Unsolved: 44 Magnum Over-Pressure Mystery

Ever go about your day doing the same things you’ve done a thousand times before and then WHAM! something unexpected happens? That’s what happened to me recently when I was shooting some 44 Magnum handloads. Having just gotten my S&W 329 PD setup for summer carry, I thought I would test some ammo with it. What happened surprised me!

Pressure Signs: Proceed Carefully

When I opened the cylinder on my S&W 329 PD, I saw a problem immediately. What looked like charred edges around the primer of one of the cases, and the rest of the cases had flattened primers. WHOA! I thought- I need to figure out what’s happening here!

So I grabbed my 4″ Stainless 629 and shot some of the same ammo. SAME RESULT. And the same result with my 6″ 629. This was definitely an ammo problem! I’ve shot this load in these guns for years and have never had an issue until now. And it was clear that this was something to take seriously.

The Load

The load in question is the following:

  • Starline previously fired 44 magnum case
  • Hornady 240 grain XTP bullet
  • 24.0 grains Hodgdon H-110 (max load)
  • Winchester Large Pistol Primer (for standard or magnum loads)

Use load data at your own risk. Ultimate Reloader is not responsible for errors in load data on this website. Always cross-reference load data with manufacturer’s published data.


Powder Charge

The first thing I took a look at was the charge weight. I broke down a few cartridges using my Frankford Arsenal Impact Bullet Puller so that I could weigh the charges. It turns out, the charges were at or below the 24.0 grain load.

Correct Powder

I did wonder if I used the wrong powder, or if the powder had been contaminated. So I compared the appearance of the powder from a broken down cartridge to some H-110 from a sealed container- they appear to be the same albeit with a VERY slightly different color. I suspect the color difference could be due to lot-to-lot variances. The consistency of this flattened ball powder looks the same.

Here’s a closeup showing the powders side by side: (click/tap to enlarge: H-110 on left, mystery powder on right)

Correct Primer

The second thing I did was to use a decapping die to knock a primer out of one of the cases from the broken down cartridges. I carefully compared the primer to the correct one (from my primer storage area) and found the color coding to be identical, and the outward appearance as well. Yes, this was a standard Winchester Large Pistol primer as it was supposed to be…

Correct Velocity

I shot some of this ammunition over a chronograph, and got velocities within the range I expected… And I also got some BIG FLAME BALLS! Gotta love that.

The Hornady load manual indicated just over 1300 FPS for this load, and I measured average velocity at 1287.6 FPS. So velocity isn’t out of spec.

Other Things I’m Going To Look At

I haven’t solved this mystery yet, but I’m going to keep working at it:

  • Check primer pocket diameter on burned-out cases- perhaps the brass is worn out and primers aren’t held securely.
  • Replicate the exact load, test in my three 44 magnum revolvers.
  • [I’m open to suggestions! Please leave a comment]

I’m hoping that I can figure out what was going on here- both to satisfy my curiosity, and to avoid these kinds of issues in the future. If I do figure this out, I’ll certainly keep you all updated.

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11 thoughts on “Unsolved: 44 Magnum Over-Pressure Mystery”

  1. There are lot to lot variations on powder and primer, I’ve seen as much as 10%, but that was many years ago, today things seem a bit more consistent, but still a possibility. With your 24g load, being max book load, get a slightly more energetic lot of powder/primer combination and that might be enough to get you to over acceptable pressure.

    Check the bore of the revolver for excess jacket fouling? Unlikely as it happened across 2 different firearms.

    Has the level of crimp changed possibly? That initial pressure rise on an over crimped projectile could get you an momentarily high pressure spike.

    Also check the flash hole diameter, functionally the primer/flash hole is a kind of hydraulic piston setup, so a oversize flash hole could allow more pressure to act on the primer, giving the over pressure signs.

  2. My first thought was that the crimp might be too tight inline with what JD posted. It has happened to me with .44 mag but it was my fault for not keeping the cases trimmed enough.

  3. Hey Gavin. What about the brass? Could the primer pocket have been slightly oversized on a few cases (the ones you had the over pressure signs on) allowing the gases to escape thus leaving and giving you the blackened powder marks at the primers as seen?

    Ask me, I don’t know. Just throwing it out there for you to check.

  4. Hi Gavin, I have found that powders such as W296 and H110 are very temperature sensitive, ie pressure increases with temperature increase. Given that it is a max load, if it was quite hot when you were test firing, reduce temperature of ammo in a coolbox (not too cold) and try again.

  5. Yes you should be concerned. Multiple over pressure signs each one significant in its self. I don’t know how temperature sensitive H110 is, but I’ve always heard this a powder that’s quick to SPIKE.

    In this day and age of optimum manufacturing consistency, the advice to rework a load with every new lot just might be prudent.

    One last thought, 10% still leaves room to reduce your powder charge and I’ll bet there’s no reduction in the fun factor. Your revolver might like you better too?

  6. had the same issue after a change to federal primers. 250 gr cast bullet, 21 gr 2400 powder. a switch to any other primer solved the issue. Hope that is helpful.

  7. I have read something about “bullet weld” on centerfire rifle cartridges. Haven’t heard anything about it on handgun cartridges but could this be another possibility?

  8. Had something very similar to this with my 338-06 and H380 powder, new winchester brass and primers. Turns out it’s a known winchester primer problem. I switched to CCU primers and all gasses went out the proper end of the firearm.

  9. Did the “over pressure” cases extract harder?

    You could set up 2 loads
    A. 6 rounds with same primers and plastic practice bullets.
    B. 6 rounds with different primers and plastic practice bullets.

    Cut 12 wooden blocks 2×2 that will slide into a piece of pvc pipe. Adjust wt. by sanding (use that niceFX120i)
    Set up and shoot 12 shots alternating shots from A and B.
    Load block into pipe(aimed in a safe direction obviously) push it same distance into pipe for each shot with end of barrel.
    Shoot and carefully measure distance block has moved. You may have to tinker with block wt. till you get measurable results.

    If there is much difference in the primers it will show up in the distance the blocks move.

    Did you load any rounds with different primers and same powder and charge?
    Different lot powder and suspect primers?

    Have you used any of the suspect primers in any other caliber loads with same powder?

  10. Have you miked the bullets? Over the years I have had two incidents (one with cast and the other with jacketed bullets – both were sold as .429) where the bullets were oversized. Both bullets showed signs of overpressure. I resized the cast bullets and that not only fixed the over pressure signs but also improved accuracy. I contacted the manufacturer of the jacketed bullets who requested I send them back. They sent replacement bullets and when I miked the replacement bullets they were correctly sized. Now when open a new box of bullets I spot check a few of the bullets to confirm correct bullet size.

  11. Gavin,
    I had this same issue with my S&W model 57 41mag using Winchester LP primers and Remington brass. I did the same thing, pulled several apart and checked charge weights. All within a 1/10th of grain from my 17.0g of 2400 which is well below max book load. I found blog posts about Winchester primers being the cause. I don’t record production lot #s on my loads, but I wished I did in this case because the manufacture would know if they had a bad lot and replace them. I switched to CCI.

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