Pierced Primers, Lapua and AI AE

[Lucky Se7en]

A few years ago I had bought some Lapua ammo to shoot out of my AI AE MkIII and experienced my first pierced primer. I ended up putting those rounds off to the side and started shooting mainly FGMM and hand loads without any problems or other pierced primers since. Recently i came across a deal for some of the 155 gr Scenar factory ammo so i figured I'd give the lighter bullets a try. At the range this past weekend I ended up with another pierced primer. Has anyone had this issue before with factory Lapua ammo? Pierced primers from factory ammo across separate bullets (185 gr D46 and 155 gr Scenar for my instance)

 

[Supersubes]

It’s likely your firing pin that’s causing it, not the ammo.

 

[Huskydriver]

It’s likely your firing pin that’s causing it, not the ammo.

Bingo

 

[b6graham]

Bush the firing pin and you'll be good to go. Known problem with AIs with large firing pins and especially with small primers

 

[6brshooter]

Bush the firing pin and you'll be good to go. Known problem with AIs with large firing pins and especially with small firing pins

Um, the small firing pin and aperature took care of the problem. Ai ae were designed as 308s, not many problems there with good primers like cci. Fgmm primers are known to be thin cupped. When ai started putting 6.5 barrels on ae's, that's when issues arise. My 6.5ae was fine, but others had to run slower loads to keep from blanking primers. The aes I've measured have a .090" aperature and .080 fp. My mk3 was bushed recently, as it's getting close to a rebarrel. The mk2 I picked has its bolt at lri getting bushed right now. I think, on the 6.5s, it came down to luck of draw. Seemed some barrels caused more pressure and blanked primers. I could run 2810 with 139s in mine with no issue, some guys couldn't get over 2700 without piercing.

 

[6brshooter]

What's fp protrusion? .045-.050 is plenty.

 

[b6graham]

Um, the small firing pin and aperature took care of the problem. Ai ae were designed as 308s, not many problems there with good primers like cci. Fgmm primers are known to be thin cupped. When ai started putting 6.5 barrels on ae's, that's when issues arise. My 6.5ae was fine, but others had to run slower loads to keep from blanking primers. The aes I've measured have a .090" aperature and .080 fp. My mk3 was bushed recently, as it's getting close to a rebarrel. The mk2 I picked has its bolt at lri getting bushed right now. I think, on the 6.5s, it came down to luck of draw. Seemed some barrels caused more pressure and blanked primers. I could run 2810 with 139s in mine with no issue, some guys couldn't get over 2700 without piercing.

meant to say small primers

 

[ShtrRdy]

While the OP didn't say in the original post, it sounds to me like he's experiencing this on a .308 Win.

 

[6brshooter]

I caught that, I'd chalk it up to thin cups in lapua factory ammo. I assume this is large primer brass?

 

[Lucky Se7en]

This is a problem with 308 and they are large primers. It seems a little strange it is just happening with Lapua ammo. Other people don't seem to be having this problem with Lapua so I wonder if the firing pin problem is applicable to 308 also.

 

[6brshooter]

Check firing pin protrusion. Is there any damage to bolt face, from a pierced primer?