Firing pin bushed, now poor grouping

[potatoe]

I recently had my firing pin bushed (cratering primers) in my dasher. The gun was shooting real well, but now its shooting around .4-.5 groups. This is obviously using the same load as before. My ES has been less than 15 with all my groups. Has anyone else experienced this after getting the firing pin bushed?

 

[markr]

Remove the firing pin assembly and make sure there is nothing in the bolt to impede firing pin movement (burrs or other impediments). Also check headspace if you can. Other than that, no clue

 

[potatoe]

Thanks mark. Did you have to tweak your load after bushing the pin?

 

[Robert]

I recently had my firing pin bushed (cratering primers) in my dasher. The gun was shooting real well, but now its shooting around .4-.5 groups. This is obviously using the same load as before. My ES has been less than 15 with all my groups. Has anyone else experienced this after getting the firing pin bushed?

Potatoe,

Is the indentation well centered on the primer?

Also, you do not mention protrusion..Is this correct?

R.G.C

 

[Steve Blair]

I had the firing pin in my Savage .308 bushed. After bushing, it would occasionally fail to fire. I checked the firing pin protrusion and found it on the low side. After adjusting out a couple notches, there has not been a single misfire.

This correction would not apply to fixed firing pin protrusion, like a Remington, but Robert's point is still good. Protrusion is the first thing to check.

 

[potatoe]

Robert: I did notice that the primer is being struck slightly off center. Also I'm getting some flattened primers now even with a lighter load than what I was using before the bushing was installed ( I wasn't getting flatten primers prior to the bushing.)

When your asking about protrusion, are you asking if the firing pin is sticking out prior to shooting or how deep the hit is on the primer?

 

[Robert]

I had the firing pin in my Savage .308 bushed. After bushing, it would occasionally fail to fire. I checked the firing pin protrusion and found it on the low side. After adjusting out a couple notches, there has not been a single misfire.

This correction would not apply to fixed firing pin protrusion, like a Remington, but Robert's point is still good. Protrusion is the first thing to check.

Potatoe;

Protrusion is the amount the FP PROTRUDES out of the rear face of the casehead recess when the FP is decocked (in its forward position). It is normally between .055 to .059 for a SR primer, and .059 to .063 for the LR.

The primer now flattening seem strange for me, as it is usually the contrary. Maybe an excess of protrusion or soring force can be the cause??.

It is to bear in mind that a .0625 FP tip requires 60% of the impact energy needed for a .080 one..

R.G.C

 

[clowdis]

I'd shoot the rifle over the chronograph again and readjust the powder load to give the same vlocity as before. I think you may have changed the load a bit and raised the pressure in the case. I don't believe bushing the firing pin would raise the case pressure that much.

 

[BoydAllen]

I think that you have given us a clue, the flattened primers. If the smith that bushed the firing pin took a cleanup cut on the bolt face, not enough to cause a dangerous difference in headspace, then you have a different seating depth, and there is room for the case head to get farther from the bolt face during firing. If it gets farther forward when the firing pin hits the primer, and the primer goes off, there is more room for the primer to slightly back out of the case, and expand slightly before the case head comes back around it. This would show up as increased flattening. The other thing that could happen is that the bullet would be driven forward with the case, before pressure rose to the point where it would be pushed out of the case neck. Has the temperature that you are shooting in changed? If you have any tight cases that were shot after the work was done, use these to set your FL die and recheck you seating depth, or better yet, do a minor load reworkup. From a distance, it is hard for any of us to know exactly what is going on. I can tell you that my Viper action has a firing pin tip that is probably just as small as yours, and it has shot its fair share of 2s and 1s, so there is not a problem with that tip diameter. Recently, I fitted a heavier spring, 25#, and I think that I like it, although it is hard to find fault with how it was working before. Good luck.
Boyd

 

[artbosco]

I recently had my firing pin bushed. The gun was shooting real well, but now its shooting around .4-.5 groups. Has anyone else experienced this after getting the firing pin bushed?

Never ... my smith was Greg Tannel: http://www.gretanrifles.com/

 

[potatoe]

I called the smith and told him what was going on. He thought that the cause might be the more intense ignition of the turned firing pin might be what has made the change. I was also a little concerned with the primers being flatten so I decided to try lowering the pressure (even though it should not be showing any at that charge) My original load was 32.5 grs of varget with 105 bergers.

So I loaded up some 105's with only 30.5 grs of Varget and I had both CCI BR-4's and Federal 205M's. I know that the 205's aren't popular because of the CUP, but they shouldn't burn as hot as the CCI's. The CCI's shot a little better than before, but surprisingly the 205's gave me a .26 group, with an ES of 10. I'll be trying some more out in the morning @ 200 yards to see if they can prove to be consistent.

 

[artbosco]

I know that the 205's aren't popular because of the CUP, but they shouldn't burn as hot as the CCI's.

Just for info. In the world of short-range BR competition, Federal 205s and 205Ms are the primer of choice ... the most widely used.

 

[Eddie Harren]

Or at least they used to be. I've noticed in increase in the use of Winchesters and Wolf over the last several years, as well as CCI.

 

[rcw3]

I have always taken the view if you have something running well and it's accurate, don't mess with it!

What the heck is the difference if the primers are cratered if they are not rupturing?

Sometimes I think we over think things to our own detriment.

I have a Model 70 in 6BR that shot real real well and it cratered primers and that annoyed me, so I had GT bush the firing pin and accuracy went away just like that. Nothing wrong with GT's work and he did nothing wrong, but the change made by bushing the firing pin made a dramatic change in accuracy, and if I had even suspected that was going to happen, I never would have bushed the firing pin (didn't really need to, just did not like the way the primers looked).

I have a Rem 700 Tube gun in 6mm BRX that shoots very well with a stock (big) firing pin and yes it craters primers, but unless primers start rupturing (which they never have) I won't even consider bushing the firing pin now.

Some truth to the saying "if it ain't broke, don't fix it!"

Robert

 

[BoydAllen]

Good Morning Robert,
After your accuracy went away, did you do much experimenting with your load to try to get it back? My Viper came with a small diameter firing pin tip, so of course my load workups have all been with that feature, and the best of them have produced results in the ones and low twos, the difference between those being factors other than the load or rifle (how the rifle was supported, held, conditions, etc.) My point is that the small pin tip is able to produce good results, but perhaps it's "likes" are slightly different than larger ones. In one of the previous posts the primer was changed, and that seemed to put things back in order. I am pretty sure that small firing pin tips allow thinner and softer primer cups to be used with high pressure loads, without the problems that can occur with the bigger tips. It may be that they also produce better results with them than with thicker harder primers.
Have a good Thanksgiving.
Boyd

 

[Robert]

My point is that the small pin tip is able to produce good results, but perhaps it's "likes" are slightly different than larger ones. In one of the previous posts the primer was changed, and that seemed to put things back in order. I am pretty sure that small firing pin tips allow thinner and softer primer cups to be used with high pressure loads, without the problems that can occur with the bigger tips. It may be that they also produce better results with them than with thicker harder primers.
Have a good Thanksgiving.
Boyd

Boyd,

+1 on that....
Robert mentionned 'cratering' when the original poster mentionned 'flattening'. This is a totally different observation. It is notorious that small pins are causing less cratering than the big ones..
R.G.C

 

[artbosco]

Or at least they used to be. I've noticed in increase in the use of Winchesters and Wolf over the last several years, as well as CCI.

I think what we're seeing is more of a function of the hording that took place, and the lack of 205 and 205M inventory that was available because of it, and some quality issues that they were having. I remember the ones I was using fell apart in pieces when I was decapping the cases. I called Billy Stevens to see if he had seen the same thing, and he told me at the time, that he had switched to WSRs because of the QC problems. Also, a few years ago folks bought whatever they could get their hands on and bought tons of it, because of the paranoia associated with that period. I think they're still using up their inventory of horded cases. I'm still using up Remington 7.5s because that's all I could find at the time.

 

[Eddie Harren]

Oh, Mea Culpa.

 

[artbosco]

Ed, No need to be so sensitive to a working hypothesis. ;D Hope you had a Happy Thanksgiving.

 

[Eddie Harren]

Sensitive? No. Forgetful of who I'm dealing with, Yes.
I had a wonderful Thanksgiving. You?