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Old March 16th, 2009, 02:37 PM   #1
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Join Date: Jul 2006
Location: Annapolis, Sheeples Republik of Marylandistan
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.45ACP AR45

I am about to "pull the trigger" on one of these:

AR45 Lower

along with one of these:

Olympic Arms .45ACP Upper

...to build up a .45ACP AR45. Has anyone got any experience with this platform? The questions I have are:

1: Does it in fact require a different spring in the buffer than the 9mm or 5.56 NATO?
2: Does the .45ACP range get affected by the barrel length?
3: Are there any issues with using +P ammo in the AR platform?

Any experience with this would be greatly appreciated as this will be my first AR "build".

I will be building almost exactly like the one pictured (short gas block w/flip up BUIS) as my sub/fun gun.

Thanks in advance for everyones help!

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Old March 16th, 2009, 03:04 PM   #2
Join Date: Aug 2008
Location: Charles Co.
Posts: 576
I have an Oly 45 upper on a CavArms MkII lower. The CavArms lower ($125) is specially designed to take both regular M16 magazines (for 556 uppers) and 45 Greasegun magazines with Hanh magazine adapter.

1) The CavArms polymer lower does require a heavy 8oz buffer, otherwise, full auto pistol carbines can use it to increase reliabiliy.

2) I've found that the 25yd zero with 45acp is close to the 100yd PoI. If you have a 25yd zero, at 7yds the bullets PoI is halfway up the front sight post.

3) none, the Oly upper is very strong and one of the arfcom guys shoots .45 Super out of his.

With the 16" barrel, you don't really need a flashhider, and I have a simple thread protector on the end of mine. I got it from a guy on eBay for $10 (5/8"id x24 tpi, 5/8" long).

One last thing about the CavArms polymer lower, if you ever f*** it up, they'll replace it for $30. Plus you can put a regular 223/556 upper on it and shoot rifle ammo if you ever change your mind.

Heres the arfcom 45acp conversion guide for more info

One more thing, you may find it to be a long wait if you order the upper from Oly, there's a guy on arfcom who makes and sells gas operated 45acp uppers here.

Last edited by Andras; March 16th, 2009 at 08:14 PM.
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Old April 10th, 2009, 09:52 PM   #3
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Do you still use an AR15 lower parts kit with the CAV-15 MKII Receiver?

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Old April 10th, 2009, 10:21 PM   #4
Join Date: Aug 2008
Location: Charles Co.
Posts: 576
Yes, but you don't need the grip and related parts. Also the pivot and takedown pins are not used, CavArms supplies 2 pins that install from the left side.

The buffer retaining pin is held in by a roll pin, but most people just leave it off. The selector spring and detent drop in from the top, and you trim 2 coils or so off the spring.

I didn't bother to install the bolt hold back since it doesn't work with the 45 set up, but it installs normally.

IIRC, Magcatch assembly, bolt hold back assembly, trigger and hammer group, and selector assembly are the regular lower parts that are required, with the buffer pin and spring optional.
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