To the moderators, if this is in the wrong sub-forum, please place in the appropriate forum!

After my accident, I have turned to building rifles for F class that meet my needs. Last week I developed a very accurate 223-80gr load that has thousand yard potential. The downside is that this load is loaded with the bullet seated deeper than Sierra recommends (2.465"). This load doesn't show any signs of high pressure and is consistent. If I remember correctly, Sierra recommends seating their 80gr at approximately 2.635". I would think if I could load and chamber it at the Sierra length, I could pick up a few hundred more feet per second which can stabilize the bullet better at a thousand yards.

My curiosity: can an AR10 platform be modified to accept an AR15 bolt in the bolt carrier, and an AR15 barrel extension and barrel mounted on an AR10 upper receiver, which would allow magazine feeding of a full length 223-80gr cartridge?

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Judge control not gun control!

There may be a way accomplish what you're after, but the dimensions of an AR10 upper & bolt are vastly different than an AR15. I feel modifying an AR15 upper is going to be the only way to get there from here. Creedmore sports may have a solution since they make a 6.5 Creedmore AR rifle. At least that's an area to explore.

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NRA Benefactor

Magazine and magwell length seems to be the major problem here. I cannot see an AR-15 receiver has enough meat to allow modification to take a readily available magazine. I seem to recall that 220 Swift rifles were built on AR-10 platforms. That might be something to look into.

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Release the Kraken

I would suggest a call to Shilen Barrels. Because it is SOP for Shilen to provide a bolt matched to the barrel and extension with every AR barrel sold. Granted 223 on an AR10 platform isn't typical but I would expect that they can not only provide a barrel in your caliber choice that fits an AR10 receiver but can also insure the chamber has enough lead for your particular OAL. I also expect that you'll find they have already done this numerous times.

BTW, I have a home built precision AR15 in 223 Wylde with a Shilen barrel and on one of my best days I was able to get under 3/10 MOA at 100 yards off a rest. Normally I shoot this rifle in the 1/2 inch range at 100 yards but that is simply because my trigger skills are a bit lacking on most days.

I have put together a 223 Remington load with the 80gr Nosler Custom Competition that delivered a 1.5 MOA group at 500 yards last week and according to my Sierra Infinity program, stays supersonic out to 1018 yards. This round was loaded short to 2.455", with no signs of excessive pressure. My project AR has a 1:8 26" Wilson barrel cut with a Wylde chamber, provided by White Oak Armament. This round is being tweaked and will be tested at the 600 yard line this Sunday. My intention is to use this rifle and ammo combination at Camp Atterbury for the Long Range championship. I don't expect to win anything, but I shoot against myself. If I can fire the course off the sling, it will be a major accomplishment after the accident that left me disabled.

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Judge control not gun control!

I know next to nothing about rifles and absolutely nothing about AR's
but I DO admire your dedication and stick-to-it-iveness to our fabulous sport.
Please let us know how your rifle and contest shooting turn out.
To me 100 yards is long range shooting!
44 caliber bullets tend to die shortly thereafter Elmer Keith notwithstanding.
This is the only "long" range rifle I own and the trigger could be improved some.
Ironically Elmer claimed he designed that Monte Carlo stock with the slight reverse angle to mitigate recoil.
I could use one of those on the 444S.
They have the worst factory buttstocks I have ever encountered.

Attached Images

B78-6mm.jpg (271.6 KB, 16 views)

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NEMO
"Everything 44"

Nemo, that is a gorgeous M78!

I was in a medically induced coma for almost a week. Prior to my accident, I was physically active, I camped, hunted, was engaged in competitive rifle shooting for almost 40 years, and then I woke up with major musculoskeletal injuries. There was a distinct possibility that I would not walk again, and I still face the daily prospect of losing my leg from the extensive leg injuries. The only aspect of my pre-accident life that I can still partake in to a major degree is target shooting!

My target shooting is not only recreational, it is therapy AND it gives me both a goal and focus. As a result, I have learned more about precision reloading and building mission specific rifles.

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Judge control not gun control!

I have one of the Savage left port single shot bolt actions in 223 with 1:9 twist. With the BR stock and from a front rest and bag, I get 3" groups at 1000 yards with 75 A-Max or the Barns 77 Hybrid bullets, over Varget, Rem 7 1/2, Lake City virgin brass (match prepped but not weight sorted). This is still about 1/4" too long for an AR-15 mag. (somebody else fired one in an AR-15, and locked up the receiver, so there may be pressure issues too) By the way with the overmolded hunting stock and a Sinclair Tactical bi-pod it is closer to 8" at 1000. These loads hit the gong hard enough to be heard with the naked ear.

I have never competed in F-Class, I didn't know semi autos were allowed. Or is that an accommodation?

I had to relearn how to stand and walk about 5 years ago. I understand the drive to return to the activities we love. Keep up the good work. I think the AR-10 platform will be a good place to work from. If you can't do 223, you definitely do 22-250 or a 22 Cheetah from Lapua's 308 Palma brass and load down it to 223/80 grain velocity!

PS, I have 2 kids and 4 grand kids in southern N.J., I get there 2 or 3 times a year. Is there a place to shoot long range, or do you travel to Pa.?

Ivan

Currently you are seating the bullet 0.170 inches deeper than recommended. That means you have reduced case capacity and will probably generate your peak pressure earlier in the burn of the powder. If you seat the bullet further out, case capacity will go up, the speed of the powder burn will likely decrease and the peak pressure will occur later and may be of smaller magnitude.

I suggest loading the cartridge at 2.635 and feeding them one at a time into the rifle to see if you do actually get the increased velocity you are expecting before proceeding with what may be very expensive build.

AR-10s are not as standardized between manufacturers as AR-15s, so I'm not sure whether what you are asking for would be practical. You might be better off having an AR-10 bolt and barrel extension custom made for a 223 case head and M4 style feed ramps on the extension.