rgitzlaff said:
Hodgdon says starting load for this combo is 36.0 grains… I started with 37 grains…
I have three times now run into published load data for which the published starting load was already maximum for the gun or at least one of the cartridge components (like your primers). It doesn't usually happen, but when you go looking through published data and note the disagreement on what the maximum loads should be, you realize this is an approximating science and that all the published data is telling you for certain is that the described maximum load worked for the test gun employed using a cartridge loaded with the same bullet, same brass, same primer, and the same lot of powder the data developer used. Usually, that's not exactly what you have. So the recommended starting load is used to compensate for expected differences, which is why you want to start with it and not somewhere in the middle as a lot of people have suggested over the years and will assure you is just fine to do. Given that the starting load is occasionally already a maximum, these are just people who randomly never ran into one. That's the problem with anecdotal evidence. It doesn't normally involve a statistically adequate sample to assure you of anything.
As to the primers, the first thing I would do is look at the firing pin tunnel in your bolt. The cratering is pronounced, so if there is a chamfer there (as some Remington bolts have had) or if the tunnel diameter is too loose around the firing pin, it can explain the craters and should be corrected.
If the firing pin tunnel is fine, the next question is, what is your barrel length and how do your chronographed velocities compare to the published velocities for these loads? If your velocities are greater than the published velocities even after allowing for any difference in barrel length there may be, then you have higher pressure than the developer of the published loads got. There can be several reasons for this:
- Your bullet has less jump to the lands than the test gun did. This can raise pressure as much as 20% or so in rifles. It may be due to:
- Your chamber has a shorter freebore than the data chamber did.
- You are seating the bullet out further than the publisher did.
- You are using a different bullet than the publisher and that has an ogive that is further forward than the developer's bullet did.
- You have a warmer primer than the publisher used. In small rifle primers, I've seen data showing this can affect pressure by as much as about 10% in the extreme case.
- You have a case with less water overflow capacity than the one the data publisher used. In some cases, it can also cause about 20% pressure difference (300 Win Mag is notable for this extreme; most other cartridges don't have so such a great range of case capacities between makers, but it's something to keep an eye out for).
- You have a different lot of powder than the data developer used. This can cause between 3% and 10% pressure difference in some extremes.
So there is still a fair amount left for you to investigate here. If it turns out the primers are flimsy, I suggest moving to the Federal 205MAR primer, which is a standard strength primer with the cup thickened to achieve military sensitivity specs. The CCI #41 primer made for military sensitivity is a magnum primer, so you may have to cut powder charge as much as 5% for that, but also their cups are no thicker than those used for their magnum rifle primers. CCI achieves the lower military sensitivity by altering the geometry of the primer anvil rather than thickening the cup as Federal has done. So, if you need a thicker cup, Federal is the way to go.