Magnum AR Project

[Masczek]

I thought some of you would find the project I've been working on interesting. This is my AR10 style rifle chambered in 6.5 PRC and 300 WSM:

The lower receiver is my design, it accepts AICS short action mags. The mags allow for slightly longer OAL for the 300 WSM and factory length 6.5 PRC cartridges, plus they're a lot more stout than AR mags IMO. I'm still experimenting with the gas system and buffer and spring rates, both 300 WSM and 6.5 PRC guns are slightly over gassed. Other than that, the guns feed very well, no complaints on the magazine performance. I'll post more info as I get out and test more.

 

[ARlife4me]

I have a 6.5prc ar10 barrel on order, but stuck with 2.830"ish on max length. From what I gather there were suggestions on which mags to use. Something like a 20 round with a limiter or a 10 round the same way? I would rather have what you have for a lower with mags designed for the cartridges! I would prefer having a single feed/fed with either double or single stack. APF uses single fed on the LA magnums and might be single stack. Gas system length isn't as important as gas port size, period! @bamban would be the man to answer port location and size. I went with a .100 gas port +2 rifle length at a 22" barrel. Either you need to use a heavier buffer and/or an adjustable gb. A good suggestion would be to use the jp scs. The heavier buffer can delay unlocking for more dwell time that WILL reduce op issues. The 6.5 and 300 would require different gas port size at the same location. All though both have almost the same max pressure, both will have different gas volume amounts. What info do you have on your builds?

 

[cohunt]

I thought some of you would find the project I've been working on interesting. This is my AR10 style rifle chambered in 6.5 PRC and 300 WSM:
View attachment 458794View attachment 458795
The lower receiver is my design, it accepts AICS short action mags. The mags allow for slightly longer OAL for the 300 WSM and factory length 6.5 PRC cartridges, plus they're a lot more stout than AR mags IMO. I'm still experimenting with the gas system and buffer and spring rates, both 300 WSM and 6.5 PRC guns are slightly over gassed. Other than that, the guns feed very well, no complaints on the magazine performance. I'll post more info as I get out and test more.

Did you modify a dpms style lower to fit the aics mags, or build one from scratch? Looks like it's engraved "xx25 tech llc"-- I just can't read the first part of the wording.

Who's oversize bolt are you using? Olympic arms used to be a good source but it seems their web page is no longer active-- I know kak sells them.

What upper are you using-- looks like it might be an aero P upper. Who's barrel?

I see you have an adj gas block on it-- springco has a few options for "stiffer" springs to help strip rounds from the mag

There have been a few companies in the past who have done the 300wsm AR ( dtech, oly arms, kak, dpms) it's never been that popular. Keep your eyes of the extractor- they seem to be of weak design in oversized bolts.

 

[dug]

I am very interested in learning more about these builds and would very much like to build one also.

 

[jaclthr]

It's nice to hear you were able to get your mag sorted out to take factory 6.5 PRC rounds . That is what I wanted but with standard DPMS style mags the PRC factory rounds were too long , so I went with 6.5 RSAUM cartridge and hand loads . I had major problems with over gas until I turned a extra heavy buffer about 12 oz. and I was able to function after that . I've been really busy since and haven't gotten back to it for load work but would really like to know how you were able to get the AICS mags to work . New design lower or modified commercial lower ? Anyway Great work and Best fortune in your build .

 

[Earnhardt]

It's nice to hear you were able to get your mag sorted out to take factory 6.5 PRC rounds . That is what I wanted but with standard DPMS style mags the PRC factory rounds were too long , so I went with 6.5 RSAUM cartridge and hand loads . I had major problems with over gas until I turned an extra heavy buffer about 12 oz. and I was able to function after that . I've been really busy since and haven't gotten back to it for load work but would really like to know how you were able to get the AICS mags to work . New design lower or modified commercial lower ? Anyway Great work and Best fortune in your build .

What velocities were you getting out of the 6.5 SAUM?

 

[jaclthr]

I haven't got to working on loads yet , after I got it to function properly I got pulled away and have not got back to it . I am rethinking the bullet since using a 140 AMAX or similar is seating way back in the case , I'm thinking a lighter and shorter bullet . I am looking at Hammers to try as I believe they are able to take more stress I hope and stay together . If I can modify an ACIS mag and get longer OAL then that would change the bullet again .

 

[budlight]

Gas system length isn't as important as gas port size, period! @bamban would be the man to answer port location and size. I went with a .100 gas port +2 rifle length at a 22" barrel. Either you need to use a heavier buffer and/or an adjustable gb. A good suggestion would be to use the jp scs. The heavier buffer can delay unlocking for more dwell time that WILL reduce op issues. The 6.5 and 300 would require different gas port size at the same location. All though both have almost the same max pressure, both will have different gas volume amounts.

Not arguing, everyone can have an opinion! But you need to look up factual data on the 30K psi at a carbine length, 22k at mid, 15k at rifle and 12k psi at the R +2 inches. These numbers are very dependent on the type of powder used....

Pressure is pressure, a hole is a hole, gas volume is gas volume, 60,000 psi is primer flattening 308, 6.5. and 300 wsm. The pressure wave decreases at various rates do to many factors. I reasoned that you can always go up on a hole size and going to heavier buffer weight is not the correct answer because you are just beating it up with a violent bolt thrust.

Could you get

bamban

To comment on his research? Over the years I've got so much false information from shops and manufactures. Bigger is not always better.

 

[Zen Archery]

KAK industry has a good list of AR10's.

 

[jaclthr]

All of that may be , all I know is that with all that I tried first off , I had blown primers, cases stove piping and that was with reduced loads from online powder charges and with an adjustable gas block shut off and I am shooting suppressed until I went with the extra heavy buffer . I was able to load 3 rounds and it shot, eject, picked up a round, shot, eject , picked up a round , shot, eject and locked back as normal. All case were perfect , no pressure signs , round edges on primers . I just haven't gotten back to further testing and load development .

 

[Masczek]

I'm currently using a KAK bolt, along with a standard 308 bolt with the face opened up along with a modified extractor, both are working well so far. The lower is CNC machined. I designed it from scratch to specifically use unmodified AICS mags, and they also have been working great so far. The upper is nothing special, its a New Frontier Armory upper. I did cut the ejection port open a bit more, just to give the bigger cases a little more room. The barrel is a little special, I got the guys at X-Caliber barrels to make a few for me. It's marked "Kaliber Tech" along with a prototype serial number. I've got a small CNC shop along with a type 7 FFL, so I figured why not.

 

[ARlife4me]

Not arguing, everyone can have an opinion! But you need to look up factual data on the 30K psi at a carbine length, 22k at mid, 15k at rifle and 12k psi at the R +2 inches. These numbers are very dependent on the type of powder used....

Pressure is pressure, a hole is a hole, gas volume is gas volume, 60,000 psi is primer flattening 308, 6.5. and 300 wsm. The pressure wave decreases at various rates do to many factors. I reasoned that you can always go up on a hole size and going to heavier buffer weight is not the correct answer because you are just beating it up with a violent bolt thrust.

Could you get


To comment on his research? Over the years I've got so much false information from shops and manufactures. Bigger is not always better.

So, you didn't read all of my post OR you'll understand points taken.

 

[budlight]

So, you didn't read all of my post OR you'll understand points taken.

I see these points:

Gas system length isn't as important as gas port size, period!
The 6.5 and 300 would require different gas port size at the same location. All though both have almost the same max pressure, both will have different gas volume amounts.

So just for the fun of it I looked up 6.5 PRC and 300wsm in Hodgdon reloading both using magpro powder and both chucking the spear (bullet) at @3000 fps. I used the same powder and same max loaded velocity out of each respective round. I had to juggle the bullet weights to 140 for the 6.5 and 180 for the 300 to use the same powder and attain the same velocity. I think that if you did scientific testing you would find the above statements to be incorrect.

I reload 300WSM and 308. The ratio of case size volume to bore size generally requires faster powders compared to the 6.5 prc which is more overbore and generally can take advantage of slower powders.

You have to compare apples and apples

 

[ARlife4me]

I see these points:

Gas system length isn't as important as gas port size, period!
The 6.5 and 300 would require different gas port size at the same location. All though both have almost the same max pressure, both will have different gas volume amounts.

So just for the fun of it I looked up 6.5 PRC and 300wsm in Hodgdon reloading both using magpro powder and both chucking the spear (bullet) at @3000 fps. I used the same powder and same max loaded velocity out of each respective round. I had to juggle the bullet weights to 140 for the 6.5 and 180 for the 300 to use the same powder and attain the same velocity. I think that if you did scientific testing you would find the above statements to be incorrect.

I reload 300WSM and 308. The ratio of case size volume to bore size generally requires faster powders compared to the 6.5 prc which is more overbore and generally can take advantage of slower powders.

You have to compare apples and apples

Thamks for your response, but due to derailing this thread I won't comment further about this without the op's concent. We could further discussion elsewhere?