Manufacturer ratings and max tolerances

Discussion in 'Ammunition & Reloading' started by Amdac, Feb 7, 2014.

  1. Amdac

    Amdac Administrator Staff Member

    Oct 22, 2013
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    So this is an odd question. I'm looking at starting reloading 9mm for a carbine. My concern is that I've recently picked up Lyman's reloading manual and seen quotes for a few others that state a max charge for a specific round, in this case 7.6 grains. However, the manufacturer of the powder (Alliant) lists the max charge at 8.5 grains which is significantly more. (This is a slow powder)

    My question is, are all of these stats generally withing the standard max PSI rating of the round which for 9mm is 35,000PSI, or is there a chance some could be rated +P or +P+? The rifle I plan on using it for is rated for all of them, but I'd rather not beat it up too much if possible. I still want a quick round though.

    The numbers I've seen from 8.1 grains or so is insane for a 9mm.
  2. Thomas

    Thomas Decent Shooter

    Jan 1, 2014
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    Albuquerque, NM
    I do believe that Alliant has a disclaimer stating you should begin at a 10% lower charge. Here's the thing about guns. Most guns from reputable manufacturers, are tested at a tolerance pressure DOUBLE the standard PSI. For example; if 35k PSI is the average range for a 9mm, Glock would run a few rounds at 70k PSI to see how well the gun holds up. This is done for liability and safety reasons. The listed tolerance is basically the pressure rating the gun can maintain and suffer normal wear; otherwise a +P round would destroy every gun it fires through.

    You also have to consider what kind of gun you are using. If you take a weapon; built for a caliber that operates at 50k PSI; then simply put a 9mm barrel in it, you can fire +P 9mm rounds all day (you also have to consider the spring weight though, because if your recoil spring is too light you could batter the slide). Take a 1911 for example. A well made 1911 is way overbuilt for the pressure of the .45ACP(22-28k PSI); this is why you still see 1911s from 1918 firing in tact.

    You are right to use caution however. A good general rule is +P rounds will wear out your gun faster. That being said, you can certainly fire them without fear. If you see a discrepancy between to 2 loads; the smartest thing to do would be loading 10% lower than the lower number to start. This also depends on the powder. A fast burning power like Bullseye, will quickly spike the pressure way up; even with half a grain more. A safer; beginner powder; like Unique, has a much higher margin for error. On some rounds, there is a whole 3 grain difference between a regular load and a max load with Unique; where as there may be half a grain; or 1 grain difference with Bullseye.

    Also remember the Lyman guys do nothing but test loads all day long; and carefully observe the effects (and they have probably damage a few guns in the learning process). The powder companies rely on mathematics to determine safety.

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