SPR Rifle Suggestions

[bkb0000]

does cmmg know if thier 1/8 spr barrel can be fluted?

what if you go rifle length gas system and a 12" rail? it would show the gas tube right?

what's the best barrel profile for an 18" spr? bull? too heavy? I know I won't be lugging it around but a lighter rifle is always better to bring to the range
or do all of you flute your barrels?

A 12" rail should run right up to a rifle-length gas system. if you have a FSB, it'll come within 1/8th inch or so, if you have a low-pro block, it'll hover just next to it. you won't have any "exposed" tube.

I dont know if CMMG will flute their barrels for you, but they'll tell you if you call. i sort of doubt it, I think their barrels are pretty much get-what-you-get. The SPR i just ordered is not fluted, and I don't see any reason to get it fluted. I'm not qualified to explain why it's not really worth anything- but my assumption would be that a fluted barrel will lose some degree of accuracy as the barrel heats up. but you're not going to pound an SPR barrel, anyway- they're for precision shooting, not bulk-bullet-disposal.

as far as profile, i'd say medium profile is probably "best," and medium is what you're going to find in most of the SPRs on the market. it's thick enough to retain it's form while hot, but not so heavy as to make a hike suck ass.

[lanceriley]

you mean that with a 12" rail I won't be able to cover the gas block right? I can probably live with that. I figured a 14" rail is hard to comeby and probably a lot more expensive than the 12"

when you say rifle length rail. it means 12" right?

Med contour it is then. but I didn't know that fluting kills accuracy. anybody can chime in on this?

I probably won't lug it around. maybe put a bipod on it.

[bkb0000]

but I didn't know that fluting kills accuracy. anybody can chime in on this?

not kill... i should have clarified. my guess would be that you'd find an accuracy reduction somewhat less than you'd find in a hot light-weight barrel profile. the rule is, the more rigid the barrel, the less it's affected by heat expansion. seems to me fluting reduces a barrel's ability to retain it's form when hot.

hopefully one of our resident experts will set the record straight.

[Face_N_The_Crowd]

bkb - not quite

Fluting saves weight and is stiffer than a same contour round profile barrel.

With respect to heat disapation - since it is no longer a round piece of metal but has many surfaces - it provides greater surface area and thus cools faster.

My .308 and .300WM are fluted. My Noveske in a VIS isn't.

24.2 of RE15 and 77 SMKs; 4.2 MILs of elevation and 3/4 MIL hold for wind - 1/2 MOA 5 rnd groups yesterday at 625 prone. 10 rnds center mass A zones seated and slung at 625 - too fooking easy - it is by far the most "fun" toy of all my long range rigs.

[spamsammich]

...I figured a 14" rail is hard to comeby and probably a lot more expensive than the 12"
...

Hard to come by, perhaps. A lot more expensive? If you consider 10 bucks a lot, then yes.

[bkb0000]

bkb - not quite

Fluting saves weight and is stiffer than a same contour round profile barrel.

With respect to heat disapation - since it is no longer a round piece of metal but has many surfaces - it provides greater surface area and thus cools faster.

My .308 and .300WM are fluted. My Noveske in a VIS isn't.

24.2 of RE15 and 77 SMKs; 4.2 MILs of elevation and 3/4 MIL hold for wind - 1/2 MOA 5 rnd groups yesterday at 625 prone. 10 rnds center mass A zones seated and slung at 625 - too fooking easy - it is by far the most "fun" toy of all my long range rigs.

You loading your own 77smk?

A thinner barrel expands more- fluting obviously won't cause any more expansion than a barrel of the same thickness as the narrowest point in the fluting, but certainly causes much more than a barrel the same thickness of the OD of the fluting... as to added rigity, it could only ad strength equal to some kind of equation factoring these considerations... if that makes sense(i'm no math guy). Since the barrel is expanding outward from the bore, it seems to me the low spots would only allow relief, allowing the barrel to expand more, and therefor losening up the bore. No?

I've gathered from bits and pieces here and there that fluting is nothing more than an added expense on any AR. I don't know what rifles your 30's are, but I can see a need for weight reduction on larger rifles, and possibly an advantage in fluting if you need your barrel cool for extended single-shot firing-Fire, aquire, fire, aquire, fire, aquire... as from a bolt-action rifle.

The barrel would obviously cool faster after sustained rapid firing, as from an AR- but do you need a hot, expanding barrel that cools faster, or a hot barrel that cools slower but stays tigher...? assuming a fluted barrel DOES expand more. does a fluted barrel STAY cooler, or just cool faster after firing?

we're getting into technical crap that's beyond my knowledge / beyond my needs, but I'm curious, now that the door's been opened.

[lanceriley]

i thought that the fluting will increase rigidity due to it's form.

if fluting increases surface area, then the barrel cannot be as hot as a regular barrel. then maybe it doesn't have to flex?

[Face_N_The_Crowd]

BKB - if you are really interested in all of this stuff - take Precision Shooting Magazine for a few years http://www.precisionshooting.com/ it explains a wide variety of very technical stuff that in one way or another will make one a better shooter / reloader / or just give an enthusiast more info. Some of the articles are so technical they are great to read if you have trouble falling asleep.

The really simple version of it all is heat changes harmonics. Once the barrel gets too hot, to continue to fire has a compounding effect on harmonics and that is why shots 'walk around'.

As for is it necessary? No esp not on an AR. AR tubes aren't nearly as heavy as a .30 cal so yeah, while they may look kool, it is largely an added expense.

As for the balance of contour weight vs heating and cooling - most shooters have pretty similar contours for specific types of weapons - ex many / most purpose built hyper accurate .308s have something close to a #7 contour. Fluting will pull some weight out, make it cool faster due to increased surface area (they will heat up at the same rate - b/c heat is imparted from in to out) but will cost more. In my experience those with the same contour as mine but not fluted - their barrel stays hotter to the touch much longer once it gets hot. I have never been able to shoot mine to the point where shots walked around with out a suppressor. With a suppressor (b/c it gets much hotter than the barrel), the suppressor is the governing issue - it begins to throw off so much mirage it is like looking at the target through vaseline on the end of a coke bottle.

As for reloading 77 SMKs - you bet. Any gun will shoot better if you tune the ammo to it, not to mention that is so much cheaper.

[Face_N_The_Crowd]

lanceriley - you are correct it does increase the stiffness of the same contour and due to the increased surface area they do cool faster.

[Azrael2004]

Just a note: The SPR barrel is actually defined by it's contour.
That's what sets it apart from just any 18" blank.