Can undersized brass cause light primer strikes?

[fyrewall]

I was replying to your last post that said that all primers of the same type are assumed to have cups of the same thickness. In that post, you spoke in more general terms. If you had said all large rifle primers, I probably would have looked for the table before responding, but you did not. Many times we post not so much for the OP but for the benefit of those who are lurking and may be led astray. In this case, as you are aware, all primers of the same type do not have cups of the same thickness, but yes all large primers do. Before you caution someone to read more carefully....

Why is its pressure mighty high?

I don't think it has mighty high pressure. Many people load their non-magnum cartridges to the same pressure it has.

The 338 Lapua Mag is SAAMI spec'd at 65,000 psi max average pressure. Same as many belted or rimless "magnum" cartridges.

Regarding light primer strikes, I've seen some instances of weak firing pin springs causing more muzzle velocity spreads. Vertical shot stringing at long range is an indicator. Primers need smacked consistently hard to produce repeatable flame output. Some striker springs weaken with age.

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just more "nit picking" of the speculative, distractive and mitigating type

Additional comments might include comparisons of chamber pressures of various cartridges, an analysis of the use of the word "type" within the context of regarding primer cup thicknesses, or providing documented analyses of primer blast pressures vs. time in .002 second durations (2 millisecond), weighing every primer in an entire brick (1000) of primers to obtain explosive weight variations, analyzing primer hardness via Rockwell method or searching for documentation of firing pin impact force vs. primer blast waves and tired deformed springs (Hooke's law) and other esoteric stuff.

At this point I will cheerfully withdraw - I have no desire to argue because being some type of internal or external ballistic lawyer has no appeal and/or opportunity for financial gain - shoot, hunt, fish, and eat are more important.

 

[BoydAllen]

A cloud of dust, and change of subject...Yes this is all relatively unimportant. I agree.

 

[Campbell]

This is a very interesting thread!

One of my club members, after buying a new F/TR rifle, has had a very high proportion of light primer strikes (12/22, in one session, IIRC).

He had made sure that the primers (CCI Small Rifle) were seated properly.

He looked at this fine forum and decided to seat his Dyer HBC 155's a couple of thou back. Result: no light strikes!

In his case it would appear that the firing pin's force was being partially absorbed by the bullet being pushed further into the case/lands

 

[NorCalMikie]

In his case, it would appear that the firing pin's force was being partially absorbed by the bullet being pushed further into the case/lands

BINGO!!
So, you pull the bullets out a bit on the loaded round to make the OAL a little longer, which in turn holds the case head back against the bolt head and that round will fire.
Then, you make sure you don't push the shoulders back too far when you reszie and end up having the same problem all over again.

 

[Webster]

I took a new rifle out to the range today, a savage 112 in 338 lapua.

Ammo was mid ranged reloads
Brass was unfired peterson brass.

Over the 20 rounds I took out today, 5 failed to fire. Each round that failed to fire had a light primer strike.

Load: 86.5gr of H1000 with a 285gr amax

The way I see it, there could be a number of possibilities:

1) Issue with the trigger itself. I left it how it came from the factory (1.5 LB)
2) Something impeding the firing pin enough to slow it down
3) Firing pin protrusion too short.
4) Bad lot of primers? These were CCI 250 (seems unlikely since the affected rounds had smaller indents than the fired rounds)

I am looking into these possibilities but one possible explanation that I came across on the web is undersized brass.

If the Perterson brass had the shoulder pushed just a tiny bit to far, or if the chamber in the rifle were a slighty out of spec, could that result in light primer strikes?

The rounds that it did fire shot extremely well. My goal today was to just zero the rifle.

Not familiar with Savage. Try putting oil on the shroud & cocking piece in the bolt. Possible high friction area. Look for rub marks where the cocking piece protrudes from the shroud.

 

[jimbo88mm]

Update:

I don't believe the new Peterson brass was undersides. I took measurements of both fired and virgin cases using the hornady comparator. They all had the same measurement.

I took the rifle out yesterday. I had 20 loads with Winchester LRM primers and 15 loads with the same CCI 250s. All of the Winchester loads fired. With the CCIs, I had 3 failed to fire. I'll upload a photo of the primers tonight. What I've been calling a light primer strike may not really be a light primer strike.

At this point I'm suspecting the primers.