30-06 primers backing out

[centerlineseal]

I'm working up a load for a friend's 700 BDL, very early vintage which he says he's owned since the early eighties and has shot very seldom.

We shot off a mix of old reloads or factory rounds he had with no issues except the best I could get out of them was 1-1/2 moa. Nothing surprising. (I did not notice any primers backed out, but did not look for such)

Brought the rifle home, figured out max OAL using 165 gr Hornady SSTs using Sinclair tool and backed them out about 20 thou for the initial reload batch. OAL was 3.410, well above Saami, but rifles mag length was very generous, so I'm able to go with the longer round.

Full length sized, trimmed, primer pocket and flash hole uniformed using sinclair hand tools. Ran all brass through the rifle chamber to assure properly sized. All R-P brass. (Older Pacific dies - I haven't loaded 30-06 for over 30 years)

Started powder ladder test with 53.0 gr IMR 4350 over CCI 250s. Used 6-7 rounds to sight in at that charge and was able to get an initial 3 shot group of about 3/4 moa. Again, as expected.

I then shot a ladder up to 57.0 gr in 0.5 gr increments looking for powder nodes. Found one at 53.0 & 53.5 and another at 56.0 & 56.5. No pressure signs at all.

However, All primers backed out at least a couple thousandths, maybe more (all very visible to naked eye at the range) UNTIL I shot the 55.0 gr load and heavier, where the primers remained fully seated and actually flattened a bit (Again, nothing excessive and no bolt lift issues and and/or case head smears)

I have NEVER had an issue with primers backing in in the 10 - 15 rifles I reload for.

What is going on here? Excessive headspace? Too low of initial powder load? (Beginning load from Nosler manual)

Should I be concerned? I may have to get an RCBS Precision Mic to check the shot brass.

My intent is to load him up a couple of hundred rounds in 56.0 gr using once fired LC brass after a bullet seating testing regime and send him on his merry way.

Thank You for your thoughts.

 

[Bc'z]

Be sure to check case capacity of the LC brass next to the RP.
I have a .6gr variance from my RP 55.8gr next to lapua of 56.4gr h4350.
As for the primers backing out, from what you described it very well could be from the lower charges.

 

[centerlineseal]

Thanks Bc'z. I'm thinkin' the seating test, with the bullet going further into the case neck, may make a difference as well. Any one else with some thoughts?

 

[243winxb]

A starting load , with slow powder, may let the primer back out.

The head to datum measurement may also get shorter. The case body expands outward & pulls the shoulder back. Trim length will get shorter.

When inserting a bullet into a fired case, it may be a snug fit. Low press & slow burn rate powders (IMR 4350) dont always fully expand the necks on firing.

COL longer then SAAMI may be ok? I like to see full contact between bullet shank & case neck.

Rem brass & LC may produce very different results and pressures.

I do not load for others any more.

 

[Laurie]

Primers backed out are a classic symptom of a combination of excess headspace and mild pressures. When the firing pin falls it pushes the round forward in the chamber leaving a small gap between the case-head and bolt-face. When pressures rise the front of the case-body obturates tightly in the chamber holding the case there and without support the primer backs out until stopped by the bolt leaving it slightly proud after firing.

When the load / pressure pass a certain point two additional steps take place - the front end of the case-body remains locked in place but the lower body walls stretch under pressure and the case-head is forced back onto the bolt. This pushes the primer back into the pocket leaving its face flush with the case-head and also flattens it giving a potentially false appearance of excessive pressure having been produced.

The answer is to adjust the sizer die to reduce the amount of shoulder 'bump' in sizing so that the resized case still chambers freely but with minimal longitudinal clearance. Small amounts of such excess headspace with sized brass isn't in itself dangerous but is undesirable. Repeated shoulder set-back followed by case stretching sees case OAL grow more rapidly than otherwise and the need for constant trimming, and more seriously it weakens / thins the lower case walls just above the solid web resulting in early case failure / scrapping through separations / incipient separations appearing.

http://bulletin.accurateshooter.com/?s=incipient+case+separation&submit=Search

These are two lots of 7X57 cases from factory ammunition fired in a rifle with serious headspace issues. The full pressure RWS cartridges in the top pic have flat primers and show case stretching; the low pressure PMC ammo in the lower pic shows considerably protruding primers but lacked the pressure to stretch the case and force it back onto the bolt.

 

[243winxb]

Hodgdon Youth Loads in 30-06 will produce backed out primers and shorter head to datum. Has nothing to do with chamber headspace.


Use this brass for reduced loads only. Switching between reduced and full pressure loads, using the same brass, may produce case separations.

 

[Laurie]

Hodgdon Youth Loads in 30-06 will produce backed out primers and shorter head to datum. Has nothing to do with chamber headspace.

I'd respectfully disagree with that. By definition, the primer simply cannot back out if there is no clearance between the bolt and case-head. The reason for ultralight loads creating backed out primers is that the action of the firing pin creates a small - and cumulative - amount of extra headspace on each firing in bottlenecked cases. The low pressures fail to produce a fireformed case to chamber fit. Back in the days when very light to ultralight loads were much more popular than today, people like George C. Nonte Jnr and P O Ackley frequently commented on this occurrence and both warn that cases used for very light loads should be kept aside and never subsequently reused in full pressure loads.

I was careful not to suggest that the 30-06 rifle in question necessarily has an excess headspace condition as shown up by a no-go gauge. However, a small degree of wear in an older well used 30-06, 270 or similar hunting rifle will often see some 'slack' here and setting the sizer die up in the default hard-contact position often produces enough clearance to see primers back out a little in low loads and/or produce an incipient case separation after relatively few firings with standard working pressure loads.

However .......... if the OP saw as much primer movement as in the PMC 7X57 brass in the lower photograph with his light 30-06 loads then there very well may be significant excess headspace in the rifle and it should be checked out by somebody with headspace gauges. The rifle that produced those cases was a junker and ruined most factory round brass on a single firing.

 

[centerlineseal]

Thank you all for your guidance.

As best I can measure, primer backout was in the 5 -6 thousandths at low end, about 2 thousandths at mid range and none at the top end. Laurie's picture of brass used in an excessive headspace chamber "looks" quite a bit more than what we have here.

The load I started with, 53.0 gr IMR4350 was the starting (low end) load in the Nosler manual. Sierra manual was similar. I would not have considered that as an excessively light load. Primers backed out well into mid range charge from the manuals. I did not go past the max load recommended, but I did not experience classic indicators of excess pressure in the upper range. (as detailed in the link provided by Laurie)

That said, I believe this rifle probably has some headspace issues. We will have it looked at professionally, but I want to try the LC brass , starting at mid range charges, to see if the issue persists. Also, will try shortening out the OAL to get more bullet bearing surface into the neck.

This may very well be one of those hunting rifles that gets fed factory ammo or 1x fired reloads and then the brass gets discarded. Belongs to a 70 yr old neighbor who will only get to use it elk hunting a few more times before he's done.

Thanks again!

 

[AlNyhus]

.....I believe this rifle probably has some headspace issues

Head space is the distance between the bolt face and the datum line of the chamber.

If you have primers backing out due to excessive case sizing (shoulders being pushed back too far), this is not a head space issue. It's a sizing issue.

Good shootin'. -Al

 

[centerlineseal]

Indeed. I could have pushed the shoulder back 7 - 8 thou. I have backed off the full length resizing die for the next batch. I'll let you guys know.

 

[Rsadams]

Indeed. I could have pushed the shoulder back 7 - 8 thou. I have backed off the full length resizing die for the next batch. I'll let you guys know.

If you don't have one , pick up a Hornady headspace comparator.... It will help you to adjust your dies to min. shoulder bump... Setting up dies per the instructions will almost certainly result in huge setback because the die makers want to make sure the cases will fit pretty much any chamber after sizing and they don't want the phone ringing off the wall with people calling and asking why their sized cases won't chamber.... As you probably already know 1-2 thousands setback for a bolt action and 3-4 thousands for an automatic and you will be in good shape.... If you're using these rounds for hunting or even self defense I suggest going on the bigger side because you don't want to have it sized so it gives you problems when that big buck walks out etc..

 

[centerlineseal]

I usually use an RCBS precision mic to set up my dies for minimum shoulder bump, but don't have one for 30-06. These are strictly for hunting, so I will err on the larger side of shoulder bump. all things considered, I expect to tell the shooter to ashcan the brass after use.

 

[NorCalMikie]

Primers backed out are a classic symptom of a combination of excess head space and mild pressures

I would lean more to the "head space".(brass problem) Brass probably too short for the chamber. Once fire formed, backing out will probably no longer be an issue.

 

[Laurie]

There's a bit in the way of semantics here. By 'excess headspace' [allied to a mild or low load], I mean anything which creates a significant gap in the case to chamber longitudinal fit. That can be a combination of a maximum allowed bolt to chamber datum line dimension allied to a minimum allowed case-head to shoulder datum line distance in a new case or factory cartridge; cases resized with excessive shoulder 'bump' for that chamber's dimensions; or, a fault in the rifle where there is excessive bolt/chamber headspace so that maximum SAAMI or CIP chamber tolerances are exceeded.

These are causes and irrespective of which applies, the actual condition remains the existence of more clearance than is desirable, or in the worst situation involving a faulty rifle, is tolerable. It's that clearance, that bolt to case-head gap at the time of ignition and early burn whether caused by a true 'headspace issue' or a as Al Nyhus says, a 'sizing issue' that allows a primer to back out enough to be significantly proud of the case-head in the fired case, bearing in mind that the unfired primer cup is normally slightly recessed below the case-head before firing. No gap, no proud primer. However, the shooter will only normally be aware that the primer has been excessively extruded from its pocket if the load is mild such that the gap isn't closed through case stretching to match the chamber under peak pressure thereby leaving the primer 'hanging out'. When cases stretch they push the primer back into the pocket, so the only immediately visible symptom is usually a very flat looking primer in relation to the loading used (sometimes too with its outer edges actually overlapping the pockets edges slightly). Significant case body stretch may also show up as excessive case length growth requiring trimming on each reloading and poorer than expected case life thanks to incipient separation appearing after a few firing / sizing cycles.

In practice, primers move out slightly initially even in an optimum case to chamber dimensional match. Then as the internal pressure peaks the case stretches marginally so that the flattened face of the primer normally ends up level with the case-head in a full-pressure loading.

I'd suggest most handloaders other than those loading for precision rifles for the more demanding applications have become complacent over the issue of die settings and the amounts of shoulder 'bump' they're applying. (That's assuming of course that they're even aware of it being a possible issue.) Read the older literature by Nonte, Ackley et al from as late as the 1960s or 70s and they stress the importance of not taking it for granted that the hard contact default die position will size the case properly. It seems that today's dies and factory rifle chambers are much better matched in this respect than applied a generation or two back and I rarely find now that the optimum setting is far removed from the default one. On the contrary, there are an increasing number of forum threads on the subject of insufficient clearance, ie people asking 'Why won't my handloads chamber easily in my rifle after FL sizing? (Or sometimes why won't they chamber, full stop?)

Using the Stoney-Point / Hornady 'headspace gauge' (a bit of a misnomer given that it doesn't measure headspace and it's a comparator not a true gauge) I sometimes compare readings for new out of the box brass against those for fireformed examples. (I know, it's sad - I really must get a life!) There's usually little difference these days in 'quality' makes, just a couple of thou' less for the new examples. I stress 'usually' as starting out on load development for the 6.5mm Grendel in a bolt-rifle with new Lapua cases a few weeks ago, my first two lots of test rounds sharing case, primer, and bullet make/model but different powders in what were almost certainly modest pressure loads showed a marked discrepancy in fired case extraction and primer appearance. An extruded powder with a near 100% case fill-ratio produced harder than expected extraction, but allied to primer appearance that suggested very modest pressures. Cases had signs of a longitudinal crush fit in the chamber - witness marks on the shoulders and circular marking of the case-heads from the bolt face - but had chambered sweetly so no initial mismatch. Also no ejector marks at all. The other load using a much recommended ball powder with a lower fill-ratio was the reverse - easy extraction, no case-marks but primers so totally flattened there appeared to have been excessive pressures. Measuring deprimed but unsized fired cases on the Hornady kit saw very different readings from the two lots with the extruded powder load cases significantly 'longer' than the ball powder ones. Definitely a 'headspace issue' (ie a case to chamber match issue being more precise.) Scratch head! ....... then measure new unfired cases to see what they start at - minimum 0.008" shorter base to shoulder, some 0.010" shorter than the extruded powder fired examples. I've bought and fired many hundreds (more likely thousands) of Lapua cases for a double figure number of cartridge models over the years but never seen this before. A faulty production lot? Then I wondered that given the baby 6.5's use having until recently been almost exclusively in semi-autos, many home-assembled DIY AR-15s, had Lapua deliberately made these cases such that they'd have excessive clearance in a SAAMI-compliant chamber? The worst thing that can happen in many semi-autos is a slightly too 'long' case for the chamber but just giving enough lock-up to allow the firing pin to drop, so build a bit of 'safety' in here. It could of copurse be my rifle has a way over-spec chamber, but it's 1) a Japanese manufactured Howa and their QC is normally excellent and 2) in the UK / EU we have mandatory proof testing of new rifles before sale and an out of spec headspace example will fail.

 

[centerlineseal]

The more I learn (and I've learned a ton, ... on this forum, the loading bench, and the shootin' bench), the more complex it gets! I'm amazed how far I've gone from the Lee hand loading set my Dad gave me back in 1976. Still have all my fingers too!

On the immediate issue, I plan to section a few cases to see if I'm approaching case head separation. Might even get some fresh brass and section after firing.

Thanks for all your insight!

 

[243winxb]

case head separation.

Brass has to stretch more than .010" and may have to be reloaded about 3 times.

The 5.56 M16 brass may separarte in the middle of the case body with .014" stretch . May take more then 1 loading.

Taking measurement is the only way to know how much stretch is happening.

 

[centerlineseal]

Finally getting back on this, ...heavier load arrived at by powder ladder test, ... NO proud primer. I sectioned several cases, various load scenarios and times reloaded. No case showed any sign of incipient separation.

My conclusion (which I did not try to duplicate) is that the lower powder charge was insufficient to properly "expand" case in this particular chamber.

 

[Bart B.]

30-06 case shoulders easily set back a few to several thousandths from firing pin impact. If peak pressure isn't enough to fully expand the case to fill the chamber, case headspace will be less after firing.

 

[Uncle Ed]

Any time you make a workup load starting at the suggested starting load the primers will back out of the primer pocket. As the load increases you reach a point where the chamber pressure is great enough to make the case stretch to meet the bolt face. And at this point the primers will be flush with the base of the cases.

My 30-30 at the max chamber pressure of 38,000 cup or 42,000 psi always have the primers protruding. And the same applies to reduced loads in any rifle cartridge. Also the reloading manuals warn you to never use cases used for reduced loads again for normal high pressure loads. The reason for this is these cases get shorter every time they are fired from the force of the firing pin hit.

 

[Dusty Stevens]

Laurie is right- you sized your brass too much and shot a light load