Weird results with OAL for AR

J

jetinteriorguy

New member
Ok, so I'm trying to determine seating depth for my AR and getting some puzzling results. It's chambered in .223 Wylde and I'm using the Hornady tool to check max length to where the bullet is touching the lands. I started just seating Hornady 75gr HPBT match bullets to where they were as long as I could make them and they would still function in the mag.

With my initial measurements with the Hornady tool this was no problem. But I've been having some problems with inconsistent accuracy even though according to the MagnetoSpeed I'm in a very comfortable node. So I started adjusting seating depth and at .040-.050 thousandths he accuracy really came around. But here is where it gets hairy, the necks on my cases were sort of ballooned up to the end but the very mouth of the case was a normal diameter.

This really got me to reinvestigating my seating length and here is where I started to get some puzzling things going on. I rechecked my max seating depth with the Hornady tool, I did four groups of twelve measurements. I then threw out the longest and shortest measurement of each group. Then I averaged these four groups out, added these four measurements together and averaged them out for my final measurement. According to this measurement I had been seating my bullets at around .015 thou into the lands instead of .020 off the lands.

So now, thoroughly confused by all this I've tried one more thing to determine my max length. I colored one of my bullets with a black sharpie in one of my original loads that should have been .015 thou into the lands, and then chambered and ejected this round. It showed absolutely no scratches indicating it was into the lands at all. So, now that everyone else is as lost as I am on this, what the heck is going on. My guess is possibly excess head space? To me this would explain the difference between the Hornady tool results and why real ammo that should be too long isn't too long at all. Any thoughts or opinions on what to try next?

Oh, and the difference in fire formed brass and full length sized brass is .008 thou using the Hornady case datum measuring tool. Does this mean that when I use the Hornady tool with the brass case that it will actually seat .008 thou deeper than what my loaded round seats at and that's possibly why no scratches show up on a colored bullet?
 
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Had an issue with case head separations fire forming 280AI brass because I forgot to factor in the difference in case lengths (datum to case head) between the modified Hornady case (the case for the tool) and the brass I was reloading. I think it was something like .008" to .010" shorter for the modified Hornady case.
 
Sounds like you have a whole bunch of technical equipment and not nearly enough plain old experience. I've never used any of those widgets you mentioned and never had any of the issues you describe.
 
Sorry for all the rambling, I'll reorganize my thoughts and repost it later today. It was late and I was tired.

Yes, I am new to this type of reloading even though I've been loading for over thirty years. I've loaded a ton of pistol and plinking ammo for rifles but am just getting into trying for better accuracy at longer ranges and it's definitely a learning experience.

Basically for now I guess what I'm trying to figure out is why I'm getting these discrepancies in length measurement. Do I need to have my rifle checked out by a gunsmith. Or do I need to use a different method for determining my seating depth. I'm just trying to develop good safe procedures for improving my accuracy.
 
So brasscollector, what your saying is I should measure the difference between a fire formed case and the Hornady modified case and this might account for these differences? Of course I'm talking from the base to datum measurement. This makes sense, hopefully it's something this simple.
 
Yes, correct.
It was definitely an issue for me as I was attempting to fireform brass where it was necessary to keep the case head firmly against the bolt face. The difference in length that I forgot to account for was more than enough to stretch the brass and cause indigestion.
 
Thanks, the light bulb is starting to shine. Unfortunately all my brass is processed right now so I'll have to wait until my next session to check this difference. I hope this is all it takes to account for these differences, but it makes sense to me.
 
Then I averaged these four groups out, added these four measurements together and averaged them out for my final measurement. According to this measurement I had been seating my bullets at around .015 thou into the lands instead of .020 off the lands.
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If you take a measurement of something that isn’t changing and get different readings, you need to figure out if it’s the tool or how you are using it.

.035” is a big difference in “precision” measurements, might as well be using a tape measure.

Have you tried the simple method of marking a bullet with a sharpie and having it touch the lands/or not, leaving witnesses marks/or not to determine at what point the bullet actually contacts the rifling? That should be repeatable well inside .035”
 
.035” is a big difference in “precision” measurements, might as well be using a tape measure.
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yep

I had been seating my bullets at around .015 thou into the lands instead of .020 off the lands.
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Although not impossible you are jammed into the lands , because of the first quote and the fact at mag length most bullets will never see the lands in an AR . I find it not likely unless you are using a round nose bullet or maybe V-max . I read the V-max has a pretty short rose in relation to the ogive .
 
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Stop sweating actual distance to the lands, it will drive you nuts. Find a base to ogive or a base to meplat number that gives you the groupings you desire and are magazine length if that is what you want then shoot the heck out of them

I have Berger VLD's that like it .075 off lands and SMK's that want to be jammed .010 into the lands according to my comparator. Those numbers could be .020 or .030 off and I would not care as long as when I seat the bullets the groups continue to be consistent

All that matter is the results on target. Just my two cents.
 
I too have a rifle with a Wilde chamber. Loaded ammo to fit the mag. Jams the bullet into the rifling. Showed high pressure signs with 3 rounds of odd brass, none with new Winchester brass, don't know what this means other than to back down to starting load if I switch brass. Meanwhile, I bought an upper with a .223 chamber and it seems to shoot like a house afire with AE 55 gr factory loads. No time in the last year or so to mess with it.
Will shoot the AE stuff thru the Wilde again, I was not impressed with it before. Guess I forgot how female rifles could be, I shoot mainly handguns and shotguns.
 
Thanks all. I know I'm having issues with my measuring technique. This is why I am throwing out any obvious discrepancies and then averaging the more consistent ones for a final number. Mostly I'm not concerned with getting an exact number, more of a reference number for a starting point. Provided this number keeps me from jamming into the lands.

I did find some fire formed cases and measured them from the base to the datum point and compared this to the Hornady modified case. Sure enough the fire formed cases were all .005 thousandths of an inch longer. Once I added this in, it was within 1/1000" of the measurement I averaged out using the OAL gauge. I feel pretty comfortable using this measurement as a starting point.

I'm also going to do the sharpie colored method in a modified case to verify that I'm not way off base again. If this affirms that I have a solid starting point then I'll proceed with my depth seating testing again.

I know this may all just be a waste of time, but I enjoy solving problems and learning new things. It's what has reinvigorated handloading for me again and is making shooting a lot more fun again. I know this rifle will shoot under 1/2" at 100 yds and I'm just trying to produce ammo capable of this. I feel the only way I can improve my consistency and technique is with capable ammunition. This is my final goal.

Thanks for all the help, any other ideas I'm open to listen.
 
http://www.bergerbullets.com/getting-the-best-precision-and-accuracy-from-vld-bullets-in-your-rifle/

it works for all bullets. Do this and write down the base to ogive or base to metplat number depending on how you are measuring the cartridge.

Using your Hornady 3 times write it down and average it. This is your starting number. That is the last time you will need to measure the chamber for that bullet for a long time. It will be your comparison number for that bullet for the next 500- 750 rounds of throat wear. Pick the best group and examine the results from the targets on either side of the best group and work towards it.

For example you run the test and groups end up at

.100 jump = 1 MOA, .75 jump = 1.25 MOA .050 jump = .5 MOA , .25 jump = .8 MOA and .000 jump = 1.3 MOA.

In this example I would start at whatever seating depth gave me the .050 group , then try .045, then .040 etc until the groups start working up in size.

This is where a Lee hand press comes in handy for preloading powder with the bullets seated long and adjusting the length at the shooting bench

Again that comparison number can vary several thousandths between measurements at times. That is why I only remeasure when I think I have fired enough rounds to wear the throat sufficiently to change my seating depth
 
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Adjusting the seating depth is not that simple when loading for an AR with a long bullet to mag length . OP says he's using the 75gr BTHP which I assume means Hornady ?

This photo is the 75gr BTHP seated to 2.260 ( left ) center is same bullet seated to 2.210 and right is how deep that bullet would need to be in the case to seat it to 2.210 .

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Generally I'd say seating deeper is no big deal when it comes to pressure spikes because seating closer to the lands will spike pressure faster in smaller COAL increments . How ever I've found when loading heavy/long bullets to fit in an AR mag the base sits quite deep into the case . One might ask , sure but why does that matter when I just said seating deeper is generally not an issue ? Well it's not when you have room in the case for the bullet to be seated deeper . I have found that my cases are pretty full of powder when using the traditional powders used for 223/5.56 and heavy bullets . This means even if my COAL is at the magazine max of 2.260 . I'm already compressing the powder . No way I'm going to get the bullet to seat .050 deeper in most cases little lone .100 or more .


IMHO , although you can play with seating depths in the AR platform with good results . When you're using a heavy/long bullet and need it to be fed from the mag . You are limited in the amount of depth you can play with .

For me when I'm loading the 75's and 77's to fit the mag . They are seated to 2.255 average because of the inconsistency of the tips and I use the powder charge with a drop tube to tune the load . YMMV
 
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Jetinteriorguy,

When you discovered your case shoulders were 0.005" longer from the head, you discovered your bullets actually had 0.005" more jump to the lands than the Hornady OAL gauge was telling you. This is because the case is driven forward by the firing pin until it the shoulder of the case stops on the shoulder of the chamber. That is, therefore, also what determines how close the bullet gets to the throat, and not the distance of the bullet ogive from the head of the case.

I have noticed in my own ARs, the Hornady gauge can allow bullets to catch short of being fully seated in the throat and thereby giving false short readings. I assume from the feel that the bullet is cocked in the freebore area when I get the false short reading. Perhaps the edge of the bullet ogive grabs at the case mouth portion of the chamber profile, which is a sharp-edged step in the chamber, but I don't know for sure. I did discover I can avoid the problem by removing the upper and clamping it vertically in a plastic vice I have, and then inserting the gauge slowly and then, when the case has seated, pushing the gauge extension up slowly until the bullet seats. Keeping everything straight seems to be the key and this gives me maximum length readings. If you don't have a plastic vice, drive a nail part way into the edge of your workbench and hang the front sling swivel over it. Or you can just have someone else can hold the upper vertical for you.

Jetinteriorguy said:
the necks on my cases were sort of ballooned up to the end but the very mouth of the case was a normal diameter.
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If this condition obtains in loaded rounds, it usually means you are crimping the load and crimping it too hard, forcing the neck out and often bucking the shoulder some. However, if this observation is in cases that are as-fired and ejected from the gun, that is pretty normal. When pressure builds in the case during firing, the case expands away from the bullet starting at the base of the neck and rolling forward until the mouth starts leaking gas out around the bullet and into the bore. When the leak commences, a pressure drop occurs along the small gap between the bullet and the expanded portion of the neck, so there is not enough remaining pressure to expand the mouth as well. Thus, fired cases are typically curled in at the mouth (see sectioned .308 case, below). As you seat a bullet deeper, there is a bigger annular gap at the throat around the bullet ogive so you get more leaking bypass gas flow, increasing the effect.

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Thanks guys, great info here. Just what I'm looking for. I know what your saying about the neck expanding and I've noticed it before, just not to the degree I was seeing on these loads so I felt concerned. I'm trying to be very careful hear and not do anything any more messed up than I already have done. Even though I've been handloading since the mid eighties, I've never had an incident until a few months ago when I blew the top off my S&W Model 627 through a series of small mistakes using Titegroup and just being too complacent in my procedures. This was a wakeup call for me, luckily no one was hurt.
 
@Metalgod

Perhaps I wasn't clear in my post, I apologize. Wordsmithing is not my strong suit. I underlined the important part

That is the last time you will need to measure the chamber for that bullet for a long time. It will be your comparison number for that bullet for the next 500- 750 rounds of throat wear
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@Uncle nick

If you are saying that two rounds that have been sized differently with different amounts of shoulder setback will have different jump lengths I agree. However neck length or overall case length only affects the amount of bullet bearing surface that is being gripped by the neck. Base to ogive measurement remains the same regardless.
 
That's what I am saying. Bullet jump changes, but the other measurements do not, which is why they don't correspond to bullet jump directly. Bullet grip does change with case length, but as with annealing, measuring the ballistic effect of the difference is not yet clearly demonstrated. The only exception I am aware of is where crimping is involved. An inconsistent crimp that results from varying neck length can have a measurable effect on both mean velocity and velocity SD.
 
I understood what you were saying . My point was narrow in scope to this specific seating depth issue . The OP is not likely going to get that much variance in seating depths therefore may not even notice it on the target .
 
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