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Norma 6 Dasher Brass Stress Test

I’m breaking in a new 6 Dasher rifle. Kelbly Panda F action w/ TG ejector. 30” Krieger 0.237” bore, 8 tw barrel. Spec’d a JGS reamer based on Lapua 6 BR brass but with the hope that the long-promised Norma 6 Dasher brass would fit. Reamer print shown below. Brass and rifle arrived within a week of each other so I elected not to fire form any Lapua 6BR brass and instead used the new Norma brass.

View attachment 993297

Because of folks reporting primer life issues in the Norma brass when using “max throttle” but generally accepted powder charges, I followed the advice of several experienced 6 Dasher drivers like dmoran and started off with 2 firings of pretty modest loads of Varget. The idea being to “fine fit” the Norma brass to my chamber and potentially work hardened the brass. I did not exceed 32.0 grs in my initial ladder testing. I found a nice node around 31.6 gr of Varget and the 107 SMKs jumping 0.015”. But I was clocking an unacceptably slow 2875 fps.

With 2 firings on the brass, I next dedicated 14 pieces of brass to serve as “martyrs” with the goal of determining the upper limit for future loadings. These 2X cases have been resized using a Harrell’s D1.5 die, which was their recommendation based on the fired cases I sent them. Also for this test I used Berger 105 VLDs (Hunting version) seated 0.010” into the lands. The test loads were shot yesterday and the results are shown in the stress test chart below.

View attachment 993296

As shown, I measured a muzzle velocity of 3077 fps at my max loading of 33.8 gr of Varget. Bolt lift was normal until I reached 33.6 gr. Both the 33.6 and 33.8 gr loads exhibited a heavy bolt lift. In addition, at the shooting bench, I observed faint to distinct ejector markings on several of the stouter loads. Picture below. It was pretty clear to me that I had had found the upper limit of Varget in this case and with this combination of bullet and powder.

Back home, I decapped the primers. Spent primers in all the cases except the 33.8 gr case were tight. The primer popped out of this case with very little effort. Then all the cases were cleaned.

Once cleaned, I was able to observe ejector marks on essentially all the cases. In fact, you can see 2 ejector marks in the picture I’ve attached. The marks can more accurately be described as “shiny” spots. But because they are visible on all the cases, I’m now less certain that they can be used to accurately indicate unsafe loads.

View attachment 993291


Next, I measured the web diameter. Some further explanation here. Attached is a picture of a resized case. You can clearly see a "ring" around the case body about 1/8” above the extractor groove. I’m thinking that’s the bottom limit of where the resizing die reaches but perhaps I’m wrong about that. Nevertheless, that’s the reference point for all my case diameter measurements. Attached is a picture of that operation.

For reference, I’m measuring a virgin case to be 0.4682”. A twice-fired case resized each time with a Harrell’s D1.5 die measures 0.4725”. The velocity chart posted above also shows the measured base/web diameters most of the 14 martyr cases. They run from 0.4735” for the light loads to 0.4749” for the last load.


View attachment 993293 View attachment 993294

Now I recognize that these measurements exceed those of the reamer. Possible explanations? (1) Mic is not calibrated. (2) My technique is wrong. (3) The reamer is not ground as per spec. I’m guessing it’s likely due to reason (2).

However, I do think the trend in base/web expansion as a function of powder charge is interesting. It’s essentially flat out to 32.4 gr of Varget. After that, it increases fairly moderately out to 33.2 grs. But starting with 33.4 gr and continuing, the base/web expansion increases dramatically.

So what conclusion do I reach from this data? Given the hard bolt lift observed for the last 2 powder charges, the very loose spent primer found in the last case, and the rapidly increasing base/web expansion apparent in the last 3 loadings, I am thinking that max load is probably 33.2 grs.

Now, as luck would have it, my chronograph did not register that velocity for that shot. However, based on the trend, I think we can safely assume it’s around 3030 fps. That is very encouraging.

I do plan to resize these cases and see how the primer pockets feel on the 3rd loading. But I wanted to publish this data now to solicit comments and suggestions from the community before I eliminate the possibility of any additional measurements of the fired brass.

Thank you for taking the time to perform this test. It is very informative, with limitations. The one dimension I would like to have seen is missing, and that is primer pocket diameter. That's where the real limit on brass life shows up. You made some vague references to primer "feel", but no measurements. Virgin Lapua primer pockets are .1710. When I see expansion of .0005 I consider that too hot.
There are too many variables in web diameter, as others have already pointed out. You may have a large radius on the chamber face, in addition to excessive unsupported case head.
Could you possibly go back and measure your primer pockets and add that to your graph? That would really help to tell the whole story.
Thanks again for your efforts, and please extend my sincerest condolences to your "martyrs". :)
 
The primer pocket go no-go gauge Sinclair sells works very well for determining case life for single case repeat reloads. The 6BR Lapua pockets the go side will not fit in at all on virgin brass, the pockets open up with a bit of taper to them so each successive firing at a slightly too hot load you can slide the go end in a little more. Very handy tool.

http://www.sinclairintl.com/reloadi...swage-gage-primer-pocket-gauge-prod71030.aspx

This is not related to the question I asked. I'm looking for a number +/-.0005, not "go or no-go". It is very easy to measure the primer pocket ID with calipers.
 
This is not related to the question I asked. I'm looking for a number +/-.0005, not "go or no-go". It is very easy to measure the primer pocket ID with calipers.

Calipers are not intended to be used to determine accurate absolute measurements, there are other instruments for that, calipers are a very handy tool for getting +/- .001" on OD's and square lengths and square depths.
Calipers have a flat on the blade they do not measure round holes accurately, smaller the radius larger the error. You need a small hole mic or snap gauge, or a set of go no-go pins to get reasonably accurate absolute measurement on a small hole.

A comparative measurement is very useful, and easier/cheaper than an absolute measurement. That go no-go PP gauge lets you know when and how much pockets are moving very cheaply. That I don't now what the actual diameter is means nothing, it tells me what I need to know- its getting bigger, and comparatively by how much.
 
Calipers are not intended to be used to determine accurate absolute measurements, there are other instruments for that, calipers are a very handy tool for getting +/- .001" on OD's and square lengths and square depths.
Calipers have a flat on the blade they do not measure round holes accurately, smaller the radius larger the error. You need a small hole mic or snap gauge, or a set of go no-go pins to get reasonably accurate absolute measurement on a small hole.

A comparative measurement is very useful, and easier/cheaper than an absolute measurement. That go no-go PP gauge lets you know when and how much pockets are moving very cheaply. That I don't now what the actual diameter is means nothing, it tells me what I need to know- its getting bigger, and comparatively by how much.

A cheapo $20 caliper has been serving me very well and telling me what I need to know about primer pockets for more than forty years. You're entitled to use whatever tools and methods work for you. This ain't rocket surgery.
 
All I want to know does the pockets stayed tight.
Larry

All the primer pockets, with the exception of the 33.8 gr case, feel essentially normal when seating a new primer. The 33.8 gr case primes noticeably easier and the new primer can be removed with minimal pressure.

I still plan to rerun the stress test but use 33.2 gr of Varget as the new ceiling.

Thanks for everyone's comments.
 
All the primer pockets, with the exception of the 33.8 gr case, feel essentially normal when seating a new primer. The 33.8 gr case primes noticeably easier and the new primer can be removed with minimal pressure.

I still plan to rerun the stress test but use 33.2 gr of Varget as the new ceiling.

Thanks for everyone's comments.

Just reading this thread with interest and thought I would relate my 6BRX mesurements. New old stock gold box Lapua .4692" at .200" line. Reamer shows .4700"' at .200" line. After 1 light fireforming and two full match loads of 33.5 gr. N140 (3,010 fps) the cases measure .4701" at .200" line. After 1 light fireforming and 5 full match loads (same load) cases measure .4703" at .200" line. All primer pockets seat with same pressure as new. Seems as though this load does not harm the brass and the brass seems pretty durable. No bolt clicks or hard lifts in Remington action. My chamber does appear considerably tighter at the .200" line. This load is almost identical to 33.5 gr. of Varget velocity wise.
 
T
All the primer pockets, with the exception of the 33.8 gr case, feel essentially normal when seating a new primer. The 33.8 gr case primes noticeably easier and the new primer can be removed with minimal pressure.

I still plan to rerun the stress test but use 33.2 gr of Varget as the new ceiling.

Thanks for everyone's comments.[/QUO
Thanks Larry
 
New old stock gold box Lapua .4692" at .200" line. Reamer shows .4700"' at .200" line. After 1 light fireforming and 5 full match loads (same load) cases measure .4703" at .200" line. All primer pockets seat with same pressure as new.
This is NOT sloppy, and what I'd expect from your reamer. The creeping to .4703" without interference means your chamber is a tad over reamer. And the brass actually expanded ~.0005" past this and then sprung back to it. That's not to say the chamber was cut to .4708" though. Unless using a magnum diameter tenon and coned breech, your chamber is expanding most or all of that extra .0005" and then itself springing back.

With this clearance, and enough barrel steel around the chamber, enough threaded support at the breech, and a custom body die(bump & bushing NS only), you could mitigate the creeping and keep pockets tight forever.
With that, your brown box eyes won't turn blue..
 
This is NOT sloppy, and what I'd expect from your reamer. The creeping to .4703" without interference means your chamber is a tad over reamer. And the brass actually expanded ~.0005" past this and then sprung back to it. That's not to say the chamber was cut to .4708" though. Unless using a magnum diameter tenon and coned breech, your chamber is expanding most or all of that extra .0005" and then itself springing back.

With this clearance, and enough barrel steel around the chamber, enough threaded support at the breech, and a custom body die(bump & bushing NS only), you could mitigate the creeping and keep pockets tight forever.
With that, your brown box eyes won't turn blue..

Mike,
Thanks for the input. Never thought about chamber actually expanding and springing back. How much would a Remington with a heavy Palma barrel expand with full 6BRX pressures?
 
I personally feel the norma brass is good brass if you manage it with in reason is it lapua brass not even close to longevity the lapua brass is so much more versatile .
 
If your brass measures bigger than your chamber you will be experiencing clickers. If your reamer is .4708" and you brass measures larger, either the smith cut a fat chamber or you are running pressure up enough to expand the barrel, in which case you will know it.
 
His reamer is .4700, seems reasonable to me that his chamber would be a hair bigger.
His formed brass measures .4703 without issue.
Both brass and chamber(along with entire barrel) expand on firing, and both spring back afterwards.
 
His reamer is .4700, seems reasonable to me that his chamber would be a hair bigger.
His formed brass measures .4703 without issue.
Both brass and chamber(along with entire barrel) expand on firing, and both spring back afterwards.
Brass yields much earlier than steel. When the chamber expands the brass yields. When the chamber springs back the brass doesnt, you now have a clicker/tight case. Under normal pressures I dont think the chamber is expanding much. I have a small inside mic that I do measure chambers with, and brass comes out smaller than the chamber. If you run it really hard brass thats been hit a few times can come out the same size as the chamber.
 
Brass yields much earlier than steel. When the chamber expands the brass yields.
Brass does not yield from pressure, but with lack of support(clearance) high enough to allow dimension yielding. That is, if clearances are tight enough, the brass never reaches a point of yielding, and simply springs back to original dimension. Like you suggested, the chamber itself should not expand much. But 'normal' pressure is not so normal anymore. And I notice few consider chamber support per it's area.

When you run high clearances, regardless of pressure the brass will expand to that area provided(eventually), and if this is beyond the brass spring back it will yield, and will never be the same again. Once yielded, the brass has a new dimension in balance, and will head right back to it with way less energy. It is then thinner, and harder, and lost some of it's ductility(spring back). With enough pressure to expand the chamber a good bit, and this yielded brass following all the way, and springing back less, we're left with interference fit.
All this can be mitigated through prevention of it to begin.
 
I just finished a Norma Dasher for myself on a 700 over the weekend. So I did some stress testing today for my own amusement.

New style 115 DTAC's, RL17 and 450 primers. I took it up to where the bolt lift got sticky, backed it down .2gr and loaded the same case 9 times in a row. It was cloudy and sprinkling lightly off and on so I didn't get any meaningful chrono readings. Finialy it started raining pretty good so I stopped.

So after 9 loads at max+ the primer pocket is still in great shape. I expect it will easily go another 9 loads at max pressure. These cases are definately a lot tougher than Norma 6BR cases. I have shot Norma 6BR cases in my BRX and they won't take that kind of abuse.

Another day I'll continue the torture test but so far this looks like good stuff, it ain't your old Norma brass!
 
I just finished a Norma Dasher for myself on a 700 over the weekend. So I did some stress testing today for my own amusement.

New style 115 DTAC's, RL17 and 450 primers. I took it up to where the bolt lift got sticky, backed it down .2gr and loaded the same case 9 times in a row. It was cloudy and sprinkling lightly off and on so I didn't get any meaningful chrono readings. Finialy it started raining pretty good so I stopped.

So after 9 loads at max+ the primer pocket is still in great shape. I expect it will easily go another 9 loads at max pressure. These cases are definately a lot tougher than Norma 6BR cases. I have shot Norma 6BR cases in my BRX and they won't take that kind of abuse.

Another day I'll continue the torture test but so far this looks like good stuff, it ain't your old Norma brass!
Is it likely that we can expect to see case life similar to the 6mm PPC? I have reloaded cases 100+ times and that is without annealing.
 

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