Real BC of Sierra 180gn 284 bullets?

[RDavies]

Has anyone worked out what the real (not advertised) BC of the new Sierra 180gn bullet is. How does is compare to the 180 Berger VLD? They are working very well in my new barrel and I was wondering if I was giving up much BC to get the consistancy?

 

[Steve Blair]

The real question is how it compares to the B.C. of the Berger 180 Hybrid. The Hybrid has a .345 B.C. vs. the VLD's .337. I have examples of all Berger 175 & 180 grain 7mm bullets and the Sierra 180. The Sierra is a secant ogive that is slightly less aggressive than Berger's 180 VLD. We will likely have to wait for Bryan Litz to do some testing for a definitive answer.

 

[bheadboy]

Having been to the Sierra plant and in the testing range, Sierra test thir BC at the range to 300yds and at the velocities advertised,

Thus their BC's are most like ly the most accurate of all you will see printed.

Bob

 

[SpencerC]

I would wait to hear what Mr. Litz has to say about it before I took Sierra's numbers too seriously..

 

[Steve Blair]

Without questioning Sierra's methodology; why have they not provided the more conformal G7 model coefficients? The multiple velocity G1 approximation is cumbersome and unnecessary, as Berger and Lapua have concluded.

 

[RDavies]

Has Brian Litz worked out the G7 BCs of these new Sierras? I wanted to compare them to the VLDs as we dont get the Hybrids here in OZ. I much prefer accuracy over BC, but its good to know how these things compare.

 

[bheadboy]

Steve, Sierra has a 300yd tunnel, it is my observation they shoot the velocities indicated and calculate the bc from the results, they are not approximations.

Bob

 

[KevinThomas]

To be a bit more accurate about this, Sierra can test BC all the way out to 300M, but most are done at 200 yards. There's a set of hard-mounted swing out screens for BC testing permanently mounted at 200 yards, where the vast majority of their accuracy testing is done. The 300 meter testing is used in some isolated cases when Bill or Ted feel it's warranted, but it creates some difficulty in simultaneous testing at other ranges. It requires the set-up of a set of temporary, movable screens that can be placed at just about any 50 yard increment all the way down the range.

As far as Sierra switching over to G7 BCs, I seriously doubt that will happen. For one thing, they produce a great many bullets for which the G7 is inappropriate. Bryan's a lot more "cutting edge" on the Berger front, and as typical of a younger company, they are more willing step outside the box where tradition is concerned. They make virtually nothing that's agreeable to the G1 model that has been industry standard for the past fifty years, so it's entirely understandable why they'd be the first to get into the G7 model. As for Lapua, we offer both the G1 model to satisfy those who want to compare them to our competitor's bullets, as well as the G7 for those who want to use a more reliable drag model with their various programs and apps. However, the raw data we use isn't a derived BC based on time of flight, but an actual trajectory taken from Doppler radar measurments. This is hands down the most accurate measurment of flight dynamics, but to the best of my knowledge, we're the only commercial maker who uses this method. Cost of equipment is prohibitive to most commercial entities, though some do occasionally get to do very limited testing at Aberdeen or Yuma Proving Grounds.

 

[rcw3]

Sometimes I wonder if we get carried away with the published numbers and data and forget to work with what's right in front of us.

A few years ago, I did a whole lot of 7mm bullet testing at 1000 yards with the Berger 180 VLD's vs the Sierra 175's. The 180 Berger VLD's look like much longer and more sleek projectiles relative to the Sierra 175's, and I thought they would trounce the performance of the Sierra 175's, but I personally did not find they performed significantly better on the target at 1000 yards, and my point of impact with the same loading was within a click or two in elevation at 1000 yards (with a couple different rifles). I wound up shooting the 175 Sierras as my "go to" bullet because it was less finicky and enabled me to be more consistent over long strings of fire.

I think there's no substitute for putting all the published numbers and data on the side and shooting the actual projectiles and looking at what is really happening at the point of impact. I am not sure there is always a direct connection between the published data and what you actually see in the field.

Robert Whitley

 

[Steve Blair]

Kevin's comments are useful, as are Robert's. It is also worth noting that any ballistic coefficient, unless the projectile is identical to one of the "G" models (unlikely), is an approximation derived by a variety of means. Calculations are based on form factors, flight time measurements, or, as Kevin noted, direct Doppler Radar measurements.

The point that I should have made was that the model closest to the examined bullet form should be used. Long range shooters using long, boat-tail bullets are much better served by the G5 or G7 models. Shorter and blunter, flat-base bullets are much closer to the G1 model. It is fine if Sierra wants to provide a G1 coefficient for every bullet they make. The long boat-tail bullets should also have a G7 coefficient supplied. If selling bullets to long range shooters, it makes sense to give them information they might need. Vertical impact point is not the only consideration and G7 coefficients provide more accurate information for long range calculations.

 

[flatlander]

I had much the same results as rcw3 while comparing S175MKs to Beger 180VLDs in my 1st 284. Loads with the same charge of H4831, same primers, same lot of new, unfired WW brass would result in impacts within 1/2 moa elevation of each other at 1000yds.

I've got three bbls. chambered for 284 - one each: Bartlein & Krieger 30" hvy Palma, and a 28" PacNor 3-groove contoured just a tad heavier than a Rem HV (all three are 1:9tw). The PacNor absolutely hammers with the Sierras and clearly prefers that bullet to all others tried in it. The other two bbls. show a slight preference for either Berger or JLK 180VLDs, though they also handle the Sierras well.

I've kinda taken a sabatical where shooting 284s is concerned, since I've not been able to shoot 1000yd any/any matches with any regularity the past couple of years. However, I have a few boxes of the new Berger hybrid 180 that would be interesting to test against the 175 Sierras. Until I see a line drawing with the newer S180MK's bearing surface dimension (and preferably G7 BC data from Bryan Litz), I'll hold off on purchasing any of them. Laying in a good supply of any of the heavy 7mm match bullets is a serious investment, so I'm in no hurry.