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7mm SAUM AR
- Thread starter Schanen51
- Start date
Minor load work update:
I picked up an expanding mandrel from Cortina and reworked my brass process.
Shoulder bump .0025” with full length die(no neck expander on the de-caper), & .282 neck mandrel in the mandrel die. All to brass with multiple fires. The test was 10rds, average velocity of 2873, SD of 10fps, .75” group at 100.
I did stretch it out with some fire forming loads, I’ve got to get back to reading the wind. Had good consistency out to 600 on a 10” gong.
I picked up an expanding mandrel from Cortina and reworked my brass process.
Shoulder bump .0025” with full length die(no neck expander on the de-caper), & .282 neck mandrel in the mandrel die. All to brass with multiple fires. The test was 10rds, average velocity of 2873, SD of 10fps, .75” group at 100.
I did stretch it out with some fire forming loads, I’ve got to get back to reading the wind. Had good consistency out to 600 on a 10” gong.
Once I solved the mag design it’s run perfect during all the load development and testing so far. I haven’t mag dumped it but I’ve did a few quick pairs while shooting it at 300. I’ll keep updating the thread through deer season.
So I finally got it built and did my first test firing.
162gr ELDM
65gr Accurate MagPro
CCI 250
ADG brass
2860fps
26" xcaliber barrel.
It ripped the edge of the brass off, bolt locked back and left the round in the chamber. The gas block was not working properly and was over gassing the rifle badly. I installed a new adjustable gas block and turned it way down. I also worked up a couple loads with different powder, we'll see how it goes!
162gr ELDM
65gr Accurate MagPro
CCI 250
ADG brass
2860fps
26" xcaliber barrel.
It ripped the edge of the brass off, bolt locked back and left the round in the chamber. The gas block was not working properly and was over gassing the rifle badly. I installed a new adjustable gas block and turned it way down. I also worked up a couple loads with different powder, we'll see how it goes!
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So i put on a new gas block. Tried the same load and same results. Something to note is the brass had to be knocked out it, it was stuck in the chamber. I tried 50gr of H4350 and it cycled fine, but speed was 2660fps. I tried some IMR4350 and it stuck in the chamber, but not as bad as the MagPro. I ordered some factory ammo, I want to see the speeds and if I have an issue. I'm wondering at this point if I have a problem with brass. I bought it used once fired. I also loaded up some more rounds with non magnum primers. I'll post the results.
Measure your 1x fired brass at the .200” line….and down toward the base.
How much larger than factory new brass, is the 1x fired brass?
Doesn't everyone own a magnum AR10?
Mine is 7 lbs 12 oz without the heavy 25X scope. Comes in at 10 lbs 12 oz with scope, with an 18" fluted barrel in 338 RCM. They are accurate and capable for certain tasks. The 250 gr bullet around 2600 fps with RL 26 is a good moderate range big game load the 160 gr Barnes for deer.
Mag length will limit bullet choices, and it's not set up for the long 300s, but 250 gr or hunting 275 gr will work.
Mine is 7 lbs 12 oz without the heavy 25X scope. Comes in at 10 lbs 12 oz with scope, with an 18" fluted barrel in 338 RCM. They are accurate and capable for certain tasks. The 250 gr bullet around 2600 fps with RL 26 is a good moderate range big game load the 160 gr Barnes for deer.
Mag length will limit bullet choices, and it's not set up for the long 300s, but 250 gr or hunting 275 gr will work.
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I use magnum primers in my AR 10 338 RCM rifle length gas on the 18" barrel with an adjustable gas block.
The lower is standard carbine AR 10 Areo Precision, off my 308 Win, nothing added, nothing special. A KAK upper reciever and bolt carrier, & Odin handguard.
I chambered the barrel with my own reamer to headspace off the KAK bolt...so no help there.
But it handles all the 65,000 psi max loads in the loading manuals I've tried with a variety of bullets, and functions great.
I have one modified mag, with cut out, to run 2.940" COAL, but Magpul 7.62 P mag works great with the first 3 or 4 in the 10 rd mag put a total of 7 but it bulges the plastic, not good.
Keep it at 3 and stock P mags should work, but they have their short COAL.
I'll try to modify one in the future to see if it will run 5 or 6 smoothly without bulging.
KAK recommended using them on their site for the 300 WSM. The 338 Ruger is .535" dia a little smaller than the .550" & .555" of the others.
Brass is Norma 6.5 PRC mandreled up to 338, and standard 338 RCM RCBS dies, neck turned as shown and annealed.
Trying some factory loaded ammo would be a good idea, and set your adjustable block to those rounds, until it locks back.
Chronograph their velocity and see where they run and how they function. Get the same bullet weight factory ammo you plan to use in your handloads if possible.
The lower is standard carbine AR 10 Areo Precision, off my 308 Win, nothing added, nothing special. A KAK upper reciever and bolt carrier, & Odin handguard.
I chambered the barrel with my own reamer to headspace off the KAK bolt...so no help there.
But it handles all the 65,000 psi max loads in the loading manuals I've tried with a variety of bullets, and functions great.
I have one modified mag, with cut out, to run 2.940" COAL, but Magpul 7.62 P mag works great with the first 3 or 4 in the 10 rd mag put a total of 7 but it bulges the plastic, not good.
Keep it at 3 and stock P mags should work, but they have their short COAL.
I'll try to modify one in the future to see if it will run 5 or 6 smoothly without bulging.
KAK recommended using them on their site for the 300 WSM. The 338 Ruger is .535" dia a little smaller than the .550" & .555" of the others.
Brass is Norma 6.5 PRC mandreled up to 338, and standard 338 RCM RCBS dies, neck turned as shown and annealed.
Trying some factory loaded ammo would be a good idea, and set your adjustable block to those rounds, until it locks back.
Chronograph their velocity and see where they run and how they function. Get the same bullet weight factory ammo you plan to use in your handloads if possible.
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Classic 45-90 post. Off-topic rant boasting about his highschool science projects. No one responds. He doubles down.
So let's see a picture of your AR 10 magnum, and what you did to solve the problems that can sometimes come with these projects. How is it working?
The Components you used for the build.
That information might be helpful to those who are having trouble, or getting frustrated with the project.
Or inspire those interested that they too can build a magnum AR 10, and the problems can be solved.
It would be more of a high-school shop project, than a high-school science project... but you would have to be 18 or 21 yrs old depending on location, to participate.
I'm liking the builds guys, magnum ARs are always fun! I built one in 300 WSM and another in 6.5 PRC, both function flawlessly after ironing out the gas system. I use AICS mags, so bulging is not an issue, plus I have up to 2.98" of room to work with. I finally acquired some 7 SAUM brass, so that's going to be my next one to develop. Shouldn't be too difficult since I have the others worked out just fine, but we'll see.
Ding, Ding, Ding you are the winner sir! I measured all my brass and the .200 line for 90% was .551. There were about 30 that measured .545. So I loaded them up and they ran perfectly! They did stretch out to .548, but I cleaned them up and resized them. They still measured .548 and they loaded fine. So I'm guessing the guy who fired them first had a hot load and a loose chamber and they stretched out to much and didn't bounce back. This sucks, but I'm glad to know what the problem was!
Very cool! Once I figured out the brass issue it ran great. With 65gr Accurate MagPro shooting 162 ELDM it's running 2922fps on a 26" barrel with about 10rds down it, so it should speed up. It's going to be a fun mile rifle!
Thanks for sharing all of the information in this topic! I ran a 7 SAUM bolt rifle, one of the best shooters with the great 7mm bullet options. I had always considered building a gas rifle but never got to it. As with the bolt rifle, the OAL running the best high BC bullets out of a mag was always the challenge.
That then brings up this rifle https://glfallc.com/firearms/long-action-rifles/
Not trying to sidetrack this discussion, but with a platform that can run a .300 Win Mag, what could you do with that extra length?
*Full disclaimer, I have not shot or run one of those, so I have no idea how well they are working?
That then brings up this rifle https://glfallc.com/firearms/long-action-rifles/
Not trying to sidetrack this discussion, but with a platform that can run a .300 Win Mag, what could you do with that extra length?
*Full disclaimer, I have not shot or run one of those, so I have no idea how well they are working?
I'd might question the quality of the components used on that rifle at that price. Hell, the fact they say it's made out of 7075 billet aluminum (which is good stuff) has me wondering how they are that cheap. That stuff in bar form is very expensive, it's more than double the price of 6061. Then again, maybe I don't know what I'm talking about, having never handled one, they could be a well built rifle.
I ran into the same issue with the base being oversized, a cortina neck bushing die(that sizes the base) solved it.
What are your SD ES?
I’m getting random rounds shoot fast, like 3 or 4 out of 50
Thanks for sharing, I got the standard mags modified enough to run 5 rds constantly. Still a little resistance when inserting them, they fall free when empty.
They are easily workable, but not perfect.
A full 7 rds is not workable at this point with these mags, & my mods, so although 5 is actually enough...wonder how long these will last, without a permanent bulge, and be difficult to insert.
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I bought some Norma brass and my SDs are single digits and my ES was around 10fps. I actually took my rifle to a mile day challenge and hit a 1 MOA plate 17" at a mile!
