7mm Cartridge Thoughts/Questions

[mac86951]

Ok, So I'm a fan of 7mm cartridge. I don't have one yet, but someone in my family has a custom AR10 in 7RSAUM and it is a dream to shoot, however, very picky and hard to find replacement parts for. This thread has two parts. First is a cartridge discussion between best as I can tell two VERY similar cartridges. Second part is the theory of an AR10 platform for the cartridges, so I'd like to hear input on either, or both.

Part 1: 7mm Cartridges, Goal Target shooting 600-1000 yards. Barrel 28-30" Bullet 180gr Berger, or 168gr Berger.

Two that pop into my head are: 7mm-08 AI and .284 Winchester. I like the Short Action.
If it was a bolt gun I'm sure the 7mm Rem Mag, would pop up too, or STW, or ...


Part 2: AR10 chambered in 7RSAUM needs very specialized parts, from Mag Bolt and BCG, to 24" Gas tube, and on and on. AR10 was made for .308, so naturally a 308 derivative sounds like a better idea from the getting parts easily (well exclude current political situation). 7mm-08 has been done in AR10 without issue, but more velocity is what I'm looking for, so barrel length in the 28" range is what I'd use. Ignore the tuning of the gas system as I see that as what needs to be done secondary to chamber/bolt/barrel system. 7mm-08AI and .284 Win are similar in OAL, so back to the above, Other than barrel/chamber what would be needed to get one to an AR10 platform? I'm sure they've been done before as I see lots of 7mm-08s out there, but not any .284 Win or AIs.

-Mac

 

[Heman]

I have two AR-10 custom uppers one is a .308 the other is a .260. First year shot them both for NRA LR prone. Shot well, but that being said I since have relegated them both for course matches and have bolt guns now for LR prone. Can the AR rifles shoot 600yd-1000yd yes but given the same cartridge in a bolt gun they give up velocity. Plus since you will be shooting single shot why do you need the semi auto feature?

With that being said if you are going bolt gun I would go .280 Remington first or .284 Winchester. I shoot the 280 for NRA LR and love it. Will launch the 180 Berger's close to 2900fps.

As far as the AR10 and ignoring the RSAUM idea becasue finding brass is a pain. You could do a 7mm-08 or the -08AI but to have it throated properly for the longer bullets you are back to loading single and if that is the case why not just use a bolt gun. I know this becasue my .260 upper is throated so a 142 can be loaded to mag length. The other issues you will have with the .284 will be case diameter may have feed issues with the mags and that also will be a round that will be to long if throated properly.

 

[its only light]

This may be way off or at least not what you are looking for. I will admit right away that I have no idea when it comes to gas guns.

I remember seeing an AR style rifle that was chambered in 300 win mag. Would it be possible to rebarrel that for the 7mm rem mag? I think it was something like an omen arms nemo or vice versa. Dang now I want to know.

 

[its only light]

Here is a link:

http://nemoarms.com/portfolio/omen-match-300-win-mag-ar/

I pretty new to the custom world and never dealt with a gas gun at all. It seems easy in my mind though.

 

[mac86951]

You could do a 7mm-08 or the -08AI but to have it throated properly for the longer bullets you are back to loading single and if that is the case why not just use a bolt gun. I know this becasue my .260 upper is throated so a 142 can be loaded to mag length. The other issues you will have with the .284 will be case diameter may have feed issues with the mags and that also will be a round that will be to long if throated properly.

Thanks, that is what I was wondering. Single loading an AR isn't fun, I already do that for service rifle. I'll look at Bolt guns then.

-Mac

 

[Clod-NC]

Hi Mac,hi all

Mac,since you want to address this with an "open mind",and if you intend to shoot matches with it exclusively,why don't you give a thought towards 280AI? It will push tne bullets you intend to use over 3000fps no prob.It's pretty close to 7Rem mag performances without the belted case.Of course it will request a single shot long action.Just my 2 cent.

 

[effendude]

I own a couple AR-10's in .308 and they are much fun. I have shot them out to 600 yards on the F-class target and while they did ok, there are much better choices for long range rifles. The big AR is hard on brass, finicky to load for and requires much maintenance. Run a good bolt gun and you will immediately see the differences.

I love my 284 Shehane and plan to built a light hunting rifle in the same to use my supply of tired match brass one more time. I wouldn't hesitate to build another target rifle in the straight .284 or the .280 Remington. Both are awesome. Unless you like purchasing barrels and want to put a gunsmith's kid through college, stay away from the magnums for target shooting. When they shoot great, it is hard not to keep shooting. Then things go south quick.
Scott

 

[mac86951]

Hi Mac,hi all

Mac,since you want to address this with an "open mind",and if you intend to shoot matches with it exclusively,why don't you give a thought towards 280AI? It will push tne bullets you intend to use over 3000fps no prob.It's pretty close to 7Rem mag performances without the belted case.Of course it will request a single shot long action.Just my 2 cent.

Thanks Clod,
The 280 Remington and AI variant is a great cartridge, and I own several variants of the -06. For the purposes of this thread, I'm looking for short action, because if I was to go long, I would go with an H&H case for a variation from my -06 stable. (seriously, at what point do you start to get 06 brass mixed up? 25-06, 6.5-06, 30-06, 338-06, 270 Win... Hey, that brings up a side note, 22-06?

-Mac

 

[Clod-NC]

Mac

I'm presently expecting an answer from Dave Manson,towards cutting this reamer I'll need to build a 6.5x57 imp 30°,you might as well call it a 6.5x257 imp 30°,that I expect to push the 120gr Nosler BT over 3000 fps;barrel will be True Flite 26" 1/8.5,SS,Weatherby Vanguard contour,mounted on guess what,Vanguard 2 action...It's the wait that's killing me,everyone in the business seems owerwhelmed with orders!!!But it's still a long action even if the cartridge itself will be at ease in the mag well.I could also shoot 140g Nosler BTs but there's no need for it with the Rusa deer I will use it on.Hope you can find what you're after and have it built rapidly and properly,good luck to you.

 

[mac86951]

I own a couple AR-10's in .308 and they are much fun. I have shot them out to 600 yards on the F-class target and while they did ok, there are much better choices for long range rifles. The big AR is hard on brass, finicky to load for and requires much maintenance. Run a good bolt gun and you will immediately see the differences.

I love my 284 Shehane and plan to built a light hunting rifle in the same to use my supply of tired match brass one more time. I wouldn't hesitate to build another target rifle in the straight .284 or the .280 Remington. Both are awesome. Unless you like purchasing barrels and want to put a gunsmith's kid through college, stay away from the magnums for target shooting. When they shoot great, it is hard not to keep shooting. Then things go south quick.
Scott

Thanks for the input Scott. I have seen what a 7mmRSAUM can do in an AR-10 platform, and I am truly amazed already. Lets say there is no point in load testing a 180 Berger at 300y, groups are too small to notice a difference.

Keeping to short action, without the need for magnum barrel life, or mag BCG, so far only one user has suggested that a .284 loaded with 180 Berger would not fit the mag. Bolt gunners always specify the jump to the lands, however, I only just realized that is probably loaded to a 3.000" OAL or greater. The AR10 Magazine needs 2.82" OAL or less. That is what would kill this project.

As to why an AR gas gun over a bolt gun? I love bolt guns and they are awesome, but I shoot my AR15 at 600-1000 yards. That is a real challenge. .223 at 1000y consistently is true marksmanship. The AR10 was developed for the .308, but I don't see many chambered for the .308 derivatives that work well. .243 is a nightmare to properly tune, often requiring building the cartridge/bullet/powder combo before the rifle. 6.5-08 I haven't seen, 7mm-08 I've seen a few, and it works, so maybe an AI cartridge? Sounds like I won't get the velocity, however. .284 Winchester I have yet to see in an AR10 as well.

-Mac

 

[mac86951]

Mac

I'm presently expecting an answer from Dave Manson,towards cutting this reamer I'll need to build a 6.5x57 imp 30°,you might as well call it a 6.5x257 imp 30°,that I expect to push the 120gr Nosler BT over 3000 fps;barrel will be True Flite 26" 1/8.5,SS,Weatherby Vanguard contour,mounted on guess what,Vanguard 2 action...It's the wait that's killing me,everyone in the business seems owerwhelmed with orders!!!But it's still a long action even if the cartridge itself will be at ease in the mag well.I could also shoot 140g Nosler BTs but there's no need for it with the Rusa deer I will use it on.Hope you can find what you're after and have it built rapidly and properly,good luck to you.

Interesting. I have a Vanguard 2 in 30-06 and love it. I've got 5 shot groups within 0.6" at 200y straight off the shelf. I only want a thicker barrel as the standard contour is thin and heats up quickly. It loves the 173 M118 bullet.

-Mac

 

[barnesuser28]

have you considered the 260 rem? Very popular in the AR-10 crowd. It is a "6.5-08".

 

[nastynatesfish]

Just go 7 rem mag. You want long range with the heavies 1-8.5/1-9 will handle just fine.
7 mag left 7-08 right

With 140 bergers. It shoots better with 162 AMAX, just got some 180s to try with some H1000

 

[flatlander]

As you pointed out at the start of the thread, the current situation with shortages & backlogged orders for practically everything needed to put together a LR gas gun project....well, let's just say, even if it were an easily done, viable project, now's not the best time to try to put it all together.

I've done a 28" bbl'd 6.5x47 Lapua & 25" bbl'd 7-08 AR30 (an improved 7mm-08 w/30* shoulder & slightly longer body) on AR10 platforms for myself. The 6.5 shoots pretty well out to 600 with 123s, but won't push them as fast as comparable bolt rifles, nor does it handle the 130VLD or 140s as well as my bolt rifles will. It's harder on the $$$ Lapua brass than my bolt rifles, even at the lower pressures where I run it. I contoured this bbl from a 29" straight 1.25" blank, and went with a gas system with the port 2.5" forward from the std. AR10 location.

The 7-08 has shown very good accuracy at 600 with a couple of select loads, it's not what I'd hoped it'd be, and probably never will be - just too many limitations imposed on loads by the fact that it's a gas gun. Still, I'm going to use the same reamer on a bolt rifle barrel, hopefully sometime this summer. I don't expect it to be a 1000yd super-cartridge, but it'll be fun to shoot, and will no doubt be capable of decent performance at 1000.

I've got three 284s, and am getting ready to do a 280 AI. The 284s shoot very well consistently, but WW primer pockets don't stay tight for long if you push things a little. Just getting started with a box of Lapua 6.5x284 - am hoping it'll prove more durable than the WW brass, but it's a bit of a PITA because of the donut formed when you expand necks to 7mm. Not a problem in a long action bolt rifle with a chamber properly throated so you're not seating bullets down into the donut area, but would be an issue in a short action if you want ammo to feed through a magazine. That's why I'm sticking with long actions, and another reason to try the 280 AI. The Ackley's case capacity is nearly 6grs greater than the 284's, so I should be able to push 180s at least 2850fps and still get good case life.

 

[XTR]

Short actions and heavy bullets are a difficult mix, especially if you want to try to load to mag length.

The 7-08 doesn't have the boiler push the 180s with authority. It will do a pretty good job with the 162 Amax if you can load them about 3" long, but if you are shooting against 284s, and RSAUMs you are giving up a lot of MV from the start. Long bullets and mag loading will have your bullet tails way back inside of the case.

The 284 suffers the same handicap in a short action unless you are single feeding a bolt action and can pull the bolt to eject an unfired round, (they won't come out of the port loaded as long as you will want to load them.

The main idea here is that for the long range game, get a bolt action, it's all single loading anyway.

 

[mac86951]

Thank you all for your replies. A 284 gas gun properly working sounds to be too much of a pipe-dream then, and also thank you for the comments on the 7mm-08. It sounds as if 260 is about the best "selection" of cartridges that will feed well from the ar-10, thereby leaving only the gas system tuning and cartridge OAL to be the limiting factors.

I'm starting to think how extremely rare the AR10 in 7mmRSAUM is, and I got to shoot it! To get it to function it required a 24" gas tube, which was leftover army surplus from an order to try and build the 300WM AR10s. You all are right, if I want to do it right I'd build me a bolt gun and follow the tried and true practices. This pipe-dream was in theory to be on the different side, but the more I think about it (especially the single loading part) the more it becomes a PITA where a bolt gun can just be fun.

I brought this on as I am shooting my AR15 in F-class using special rules developed by my local club. The idea was to attract new members, as we have a LOT of AR people around. Problem is none of them know what an AR15 in 1:8 can really do. I've been competing with my 1:7 at 600y, however, the final rule restriction that is keeping the costs down is loading to mag length.

I'm still amazed what an average practiced marksman (myself) can do with a 77gr bullet traveling at 2650fps, and the other guys at the club are still trying to sight in their AR at 50y with their red-dot sight. More so when I totaled the build costs and found that my AR cost less than what the shelf price was locally before the trouble started last year.

-Mac