Loading Sierra 80gr for AR15

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I just built a new AR15 using a BCM upper with a 1:7 twist 20" barrel and took it out to the 600yd range and once I got it zeroed in hit the bullseye 3x in a row then the wind came up and of course my group faded but not bad. I was using Hornady 75gr HPBT ammo at the time. I want to try out some Sierra 80gr loads but have run into a slight problem. All the load data I have found says to have the oal at 2.550" but when checking my ogive it is only 2.496".

My question is would it even be possible to load at say a 2.490" oal and just reduce the powder load a bit? Say if I used Varget which has a min of 21.3gr and a max of 24.0gr would it be safe to start off at the 21.3gr with an oal that is .o60" shorter or am I asking for trouble?

 

[boltman223]

What tool are you using to measure your AOL? Im almost positive that the 2.550 from the manual is to the tip not the ogive. My ammo for one of my 223's with 80 smk's measures 2.494 I believe. My bullets could be a tad shorter or longer than yours so my base to ogive could be a little different.

It sounds like you have a wylde chamber and that would give you .077 freebore. Mine is .071 and I use 24.7 grains of varget. About 25.1 is max in my gun, my rifle is a bolt action though. I'm guessing you shouldn't have a problem especially starting at 21.3.

 

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I'm using the Hornady Overall Length Gauge And Bullet Comparator. You may be right, I wasn't thinking how long the taper is from the tip of the Sierra bullet. I'm pretty new to reloading, about 2 years now with handgun loads and just starting to load rifle.

It's a BCM barrel and the whole upper is here: http://www.bravocompanyusa.com/BCM-Standard-20-Upper-Receiver-Group-w-Midwest-I-p/bcm-urg-std-20-mi-ssk15.htm

 

[Road_Clam]

Don't beat yourself up over loading for bullet jump and an AR15 platform. I've not seen any measurable gain in accuracy loading close to the lands. I load all my rounds to 2.240 OAL to allow mag feeding and just shoot. My 1-9" Bushmaster Varmint is an excellent shooter using 69gr match bullets out to 600 yds , and I've also taken 77's out to 600 yds with good results.

 

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Don't beat yourself up over loading for bullet jump and an AR15 platform. I've not seen any measurable gain in accuracy loading close to the lands. I load all my rounds to 2.240 OAL to allow mag feeding and just shoot. My 1-9" Bushmaster Varmint is an excellent shooter using 69gr match bullets out to 600 yds , and I've also taken 77's out to 600 yds with good results.

For some reason, all 4 of my AR's(1:7 twists) hate 62gr or even 69gr bullets. Can't even get a 2" group at 100yds with them. Now that's using off the shelf ammo so maybe a custom load using them would get better results.

OK, here are the readings I got after doing it the right way(I think?). Using the Sierra 80gr HPBT bullet.

Ogive of barrel= 1.994" and measuring the OAL gives me 2.495"

Ogive of a round with a OAL of 2.550" gives me an Ogive of 2.043"

Difference of Ogive= 0.049"
Difference of OAL= 0.055"

So I'm thinking with a .010" jump I'm thinking an OAL of 2.485" which would mean I'm setting the bullet in 0.065" more than the load data books. Am I doing this calculation correctly?

 

[DeadEyeDick45]

I'm a bit confused as to what you are trying to achieve? So, I'll explain what I do and how I found the max length (OAL) for my AR-15. First, I loaded a dummy round (no primer or powder) and without a crimp to a length
that would just fit into a magazine (I use Magpul). Take a OAL measurement.
I then inserted the dummy round into the breech and allowed the bolt to close gently on the round; then extract the round and look for signs of markings on the Ogive as a sign I've got the bullet on the lands. Take a OAL measurement.
Was there any set back? Was there any markings on the Ogive of the bullet? This measurement should give you a rough length of the throat in your barrel or a more accurate way to measure would be to make a casting of the throat and that
will tell you the length of the case to Ogive of your barrel.
What I normally do, since I know the various lengths necessary to reload for my AR (depending on the weight of the bullet, which translates into length of the bullet) is to make sure that I load out as long as I can without interfering with the magazine.
Staying within the published values for powder, one can go longer with a load, but the shorter you go could greatly increase pressures.

 

[chkunz]

I got good accuracy and velocity with an AR with 20 inch 1:8 barrel with the 80 SMK using Accurate 2520, Reloader 15 and H4895. Varget gave me less velocity than I was interested in so I did not do accuracy testing with Varget. The Sierra Manual accuracy load for you application is 23.5 grains of N 140 so that would be a good place to start.

 

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DeadEyeDick, I am not using a mag while shooting, well I am but with a Bobsled so I can load a round at a time. That way I can use a longer OAL load which the Sierra 80gr bullet requires. What I am trying to figure out is a safe powder load to use since I am setting that bullet in deeper than the data books say to and in this case I believe around .060" more to keep the bullet about .010" off the lands.

T-Rex, I just used Varget as an example but I do have those other powders. I actually get better results using 4064 than Varget gives me. My concern is since I am setting that bullet in deeper should I try a load less than the minimum amount of powder like .2gr less powder?

 

[chkunz]

DeadEyeDick, I am not using a mag while shooting, well I am but with a Bobsled so I can load a round at a time. That way I can use a longer OAL load which the Sierra 80gr bullet requires. What I am trying to figure out is a safe powder load to use since I am setting that bullet in deeper than the data books say to and in this case I believe around .060" more to keep the bullet about .010" off the lands.

T-Rex, I just used Varget as an example but I do have those other powders. I actually get better results using 4064 than Varget gives me. My concern is since I am setting that bullet in deeper should I try a load less than the minimum amount of powder like .2gr less powder?

IMR 4064 should be a good powder for this bullet in your application since it is essentially interchangeable with IMR 4895; The Sierra Manual lists a load for IMR 4064 and I have a friend that gets great results with IMR 4895. I recently did a check with the Powley Computer and it selected a load of 4064. I chose the 2520 load because it gave me the best velocity and also good accuracy.

 

[Road_Clam]

I've recently found a super accurate load for my 24" bbl AR using 69gr Nosler CC , 24.6 gr of RL-15 . Shooting about .48 MOA @ 100 yds.