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Posted: 1/4/2026 11:07:37 AM EDT
| I've had good luck with 10 round, 400 Legend Duramags, but I'd like to get a couple higher capacity ones working. I've tried a 20 round 6.5 Grendel/6 ARC Duramag, but it had repeated bolt over base malfunctions. I tried to load them into an Alexander Arms 6.5 Grendel 17 round mag, but only about 6 rounds fit in before they began wedging around the forward side rib. Ammo is extremely expensive, so magazine troubleshooting is not something I want to do much of. If I'm not able to get a reliable high capacity magazine running, I'm likely to just stick with 450 Bushmaster as a heavy subsonic AR round, and 300 Blackout for lighter work. I'm only interested in subsonics for this round, so the magazines need to accommodate fat, long bullets. |
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| I've had excellent results with PRI 6.8 mags in my .338 Spectre. However, the ARC case is a little bit bigger in diameter so that's no guarantee the PRI mags will work with the ARC. |
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That ASC 7.62x39 mag is performing very well, it's feeding all the rounds into the chamber. I'm just having trouble with the BCG stopping a half inch short of battery on about half the action cycles. It's like the gas rings are catching in the BCG. I've worked the bolt in and out of the carrier a hundred or so times with heavy oil, and it's still doing it. I think I have to try some different gas rings. It's a KAK 6.5 Grendel bolt (Toolcraft BCG) and KAK barrel.  " />
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There is significant difference in the tapered 7.62x39 case and the 6.5 Grendel, 22 ARC and 338 ARC cases. Trying to run 6.5 Grendel in 5.56/223 mags are only reliable for very few rounds. I don’t think the 338 ARC cartridges will stack properly in a 7.62x39 magazine. I know there can be differences in the depth of the ribs in the side of 7.62x39 mags compared to 6.5 Grendel mags. With the shorter case body and shoulder/neck of the 338 ARC with larger diameter bullet might contribute to binding in a 7.62x39 magazine. I have no first hand experience with the 338 ARC but some 7.62x39 mags weren’t reliable with 6.5 Grendel. |
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Originally Posted By JOHNSON1911: Ok, so I have an E Lander 17rd 762x39 mag, and a 20rd 762x39 Duramag coming tomorrow, will advise. E Lander mag will only load 4-5 rounds before the front indentions screw it up. Duramag will load all 20 but they are very tight, it may work with 17-18 rounds, will report back this afternoon. AAC 300gr BTHP, haven’t tried the 307gr SubX yet. |
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Originally Posted By JOHNSON1911: E Lander mag will only load 4-5 rounds before the front indentions screw it up. Duramag will load all 20 but they are very tight, it may work with 17-18 rounds, will report back this afternoon. AAC 300gr BTHP, haven’t tried the 307gr SubX yet. Originally Posted By JOHNSON1911: Originally Posted By JOHNSON1911: Ok, so I have an E Lander 17rd 762x39 mag, and a 20rd 762x39 Duramag coming tomorrow, will advise. E Lander mag will only load 4-5 rounds before the front indentions screw it up. Duramag will load all 20 but they are very tight, it may work with 17-18 rounds, will report back this afternoon. AAC 300gr BTHP, haven’t tried the 307gr SubX yet. Loading 18rds in the Duramag, it runs to BHO. |
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My case of new factory ammo arrived. I'm going to do some testing tomorrow to see if I can get this thing running. Can't believe how much I've spent getting this thing running, but at least I wasn't deluding myself that this would be cheap, like I convinced myself with steel cased 6.5 Grendel a decade ago. |
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Well this might be a reason why I was having trouble fully chambering these hand loads. I got a case gauge with my case of factory ammo.  Attached File |
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CMMG does show a ten round 338 ARC magazine and PSA shows this magazine in stock. https://palmettostatearmory.com/cmmg-10rds-338-arc-black.html Looking at the pictures the CMMG magazine appears to be a rebranded C Products Defense Duramag. One reference I found listed the 400 Legend/338 ARC as the same. The Duramag 400 Legend magazine has a yellow follower and the same number/letter product code stamped into the body of the magazine as the 338 ARC magazine. I checked D&H plus ASC and neither Company list 400 Legend or 338 ARC specific magazines. Duramag shows a five round 400 Legend as well as the ten round AR-15 pattern mags. Gunmagwarehouse has pictures of the 400 Legend Duramag and the 338 ARC magazine where you can see the same product code stamped in the mag bodies. https://gunmagwarehouse.com/duramag-ar-15-400-legend-10-round-magazine.html?queryID=c4a26311d5958ecdba0981b43ca62adf&objectID=24179&indexName=m2_prod_default_products https://dura-mag.com/400-legend-stainless-steel/?searchid=158060&search_query=400+Legend |
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Originally Posted By VASCAR2: CMMG does show a ten round 338 ARC magazine and PSA shows this magazine in stock. https://palmettostatearmory.com/cmmg-10rds-338-arc-black.html Looking at the pictures the CMMG magazine appears to be a rebranded C Products Defense Duramag. One reference I found listed the 400 Legend/338 ARC as the same. The Duramag 400 Legend magazine has a yellow follower and the same number/letter product code stamped into the body of the magazine as the 338 ARC magazine. I checked D&H plus ASC and neither Company list 400 Legend or 338 ARC specific magazines. Duramag shows a five round 400 Legend as well as the ten round AR-15 pattern mags. Gunmagwarehouse has pictures of the 400 Legend Duramag and the 338 ARC magazine where you can see the same product code stamped in the mag bodies. https://gunmagwarehouse.com/duramag-ar-15-400-legend-10-round-magazine.html?queryID=c4a26311d5958ecdba0981b43ca62adf&objectID=24179&indexName=m2_prod_default_products https://dura-mag.com/400-legend-stainless-steel/?searchid=158060&search_query=400+Legend 400 Legend Duramags work. KAK offers them when buying a .338 upper. |
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Originally Posted By JOHNSON1911: Loading 18rds in the Duramag, it runs to BHO. Originally Posted By JOHNSON1911: Originally Posted By JOHNSON1911: Originally Posted By JOHNSON1911: Ok, so I have an E Lander 17rd 762x39 mag, and a 20rd 762x39 Duramag coming tomorrow, will advise. E Lander mag will only load 4-5 rounds before the front indentions screw it up. Duramag will load all 20 but they are very tight, it may work with 17-18 rounds, will report back this afternoon. AAC 300gr BTHP, haven’t tried the 307gr SubX yet. Loading 18rds in the Duramag, it runs to BHO. So, on the way to Tx (hog hunt). Our group stopped at a GS in Ok and grabbed a 28 rd duramag (7.62x39). And it will successfully feed 26rds of the Hornady Sub X. |
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