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Pressure and case length

 
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  #1  
Old 08-13-2012, 11:02 PM
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Pressure and case length

Can overall cartridge length make a difference in cup pressure? The reason I am asking is I have loaded some 223 rounds that will chamber and fire but the bolt will not cycle back far enough to pick up the next round out of the magazine.
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Old 08-13-2012, 11:59 PM
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Re: Pressure and case length

Cartridge and case length are entirely different.

The case is just the brass container. If it's too long, it may jam at the end of your chamber and pinch the bullet causing a pressure spike.
If the case is slightly shorter than the "trim-to" length in your reloading manual, then no big deal.

The cartridge overall length COAL is from case head to bullet tip. A cartridge with the bullet jammed into the rifling will likely have higher pressure than the same load with the bullet jumped to the lands.

If your AR bolt isn't cycling far enough, you may need a heavier charge. I'm sure there's some tuning you could do with your rifle if you're dead set on this load.

Do you have this problem with factory ammo?

This is also a common issue with semi-auto pistols that are held too loosely. But, not so much with a shoulder fired weapon.

-- richard
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Old 08-14-2012, 05:45 AM
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Re: Pressure and case length

I don't have a problem with factory ammo. I have already increased the powder charge by 1.5 grains. I am using IMR-4198.
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Old 08-14-2012, 09:15 AM
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Re: Pressure and case length

Quote:
Originally Posted by swpc629 View Post
I don't have a problem with factory ammo. I have already increased the powder charge by 1.5 grains. I am using IMR-4198.
Since factory ammo works fine, it sounds like you're not generating enough gas pressure or inertia depending on your system. Is your AR gas or piston?

I suppose it could possibly be that your brass isn't being sized down enough. But, that'd more likely be an issue with the chamber closing and firing rather than picking up the next round from the magazine.

Are you neck sizing or full length sizing?

Are you using a small base die?

What is your actual load? brass, primer, powder weight, bullet, and COAL

-- richard
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Old 08-14-2012, 06:36 PM
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Re: Pressure and case length

I am full length sizing using Dillon Carbide 223 dies. Brass is various brands, Primer is Winchester small rifle, Powder is 21.5 grains of IMR-4198, Bullet is Hornady 55 gr V-max, and COAL is 2.220.

The rifle is actually a Steyr AUG.
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Old 08-14-2012, 07:39 PM
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Re: Pressure and case length

Well, I'm stumped.

You seem to have the right dies to load for semi-auto and a plenty stout load.

Is this an intermittent problem? Or, most every round that you fire?

You did mention various brands of brass.

You might want to get a case gauge to quickly confirm that all of your cartridges will chamber every time... JP - Gunsmithing and Maintenance

But from what you've stated, the problem occurs after firing as it's not picking up the next case.

As such, I might suspect the magazine. But, you also said factory ammo works fine.

As I'm unfamiliar with the AUG, here's what a quick google turned up...
AUG not cycling - AR15.Com Archive

-- richard
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