223 AR15 loads and signs of over pressure

Grizzlypeg

Grizzlypeg

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I'm loading 75gr Hornady match bullets for my AR15 and using IMR4895. IMR lists the maximum load as 23.8 grains of 4895 for a 75 gr bullet. I'm currently loading with 23.0 grains and getting alright accuracy, and would like to try a hotter load and see if the accuracy improves, but I'm concerned about watching for pressure. Are the max loads conservative or dangerously near the limits? Not being a bolt gun, I can't feel if the bolt is hard to open, all I can do is watch primers. I'm using standard Remington primers, and they do look a bit cratered at 23.0 compared to factory Remington loads. I'm not sure if this is an accurate indication or what else to watch. I do not own a chronograph. Any suggestions? Should I try 23.5 grains of IMR4895? I'll post some pictures of the primers if anyone thinks that's of any use.
 
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Published max loads should not be dangerously near the limits, however all the usual caveats about each gun being different applies. It's good to see that you're carefully thinking over how to prudently increase your load given your constraints.

You ought to be OK to try 23.5, and if that turns our OK I would then try 23.8 also, and if that turns out OK I'd then try 24.3 - but, be sensible about assessing how things are going.

In addition to seeing how your accuracy is doing and how the appearance of the firing pin indentation in the primer looks, you should also pay attention to whether the primer pockets are looser when you reload the case (if so, you've gone too far and need to go back a step or two). And keep an eye out for ejector marks showing up on the case head.

In addition to pressure considerations, in gas guns you also have brass life considerations (since gas guns extract brass when they're still slightly snug in the chamber). Keep an eye on whether your brass's wear and tear (stretching, case mouth condition etc) is reasonable.
 
Thanks. I do see a small ejector mark on many of the reloaded cases that on some has slight enough of a burr you can feel it with you fingernail. All factory shells also have some smearing of brass, but nothing you can catch a nail on. So there is a difference there. The primers themselves are definately not flattened, but under the view of a strong magnifying glass, you can see the rim of the firing pin indent has an infinitismile ring of raised material, hardly different from factory shells. So in a nutshell, primers look no different than factory, ejector marks slightly more pronounced than a factory cartridge.
 
I'd tolerate a bit of an ejector smudge, provided that everything else seems to be in order. In particular, if primer pockets are not loosening, then things are probably OK.
 
Keep in mind that the "sight cratering" you are seeing on your primers could also be a sign of a firing pin that is smaller than it should be in relation to the firing pin channel in the bolt.

A better way to check for over-pressure is to measure case head expansion. Also consider whether you are shooting a .223 chamber or whether it is .223 Wylde or an actual 5.56 chamber as these will all make a difference in what you see...


blake
 
What do ejector marks on the case mean? My Stag always leaves an ejector mark around mid case,factory and reloads//Nice neat shiny nick.
 
Johnnyreb65, what you describe sounds like the characteristic marks left on brass by semiautos when they eject their brass - i.e. what you describe are "ejection marks". "Ejector marks" refers to a round raised and/or bright bit of brass on the case head, and can be one of the signs of high-ish pressure.
(longer version: The ejector is a spring loaded plunger on the bolt face. When a very high pressure round is fired, some of the brass may "flow" a little bit, pushing back the plunger a bit. When the bolt is rotated to unlock, the solid part of the bolt face rubs against this raised bit of brass (this is one of the reasons that a high pressure round can result in a stiff bolt lift).)
 
Mine's leaving a slight burr at the edge of the ejector mark on the Remington Brass, but not the Winchester. Maybe the Rem brass is softer? I compared the weight of the two cartridges after sizing and trimming and they are within 1 gr of each other, so I don't think (hope??) one is thicker walled and causing more pressure. I've tried batches of each kind of brass to see if one is more accurate than the other, but no diff. I'm getting 5 rounds into 1" regardless of brass type, but I want better than that if I can get it.
 
One kind of brass might be softer than the other.

My AR-15 (a stock Colt Sporter) shoots 10-shot groups of 2.5"-3" at 100m, no matter what I've tried (various match bullets, different 20X target scopes, etc). I suspect that this is probably a realistic accuracy figure for a non-accurized, "service grade" AR-15. Keep on trying of course, but unless you have a free-floated match barrel, it may well be the case that honest 5-shot 1" groups is simply the best that is going to happen.
 
It's a free floated stainless heavy barrel, 1:8 twist. I don't know the brand, as I bought the rifle used,and would have to remove the gas block to see what's printed on the barrel under the tubular handguard. It sure looks like the Armalite's made by Krieger. I can get 3/4" groups with Remington match grade 69 gr ammo, but that comes to $38 a box with taxes. This roll your own is a lot cheaper. And it does not shoot consistently with Remington UMC 55 grainers. Might get a tiny group from one box and a 2.5-4" group from another. Wildly erratic with those. So far the 75gr Hornady match bullets with IMR4895 have never had a wild one. Consistency is good, even if its a consistent inch. I keep hearing these stories of people shooting 1" groups at 200-300 yards and I'm envious. Not even sure I'm capable of it except by some degree of luck.
 
OK, then you have a realistic chance of getting better than 1" 5-shot groups, and it's probably worth trying (BTW: ignore tales of 1" groups at 200 and 300 yards, they are not real/realistic/typical).

Since you've gotten 3/4" groups with Rem 69 match ammo (I am assuming that you mean consistent or typical 3/4" groups, not "my best group, not counting flyer(s)"), you know that at least that level is achievable by your rifle and your shooting technique. (BTW I might be out of touch with current prices but my gosh $38/box of .223 match ammo seems scandalous!!!).

Hornady bullets are often a bit higher performance (lower drag) than Sierras, and oftentimes this makes them a bit fussier to get shooting well.

Are you using the Hornady 75 BTHP, or the 75 AMax? (the AMax is a very high performance bullet, but can be quite fussy; it'll most likely *NOT* shoot well from magazine-length ammo).

Assuming you are using the Hornady 75 BTHP and loading it to magazine length, it's probably worth a bit more trying before giving up on it. Trying working up in 0.3 gr steps to published max loads; it probably won't help accuracy much, but it's worth trying.

If you can try a somewhat blunter bullet, e.g. a Sierra 77 or Sierra 69, you might find that they are easier to get shooting well.

But once you are shooting better than an honest 1" 5-shot groups, a lot of things start to matter, and can show up as obstacle to further improvement. Is your scope good? (it would be nice if you knew that the scope you are using is capable of firing 1/2" groups when mounted on another known-good accurate rifle) What about your own technique - are you able to shoot better than your rifle is presently shooting, when shooting another known-good rifle? If not, can you borrow a "known-good" test shooter? Are you able to remove your flash hider and see if that improves your accuracy? When you do this, clean the face of the muzzle and inspect it after having fired a number of shots - is it a clean symmetrical "starburst" pattern, which indicates that your crown is good?
 
It has been my experience that the Remington Brass is 'softer' than Winchester. Primer pockets loosen quicker and generally not as suitable to reloading in a semi auto like an AR than is the Winchester brass.

I'd really recommend a chrono - they do help with staying inside the realm of sanity, as your rifle may or may not show signs of pressure. If its barfing primers it will be a case similar to the above brass issue, or you be over pressure.

Hornady and Sierra manuals have data specific to ARs and are a good reference to have.
 
These are the 75gr BTHP's, not the A-max's. There's a real shortage of selection of bullets here in town. All the popular one's are sold out. I'd have used 69gr SMK's if they'd have had any.

I only shot the one box of Remington match, to see if the gun was the problem, or the UMC 55 ammo. Good to see it was the cheap ammo, not the gun. So given only 20 rounds of it fired, I can't say I have a long history with its performance in this rifle.

No flash suppressor, just a recessed, step type target crown. Powder pattern forms a nice symetrical starburst.
 
rnbra-shooter said:
Johnnyreb65, what you describe sounds like the characteristic marks left on brass by semiautos when they eject their brass - i.e. what you describe are "ejection marks". "Ejector marks" refers to a round raised and/or bright bit of brass on the case head, and can be one of the signs of high-ish pressure.
(longer version: The ejector is a spring loaded plunger on the bolt face. When a very high pressure round is fired, some of the brass may "flow" a little bit, pushing back the plunger a bit. When the bolt is rotated to unlock, the solid part of the bolt face rubs against this raised bit of brass (this is one of the reasons that a high pressure round can result in a stiff bolt lift).)
Click to expand...

Thanks for your detailed explanation, I just learned something new..
 
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