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Posted: 4/30/2009 4:07:30 PM EDT
[Last Edit: 4/30/2009 4:11:16 PM EDT by batmanacw]
I just measured my chamber in my RRA Predator Pursuit for the first time. I used my brand new Hornandy O.A.L. gauge. to find out that it measures my chamber at 2.9155" deep for three straight measurements with a 75 grn Hornandy HPBT. My Hornandy Bullet comparator & insert set made that really super easy to measure up the O.A.L. gauge.

Now, what do I do with it?

I have been told that I should set my bullet back another .010" to avoid overpressure. Is that a good place to start? What is the maximum over all length that will run in a magazine?


I measured my original 68grn HPBT loads, done without the benefit of a gauge like this, or really any idea what I was doing, and they measured 2.855" on the same measuring tool. Hornandy TAP 75 grn measured 2.860". Notice, I did not zero my calipers the way they recommend. I just used the regular caliper zero at the closed position. Its only a comparator so it really shouldn't matter.

I am guessing that I must check different bullets on this rig to make sure they have as small a jump as possible. My first loads will be with 68 grn and 75 grn HPBT. Both Hornandy bullets. Because the oglive changes, the measurement by this tool also changes, so the comparison would not be the same.


Fortunately, I bought the Cartridge Head space gauge kit so I can accurately measure the set back of the shoulder as I size fire formed cases from this same rifle. I am still going to full length resize for now. I can get more picky once I get going. I will start with .001" or .002" of shoulder set back.

Any feed back you can give me would be helpful. I have all these great tools to play with now!  I am using a pair of Mitutoyo Digimatic calipers for the gauges.

I am limiting my reloading to .223 until I really understand how to get it right, then I will branch out into .308.
Link Posted: 4/30/2009 4:45:42 PM EDT
Just remember, seating the bullets out that long makes them single feed only.
'Borg
Link Posted: 4/30/2009 4:47:56 PM EDT
[Last Edit: 4/30/2009 5:02:23 PM EDT by batmanacw]
Originally Posted By We-rBorg:
Just remember, seating the bullets out that long makes them single feed only.
'Borg


What is the absolute maximum length that will feed in a magazine?


ETA: The length numbers I gave are not over all length, they are just a comparative number indicating the size of my chamber on this gauge from the oglive. It has nothing to do with the final OAL. I did not measure the OAL that resulted from this test because I didn't think about it. Probably should check it.


ETA: I just measured my OAL just with calipers. If I don't set the bullet back any, it would come to an OAL of 2.328".  I would probably start by setting it back to 2.320" if it would run in a mag.
Link Posted: 4/30/2009 5:10:19 PM EDT
My Hornandy reloading manual gives a OAL of 2.250", but my cartridge would have to be 2.328" for no jump at all. That is a .078" jump with this 75 grn bullet.

How do I work this out?
Link Posted: 4/30/2009 6:25:29 PM EDT
You have one of two choices ..... single feed em and set for .010 jump .... or load to mag length and have greater jump.

Link Posted: 4/30/2009 8:24:54 PM EDT
2.260 COL will fit most mags.
'Borg
Link Posted: 5/1/2009 7:05:59 PM EDT
I found that using an O.A.L gauge to seat the bullet to a .001-.002 rifling jump to improve accuracy for an AR is not practical and really is impossible.  I suppose maybe with some longer bullets it's possible, but you will exceed the max overall cartridge length for the 223. Your defeating the purpose of the semi auto AR.  I load 55 or 62 grain FMJ's with the crimping groove and seat them to the groove.  It's that easy.  I want my loads to be reliable and not hang up in the magazine.  I would never exceed the max OAL of 2.260.  And I would never consider single feeding longer rounds either to get that kind of accuracy.  Experiment with your powder loads, different bullet types, etc... to get better accuracy.  You can only get so accurate with an AR.  It's not a precision bolt action rifle.
Link Posted: 5/1/2009 7:27:32 PM EDT
Originally Posted By lear60pilot:
I found that using an O.A.L gauge to seat the bullet to a .001-.002 rifling jump to improve accuracy for an AR is not practical and really is impossible.  I suppose maybe with some longer bullets it's possible, but you will exceed the max overall cartridge length for the 223. Your defeating the purpose of the semi auto AR.  I load 55 or 62 grain FMJ's with the crimping groove and seat them to the groove.  It's that easy.  I want my loads to be reliable and not hang up in the magazine.  I would never exceed the max OAL of 2.260.  And I would never consider single feeding longer rounds either to get that kind of accuracy.  Experiment with your powder loads, different bullet types, etc... to get better accuracy.  You can only get so accurate with an AR.  It's not a precision bolt action rifle.


I am probably going to just load to 2.260" and work on limiting my case sizing as much as possible to help keep things tight. I am planning on setting the shoulder back .001 to start. I am using regular dies, not small base since my AR's did just fine with regular resizing. If this was a bolt gun I would definitely just neck resize. I already measure every single charge.

I have seen AR's that flat out shoot, so extremely good accuracy is possible. Les Baer makes a living making phenomenally accurate AR's so it is definitely possible, just not with a $1200 rifle.
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