Fine Tuning Palma Loads

[257Roberts]

I've got a Winchester 70 Palma gun that I working up loads for. Its a shooter for sure and I am trying to squeeze the ES/SD down.
All the usual brass prep, Lapua brass, BR primers, wet tumbled, primer pockets trued, length trimmed, annealed, bushing dies. Everything short of neck turning, which in high quality brass maybe isn't a great factor. I've never sorted brass or bullets, but the bushing dies really helped take all my other cartridge loads into single digit SDs.

Question: Is there a single most important factor for squeezing the last bit of SD out of a load?

In this case, Sierra 2156, 46.0-46.5gr Varget shooting in the 0.4-0.5 MOA range. I went up as far as 47.0gr and then the groups open up to more like 0.75MOA. 47gr is a nice 3030fps but an SD of 12. I haven't checked 46.5gr on the chronograph yet, so maybe I am already there.

Do you folks tweak powder charge or seating depth [or other] as a first means of reducing ES/SD?

 

[DRNewcomb]

What's your chronograph setup?

 

[257Roberts]

Magnetospeed, best chronograph I've ever used.

 

[NZ_Fclass]

46.5g is the magic number in Lapua Palma brass. I got better numbers when I played with the neck tension. And even better results when I had the barrel re -chambered with a slightly tighter neck. I was getting the best results with Federal Gold SR's, but I will be revisiting that in the off-season - providing I can get some supplies...I have also been playing with IMR4166, 45.5g in ADI cases. OK anecdotally - but again, I will be testing over winter. Only one more shoot before our season close - and that will be more of a social one.

 

[NZ_Fclass]

Better stop posting and get this back together, before she wants the massage table back!

 

[Twdmar]

46.5 varget with a small primer with a 155 is about as certain as death and taxes. drop a grain or so if using a large primer and quit dinking around with it. If you're holding 0.4moa, you can clean at 1k. Put your time into practice instead playing with your reloader.

 

[DRNewcomb]

Magnetospeed, best chronograph I've ever used.

The reason I ask Is that I've been giving some consideration to my chronograph setup. I have a CED M2 that I set up on a good quality photographic tripod. The issue is understanding the limits of precision of the instrument. A variation of 25 fps is just ~1% of what's being measured. Assuming that the M2 has zero internal errors, the difference induced by just rotating (slewing) the rail to one side or the other can cause up to a 8% drop in recorded velocity*. If one were to allow the rail to change pitch, the error could be up to -16% (worst case).. On windy days the sensor bar tends to wander around a bit.

This is only one source of error in my chronograph. There are all sorts of other variables to consider.

My point is that while we are concerning ourselves with SDs approaching 9-5 fps (~0.2%), we also need to worry about the precision of the instrument used to take the measurements. I don't use a Magnetospeed but the gates seem very close together. Has anyone analyzed the practical precision of the Magnetospeed?

*This is due to simple geometry as the path is longer if you're not perfectly aligned with the rail.

 

[257Roberts]

The following does not originate with me but I will pass it on and you can take it for what it is worth.

ES: Combustion
Low ES W/Big Group = Seating Depth
Small group W/Big ES = Powder charge/type/primer
Other ES factor = Neck Tension

SD: Consistent BC
Bullet quality & prep/ Sorting bullets by Base to Ogive

Great info here guys! Appreciate it! And yes, I want to get somewhere quick and just shoot.

Maybe a follow up question, can tweaking the seating depth in say, 0.010" increments have much effect on ES/SD?

As stated above, I think powder has more impact on this than depth, but intuition tells me that how consistently the bullet enters the barrel, and possibly the slightly different pressure curve could affect velocity spreads to a lesser degree.

 

[Straightshooter1]

The reason I ask Is that I've been giving some consideration to my chronograph setup. I have a CED M2 that I set up on a good quality photographic tripod. The issue is understanding the limits of precision of the instrument. A variation of 25 fps is just ~1% of what's being measured. Assuming that the M2 has zero internal errors, the difference induced by just rotating (slewing) the rail to one side or the other can cause up to a 8% drop in recorded velocity*. If one were to allow the rail to change pitch, the error could be up to -16% (worst case).. On windy days the sensor bar tends to wander around a bit.

This is only one source of error in my chronograph. There are all sorts of other variables to consider.

My point is that while we are concerning ourselves with SDs approaching 9-5 fps (~0.2%), we also need to worry about the precision of the instrument used to take the measurements. I don't use a Magnetospeed but the gates seem very close together. Has anyone analyzed the practical precision of the Magnetospeed?

*This is due to simple geometry as the path is longer if you're not perfectly aligned with the rail.

Your point is what moved me to consider the MagnetoSpeed v3 and the Labradar. At the time I did some extensive research and came across a couple of different tests on chronographs that included these two and were technical enough to satisfy the engineer within me. Both of these chronographs did away with a lot of those issues that optical chrono's have and they were at the top of the heap for their accuracy, consistency and ease of set up. I'd like to quote details and give links, but it's been a long time and I don't remember where I read the reports. I'm sure if one is decent at internet searching, one can find such detailed reports. I chose MagnetoSpeed over Labradar mostly because of price and some due to ease of set up. But for serious LR or ELR shooters, I feel Labradar is the way to go (like the down range velocity measurements can be very helpful for one's ballistic dope), though there is some minor technological faux pas in their design, which I think is being addressed in the new models.

 

[DRNewcomb]

Your point is what moved me to consider the MagnetoSpeed v3 and the Labradar.

At the time I purchased the CED M2, it was probably the best available option. The Magnetospeed and Labradar had not yet come to the market.