Ruptured Primer

[Justintoxicated]

My 3rd trip out with this LR308 rifle. Finally got past all the bolt catch issues and got a replacement adjustable gas block.

Even my starting loads show high pressure signs. I have read that primer cratering and flattened primers and ejector smear are normal for LR308's. I just can't get used to that. My rifle has a rainier arms ultra match barrel and its very accurate for what it is but it must have a tight chamber or something?

pressure signs by Glamisduner, on Flickr

The loads with the mil brass were not starting loads, I used hard tula primers. This piece was probably from one my my hotter loads 43 grains varget behind a 175 SMK.
The ruptured gold colored winchester primer however was just a hair above the starting load recommended for 155's. It uses 155 grain Palma SMK, behind 44.5gr varget. (I went up to 46gr without any failures like this though).
This burned a small pit hole in my brand new JP bolt. (I say new but it has about 100 rounds or so shot out of it_.



bolt damage by Glamisduner, on Flickr

You can see the pit right next to the ejector.

Not sure what I could be doing wrong here, or maybe its a defective primer because my friend had the same thing happen with winchesters we bought around the same time on his 1903a3 with a light load as well. I'm loading rounds to maximum magazine length (max length that will fit in my magazines not published magazine length. And when I say this I mean I'm loading such that I won't end up with rounds that are too long due to inconsistent tips on SMKs, but I mean it is longer that published mag length.

[noylj]

With rifle cartridges, unlike pistol cartridges, pressure can go up quite a bit as you load longer as the bullet will impact the lede/rifling and still have a lot of bullet in the case mouth, where as loading a bit shorter can actually drop the pressure.
Then you add an "Ultra Match" barrel that may just have a tight chamber that may require having the neck walls thinned so there is enough expansion for case to release the energy, and you might see a starting load be hot.
Call about the chambering and if they meet SAAMI tolerances or tightened up the chamber.
Also, check the firing pin and the firing pin hole. If the hole is larger than the firing pin by some, I don't know, number of thousandths, it produces a "hole" for the primer to flow into. You may simply have a bad combination of small firing pin and large hole.

[Justintoxicated]

With rifle cartridges, unlike pistol cartridges, pressure can go up quite a bit as you load longer as the bullet will impact the lede/rifling and still have a lot of bullet in the case mouth, where as loading a bit shorter can actually drop the pressure.
Then you add an "Ultra Match" barrel that may just have a tight chamber that may require having the neck walls thinned so there is enough expansion for case to release the energy, and you might see a starting load be hot.
Call about the chambering and if they meet SAAMI tolerances or tightened up the chamber.
Also, check the firing pin and the firing pin hole. If the hole is larger than the firing pin by some, I don't know, number of thousandths, it produces a "hole" for the primer to flow into. You may simply have a bad combination of small firing pin and large hole.

I'll double check but I believe its a pretty tight fit. It's a JP Stainless complete BCG. Supposed to be the best you can get. Was almost $500! Rifle headspaced with a SAAMI gauge, but the chamber is a hybrid like the Wylde chamber only for a 308 and 7.62.

Groups are heard to read too, I'mm not seeming much difference with 175's but the 155 palmas are dialed in for the load that ruptured the primer and damaged my bolt.
lr 308 100 yards by Glamisduner, on Flickr

Or maybe I'm just a bad shot so I'm not able to tell the difference.

[mark501w]

I don't use GI cases in .308 . I had a massive overload in a starting load! I know a lot of guys do & if I was going to I would use LC brass . If you are going to use GI brass pick a lot ( same manufacturer ) & reduce by a further 10% from this load. You could have other issues with a fireering pin but, first you have to get pressures down.

[Justintoxicated]

I don't use GI cases in .308 . I had a massive overload in a starting load! I know a lot of guys do & if I was going to I would use LC brass . If you are going to use GI brass pick a lot ( same manufacturer ) & reduce by a further 10% from this load. You could have other issues with a fireering pin but, first you have to get pressures down.

The ruptured primer was not using LC brass though. In fact I'm finding I like the LC brass better than the BH.

[OldeNavy]

Good job documenting it. Looks like the same cratering I got from my LC rounds that I purchased from a gun show. I did not think they were hot, but I guess they were. I did not have a rupture though.

[mark501w]

The point is reduce your load.

[OldeNavy]

The point is reduce your load.

Oh yes. Quite true. Just like normal reloading, high pressure signs then reduce your load.

[Justintoxicated]

Oh yes. Quite true. Just like normal reloading, high pressure signs then reduce your load.

Right but I get the same signs at like 40gr varget, how much more under the starting load should I go and at how much cost to accuracy?

[nubrun]

You will most likely find multiple accuracy nodes. You may have found a high node, but there will also be a low node.

[jameshenry]

Do not reduce your loads and equipment cost might go up.

[mark501w]

The way the brass looks there's pressure there , get some Cerrosafe & check the mouth demensions . You didn't mention anything about trim length?

[Justintoxicated]

I'm not really sure how to identify issues using Cerrosafe and you expand?

Trimmed every case to min using hornady cam lock trimmer. This thing holds it's setting really well.

[mark501w]

Then maybe you need to check dimensions . Call the maker & ask check mouth dimension against a reloaded round.

[Justintoxicated]

Then maybe you need to check dimensions . Call the maker & ask check mouth dimension against a reloaded round.

It's a rainier arms ultramatch barrel, not sure even rainier would know but I'm not getting stuck rounds or powder burn marks on the brass. The rounds do however come out much cleaner than other ARs, so it's probably got a tight chamber, although it passed SAAIMI Go and No Go gauges with flying colors.