Reducing H110

[Photog]

I ran the load through Quickload: and its says that you are still safe at 38gr at 2.150" OAL with 40k psi your max is 61931psi for 460mag. Drops considerable in pressure with every .05 of extra length, which tells me that the powder is at its near complete burn point. QL says that it is at 98.86% burn, so H110 is *just* about fully burnt. Now QL is not perfect, but I've got enough experience to say that looking at the graph and the data, I think your loads are too short, or the bullet is seated too deep, or you have something else going on like a mislabeled bullet or powder, or you have mismeasured powder.
The 38gr load should be getting you 1950fps, and i can say that trying to reload magnum cartridges without a chronograph is kinda dangerous.
As for w296/h110, the internet says that its a kaboom factory, Hodgdon has no such warning on their website or product labeling. Many download H110 successfully, and many claim that they can create a SEE at will using the right combination of dance moves.
My .02 = double check your components, measurements and OAL before condemning the H110.

[Kosh75287]

The recommendations that I remember about W296 was to not reduce the max load by more than 3%. Since H110 and W296 are the same propellant with different labels, I'D be very inclined to treat one of them with the same precautions as the other.
If hand-weighing propellant charges and carefully checking cartridge o.a.l./seating depths reveal no obvious problems, then a SLIGHT reduction is likely the way to go.
A 3% reduction from 36.0 gr. is 34.9 gr. I don't think you'd be tempting fate by using a charge weighing 34.8 gr., and you'd be surprised sometimes how much an extra 0.1 gr reduction can do for excessive pressures. I think I'd load 6 rounds at 34.8-34.9/H110 with the projectile you use, and check to see how the primers look. If you are still getting flattening (though likely not as much), reducing by another 0.5 gr. will probably not give rise to erratic ignition, and may give you "normal" looking primers. You can work up from there.

[TurnipEaterDown]

Maximum reduction of W296/H110 of 3% from max load is simply NOT factual.

Look at loading manuals for actual data.
Almost any straight wall pistol case using W296/H110 will have a spread of about 20% from max to start.

Hornady 30 Carbine: ~ 20%, 357 Mag: 15-20%, 357 Max: ~15%, 41 Rem Mag: 15%, 44 Rem Mag: 10- almost 20%, 445 Super: 15%, 45 Colt Ruger data: ~18%, 454: ~10%, 460 Smith: ~ 20%, 480 Ruger: ~ 25%, 475 Linebaugh: ~ 15%.

There can be problems reducing this powder class, and it is related to poor ignition and bullets stuck in barrels & forcing cones.
I have had it happen.

A bullet stuck in a forcing cone from initial primer force and/or the initial ignition should the powder then fail to fully ignite in a smooth progression, can cause a serious issue should the powder reignite due to residual hot spots having formed during the primary initiation.

Some of this tendency can be mitigated by use of a magnum primer, which I do not generally bother with.

Stay with the published data, but it is not true that minimums are 3% from max loadings.
There is more variability than that in powder lots of W296/H110.

BTW: AA#9, WC820, PP300MP, WC297 -- all right there w/ same tendencies due to near identical specification.
1680 (WC, WW, Accurate Arms) isn't that much different either in terms of the construction and ignition characteristics, though it is notably slower buring.

[justindad]

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If you have two very different boolits, say one full wadcutter of cast alloy, and a jacketed hollowpoint, each boolit close in weight to the other, as long as the BASE of the boolits are seated to the same depth in the case, which leaves each boolit the same case capacity under the boolit, then it would be fair to say that using the same powder charge, same primer, same crimp, etc, would be a safe practice.

I’ve been successful with that process in the past and I’m sure I’ll do it again. One thing I’ve come to believe is that this process is safer with some powders than others. If you study the 150-160 grain bullets for .357 Magnum in Lyman’s #49 and Lyman’s Cast Bullet #4, you can see that some powders have a wide range in max allowable charges and other powders have a very tight range in max allowable charges (compare max charges for AA#9 and HS-6 across multiple bullets). What this suggests is that, for some powders, bullet design can have a significant impact on pressure (beyond case capacity and bearing length).
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So when extrapolating load data, review max charges for several bullets in the same weight range. If several bullets of the same weight have very different max charges, then the risk of an overpressure in your extrapolated load is higher. That is why I would rather extrapolate with HS-6 than with AA#9 in .357 Mag.