I thought I had spared no expense on my latest build. I went with a Mega Arms monolithic receiver set, and one of Rainier Arms 5R barrels made from Rock Creek blanks.  About the only thing that didn't cost me excessive cash was the Aim Surplus V2 Black Nitride BCG.

From the first shot with this new build, I was piercing primers.  I was running my go-to 77g SMK load using new brass and CCI #400 primers.  It closely matches MK262 ammo performance.  It has always run fine in my rifles.  Nonetheless, after a few shots I checked the firing pin.  It could have been damaged initially, but it was certainly damaged when I checked it after my first few shots.  The tip looked worn away, like some sort of pressure erosion.

I promptly replaced the firing pin with a brand-new one, and started again. Pierced primers continued, and this time I managed to seize up the entire rifle.  I'm assuming from a bit of primer material that found its way into the bolt.

After disassembling and cleaning, I tried a third time.  This time I dropped in a completely different BCG. It was a barely used one from Bravo Company that I took from a different rifle.  After ten shots (ran out of ammo), I had zero (0) pierced primers.

So is my problem gone?  Am I on the right track?  I read somewhere that the problem could be excessive headspace.  If so, do these AIM BCGs have such a reputation?

Any input would be appreciated


w/ Aim Surplus BCG  (two different firing pins)



w/ Bravo Company BCG

Looks like you already figured it out.

No, the AIM BCGs don't have a reputation for that.  The most recent batch did have gas key staking issues, however.

More serious reloaders than I will weigh in soon but pierced primers come from over-pressure in some way. Can be things like too much powder, tight crimp, and other ammo related issues.  If this is a known round to you then it probably is not the issue, but I would still try some White Box or other quality US made ammo with thick primers and sort out the ammo issue.
On your pierced primer pics, only the middle one showed primer flattening to my viewing.

Otherwise it can be either excessive headsppace or tight headspace.  On excessive headspace, there is a "slapping" effect as the case moves in the chamber, and the primer can make contact twice, causing a pierce. I vote that this is your issue.
The tight headspace issue is a straight overpressure issue.

As the other poster commented, It looks like you have figured it out, as least as far as having a functional rifle.
Otherwise, you should think about having some case gauges to check the headspace.

FWIW, I always:
1) check headspace
2) use known US made ammo (Federal Green tip in my case) before anything else in a new build.  

Just keeps the variables to a minimum.

There are many more on this board more knowledgeable than I on this issue and they will be along shortly.

Pierced primers are not always from excessive pressures.  Did you check firing pin protrusion?  Spec is .028 to .036, and a long FP will most certainly cause pierced primers and I have been down that road more than once on some wildcats that use pistol primers.  They need their FP to be buffed back to .029-.030 so while yours is not a wildcat, you may benefit from checking the length of the firing pin protrusion.

You're right.  He did replace the firing pin once but if the bolt is out of spec it wouldn't help to change the pin.  Easily checked.

Check the size of the FP hole. If it is oversized, the edge will cut the center of the primer out. Diagnoses:  bolt -- OOS. You could try bevelling the edges of the hole, but your best course of action is send it back to AIM.

Thanks for the feedback, guys.

Firing pin protrusion seems about equal between the two bolts;

AIM - 0.0295"
BCM - 0.0290"


Firing pin hole diameter is a different story. The AIM is 0.006" larger at 0.069".  You can almost see it (below)

Does this warrant a return claim to AIM?


(guess which one is the AIM)

Find a way to check the headspace so you have data.

Your brass is suspect IMO. Weigh an unprimed case and report back what it weighs. Foreign made military surplus brass is all over the place when it comes to internal capacity. Old lots of Lapua weigh over 100 grains empty. FNM (Portugal) weighs close to 104 grains empty. I need to download this brass 1.0 whole grains.

USA manufactured Lake City and commercial brass does not suffer from these wide variations. Most of it weighs around 92 to 95 grains empty and loads can be safely swapped using the different brass.

Whenever someone is piercing primers they are too hot. It doesn't matter that "they looked fine in other rifles". The load needs to be reduced, probably .5 to 1.0 whole grain. Without chronograph information and barrel length we're running blind.

These are your personal reloads?

The pictures show a purple "sealant" around where the primer meets the case, usually only found in factory loaded "combat" or military surplus ammo.....

I see ejector flow, hard extractor marks, and primer protusion around the pin strike - both indicate your load is too hot for that chamber.

You took a brand new build, didn't check headspace, then immediately started shooting a reload that is beyond SAAMI spec maximums?

Granted - a lot of people do that.... build a new gun and immediately start shooting 5.56 pressure ammo from day one.... but occasionally you see this.  My gut is your load is far too hot for this chamber.


The AIM bolt could be a bit short on OAL, which will lead to a longer firing pin protrusion.... but my guess is that having no wear, it headspaces shorter than your slightly broken in Bravo one.

When you have issues like this - you need to break out the headspace gauges.


How do you have primer sealant showing on brass you primed?  You do this?

enhance

enhance



enhance  




it looks like blue Sharpie to me not sealant

There are at least two or three companies that sell primer sealant. I used to use one called George and Roy's.

Thanks for all the feedback.  I do agree my go-to load may be called into question. I guess I'll need to develop a new for this setup.

As for the primer sealant, I do it myself with a syringe and some Dykem Steel Blue

Thanks

 

STOP THE PRESSES!


Dykeem Steel Blue increases chamber pressures by 0.00025%

Before doing anything try some factory M855 or 193. You want to rule out your own loadings. I learned about oversize FP hole syndrome years ago. My rifle would punch out steel case 223/556 primers and my handloads (reduced powder chgs many times with no change). Finally I got clued in after looking at the slide face of a Beretta 96 -- the FP hole was slightly concave. When I chamfered the FP hole on the 556 MAK90 (same issue on an NHM90 -- Boom - no more pierced primers.  So to complicate the landscape in diagnosing chamber/head-space/bolt issues -- primer flow does not always equal high pressures.