Seating depth for AR

[EvilKidsMeal]

So I am loading Sierra 69gr. HPBT for my SPRish AR and the manuals using that exact bullet recommend seating to 2.260" which I am aware is max for mag length.

I had always thought, since bullet tips can be varied slightly, that you seat based off of the shortest projectile. Obviously when I do that all others come out over mag length.

I guess my question is, how much play is there in seating depth for a load like that? Do I need to measure each OAL (huge pain) or should I set my die based on the longest projectile? Obviously people load on progressives and it would be crazy to check and re-seat each and every one.

So If I set my die to seat the longest at 2.260" and most others come in somewhere around 2.256"+ am I still good? I am working up loads starting from minimum charge for now.

Is there a preferred seating depth for a load like this or should I keep it close to mag length?

 

[sloughfoot]

Seat your 69's to mag length. It will vary, but if you set the depth to 2.250, it will be under maximum mag length for the extreme and rare long round. The 69 is very forgiving.

 

[EvilKidsMeal]

So you're saying set my die to 2.250" for the shortest projectile and just load from there? Or conversely I could set my longest projectile to mag length and not worry about the ones that fall under that?

That works for me I just didn't know how much variance is too much when you're under the manuals stated OAL.

 

[Sniper 79]

I set mine at 2.250 on the first bullet out of the box and loaded away. They shot great! Kissed it with a little Lee factory crimp just for piece of mind.

I loaded for accuracy in the middle of the road powder charge. Sure there is a few thousands difference although not anything to worry about in an AR.

 

[OHOIAN]

It is not likely that you will even notice a seating depth difference of 0.005 inch out of an AR

 

[NyleRN]

It is not likely that you will even notice a seating depth difference of 0.005 inch out of an AR

Yep. Don't know exactly why but I can set my die to 2.26 on the first load and the next few may be 2.257, 2.258, etc. I've done 2.25 before and my SPR's don't shoot any better or worse. If I'm not mistaken, even at mag length you're still not even close to the lands in an AR.

 

[Leo]

Seat your 69's to mag length. It will vary, but if you set the depth to 2.250, it will be under maximum mag length for the extreme and rare long round. The 69 is very forgiving.

This is correct. If you are seating for specific performance, you should be measuring off the ogive not the tip anyway. Unlike Berger VLD and some other specialty bullets, the 69 Sierras are not too sensitive to variance in chamber leade distances.

 

[sgreen3]

This is correct. If you are seating for specific performance, you should be measuring off the ogive not the tip anyway. Unlike Berger VLD and some other specialty bullets, the 69 Sierras are not too sensitive to variance in chamber leade distances.

I was going to suggest the same, there is to much variation in bullet tips to get an accurate measurement from round to round. A bullet comparator is the only way to go if loading for precision. As mentioned though I haven't seen any noticeable difference in a .005" variance..

 

[EvilKidsMeal]

Alright. I figured the variance was no big deal, I just wasn't sure how much deeper than the manual was safe.

I am planning on shooting some of those loads today. IMR4064 and 4895. Hoping I can get some decent groups off the bat and start cranking out rounds for spring time.

 

[sgreen3]

Try some 4320 if you can find some, I've had very nice results out of it when loading for the ARs.

 

[Sniper 79]

I had good luck with Win 748 and Benchmark although at 150 yards probably won't see a diff

 

[noylj]

YOU have to find the COL that gives the best accuracy. You can not set the seating stem for one bullet and expect to get the same COL with a different bullet, with a different meplat/ogive. Next, COL in manual is NOT what YOU necessarily want, it just tells you what they used for testing with that specific bullet (and not that that was the best COL, just the test COL).
I find that all my rifles have always given me best accuracy with the longest COL that does not jam the bullet into the lede. Thus, for all box magazine rifles, including my ARs, COL is really really simple--the COL that will just fit the magazine without dragging on the magazine walls.