.308 Norma case head expansion in R8

Hi there

I tested some 180 Interlocks in my Blaser R8 on the weekend. Norma cases, .308 cal. With 43 gn of 2206H, which is book max for Nick Harvey, i have expansion at the web of .004 ie from .467 to .471. I measured this parameter because I’ve been told that primer behaviour is not a good indicator for Blasers, due to the way the bolt operates. Anyway, is this much case head expansion normal or does it indicate excessive pressure? I don’t have much experience with using this parameter. The best group was with 42 gn but I need to chrony the loads to see what’s happening velocity wise.

Cheers guys

I think that's more than my Nick Harvey manual recommended, I'll check later.
I think it also said cases should have been fired previously (i.e. not new) as there is always expansion at the first firing???

Ah ha! Thanks for that. They’re new cases. Maybe that’s an explanation right there. I’ll double check Nick Harvey too. Cheers

I’d measure them on the second firing, if the primers aren’t flat you should be good, with my R93, all my loads are either at book max or under, unlike some of my bolt rifles you don’t need to push the powder load to get book speed.

Cheers for that sounds good. I’m all in favour of milder loads. My 168 ELDMs do 2660 with 43 2206h which is half a grain under book max. They work great. If the 42 gn load continues to be accurate with the 180s that’ll do nicely.

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Originally Posted by Cigar

I think that's more than my Nick Harvey manual recommended, I'll check later.
I think it also said cases should have been fired previously (i.e. not new) as there is always expansion at the first firing???

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I checked my book (first edition).
Cases should be new and unfired (I was wrong above).
My book says if you get 0.0005 inches expansion (Yes, that is the correct number of zeros), back off by 1 grain and try 10 rounds.
If not confident or able to measure to that level, if you get 0.001 inches expansion back off by 5%.

Awesome yeah that was the other thing I wasn’t sure of - how much does it have to be to be significant anyway

4 thou if occurring every firing is cause for real concern.
4 thou at first firing maybe not so. Depends upon the rifle's individual chambering. I would be surprised that a Blaser would have an oversize chamber?

After the first firing (and case forming) I would then be concerned at any continual expansion of say 0.5 to 1 thou.

It will all show up eventually I guess when primers fall out :o

I would back off for your next few firings, check, and go from there.

PS: To do the measurement most accurately I use a blade micrometer. You can do it with a vernier but best use a non digital as the digital will round up or down.

Primers are no different for accessing pressure in a blaser action than any other crank bolt.

Depending on the brass I almost always get. 0003-.0004 on first firing. Especially Norma and Nosler.
Once formed they settle down to nothing. I run moderate loads and once my cases won't seat a primer with resistance I bin them.

What you lack in a blaser action is powerful primary extraction. The rifle will tell you quick smart if you're getting too hot.

Quick tip is to work out your loads mid summer and you will never have a problem with your ammo for your blaser in NZ.



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This is all great stuff guys and much appreciated. I’ll back off for the next firings and see if it goes past .471. I’m not getting any other pressure signs