Blanking primers??

[Preacher]

I just got my new BAT actioned 6br together and started to fireform the cases, 29.0 grains of RL-15 @ 2688 FPS out of a 28 inch 3 groove Pac-Nor is causing the primers to have a raised circle around the firing pin indent. I can not believe this is a hot load. The web area has not gone over.0007 since the first firing,
and I have gone up to 31.2 grains 7 times with the same case with no bolt being sticky, no loose primer pockets or any other signs of high pressure other than the circle showing more.... I have seen primers so flat on a 22/250 AI you could hardly see the parting line, and they didnt raise a circle on the primer, but they were really flat. These are not even close to becoming flattened. The firing pin hole and the pin itself seem to be OK.
What is causing this problem, any ideas ?????

 

[jb1000br]

Doubtful on a BAT, but sure sounds like the FP hole is oversize...

JB

 

[Preacher]

Thats what I thought until I checked it.
It's not over .0006 oversized.....

 

[Forum Boss]

Preacher,

These are NEW cases being fire-formed for the first time...is that correct?

If so what you can be seeing is not uncommon as the case moves forward slightly to reach the max headspace, then pushes back against the firing pin, causing slight extrusion aroud the pin head. All that happens in micro-seconds. Greg Tannel can explain this.

I'd also say that raised circle is not all that prominent at all, at least in the photo.

 

[Allene]

Preacher
I totally agree with JB concerning Bat, but here is what I would do. First remove and disassemble the bolt and remove the firing pin assembly. Mike the tip and get hold of a numbered drill index to try and find the size of the bolt firing pin hole. The preferred or common size which Gre-Tan and similar smiths try to bush and fit smaller pins to is around .062 with about .001 to .0015 clearance for people wanting smaller firing pins and bushed bolts. Have this information handy if you need to call Bat. Next would be to measure the firing pin protrusion which should be in the .050 to .055 range on a un-cocked bolt. I'm not knowledgeable on the specifications to which Bat uses for their actions so please use the info I've given you only as a reference. Last I would question you on your brand of Primers and are they primers which you have used previously and not experience any similar problems with. I know that I use typically Russian and on the small pri.,I had to use the Mag. one for just that reason. Good luck on getting this resolved and hope I've helped.
Allen Elliott

 

[Hipshot]

I agree with everybody on this. What primers are you using?

 

[Preacher]

Sure appreciate the answers.
The pin measures .070..
The hole measures .069.4.
Thats .0006 clearance as close as this ole guy can measure.
Russian primers are what I normally use, but it does it to the CCI 450's, and the Rem 7 1/2's also... and the circle gets worse when more powder is added.
I did manage to get BAT on the phone just now, he is sending me another stronger spring, and said it would probably take care of the problem. He said the firing pin, and spring in the SV action don't quite have enough mass to keep it from pushing back into the bolt body when it's fired, and that is probably the cause of the circles.
I guess I'll know the first of the week when the spring gets here, and you can bet I'll post the results. Thanks again for helping with the answers.......

Here's 31.2 -RL-15 Russian SRM @ 2815 FPS and the primer is still not getting flat, nor is the bolt hard to open.
New Lapua cases turned to .012 for a 269 nk.

 

[jb1000br]

31.2 and only 2815fps!! Wow that is a slow barrel!

Yep, weak spring makes sense...

JB

 

[mikecr]

I don't see it as a problem.
Wouldn't anyone desire the lightest spring/pin mass that works?

 

[techshooter]

I had the same thing happening on my 6 Dasher. My bolt is getting bushed as of this writing by Greg Tannel, to 0.062". This is the source of the problem, not the spring rate.

I got nice rounded primers, and no signs of pressure, but I blanked three primers, and the last one busted my Jewell trigger. A few people recommended the bushing process, and this was affirmed by Greg Tannel as well.

It is impressive how much force is on this little part during a burn. For a standard,I measured two of my M700 bolts) Remington firing pin/hole, the pin is 0.078" in diameter. This yields a surface area of 0.004778 in^2, and at a pressure of 60KPSI, this is 287 pounds of force on this little circle. The firing pin inertia and spring force buck this somewhat, but only to a point. If the pin is reduced to 0.062" in diameter, the area goes to 0.00301 in^2, and the force at 60KPSI is now 181 pounds, a reduction of about 37%. This makes all the difference.

Even though I do all my own work, Greg charges less than $60 to do this, with very fast turn-around. My spare time is worth more that this would save, as I am sure that it would take me hours to figure out how to do this, fixture it, and do it.

Hope that this helps.

Cheers,

 

[Preacher]

Gre-Tan has done bushing work on 3, 700's and 3, XP bolt's and they preform very nice. This BAT bolt and firing pin assembly as stated is working with only about a .0006 clearance and that is as close or closer than Tannels work. The new spring should be here in a few days, and I'll go from there.

 

[Preacher]

The new firing pin spring came in for the BAT and the circle problem is solved.
The photo is showing the results of 31.5 grains of RL-15 and finally looks normal.
It rained all day yesterday so I didn't do any crono work on this charge.
The web still has not changed from the original .0007 web increase.

 

[techshooter]

Interesting. Could you tell how much stiffer the new spring was from the original?

I just got back from a business trip, and the bushed bolt was waiting for me. Greg turned it around in one day. I might get a chance to test it out this weekend. I'll post results.

 

[Preacher]

I have no way to measure the increased pressure in the new spring but I can feel the difference, and as I said it now works just fine.
Greg has always turned sent stuff back really quick. Did you do the firing pin assembly replacement he offers ?
I did and it seemed to help out.

 

[techshooter]

Preacher:

No, as I had already replaced the pin and spring with a David Tubb SpeedLock assembly. I did notice that the pin protrusion is now 0.070", about 0.025" more than before.

I have the SpeedLock in my other M700s, and have never seen this problem before this time. Must be something unique about that small case and flash hole, along with the pressures.

I suspect that this will help a lot. I'm going to the range tomorrow, and will post results.

Cheers,

 

[Preacher]

Techshooter-
.070 is a lot of pin protrusion, it can cause a peircing on some primers if your not careful. I never like them more than about .055, or what ever is reliable to set the primer off. If you have not shot before with this setup, be careful and keep a good eye on the primers to see if all is well.

 

[BoydAllen]

It is my impression that the pin only stops on the firing pin shoulder when dry firing. Otherwise it is the primer that stops the pin. There could be a problem with ignition if protrusion is insufficient, but "excessive" protrusion would only shorten the pin fall. Most factory actions have more fall than is needed.

 

[techshooter]

All:

Tests today indicate problem solved. The primers looked perfect, no signs of cratering, or other pressure indicators. I got one about 1.5" 5 shot group at 600 yards with these fireforming loads. The rest were in the 3 to 4" range. I'm happy. More bolts will be going Greg's way very soon.

Thanks for all the help!

 

[Shelley]

Lynn

According to Preacher, the owner of the Bat, his action has a .070 firing pin which is a large pin. An .062 pin is the small size as developed by Stiller. I'm not sure but I think the .062 pin is an option on Bats.

Shelley

 

[techshooter]

Just to clarify the exact configuration - the action is a standard Remington M700, but the pin and spring were upgraded to the Tubb SpeedLock Systems lightweight spring, and chrome-silicon spring. I do not know if the spring rate is higher on the Tubb unit. The pin measured about 0.078" before the bushing process. I was getting bad cratering, and even blew a few primers. After the bushing modification, the pin measured 0.060", and the protrusion was about 0.070". The field results were, in short, perfect. The cratering was gone, and the strikes look perfect, and not too deep. I'm sold.