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Old February 1, 2018, 03:13 PM   #1
stagpanther
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New xx308 build: 284 win

I'm embarking on yet another winter-time build in the xx308 platform, decided on something kinda "out there" since it's not exactly a well-known cartridge in any platform, let alone an AR...and that is 284 winchester.

Probably going to be months before all the parts are ready--but here's the beginnings; an Aero lower with assorted LPK parts and a Giessele super dynamic enhanced 2 stage trigger group. I'm leaning towards replacing the adjustable carbine stock set-up with a fixed rifle stock set-up.

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Old February 1, 2018, 04:48 PM   #2
Jim Watson
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Magazine?
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Old February 1, 2018, 06:11 PM   #3
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I've always liked the .284 cartridge for its sweet balance between having relatively light recoil and offering good downrange ballistics in terms of flat trajectory and retained energy while using 7mm bullets. The first rifle I ever shot using this cartridge was a circa 1964 Winchester Model 100 semi-auto.

I'm one who will look forward to how your project turns out.
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Old February 1, 2018, 06:15 PM   #4
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What bolt you gonna use?
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Old February 1, 2018, 06:44 PM   #5
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OK--answers as best as I can make out:
I've stuck some 6.5 x 284 norma cases in a 308 mag and near as I can tell that's not an issue--but that doesn't necessarily mean they'll feed well I guess. The SAAMI spec for COL is a smidgen above a the typical 308 design but shouldn't be an issue.

What I'm pretty sure will be an issue is relatively far shoulder-forward case design and short neck--I know that's going force limitations on just how high a BC bullet design I'll be able to get held by the neck--and will also result in case capacity encroachment. I see it as being sort of analogous to a "super-sized" 6.8 spc. Obviously extra care will be needed in developing loads.

I've been advised to use standard mass BCG--the rim face is the same as a 308's so I'm guessing a standard 308/AR10 BCG will do the job (?).

The barrel is being made 1:9 twist with rifle + 2" gas system, I plan on running bullets in the 140 to 160'ish grs range--not sure bigger bullets could work.
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Old February 1, 2018, 07:08 PM   #6
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BTW--did I mention I'm buying my first nightforce scope?
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Old February 1, 2018, 07:13 PM   #7
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Quote:
The first rifle I ever shot using this cartridge was a circa 1964 Winchester Model 100 semi-auto
Does anyone even make a 284 winchester rifle these days? I've heard there's been a moderate resurgence of interest in competitive shooting using it--but other than that current information is pretty hard to come by.


My inspiration for trying this chambering is the original 50's era FN FAL introduced in 280.
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Old February 1, 2018, 09:42 PM   #8
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I would consider a HP bolt instead of a standard. I've read numerous post of people having problems with regular AR10 bolts especially with 6.5 CM. Can't image a .284 could be much different. Aero has in Black Nitrade and Phosphate. Their nickel bolt is a standard pressure bolt. I used the Black Nitrade BCG on 6.5 CM and it worked well for my my build. Plus the black really stands out against the FDE background color.
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Old February 2, 2018, 02:11 AM   #9
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Quote:
I would consider a HP bolt instead of a standard. I've read numerous post of people having problems with regular AR10 bolts especially with 6.5 CM. Can't image a .284 could be much different.
I've built a couple of creedmoors and haven't encountered any issues with 308 bolts so far--what kind of problems have you heard about? The 284 is actually rated a bit higher pressure-wise. I ordered Aero's NB BCG--mostly cause of all the manufacturers of xx308 stuff they seem to be the most finicky in making their parts work reliably only with their own stuff. If there's an issue I'll look around for a hardened-steel bolt. Aero's bolt uses 9310 tool grade steel.
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Old February 2, 2018, 07:06 AM   #10
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When I was looking to buy an F class rifle I did some research on the 6.5-284 and admittedly it seems a top precision round, however after asking the seasoned F class shooters their opinions they all conclude the 6.5-284 is a REAL barrel burner of a cartridge. i'm just an amateur and didn't want to deal with a barrel burner. I ended up going Savage FTR 308. Might not be an issue with your particular build.
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Old February 2, 2018, 08:02 AM   #11
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I have a 6.5 x 284 Norma bolt gun and haven't noticed the accuracy go off yet--but then I don't shoot it competitively either. Haven't encountered any "notoriety" for the 284 as a barrel burner as of yet; could be though.
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Old February 2, 2018, 08:03 AM   #12
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"The SAAMI spec for COL is a smidgen above a the typical 308 design but shouldn't be an issue."

I'd be more concerned about the case diameter and relative lack of taper.
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Old February 2, 2018, 08:18 AM   #13
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Quote:
I'd be more concerned about the case diameter and relative lack of taper.
I thought about that--I'm probably going to end up bugging the nice folks at Accuracy Systems a lot since they are the only ones I've found with any experience with this in an AR.
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Old February 2, 2018, 08:18 AM   #14
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I suspect there might be a feeding issue due to the larger case diameter and you're definitely going to have an issue with mag length limitations.

I think, the 7-08 for 7mm, and .260/6.5 Creedmoor are close to maximizing performance within the limitations of the AR-10.

Hope you prove me wrong! Let us know how it works out.
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Old February 2, 2018, 08:33 AM   #15
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Quote:
I think, the 7-08 for 7mm, and .260/6.5 Creedmoor are close to maximizing performance within the limitations of the AR-10.
Just like in the AR 15 platform you can do slight modifications to get a bit extra out of the magazine. Actually my information above is incorrect--it is the 308 which has a extra .01 COL over the spec for the 284. Fortunately I have an extra modified case for the 6.5 284 which I'll simply neck up to 7mm.
Quote:
you're definitely going to have an issue with mag length limitations.
Yes--I can see that everything is going to depend on the ogive of the bullet and whether or not it will allow the bullet to be seated. Simply truth is I don't know--but I've got a couple hundred in the 140 to 160 range on the way so I'll find out soon enough.
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Old February 2, 2018, 09:48 AM   #16
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The problems I've read about were on AR15.com and the Creedmoor forum. From what I've read, the HP bolt handles higher pressure loads better, reduces/eliminates primer flow and pierced primers plus increased the lock time. That is accomplished with a enhanced bolt designed, smaller firing pin hole and smaller firing pin. But the problems I read about were for 6.5 and 6mm Creedmoor builds.
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Old February 2, 2018, 10:14 AM   #17
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I'm no expert--but my guess is that even conventional bolts are ridiculously overbuilt in terms of maximum pressure they will handle--probably your extractor will blow first would be my guess. I'm a bit suspicious about using an extra-strength bolt to "cover up" for over-pressure issues arising from other tuning problems--but that's just a guess.
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Old February 2, 2018, 09:41 PM   #18
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"I'm a bit suspicious about using an extra-strength bolt to "cover up" for over-pressure issues arising from other tuning problems--but that's just a guess."

Yeah, I'm on that plain myself.
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