Realistic accuracy expectations on the AR-15 platform

[Zak Smith]

I strongly recommend against loading into the lands, or particularly close to them, in a semi-auto. (I recommend against this for bolt guns too, but that's another topic.) From time to time this can cause a bullet to get stuck when you try to eject a live round and it's a mess.

 

[center shot]

In my rifles 52gr MKs are not in the lands when loaded to fit the mags. I use this load for 200 yard awful hand. I load a 68r. to fit the mags. for 300 yard rapid fire, and 77 gr. MKs loaded to the lands minus .010" for 600 yard prone which are loaded single shot.

 

[MEHavey]

I hate to keep butting in, but does the above mean that when loading the 52gr SMK to mag length, that it will be in the lands?

Not necessarily. It depends entirely upon how the throat is reamed. In my particular case the throat engages the 52gr SMK by at least 15 thousandths (0.015") when loaded to magazine length/2.26". I discovered that when I finally got the modified case for my Hornady/Stoney-Point gauge.

http://www.midwayusa.com/viewproduct/?productnumber=570611

And I also discovered that my 77gr SMK was off the lands even more than that when loaded to mag length. It all depends on bullet shape, not overall length.

OAL can only be determined (with any accuracy) for a cartridge/bullet combination using an OAL gauge like Hornady's, the exact bullet, and a Comparator insert that goes in the measuring/digital caliper.

http://www.midwayusa.com/viewproduct/?productnumber=231904

As you see, one size does NOT fit all, and there's no end to the games you can play


As to "engaging the lands" I suggest no one try this who has not very precisely run the bullet-by-bullet measurements as noted above -- and who uses a Comparator to detemine seating depth, not simple calipers and overall length. Bullets vary one to the other too much.

As before, be either in, or out of the lands -- not "close." I've chosen 0.005" into them to ensure the bullet and lands are just 'talking' to each other, not engaged in illicit coupling.

 

[TonyAngel]

I have no desire to load into the lands. I'm using SMKs because I read that they don't mind, and in some cases prefer, making the jump to the lands. At this point, I'm taking baby steps. I'm using a Lee crimp die for consistent pressure. Maybe it's working, maybe it isn't. All I know is that I wasn't shooting the groups I am now three months ago.

My barrel has a 5.56 NATO Match chamber, whatever that means. Well my 52s come in, I'll just have to load up a few dummies and see if I'm getting close to the lands or not. Then again, maybe I should just stick to what I know and concentrate on my skills for now.

 

[Canuck-IL]

"5.56 NATO Match chamber" - interesting combination ...sounds like a contradiction to me, marketing at play. I believe a standard NATO chamber has a longer, flatter leade as compared to a .223 or a Wylde - not likely you could keep a 52gr in the case and touch the lands in a NATO, let alone at mag length.

My WOA upper has a Wylde chamber (and they can differ somewhat among brands). The lands engaged an 80 SMK at 2.475 when new - way beyond mag length.
/B

 

[TonyAngel]

Yeah, that 5.56 NATO Match Chamber sounds like Voodoo, but the barrel shoots. I got it from Bravo Company. I did do some research and it's supposed to be some form of actual match chamber for 5.56 pressure rounds. I really don't know much about it except that I trust the vendor and my results have at least rivaled those of others with name brand barrels. It can certainly do better than I can.

Thanks for all of the info and sorry for steering this thread off course.