Longest OAL that will feed reliably from an AR mag?

[Samgotit]

I used the Stoney Point OAL gauge on a new AR. OAL to the lands is a whopping 2.445". Is that out of the of the norm? Lyman spec is 2.260". I know it's only a "suggestion", but I assume a 2.445" inch round isn't going to feed, right?

What is the longest OAL .223 that will feed reliably from an AR mag?

The bullet is a 55gr FMJBT:
http://www.midsouthshooterssupply.com/item.asp?sku=001532267B250

Should I try a different bullet. Can the ogive be that wacky on cheap bullets? Am I missing something or is this just a characteristic of an autoloader?

 

[rg1]

Yes 2.260" is as long as you can seat ANY bullet to feed from an AR magazine. I seat the Hornady 55fmj bullet at 2.218-2.220" which is longer than Hornady's recommendation of 2.200". Anything longer than 2.260" would have to be single loaded into the chamber. Long range match bullets such as the Hornady 75 grain A-Max or 80 grain Sierra match bullets are recommended to be loaded to 2.390 and 2.550" with the 80 grain Sierra. The Hornady 55 fmj has a different ogive and tip shape than some 55fmj bullets which have a longer more sharply pointed tip. These sharply pointed 55fmj bullets normally seat to 2.250". Winchester 55fmj's that I've loaded in the past were made to be seated to 2.250" as well as military surplus 55 fmj's. The Hornady 55 fmj bullets are generally considered to be the best for AR loading compared to most other 55 fmj bullets. I wouldn't seat the Hornady 55fmj bullet any longer than 2.230" for your AR but again Hornady recommends 2.200" and 2.230 could be too long for a bolt rifle and should be measured for loading for a bolt rifle.

 

[HJ857]

I have been seating at 2.265, loading in to PMags and have not had any issues at all. I also load to 2.265 for a 6.5 Grendel upper in C Prod mags, also without issues.

2.260 vs. 2.265 is not really enough difference to worry about in a standard AR, but it does give you a bit more bullet seating tolerance.

If you don't have one already, get the Hornady bullet comparator. This allows you to measure cartridge length from the ogive, rather from the tip. Ogive differences are usually insignificant, but bullet tip lengths can be all over the place and give you a false reading if you measure to the tip.

When setting up, just seat 10 or 20 rounds to get an average of your desired OAL from the tips, then choose the cartridge with the best fit to the average, measure to the ogive and use that for your bullet seat depth, you probably will never have to change seating depth again until you switch to a different bullet.

If you use the Lee FCD, check to see if the crimp process is lengthening the OAL, then account for that in your seating.

 

[jmorris]

I load </=2.250 any longer and I've seen problems with some mags

 

[ny32182]

I have been shooting 77gr SMK's recently, and loading them to absolute max length for the magazine. I believe the quote for milspec mags is 2.26. I loaded mine to an average of 2.26 to get the max possible length. Some individual cartridges measured as long as 2.264". I did load 20 rounds into a 20 rd mag, and all of them fed. I could tell that the longer ones were physically scraping on the front of the magazine, and I was expecting a failure to happen, but never did in 3 full mags that I shot recently. I suppose the recoil in this case is enough to jar them loose in the event that one or two is getting slightly hung up.

Is there some danger in loading some bullets to max mag length if the manual suggests a shorter length? I don't think anything that fits in the AR magazine is in danger of reaching the lands in a 5.56 chamber?

 

[MutinousDoug]

Max magazine cartridge OAL

I have removed part of the front of the 4 mags I use in High Power without a problem. This allows me to load rounds as long as 2.33". The relief is only wide enough to accept the tip of Hornady 75gr bullets and deep enough to accept 8 rounds.
My 600 yd load is an 80gr Sierra at 2.515" and is, of course, single loaded.

 

[docgary]

I seat my 69 g SMK with 25.3 g Varget to 2.261 -2.262 as my pet loads.

Never had a loading problem using Pmags
(my Pmags are 20 rounders cut down to 15 by a company in NJ.)

your rifle may vary...

docgary

 

[rodregier]

The AR15 pattern box magazines I measured ran around 2.260" at the interior front-to-back.. So unless you have magazines that you know have more clearance, I wouldn't recommend going any longer.

 

[Samgotit]

I'm glad you guys made some sense out of my first post. I just reread it and confused myself.

Thanks for the info. I'll keep OAL in spec unless I feed it by hand.

I'm still wondering if 2.445" (bullet on the lands) OAL is normal (i.e., what's the normal throat set back for an AR [if that's the right terminology])? Also, is putting up with bullet jump just part of an autoloader? Which leads to the next question: Relative to each other, is minimizing headspace or minimizing bullet jump more important for accuracy?

My 600 yd load is an 80gr Sierra at 2.515" and is, of course, single loaded.

Curious how you came up with that OAL?

 

[ocabj]

I've been seating Berger 80gr VLDs .005" into the lands. I noticed no difference when seating at the lands vs .005" in, but I figure it's safer to seat them in so they 'soft-seat' upon chambering. But this requires 'chasing' the lands by measuring the distance to the lands every few hundred rounds and adjusting the seating depth accordingly.

Sierra Match King 80s are very jump tolerant. Just take your initial measurement at zero round count, seat .010" off the lands and use that seater setting for the competition life of the barrel (3000-4000 rounds or so), or for a single season.

I started HP using the SMK 80 on the long line. It's a great bullet and like I said, it's jump tolerant and you don't have to worry about the chasing the throat. But I switched to the VLD because I wanted that extra BC.

If you want a good 77gr bullet that can be loaded to AR mag length, get the new Lapua Scenar 77gr BTHP. I bought a box of 1000 from Grafs a few months ago, and did some initial testing in a brand new White Oak CMP/NM upper (.223 Wylde) at 600 yards and they shot excellent for a 77gr at magazine length (2.260") at that distance. The Lapua 77gr has an advertised BC of .402, whereas the Sierra 77gr MK maxes out at a BC of .372. If you wanted to shoot NTIT, I would definitely recommend this bullet.

 

[matrem]

Another point to consider: When using some hollow points,the meplats may not be exactly the same.IMO anytime you get to about 2.255 or over,I'd suggest checking every round.I've seen a couple (2 I think?) FTFs with .224 Bergers when "seated" at 2.257.Some in the mag were a bit too long & "hung-up".That was in one twenty rd mag.I didn't load the mag,don't know if he had any trouble loading it.I suggested he "run them in" about 5 thousandths more,he told me later there were no more problems.

 

[tiger rag]

I load all of mine at 2.250 no problems with feeding.

 

[jeepmor]

Give it a try, the difference will likely be in 0.001 in range. Subtract a couple for reliability purposes. Then skew for accuracy.

 

[MutinousDoug]

"Curious how you came up with that OAL?"

The OAL is approximate as I use a Stoney Point Bullet Comparator to check bullet seating depth.
In place of the Stoney Point OAL Guage, I chamber dummy rounds long until a smoked Sierra bullet is just skuffed by the lands, then backed off .005". Every 1000 rounds shot I repeat the process. At 5000 rounds I'm overdue for a new barrel.

 

[ny32182]

Are Pmags actually longer than USGI by a measureable amount?

I am shooting in a 3-gun match this weekend, and would like to use some loads that just *barely* fit in a USGI mag. I have not had a feed failure with the load yet, but would not be at all surprised if one occured. If using a Pmag allows for just a little bit more tolerance in the front, that would probably help my case, and I can do that.