in half thou, but when measuring an action for turning tenon and reaming chamber chit can happen. I don't think that was the case, just posting too many thoughts I guess.

As for the hole, yes, needs to be smaller and I'll correct that, just won't be this week or in time for a little prairie dog trip next weekend.

Thanks for the help.
Click to expand...

:)


Prairie dawg trip is an easy fix, drop your load down...... You'll still be able to run 'normal' pressures, those achievable with large primer pockets and factory boltfaces.
 
Actually that's just it, I'm getting blanked primers with even starting loads right out of the berger manual. Standard 6X47 Lapua PTG reamer (think I picked that one up from Grizzly). There's just issues there I'll have to correct before I shoot it any more. Last night I pulled the scope (Nightforce 5.5-22) and put it back on my 30" bbl 243 on an SPR action. It shoots very well, it just wasn't the toy I wanted to play with next week:).
 
Have the bolt bushed and pin turned to .062

I have fit & chambered barrels to several F/N and Winchester rifles and bushed the firing pin on all of the actions that were chambered in a small primer case to prevent the problem you are having.

If the rifle is for me or if I can talk the owner into letting me do it I'll bush every one of them, small primer or not.
 
msalm said:
Actually that's just it, I'm getting blanked primers with even starting loads right out of the berger manual. Standard 6X47 Lapua PTG reamer (think I picked that one up from Grizzly). There's just issues there I'll have to correct before I shoot it any more. Last night I pulled the scope (Nightforce 5.5-22) and put it back on my 30" bbl 243 on an SPR action. It shoots very well, it just wasn't the toy I wanted to play with next week:).
Click to expand...

If you're blanking primers then regardless what the loading manual says you're HOT.... I think, unless you're using something like pistol primers. Hopefully someone will correct me if I'm wrong but IME small primers are just as tough as large primers. I've punched buckets of Rem, CCI, Win and Federal primers and even a few thousand Roooskie Wolf's/Tula's/PMC's, never found any of them to be weak-in-the-cup.

Sounds like you need a chronograph.
 
oversize pin is not helping but this is strange at lower end loads, I follow what you are saying about excessive headspace but have never blanked a primer with it but I do not use large dia. pins. probably best to start at what you know is not correct first....george
 
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I'm pretty certain it's just the firing pin size. I'll bush the bolt and turn down the pin and we'll see where that takes it, chances are that'll be it. Oh, and I did chrono some of the loads, they were not in the upper realms of velocity...pretty mild in fact.

Thanks for the help, I'll let you know how it turns out.
 
Try changing your firing pin spring first before you bush the boltface.
 
Too late, it was bugging me enough that I went to the shop and bored out the face, installed a bushing and drilled to .068". Turned the FP down and problem solved. Shot the hottest loads I had loaded for testing and no problems at all...looks like a normal primer indent with the exception of the flatter surface from previous tinkering. The firing pin spring may be a little weak w/ the larger pin diameter and the smaller primer as the large radius on the tip didn't protrude enough w/ a primer ahead of it leaving a gap around the outside that was shearing the cup material. Now with the smaller pin dia. there's no raised edge around the indentation at all. Looks like it'll go along on the prairie dog trip at the end of next week.

Thanks for the help guys.
 
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