Cratered Primers on 308

[Lawren5]

The primers on my 308 load are showing signs of cratering in which the sides of the firing pin indentation rise above the surface of the primer. Normally this would indicate excessive pressure but the load I’m using is Hodgdon’s recommended starting point: 41.0 grains of H4895. I reduced the load to 36.0 grains but the cratering still occurs. At 36.0 grains, the bullet chronographs at 2,381 fps which is well below the 2,551 fps of Hodgdon’s starting load. I thought it could be the Winchester WLR primers but I also use them in my M1 Garand with no sign of cratering whatsoever.

Would appreciate any suggestions you have on what may be causing the cratering.

[Geezerbiker]

Do factory rounds do this? If it's not over pressure, then it could be a weak firing pin spring or an under size firing pin for the hole in the bolt.

Tony

[Lawren5]

Well now that you mention it, I've never shot factory rounds in it, only reloads. Of course with the ammo shortage right now, it's going to be difficult finding a box of factory 308's.

[Metal god]

With that charge and velocity ( 36gr = 2381fps ) It appears you are not over pressured unless it's from a 10" barrel . That leads me to think it's an over sized firing pin hole and the primer cup is being forced into the gaps . You see this A LOT with hand guns , Beretta 92's do it but I don't see it as much with rifles .

[HiBC]

You might check to see if large pistol primers found their way into those primer pockets.
Maybe the empty box is in the trash.

[hounddawg]

Do factory rounds do this? If it's not over pressure, then it could be a weak firing pin spring or an under size firing pin for the hole in the bolt.

Tony

X3, I think Geezer and MG nailed it

[mehavey]

under size firing pin for the hole in the bolt.

^^^^^^^^^ Yup ^^^^^^^^^
Everything (even crater edges) are still soft/rounded

[Shadow9mm]

Could be an under sized firing pin. I had a tc compass they chamfered tge firing pin hole that did that. My other thought would be seating depth. If your bullet is too far out and touching the lands that could spike it too

[Lawren5]

Shadow - Thanks for your comment. I compared the firing pin holes on both the Remington 308 and the M1 Garand. The holes and firing pins appear to be the same size on both rifles. However, the Remington has a chamfered edge around the hole whereas the Garand has a squared edge. That might explain it.

[Unclenick]

I was going to ask if the rifle was a Remington. Why they started chamfering the firing pin tunnels awhile back, I'll never know, but it sure has caused a lot of confusion about pressure.

The perimeter edge of your primer looks fine. Not overly sharp, so this is definitely not a high pressure sign.

[T. O'Heir]

What bullet weight?
A 168 shows a 2551 FPS start load. 41.0 is the Start load. 36 is possibly unsafe.
The only weight that mentions 36 grains of H4895 as a Start load is a 208 and a 215. Any other weight 36 is below minimum.
And cratering is just one of the pressure signs. You having any others? Hard extractions for example.

[Unclenick]

T. O'Heir,

With most any powder other than H4895, you would be absolutely right to be concerned about the sub-starting load. H4895, however, can be loaded down as far as 26.1 grains with Lawren5's bullet. I know it sounds like that is leaving an unsafe amount of empty space, but the reason it is safe with this particular powder is explained in the second paragraph of this Hodgdon document.

He found the cause of the primer crater wall. His Remington bolt face has the firing pin tunnel chamfered, so the primer cup is simply flowing into the chamfer.

[Jim Watson]

Old DuPont literature said IMR 4895 could be loaded as low as 3/5 maximum, too; but now that General Dynamics does the manufacture and Hodgdon has their distribution sewed up, it is no longer mentioned.

[Unclenick]

Yes, though I don't know if the manufacturing process change at Valleyfield circa 2012 has affected it. H4895 was just surplus IMR 4895 originally.

[Metal god]

Yes, though I don't know if the manufacturing process change at Valleyfield circa 2012 has affected it. H4895 was just surplus IMR 4895 originally.

Well at least the look is not the same anymore , not only color but H has a bit shorter cut to it . My test seem to indicate H-4895 is a tad faster now as well . Not sure if factual but it's been said H-4895 is more temp stable as well .

________________H-4895 on left _________________________________IMR-4895 on the right

[Unclenick]

Yep! That gold color is on Varget, too, and is part of ADI's process for that particular Extreme powder. No graphite to produce the traditional black color. But Hodgdon hasn't changed the "Youth Load" claim attached to H4895, so, presumably, that characteristic has carried over. As Jim mentioned, they don't make the claim for IMR 4895, and I don't know if that's because of marketing or because of a real difference in their suitability for light loads. I suppose I should call and ask.