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AR shoulder bump

jLorenzo

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Full Member
Minuteman
Feb 20, 2017
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How far should I be bumping the shoulder for a 223 wylde chamber? Im using a Hornady custom full length die, any tricks as far as starting out? Right now I set it until it barely touches the shell holder then I back off a tiny bit.
 
0.002" should be plenty. As far as where you need to screw the die in to achieve that you need a comparator to measure the difference between your unsized and sized brass.

How Erik Cortina adjusts his:
 
For bolt guns I would bump 0.001” to 0.002” but for an AR I bump 0.003” to 0.004” to be on the safe side.

But agree that you need a comparator in order to set the die correctly to achieve this desired bump. Most dies give you the best performance when they contact the shell holder. I prefer a little cam over in my setups but every die / chamber combination is different.

The other consideration is will these rounds only be for this AR? If yes, shoulder bump is fine, if not I would size them back to SAAMI specs.
 
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The comparator that Erik uses in the video is a Whidden comparator. I've already purchased my comparators. If I was just starting out, I'd buy the Whidden They're under $20.00 and seem to be a good design.


If you're not measuring your shoulder bump using some type of gauge or comparator, you are just guessing at how much you are shoulder bumping. Yes, you can use you rifle's chamber to figure that out, although it's a bit time consuming and can get tricky on a gas gun. A comparator makes it a simple task and you get to see the actual numbers of what will fit and what will not.
 
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0.002" should be plenty. As far as where you need to screw the die in to achieve that you need a comparator to measure the difference between your unsized and sized brass.

How Erik Cortina adjusts his:

I have seen that vid and I like his stuff. I have the Hornady comparator. I found a load my barrel likes but when I went to load some more I tried setting up the sizing die like in Cortinas vid but some how I bumped the shoulders too much to the point of some of them not chambering fully, I may have read the comparator wrong and bumped .020 instead of .002 not sure what happened though. The shoulders on some were just barely bulged enough to see visually. Luckily I caught it on visual inspection before actually going to the range and trying to shoot them.
I have the Hornady lock n load bushings on all my dies which makes dialing them in a bit tough because you have to account for how much the die rotates when locked in place. I only have one set of comparators making the Cortina method a bit tougher but Ill need to watch the vid and try again. This rifle being an AR I figured maybe I should bump a hair more than a precision bolt gun.
 
Also a bit on confusion on my part, when using a FL die are you not bumping the shoulder or is this just setting the die higher up in the press?
 
If you don't have your F/L die screwed in far enough, it will not bump the case shoulder. Screw the die in until you just lightly touch the top of the shell holder, measure the fired case shoulder, note it down. Size a case. Measure the shoulder. If you're not far enough down, you may see a slight lengthening. Keep screwing the die down and keep measuring and screwing the die down until you start seeing the shoulder measurement getting shorter. You will find the sweet spot. You go in small increments like 1/12th of a turn or less. It's a fine adjustment when you hit it, just like Erik pointed out in the video.

For a gas gun, I bump .004"-.005".