Kyle Schultz
Gold $$ Contributor
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.
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.
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.
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.
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.
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.
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.
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.
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.
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