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Discussion Starter #1
My nephew called me last nite and asked if using small rifle magnum primers in 223s instead of small rifle primers is dangerous. I guess he has the magnum primers on hand and would like to use them. I personally feel "nope, don't do it", but has anyone had experience with this?

Where would you use small rifle magnum primers...?
 

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It depends on what kind of powder he is using. Slow burning powders need magnum primers to completely burn the powder. Using magnum primers with fast powders is not needed, and could increase pressures. I have never done it in rifles, but I have used magnum primers in handguns with mid burning powders like Unique with no problems. However, rifles develop much higher pressures, so I would proceed with extreme caution. Find out what kind of powder he is using and we should be able to say for sure. And if he does not have a reloading manual, please talk him into buying one!
 

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The .223 is already a high pressure cartridge. Regardless of powder, magnum primers will increase the pressure to some extent. Whether or not it will increase to a dangerous level depends on powder, bullet weight and hardness, seating depth, etc. Personally, I wouldn't do, especially in a case as small as the .223.
 

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In general the use of magnum primers requires a slightly reduced powder quantity for the same pressure.
In my old Lyman handbook it is stated that pressure differences of up to 2,000 CUP exist in between different primers.
The difference in between Magnum and Standard primers is usually not critical (unless it's a max/max load) but any variation will effect accuracy.
For light loads in handgun cartridges I use about .2 grain less with Mag primers.
 

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Discussion Starter #5
Thanks folks, for safety's sake I'm going to trade him a box of regular primers for his magnums,,,not sure where I'll use them, probably in my 10FP...with a slightly reduced load.
 

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What Andyd said. Use them in slower powders and work up the load. You should have a chronograph to verify your loadings are within specs.
 

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Discussion Starter #7
Well, we did the reloading last nite, took forever, my nephew has never reloaded so I was having to take it slow. Anyway, he was using some Barnes 53 grain 223 bullets, I think they were Triple Xs. I don't like them for reloading, they have three concentric cutouts on the base that I don't like. We also reloaded 50 Speer flat base, 55 grain spitzers. We ended up not using the magnum primers, I traded him some regualr small rifle primers.

he's going to the range today and try them in his AR-15. I told him to singly load till he's comfortable, then do strings of 3.

He's still breaking the barrel in, he says, so he's not after super accuracy at this point.

Big difference between me and him, I like to shoot, I find a good load thats accurate and stick with it, he wants to play with various loads and worries about 1/4MOA at 100 yards, I worry about minute of coyote...
 

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Some manuals show their .223 loads are based on using small rifle magnum primers. Other manuals used standard small rifle. You just have to read carefully.

One common use for magnum primers is when extremely cold conditions are likely to be encountered, when both rifle and ammunition are soaked clean thru with frigid temps. Of course, load workup is still necessary beforehand.

Another "for instance" is the use of CCI #41 primers in .223 and 5.56mm ammunition. CCI's #41 primer is for use in semi-automatic rifles with floating firing pins (which military rifles including the AR-15) have. It is very common for AR-15 shooters to deliberately choose #41 primers. It's a harder primer cup, but is also a magnum primer.

So you see, small rifle magnum primers are used quite often in .223 loads.
 

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Oh, another thing. Nearly all AR-15s have chrome-lined bores which makes break-in totally unnecessary. The barrel will not get any better. Unless his AR-15 barrel is all stainless or chrome-moly without a chromed bore there is no barrel break-in.

I have one AR-15 with a stainless heavy target barrel. Breaking that thing in was an unbelieveable PITA!
 
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