Pierced primer question

[fatelvis]

After shooting F-class all year with my RPR 6 Creed, using Hornady and Lapua brass (reformed 308) with large primers (using Fed 210m) and always sticking to the same 40grn charge of RL16, I was excited to buy the newly offered Lapua brass in 6 Creed. I had no pressure problems, or pierced primers UNTIL using this new brass. At first, I used 205M Primers and got 5 piercings out of 34. After research, I saw that Federal’s SR primers were a bit thinner than others, so I instead used CCI BR4 primers, with the same powder charge. I had one piercing out of 33 yesterday. Can anyone explain what is happening to cause the piercings? I pulled apart my bolt and cleaned and inspected my firing pin. The bolt face and pin are unhurt. Thanks for your help guys!

 

[KMart]

If you are still using the 40 grain charge, you need to back down a couple of grains and rework your load.
There is a chance that the internal volume of the new cases is smaller and builds pressure sooner.
I have shot a bit of RE-16 in several cases ranging from 6 Dasher to 6.5x55. It seems to build pressure a little slower than other powders. I have never had it pressure out in anything before running out of case capacity.
The first thing I would check for is a carbon ring. They sneak up on you when you least expect it.
The next thing would be to lower the powder charge and rework my load after the new cases have been fired 1 time.

 

[fatelvis]

Thanks Kmart. So I guess it’s not a good idea to fireform new cases with full weight powder charges? BTW, after reading about carbon rings on this site, I religiously scrub the throat with Chameleon and felt pads, when cleaning every 100 rounds or so.

 

[Laurie]

Unless you have other pressure signs, it's almost certainly a firing pin issue. The relevant factors are pin tip diameter (small dia. = good in this matter), tip fit / clearance in the bolt-face aperture, striker mechanism weight, and mainspring strength.

For some reason I've never understood, LR primers don't crater / 'blank' (the proper name for creating a hole) nearly as easily as the SR variety. LR use 0.027" thick cups; SR Magnums/BRs mostly use 0.025", so 0.002" won't make that great a difference.

What happens is actually very complex - there was a massive multi-part article on this years back in PS magazine which I struggled to follow the engineering descriptions in - but in essence, the cup is extruded back onto the firing pin tip initially 'cratering' around it in an increasingly raised form; then stage 2 sometimes sees a plug forced into the bolt pin aperture which if you're lucky remains attached to the primer; finally stage three sees the plug or a shallow disk more usually detach from the cup leaving a hole in it and it invariably ends up in the bolt. If lucky, it may sit on the firing pin tip just inside and decocking the bolt firing mechanism will eject it. More commonly, disks build up inside the bolt and will eventually affect the striker mechanism causing light strikes.

Do not carry on and accept this condition. It'll erode the pin tip and the pin aperture and may affect the trigger assembly through escaping gas. Then there is the risk of mis and hangfires.

Answers. Get something built to closer tolerances (custom actions rarely suffer this); or have Gre-Tan or some other gunsmith turn the pin down and fit a bushing into the bolt face with a smaller aperture that gives a close fit; or return to LR brass and sell the Lapua. With a choice of good LRP Creedmoor brass or parent cases to neck down, option 3 seems your best option. I have an FN SPR I rebarrelled initially to 6.5X47mm Lapua for which only SRP brass is available and it was hopeless - I had to have it rechambered to 260 Rem to return to the LRP type. (At the time nobody in the UK would do the Gre-Tan Engineering job - today I'd maybe have it done, but it costs £300 in the UK, or nearly $450 US.)

 

[fatelvis]

I just called Gre-Tan and spoke with the owner. Very professional, and I will definitely be sending him my bolt, as he does do bushing work on RPRs. Wait time right now is 6-8 weeks. I will send it out after competition season is over, until then, I’ll be shooting the LRP brass!
Thanks guys!

 

[Uncle Ed]

You didn't have pierced primers until you used new Lapua brass.
How much head clearance did these new cases have?
Meaning short cases will let the primer back out further after being fired and cause the primer to blank.

 

[alinwa]

.......
Meaning short cases will let the primer back out further after being fired and cause the primer to blank........

how?

please explain how the primer backing out makes it blank?

 

[fguffey]

Can anyone explain what is happening to cause the piercings?

No they can't. Reloaders refuse to consider the balancing act between the pressure inside the case/primer and the firing pin spring. The only time I get pierced primers is when the pressure inside the case/primer is greater than the firing pin can hold.

The pressure pushed the firing pin back, when that happens there is nothing to support the primer.

Not long ago reloaders made up another saying they do not understand; they were spreading a rumor the whole problem was caused by 'blanking' and they claimed they had to empty the rifle of chads caused by blanking.

Like there is a little trip hammer punching those holes??


F. Guffey

 

[fguffey]

Thanks Kmart. So I guess it’s not a good idea to fireform new cases with full weight powder charges?

What else are you going to do with a case that is smaller than your chamber?

F. Guffey

 

[fatelvis]

What else are you going to do with a case that is smaller than your chamber?

F. Guffey

Maybe drop the powder charge down a couple grains?

 

[fguffey]

Maybe drop the powder charge down a couple grains?

Or when developing loads start developing your loads by reducing the powder charge. That does not change the balancing act between the strength of the firing pin spring and the pressure inside of the case/primer.

F. Guffey

 

[Uncle Ed]

how?

please explain how the primer backing out makes it blank?

As the chamber pressure increases the case is pushed back against the bolt face and back over the firing pin.
The primer is then hit a second time by the amount of head clearance that can cause it to blank.
This action is like a cookie cutter and punches the center out of the primer.

Again nothing changed other than using new cases, so all that changed was the head clearance.

Below example of excessive head clearance on a over gasses AR15 and bumping the shoulder back too far.

Below pressure forced the anvil through the hole in the primer.

 

[alinwa]

wheewwww

 

[Uncle Ed]

I have had old milsurp rifles with over .017 head clearance. And if the cases are not fire formed with the case held against the bolt face when fired the primers can blank.

Again the primer is hit again a second time by the amount of head clearance as the case is pushed back against the bolt face.

The OP was not blanking primers with his old brass so what changed by using new cases?

 

[Laurie]

The OP was not blanking primers with his old brass so what changed by using new cases?

Simply the move from LR brass to SR brass. It's a well known situation. Do a search on this forum about Remington 700 actions and blanking with the 6BR. The 700 rarely has issues with large rifle primed brass but a significant percentage of examples cannot cope with the BR and pressures beyond a certain level. When this was the early days of 6mmBR.com pre the name change to Accurate Shooter and it concentrated on this one cartridge 'family', also use of this action in custom and semi-custom rifles was much more common than now, there was a great deal of discussion on how much the blanking issue could affect the usable maximum load unless a bolt bushing job was done. I imagine that Greg Tannel started this side of his business almost exclusively on 700s and with a good percentage of customers having rebarreled to the BR or built a BR rifle around the action.

My FN SPR in 308 - no issues; in 6.5X47L - cratering at every load level and blanking at around 1.5-2gn above Viht's (mild) starting loads; rechambered to 260 Rem - no problems again. (And ... I can assure you I wasn't running 6.5X47L brass with excessive headspace.)

The issue has resurfaced recently in the UK amongst our significant community of Accuracy International tactical rifle owners. AI doesn't offer any SRP cartridge options, but its marketing and service affiliate Sporting Services offers 6.5X47L chambered match quality barrels and as the latest AI model is a QD barrel change, lots of people have got them. They soon found that as I did with the FN (another 'tactical' rifle designed to stand up to users crawling down water and mud filled ditches and still give 100% ignition reliability) the blanking issue makes them nearly unusable in this chambering. The AI bolt is not an easy one to bush (I notice Gre-Tan specifically excludes them) because of its hardness and some bolts have been ruined by gunsmiths attempting the operation with warnings from AI that its warranty is void with such unauthorized work. It has become so bad a problem that AI recently announced it is putting an alternative bolt into production with a smaller diameter pin and closer fit in the bolt as an optional extra.

 

[Ggmac]

I'd start by weighing the 2 different cases . If the Sr case is more ( should be ) it could be case volume has decreased and pressure rises . Remember anytime any component is changed or replaced with different lot #s , lower charge and work back up

 

[Uncle Ed]

Laurie

You are correct, I did not catch the part about the small rifle primer cases with their thinner cups.

I have a Remington 700 30-06 that has a beveled firing pin hole in the bolt face like below. But I do not get brass flow around the firing pin and firing pin hole.

The Remington 7 1/2 primers have worked well for me with my AR15 rifles, and the OP can try them.

CHOOSING THE RIGHT PRIMER - A PRIMER ON PRIMERS
http://www.sksboards.com/smf/?topic=56422.0

 

[Laurie]

I'd start by weighing the 2 different cases . If the Sr case is more ( should be ) it could be case volume has decreased and pressure rises . Remember anytime any component is changed or replaced with different lot #s , lower charge and work back up

Excellent advice, and the Lapua case does have rather less capacity than some Hornady lots. However, as with 308 Lapua LRP and 308 Palma from the same manufacturer with near identical capacity, the move to SR primers usually depresses pressures and MVs due to the major change in ignition power and flash-hole diameter. As a result an increase in powder charge of a half grain or so is usual to restore LRP Brass MVs, but in some combinations, the SRP variant will need a grain or more powder to restore the status quo ante on a switch from LRP.

I'm a considerable fan of the SRP concept (in whatever cartridge up to 308 Win size), but have two reservations - 1) the subject of this topic and 2) serious concerns over transmission of loads data over forums and by word of mouth. Where there are two such variants of a cartridge, they should be treated as two designs, or at any rate the risk of switching SRP Max loads to LRP brass without considerable charge reduction and then working loads back up has to be stressed. It isn't just the matter of the LRP variety increasing pressures with a warm but safe SRP charge weight - which it does - but many people run these cartridges (as a type not just the Creedmoors) at well over maximum SAAMI or CIP allowed pressures. As the case-head is so strong it will often happily accept firing after firing at such pressures BUT may well see its LRP equivalent blow the primer or worse on a straight transfer.

 

[Laurie]

Here's a pic of the 6.5X47s fired in the FN with a very mild load before rechambering to 260. (These are Remington 7 1/2 BRs.)

 

[Uncle Ed]

fatelvis

Sell your new SR primer brass to someone who didn't read this posting and buy some regular Lapua LR primer brass.