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Thread: 45ACP straight blowback handloading considerations?

  1. #21
    Boolit Master

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    Quote Originally Posted by alpining View Post
    …Can anyone comment on early opening issues with straight blowback actions? Do I figure correctly that a heavy bullet combined with a slower powder is going to have the worst potential for causing it? Or are load specifics insignificant compared to having the "correct" bolt (and buffer) mass?
    A blowback action relies on the inertia of a bolt’s (or slide’s) mass to delay opening until propellant gas has exited the barrel. Chamber grip of the shell case helps a little but even a ring grooved chamber (look up the Kimball 30) is insufficient for higher power cartridges. Chamber pressure of 45 acp ball ammo is around 20,000 psi. Muzzle energy is 350 ft lbs.
    ‘For every action there is an equal and opposite reaction’. If a recoil spring were to help delay the bolt’s first 1/16 inch of rearward movement it would have to be one heck of a strong spring. Since you can compress most recoil springs a half inch with your little finger they aren’t doing much to delay early opening. It will slow the bolt more as it compresses but not at first.
    In my opinion a fast burning powder & heavy bullet will produce high chamber pressure faster and would be more likely to overcome the bolt’s inertia faster, all other conditions being equal.

  2. #22
    Boolit Mold
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    Sorry for the delay folks, I haven't had much time to look into this lately.

    Thanks very much for all the helpful info. This mostly confirms my poorly educated understanding about what's going on with straight blowback actions. There's really no effect that the action spring has on opening, it's all about the reciprocating mass. Since this ASR carbine is the same as the 460 Rowland version (just a different barrel), it's capable of handling some stout loads. I don't need to get every last bit of energy out of it, I'm happy with "soft" 45 Super performance at the high end.

    The surprising thing to me is that my unmodified carbine also cycles softball TrailBoss loads so well (255gr LSWC with 3.6gr TrailBoss at about 730fps). These are nice and quiet, though I'm sure it helps that I have an 18.75" barrel on mine (standard length for us here in Canada).

  3. #23
    Boolit Mold
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    Quote Originally Posted by Bmi48219 View Post
    ...In my opinion a fast burning powder & heavy bullet will produce high chamber pressure faster and would be more likely to overcome the bolt’s inertia faster, all other conditions being equal.
    I see your point. Do you think the bullet's dwell time in the barrel is a factor?

  4. #24
    Boolit Master Cast10's Avatar
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    It was already stated and should be well heeded; Carbine barrel may/will be a tighter chamber than that of a pistol. Adjust accordingly.

  5. #25
    Boolit Bub
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    I have not tried to hot rod my AR-45, but I did have to do a lot of work to find what shot most accurately.
    What my ar liked was a Lee 200 gr loaded out just a tad longer than what will work in a 1911. Group size at 50 yds dropped by 30-50%

  6. #26
    Boolit Master 243winxb's Avatar
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    Worry more about, if the action is fully closed, before pulling the trigger.

    The 10 + grs Blue Dot load with 200 gr lswc is a hot one, for any 45acp.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check