AR Ammunition Reload Question


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Tetcht Seckum
February 17, 2010, 01:03 PM
So, I have just began reloading and my AR loads worked flawlessly, that is that they extracted and such fine and good, and accuracy is as good as I could expect from my upper. Only one problem. I was in Cabellas, and looked in Hornady's new reload manual. Mine is old, and was given to me with my reloading set. I compared and found that my load of 21.4 grains was in excess of their maximum for that particular load of 55gr SP bullets by 1.4 or so grains- they listed 20 grains of IMR4198 as cooking at 3100 fps, while I had loaded it at 21.4 grains to achieve the same result according to my older manual. It listed 22 grains as 3200 fps as the maximum and the 20 grain powder charge is now, according to the one I read today, the max for that load.:uhoh: I use CCI primers, which should not be "soft", I have heard that winchester primers can be soft though.

What can this be attributed to? I noticed that the primers did look flattened, and so I might be in the high pressure range, but there was no visible wear on the bolt or carrier or lugs. The only thing I could see that could point to pressure was some of the primers in my 21.4 grain charge loads. I plan on backing off, but I wonder if may have caused any damage to the gun. I would imagine that it has to be of higher tolerance for pressure, because it is NATO chambered for 5.56 which operates at higher pressure. I will get a new load book asap, but I wonder if this is because the powder is better, or lawyers are better at their jobs. I have read that primer flattening is a poor indication of pressures. I hope I have not hurt my AR any, as I am poor and do not have money for a new one any day soon .

Thanks for your input. Awesome board you guys have here!

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Quoheleth
February 17, 2010, 01:32 PM
I would say that, assuming your powder is of recent manufacture, go with the newest data and keep your charge at the 20gr weight. Your gun might be ok to shoot the higher charge because of the 5.56 chamber, but why take a chance?

Data can be very frustrating because of this very thing: a particular source whom you trust changes their info; or, worse (IMHO) is when two sources that you trust seem to contradict each other on where max is. Variables come into play such as primers, age of powder, bullet used, type of gun --- and how can you know which is correct for your use? That is my definition of "frustration".

As far as damage, how many rounds did you fire? Again, you are probably fine but if you're concerned, take it to a competent gun smith (i.e., not Uncle Berl who once fixed your stuck .22 with a ball-peen hammer) and have him give it a 1x over.

Q

rcmodel
February 17, 2010, 01:38 PM
According to Hodgdon, who currently sells IMR powder:
The max load with a 55 grain SP and IMR-4198 is 21.0 grains, producing 47,600 CUP.

You did not damage your AR-15 if it didn't blow up.
But your load is above MAX, and should be reduced.
IMR-4198 is a fast powder, and pressure will spike quickly once max pressure is reached.

IMO: IMR-4198 is a poor powder choice for the .223 in an AR-15.
It is a faster powder then the gas system was designed for.

rc

Tetcht Seckum
February 17, 2010, 08:57 PM
No, it did not blow up, and I can see no damage to the rifle in the slightest. I fired approximately 10 rounds of the hot ammunition, which was just over 21 grains. I am sure that the AR is fine- no bulges in the barrel, and the brass was not even split or marred or anything of the sort.

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