Proper cartridge head spacing for AR10 questions

Dultimatpredator

Dultimatpredator

Well-known member
I don’t own a headspace gauge so I grabbed a spent 45 ACP cartridge and slipped it over a few of my fired 243 casings. The AOL’s were 2.461”,2.462” and 2.461”.

Then I measured some casings I ran through my small base die. I followed RCBS’s instructions and lowered the die down till it touched the shell holder, raise the handle, and then turned the die down one quarter turn. The measurements were 2.452”, 2.450”, and 2.453”.

I realize this I sent the most accurate way of measuring headspace but I’m sure it probably got me pretty close.


So if I add and divide by three I’m approx .009” less. How far do you shooters Bumb your headspace back off your AR’s? I read on a couple of forums some recommend .004? I would think there’s not a lot a room for error with .004” in an auto or AR style rifle eventually causing chambering issues?


To be honest this is the first time I’ve ever checked for head spacing...and I’ve been reloading for 20 years. In the past I’ve just always turned my dies down a quarter turn after it touches the shell holder as in the RCBS’s directions and never had issues with this practice along with making sure I loaded under the chambers max AOL. I just wanted to check my 243 AR since I knew it had a tight chamber. So if I didn’t check it I’d be loading with a quarter turn down as usual. So if .004” is correct and I’m too short by .005” I would assume I’m just shortening my brass life?

I have done the 1/4 turn die set on my other bolt guns and POF P415 and can shoot .3” groups with my loads at 200 yards when I do my part so I’m sure accuracy is not as much or even an issue...it’s just the brass life, and stretching issues I would assume?


Update,

I just got off the phone with RCBS customer service and was told .009” was where I wanted to be at ...or close to that measurement range” is where I wanted to be away from the chambers shoulder, give or take, was the quote. I asked what was the acceptable measurement range variance for AR’s but he wouldn’t give me an exact range measurement for some reason.
 
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I run all of mine in the .002.004" range. All you have to do is back your die off a little bit. I would also recomend a set of the Hornady headspace gauges. They will make this process much easier in the long run. All Rcbs is concerned with is getting them to chamber... not your brass life or accuracy. I've used 9mm to measure with and it works but the gauges take all the BS out of it, and they are cheap.
 
Originally Posted By: Dultimatpredator I’m curious what the measurement of the average factory load is?

I've measured them from 0.006 to 0.010 in factory 223. Most other things I've looked at in passing are in that area below SAAMI minimum.

Greg
 
I do have more brass to resize so I would assume to resize the rest at an 1/8th turn down past the shell holder instead of a quarter turn? I would assume splitting the difference will get me in the .004/.005” range. I’ll remeasure of course.
 
I run my bolt guns .002 and my AR's .003-.004. Never had any problems at those settings. If you are going to reload I would get some proper measuring tools. Makes life easier and doesn't work the brass near as much.
 
If Im loading hunting rounds I will go .006" or .007". I want to make dang sure it cycles. Not to mention unless you check everyone it's possible to get brass that's work hardened and might have some spring back. An extra .002" or so keeps that from causing a problem. If I was just concerned with maximum accuracy I would probably go .004" to .005".
Bolt action .002".
 
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Originally Posted By: DennyrAnyone that can shoot .3 groups at 200 yards does not need to change a thing. You seem to be doing it right.

kind of what i was thinking.
 
Sorry, I meant my bolt guns (my 700’s in 243 that’s in my avatar and my ltr 223) and POF P415 all will shoot .3” at 200 yards when I do my part...and that’s without ever checking checking the head spacing on these rifles and doing a quarter turn down on the sizer die after it touches the shell holder. The 243AR I’m asking head space questions on is new and I haven’t shot it for groups yet. Once I size my brass properly I’ll work up some loads for it to get the rifle dialed in. Just want to do everything right to get it to shoot as tight as my other predator rifles.
 
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I tried a few more measurements today. If I leave the sizing die flush with the shell holder it will average .0069”. I then tried turning my die an 1/8 th of a turn up from flush. It averaged .001”, then I turned back down so it was approx 1/16 of a turn up from flush to remeasure and stuck a case in my die. I stopped by cabelas today to pick up a stuck case removal tool and will try to pull next week when I get back in town and then measure the 1/16th of a turn up from contacting the shell holder and remeasure.
 
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I have a set of redding competition shell holders, I think I use the .006 shell holder if I remember correctly. it doesn't lessen the setback by that much. because of brass spring back. it just sizes the cases a bit less and is repeatable. honestly for an AR, I don't know why I give a crap about it. get a load that shoots around .75 and call it a day. AR's are the type of guns that may shoot that same load .5 moa one day, then .8-.9 another day. if accuracy isn't meeting your expectations in the field, just shoot another time, LOL.
 
So is it OK to FL size my brass with the die turned up 1/16th of a turn from flush? Instead of turned down past flush to remove all the “play” as per rcbs directions? I
 
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Originally Posted By: DultimatpredatorSo is it OK to FL size my brass with the die turned up 1/16th of a turn from flush? Instead of turned down past flush to remove all the “play” as per rcbs directions? I

Their directions are a guide only. Adjust for optimal shoulder bump...that is all.
 
I drove by Cabelas today and picked up a hornady head space checker kit. That’s the best $40 I’ve spent on reloading in a while. I measured three fired cases with the primers removed. They all measured 1.630”. Then measured my three fired cases I sized the other day with the die tired an 1/8th of a turn up from being flush with my shell holder they all were 1.625”, so I would assume I’m good to go,or if I really want to, I could turn my shell holder up a hair more till I get a 1.626” reading to be at everyone’s suggest .004” which seems like everyone who’s anyone is suggesting for loading ARs

I also picked up a RCBS stuck case remover. I didn’t need it as the case was loose and came out when I got home! I would assume when my case and die cooled after heating it caused the case to shrink and pop out? The decapper pin was still stuck inside the case so I had to give it a good yank with a pliers to finish the removal. I’ll hold onto the stuck case remover for future use. Thought one came with my rocker checker kit when I bought it 20 years ago but I don’t remember.
 
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I'd just leave the die alone. As the brass work hardens that 0.001 will disappear quickly.

I've never sen a case puller in a kit but then I am old and memory fades. I know one sure didn't come with my RCBS JR in 1975!!

Greg
 
Like Greg says when your brass gets a few firings on it and hardens it will spring back some when sizing. I wouldn't change a thing I'd leave it right at your .005" bump. All it would take is one failure to feed on a follow-up on a critter and you'd be cranking that die back down LOL.
 
Makes sense. I’ve been reading more and more that .003” to .005”, instead of .004, is the advised auto rifle standard. I would rather be on the wider gap of the spectrum (.005”)as advised for reliable cycling. I have a bunch of brass i annealed and ran through my standard size 243 die as per the RCBS directions way....1/4 turn past flush. I’m going to run them through my small base sizer die set an 1/8” turn out as I did the fired cases that ended up at .1.625”. I’m curious if the necks will grow enough when sizing in my SB sizer to get to the same 1.625” compared headspace measurement?... guess I’ll find out soon. Well, I’m sure my accuracy and brass life will increase with a third of a turn in the opposite direction compared to they way I was originally loading them...going from .009” to .005”.
 
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