Seriously cratered primers

[dorg]

We were having a practice session this morning and one rifle was giving very seriously cratered primers, before everyone shouts. this is not an over pressure problem. The morning ended with peirsed primer and a locked solid firing pin. What would the causes of this be, my thinking are 1,firing pin spring to strong, 2 firing pin projection to far out of bolt, 3 firing pin hole in bolt to big for the firing pin.Some ideas from the wise guys would be most grateful.

[DaveT]

One for the gunsmiths I guess but ..worth checking if the firing pin end is damaged?

 

Has this only just started after 'OK' use up to now?

[dorg]

No its done it from the start.

[Laurie]

Large diameter firing pin with a lot of clearance around it in the hole in the bolt-face is the most likely cause. A weak mainspring rather than too strong can be the cause or a contributotor to the problem. (A weak spring can't stop the primer cup extruding back into the bolt, so the little plug of brass literally partially retracts or recocks the bolt's firing mechanism forcing its way past the firing pin tip into the bolt body.) Excessive pin extrusion might be a cause, but it's far more often the first and/or second reasons above that produce this condition.

 

You don't say what the action and cartridge were. This is far more common in cartridges that use small rifle primers and produce high pressures - PPCs, BRs, 6.5X47L, .223 Rem. I have an FN Special Police Rifle, originally .308 Win, and a really good Winchester 70 WSM receiver based design in a Macmillan A5 stock. After I decided that 308 in a factory 24-inch barrel wasn't cutting much mustard in national league F-Class rounds at 900 and 1,000 yards, I got it rebarrelled to 6.5X47 Lapua. It was a disaster! 0.5-1.0gn above Viht's starting loads and I was piedrcing BR primers. The 'Gun Pimp' of UKV fame rechambered it to .260 Rem (which uses large rifle primers) for me and the problem was solved.

 

Winchester and Rem 700 actions, Savage to a slightly lesser extent are often badly affected in this situation. It varies from rifle to rifle depending on how the factory tolerances affect the pin to bolt fit.

 

If the cartridge was an SR primer user, a partial answer is to use SR Magnum or BR primers. CCI-400, Rem 6.5, PMC standard SR use 20 thou' thick copper sheet to punch the cups out of. Federal 205M has 0.0225" thick cups and CCI-450 / BR, Rem 7.5BR, PMC (Russian Murom), Remington 6.5 etc use 0.025" cups. Of these the Rem 7.5BR and F205M are noticeably 'softer' than the CCIs or now unobtainable PMC SRMs and more likely to crater. (Not an issue in LR primed cartridges whose primers are all 0.025" cup thickness.)0

 

I've seen the problem you describe many times in .223 Rem Remy 700s when the shooter has used CCI-400s or Rem 6.5s thinking that 'magnum primers' are only for larger cartridges using ball powders or similar. Remington used to advise somewhere in its literature that the 6.5 was for lower pressure .22s - .22 Hornet, .218 Bee, .222 Rem.

 

Rifles with custom target actions - RPA, Stolle, Barnard, BAT - use smaller diameter pins which are also a very close fit in the bolt. They seem to be able to use almost any primer without any great problem here even in max pressure PPC loads.

 

PS when you say 'wise guys' is that in the American sense? (He GaryW where are you? We missed your humour at Diggle today.)

[dorg]

The primers are cci br2 and it is a custom action in 7mm shahane.

[Laurie]

The rifle owner has a problem then. He or she should take it back to the gunsmith. (Or maybe just try a single round with a diffrerent make of primer, It may be a faulty batch with very thin cups - but I'd say that's an outside clutching at straws option unless he's very lucky.)

[dannyt]

Most likely the firing pin lock up is a metal shard blown back into the pin assembly . Take it apart and clean it out.

 

I would try another batch of primers first , I have herd of this with Cci primers before now also seen hard primers from them ,when change of batch gave no problems at all

 

You have been short on info given about the load used.

 

Powder and weight ?

 

Neck tension ?

 

Bullet used jam or jump?

 

Chamber neck size?

 

Bushing used and die used?

 

Brass used?

 

What is the brass turned dimension loaded an dun loaded?

[dorg]

Bolt already stripped and cleaned,sadly its not a primer or load problem, as stated before its not a pressure problem either.

[dannyt]

What's the load powder ?

 

 

 

I beg to differ if your bursting primers it is the firing pin is to long or your over pressured the load .

 

Have you worked up the load or just dropped in a weight and found this problem .

 

The reason for working up a load is you start to see pressure before you have blown primers .

[taylor]

Is the firing pin end look nice and round or sharp angles to flat

Check protrusion of the pin and measure pin hole and pin to see if it's to small for the hole you will get primer flow

[dannyt]

The problem is very simple to sort out a, back off the load a few grains and work up until you find the problem Again .

 

It's also easy to work out your firing pin over length if it is at all, simple load a few cases with just a primer and no powder if you still pop primers there is your problem .

[taylor]

Cratering is normally caused by loose fitting pins

[dannyt]

Agreed but it's no the hole picture I think .

 

From a custom action it's very rare

 

And again it's very easy to determine via a few steps as stated earlier ,

 

Opinions were asked for to resolve this problem but very little data has been given from the original post

[fizzbangwhallop]

I posted this on another thread yesterday...... it's another possibility.

 

My Lee .223 shellholder was found to be the cause of misleading primer pressure problems with a less than maximum powder charge when I was developing a load for my .20Prac Sako A1 barreled by Neil McK. and it took a visit back to him to suss the root problem out.

It's inaccurate and therefore non-standard deck height was bumping the shoulders back too far on new Lapua brass and allowing it to slam back against the boltface and the primer cratered into the firing pin hole. Switched to an RCBS shellholder and the problem disappeared.... but I had to buy another box of brass. Merde.

 

atb

 

Fizz

[dannyt]

Good post , I've sen case neck separation before due to die problems .

[Laurie]

Hmmmm .... while excessive headspace due to too much shoulder bump can cause all sorts of problems, the primer condition usually gives a false impression of excessive pressure. The OP is adamant that pressures aren't excessive, and I'm assuming that one reason for that is cratering / piercing accompanying an otherwise hardly deformed and still completely rounded primer cup shape. Perhaps dorg can confirm that's the case?

 

When there is excessive headspace, the firing pin strike pushes the case forward in the chamber until it contacts the front of the chamber and creates a gap between the bolt-face and case-head/primer. Without bolt support, a non-crimped in primer immediately backs out on ignition through Newton's third law as an equal and opposite reaction to the blast of primer gasses going forward into the primer cup and it moves back until it is in contact with the bolt and partially flattens being made of soft material. As soon as the propellant charge ignites, the case-head is forced back hard against the bolt-face, the case body is stretched, and the primer is forced fully back into the pocket, but retains a completely flat rear face, often with a small lip around the edge of the pocket having expanded to a greater diameter than the pocket. This gives the impression of a heavy overload due to its being so flattened.

 

At the same time, such cases sized with far too much shoulder bump stretch an alarming amount, and if this is the situation here will quickly show up on a length check.

[dannyt]

as ever laurie a full explanation .

 

But as stated very little to no information has been given as to the load dies , are the cases fire formed or new .284 .

 

there is more here than has been stated .

 

head space has to be quite out of wack to get these results . {simples run a go gauge and no go through the chamber}

 

I know of a regular Diggle bench rest shooter who cannot get past 54 grns of H4831 without blowing primers .(in a shehane)

 

More honest info is required to get to the bottom of this issue

 

also there is a competence issue , how much experience has the home loader ?.

 

who is loading the ammo I no some shooters cannot do there own work up for a load and have got people to work up a load for them .

 

, a little knowledge is a dangerous thing

[taylor]

I have shot cases that had 10 thou bump by accident while setting up die no craters or peirced primers on stiff loads you would need to bump them a ton and he is jamming bullets into the lands with vlds so case head is firm on bolt face

[taylor]

I built over 30 shehanes and load developed a lot never seen one shoot less than 57 grms from the tightest of bores

Either not enough throat ,doughnuts or to tight fitted necks not enough clearance or carbon rings 54 grns is a mild 284 win load

[dannyt]

well loads development is the key by the sounds of it, working up rather than dropping on a load .

 

as stated no info just all guess work .

 

I no of a Shehane built by a well known scotch bench rest shooter and rifle builder.

 

this gun will not shoot at high pressure , as stated blows primers at 54 grns of h 4831 .

 

working up is the KEY to find a pressure spike if this is what it is but with out work up.

 

we are all in the dark

 

no info ?????????????????????

[taylor]

I worked the load for him - it's good to go no load issues and I done the barrel and dies so headspace on chamber is perfect

Yes like i said 54 grns is 284 mild load never seen one like that I bet theirs other issues like on post earlier reasons why he got pressure at 54 grn theirs a reason behind it

I can't blow primers at 60 grns on my guns

[dannyt]

I am with you there grant but as stated in this thread , no info , no info no info ,

 

your speaking from a point were nobody else sees what has been happening and you and you alone has had this info ,

 

now the lights are on we can go forward with this post.

 

no body is digging at any body ,there has been very little info to go on just guesses.

 

more like driver error .

 

I am the same and running 59.5 to 60 grns of vit 165 with no pressure signs at all.

 

Its clear now that this is a reloading issue ,

 

best advice is to get some one with experience to work up your brass Dorg as this is the cause of the pressure problem .

 

Ask spud to work it up for you he is just down the road , I think he still offers this service

[6mmBR]

My Shehanes run 58 gn H4831sc with no issues?

Possible causes? If the barrel hasn't been cleaned and scoped during break in a severe carbon ring has formed pushing up pressures?

Or a dodgy reloading scale giving low readings and hence an over charge.

We are all clutching at straws until we get more info from the OP.

Over to you Simon?

Cheers

Dave

[1967spud]

im shooting 58.2 no probs

 

 

1000 rounds down the barrel as of yesterday and no throat erosion either happy days

[dorg]

Please note folks, I asked what could cause this problem other than over pressure from a hot load, this is why I have posted no load data. THIS IS NOT THE PROBLEM. I use only the best reloading gear powder is weighed to the grain of powder. The barrel is spotlessly clean. Having discussed this with people who know what they are on about the problem is either a weak firing spring or an over sized firing pin pin hole in the bolt.The bolt will be on its way back to the makers today. I will post some pics of the problem when Joe gets home from work.