Ar 15 seating depth


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SifuGun
December 13, 2011, 01:16 AM
Has anyone tried to determine the max seating depth for their Ar 15, and if so what was your oal. According to my hornady book you can go to 2.39" for their 75 grain bullet. It will not work through the mag but can be shot one at a time. So, this being said. When the usual round for a 223 is set at 2.25" oal. And a round at 2.39" is safe to shoot before you hit the rifling. What does that say about people try all different types of rounds and spending untold amounts of cash. When they are a min. 0.14 off rifling. I think we can all save a lot of time and money if we know exactly what the max seating depth is for each individual rifle.

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carlsca
December 13, 2011, 04:22 AM
Each rifle and barrel can or will be different. If you want to reload first you have to find out where the rifling starts then seat the bullets as long as you can and still have them fit in your mag.

capreppy
December 13, 2011, 08:08 AM
I've loaded the Hornady 75gr HPBT to 2.26 and it'll cycle. Longer than that and it'll catch the mag lip. I've also loaded the Sierra 69gr HPBT to that length as well. The 77gr SMK would need to be loaded to 2.26 but I've not used it as I'm currently trying out the Hornady 75gr.

My other bullets are typically loaded to 2.24 or 2.25 OAL.

steve4102
December 13, 2011, 08:23 AM
As stated above, each rifle/chamber is different. It would be impossible to list the Max OAL for each bullet available due to these variations in chambers.

According to my hornady book you can go to 2.39" for their 75 grain bullet

The OAL you speak of is not for any 75gr bullet, it is specific to Hornady's 75gr A-MAX bullet. Due to the shape of the bullet/ogive it must be loaded long. Loading the 75 A-MAX to mag length will put the ogive inside the neck.

Jeff H
December 13, 2011, 08:32 AM
If you want to reload first you have to find out where the rifling starts then seat the bullets as long as you can and still have them fit in your mag.

Mag length cartridges will never hit the rifling in an AR 15.

gamestalker
December 13, 2011, 08:50 AM
Many that load for AL actions, whether it be an AR15 or a hunting rifle that is an auto loader, will use small base resizing dies to increase reliable cycling. Auto loading actions actually prefer a one size fits all ammunition, so bullets that are seated up to the lands, and brass resized to bolt action tollerances isn't likely to function well.
Oh it will shoot, and it even might be a bit more accurate than the typical AL tollerance round, but don't expect consistent and reliable cycling.

I do understand your quest for accuracy, but it would be better served with something that is action friendly to that style of hand loading. I load for B.A.'s and always bring my bullets as close to, or even into the lands and use compressed charges of slow burning powder's in a quest for accuracy.

In the end, if you don't mind single loading for your AR15 then just do what produces the best accuracy and will still eject OK, if that's how you want to roll. I can tell you that your not alone in this respect, as I have heard of other's using their AL actions in a single shot mode for this very reason. But if want to get the most from a .223 maybe find a BA model that will allow you to do what ever you want when loading for it.

SifuGun
December 13, 2011, 11:05 AM
Thanks for the replies, but i am looking for a numerical example.
I am interested in the measurement oal for their ar 15. Just to see how far off the lands are from the typical 2.2 to 2.25" load

rcmodel
December 13, 2011, 11:20 AM
The only way to find out is to measure it yourself in your barrel & chamber.

1. Seat a bullet as long as you can and get it to stay in the case.
2. Then color it with a black magic marker or dry erase marker.
3. Now chamber it.
4. If the marker rubbed off, it is hitting the rifling leade.
5. Just keep seating deeper, coloring, and chambering it until it doesn't.
6. Then measure it.

That is the max OAL with that bullet, in that rifle.

It is interesting to note however, that the most accurate .223/5.56 ammo in the world, Match, Varmint, and the military M118LR 77 grain Sierra used by SDM is seated 2.260" or less to work in the magazine.

rc

SifuGun
December 13, 2011, 11:29 AM
Thanks for the tip rcmodel. I am sure may will try your technique.

Canuck-IL
December 13, 2011, 11:42 AM
An example of what I think the OP is looking for ... Sierra SMK 80s are commonly single loaded for 600 yd HP. White Oak Armory, one of the primary builders of match ready HP uppers cuts their Wylde chamber so that the 80 touches at an OAL of 2.475.

/Bryan

W.E.G.
December 13, 2011, 12:02 PM
There is a tool for that.

http://www.brownells.com/.aspx/sid=30442/pid=12634/Product/OVERALL-LENGTH-GAUGE?utm_medium=shoppingengine&utm_source=googlebase&mc_id=10000&gdftrk=gdfV21820_a_7c187_a_7c3466_a_7c829200308_d_829200017_d_11281

SifuGun
December 30, 2011, 10:40 PM
Well forum you might or might not be surprised by the results of my measurements on my Dpms 16" bull barrel upper chambered in 5.56.
It turns out that the oal for my rifle is 2.346". I used the "Frankford Arsenal, Cartridge Overall Length Gauge" to measure it. Some people don't like this tool because parts of it are hard but possibly pliable plastic. I found it to be very accurate. Of course, if you are used to taking precision measurements this tool will give you good results. I took the measure meant four times. 2.346", 2.348", 2.348", and the first one at 2.351". I feel the last one was the best so i settled at 2.346". Now if i were to load the Hornady 75 grain #22792 with an oal of 2.39". My rifle and me might experience over pressure of even an explosion. Wow. Now the PMC 55 grain factory bullets all measure btw 2.213" and 2.225" oal. Which puts this bullet btw 1/8" and 3/16" off the lands which is close enough for comfort. Now this leads me to believe the chamber for this upper was cut with a 2.25" max oal bullet in mind that would put this bullet 0.096" off the lands or about 3/32" (very close). One can see this bull barrel upper should be very accurate. Alright everyone i hope you all check your oal to save time and money. And not to mention to be on the safe side. Peace :cool:

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