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+--- Thread: Doesn`t make sense ??? (/showthread.php?tid=24503)
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Doesn`t make sense ??? - LRRPF52 - 05-06-2022
AA didnt load Varget under 123gr Scenar for factory ammo, rather its one of the many powders tested when Bill A. laid down the initial baseline of published load data for 6.5 Grendel to support the cartridge.
Powders he tested with calibrated test breech under the 123gr Scenar included:
N140
N540
H4895
Varget
W748
BC-C(2)
AA2520
Factory canister powder
Not only was the pressure test breech used for developing those loads, but was maintained and constantly referenced for their ammunition manufacturing operations, to sustain a set of safe standards applied to each batch.
Weve had that data since the mid-late 2000s, and it wasnt just tested ad hoc, since hes a formally-trained ordnance engineer from the UK MoD intimately familiar with those processes.
As to simulations, I grew up in an environment where Computational Fluid Dynamics simulations were constantly being modeled, where DoD was looking for faster and faster computers to run those simulations, but still always tested that data in the real world.
Even after testing the CFD modeling iterations in extremely expensive wind tunnels, the real-world performance of several programs proved to have nasty surprises once taken to the air, including catastrophic failures and loss of life.
More often than not, the simulations were not really valid, and surprises seemed to rear their heads as a rule.
The main attraction to CFD and computer modeling is cost-savings. If we can model all the variables accurately, then it can save a lot of money in trial and error in the real world.
We might be inching closer and closer to that place in limited aerospace circles who have billions in funding, but QL is nowhere near there when it comes to internal ballistics, as proven by the 9,000-20,000psi variances we see when compared to real-world pressure test data.
The way to know what the chamber pressure actually is involves building a pressure test breech with gauges and an instrumented measuring apparatus, calibrating that test set, then taking measurements.
The published data you see from AA, Hodgdons, Lapua/Vihtavuori, Western Powders, Sierra, etc. follows SAAMI standards with test breech data, not highly-flawed simulations.
Doesn`t make sense ??? - Double Naught Spy - 05-06-2022
Redwoodcity1955 Wrote:I`m running Lapua cases.
Lapua Scenar 123 HPBT.
CCI #200 Primers.
28.5 GR. Varget.
Wilson 22" Barrel.
Cryptics Coating BCG.
Deviation is under 10
Some of the FPS are identical !
The problem is at 100 yards the spread is more that 2" ???
What is going on here ???
Please help I`m stumped ???
Simply put, velocity and standard deviation are not the the only components of precision. The SD and velocity are just telling you that your loading and burn rates are producing consistent results, but that may not jive with your particular barrel and harmonics, assuming that you didn't introduce in problems into the equation as the shooter. You need to find the correct combination that works with your barrel, not just the combination that produces good SD. You may need to be consistent at a different velocity.
Redwoodcity1955 Wrote:I just noticed, the brake had come loose !!!
Or your muzzle brake has come loose and messed up things at the end of the barrel.
So did tightening it down resolve the issue?