Working up with some lite loads today in my Model 70 6.5x55.....very accurate
Noticed some of the primers are backed out just over edge of pocket.

Internet search is saying not enough pressure in my lite load. Or check my headspace.

Is this even an issue ?

What is the load data?

Too much clearance between your brass head and bolt face, allowing the primer to back out in loads that do not stretch or otherwise move the case head rearward to touch the bolt face.
Solution? Properly fire form brass and do not make it too short in resizing. No matter the load, this is what is happening and what you must do to correct it. Or up your loads until your brass stretches to meet the bolt head and do not resize it too much afterwards.
Some will lubricate their brass to allow it to back up without stretching but I do not recommend that.

A load too light will always back the primer out as the cup never swells and seals the pocket.
We shoot a lot of 6.5x55 in my club and have seen this happen many times.

physically, your brass is undersized - this can be addressed, several ways -

if your dies are set but you have "never seen this before with identically resized brass" then .. your brass is undersized, but has been covered by higher-than-these pressure loads

soot on neck AND shoulder, i expect?

What Jeff said.
It is not that the primer cups are going to "seal"; they are already sealed; no amount of "swelling" is going to keep them in the case, if there is room for them to back out. If anyone sees primers backing out, then it shows two things; low to moderate loads, and excessive headspace, or brass clearance, whatever you want to call it. A light load in a properly fitted brass case will never show primer backing out; how can it if there is no space for it?
What this shows is that rifle brass is capable of holding a relatively large amount of pressure, ALL by itself; in this instance, you do not need the locking lugs on your bolt. And since you are not placing any stress on the bolt at all, your receiver will last, literally, forever.
Read more P.O. Ackley testing.

P.O. Ackley did a experiment with a 30-30 Winchester and removed the locking bolt.

The rifles chamber was cleaned of any oil and the rifle was remotely fired.

And nothing adverse happened, the cartridge fired and gripped the chamber walls. And the chamber pressure at 38,000 cup or 43,000 psi was not great enough to cause the case to stretch to meet the bolt face. And the primer backed out of the primer pocket and it stopped when it contacted the bolt face.

Bottom line the primers in my 30-30 always back out of the primer pockets. And so will any cartridge until the chamber pressure is great enough to cause the brass to meet the bolt face.

Any time you make a workup load and start at the suggested starting load the primers will back out of the prier pockets. Then as the load is increased the primers will gradually become flush with the base of the case.

And many reloading manuals tell you to not use cases used for reduced loads with full power loads. This is because the case will become shorter each time it is fired with low pressure reduced loads. And if fired with a full pressure load the chance of a case head separation exists.

The amount of shoulder bump when resizing a case will be your head clearance when the cartridge is chambered.

Head clearance is the "air space" between the rear of the case and the bolt face when the cartridge is chambered.

And chambers can vary in size meaning headspace length. And a full length resizing must be able to size any case to minimum SAAMI dimensions.

And this is why it is recommended to only bump the shoulder back .001 to .002 on a bolt action. And this keeps the case from stretching and thinning when fired.

NOTE, this is why you are told to remove any case lube from your cases and any oil from your chamber. The lube prevents the case from gripping the chamber walls and will more than double the bolt thrust.

All,
thank you all for your responses. This makes sense.

Learned a little something today.

I run a lot of light loads for practice, most all of the primers are backed out slightly. When I load the brass to normal pressures all is fine, and no backed out primers.

Certain cartridges and light loads of slow burning powders do not do mix well. The primer drives all the powder forward and when it ignites it causes a large pressure spike.

I don't recall the 6.5x55mm being notorious for this - but it may be your culprit.

If he had high pressure, that would drive the brass case back and the primer would have no where to go so it would fully stay in the case. He has, conversely, low pressure, and for a couple of possible reasons, room for the primer to back out.
Read some PO Ackley and you will see.

quote:

Originally posted by Charlie P.(NY):
Certain cartridges and light loads of slow burning powders do not do mix well. The primer drives all the powder forward and when it ignites it causes a large pressure spike.

I don't recall the 6.5x55mm being notorious for this - but it may be your culprit.

Ignore. The poster is trying to describe Secondary Explosion Effect (SEE), which is a rather rare phenomenon of pressure excursion and is NOT in any way in play here.

quote:

Originally posted by dpcd:
If he had high pressure, that would drive the brass case back and the primer would have no where to go so it would fully stay in the case. He has, conversely, low pressure, and for a couple of possible reasons, room for the primer to back out.
Read some PO Ackley and you will see.

My second rifle was a sporterized 8mm Mod. 98 Mauser. In those days, they were quite common and you could get Remington and Winchester factory ammo for them. I shot the 200 grain round nose and every single one of those primers backed out.

The problem the ammo manufacturers had was that earlier 8mm Mausers were built for a .318 in bullet, latter ones for a .323 inch bullet. So, to guard against a catastrophic failure if the larger diameter bullet was shot in a .318 barrel, the .323 bulleted cartridges were significantly underpowered. There just wasn’t enough ooomph for the case to be thrust backwards and reseat the primer.

quote:

Originally posted by 22-250guy:
Working up with some lite loads today in my Model 70 6.5x55.....very accurate
Noticed some of the primers are backed out just over edge of pocket.

Internet search is saying not enough pressure in my lite load. Or check my headspace.

Is this even an issue ?

At low chamber pressure the primer will always back out of the primer pocket by the amount of the head clearance.



When people ask this question it makes me wonder if they ever make a workup load starting at the suggested start load.

The last new .243 cases I bought had .009 or or more head clearance. Meaning the cases were .009 shorter than the chamber. And the primers would back out that much at lower pressures.

And these same .243 cases were fire formed by seating the bullets long and jamming the bullet into the rifling. This held the case against the bolt face and allowed the case shoulder to form to the chamber.

bigrdp51: Great graphic!

Nine thousandths is well within manufacturing tolerance for chambers and brass, lest anyone think something is wrong with the above scenario.

quote:

Originally posted by dpcd:
Nine thousandths is well within manufacturing tolerance for chambers and brass, lest anyone think something is wrong with the above scenario.

The GO gauge is 1.630

The NO-GO gauge is 1.634

Maximum headspace is 1.640 (Field gauge)

Manufacturing tolerance for the case is 1.634 -.007 or 1.634 to 1.627

My .243 will not close on the NO-GO gauge. So these cases were shorter than SAAMI minimum headspace length of 1.627.

The only other way the case could have .009 head clearance is if the rifle was close to the field gauge.

Bottom line a case with .009 head clearance will stretch and thin if it is not fire formed properly.

Basic headspace in many cases..Ive delt with it on old German guns and Winchester lever actions..nothing to get excited, the case comes out fireformed, so necksize the cases from then on until they show signs of not chambering...You would be surprised how many old Winchesters have a little to a lot of headspace.

If you want continue to shoot reduced loads and not have the primers back out you should enlarge the flash holes. You must mark these cases and separate them from your full power cases so that they are NEVER used for full power loads.

Point is that the tolerance allowed is .013 between min ammo and max chambers.
It is a miracle that things work as well as they do. Given rifles, ammo, dies, brass, all made over the past 100 years.
Very few guys get into serious trouble with them.