16" vs 18" 308?

[Queen Bee]

Anyone have info on a 308 AR 10 style and which barrel length would be the most versatile for a precision rifle?

16" is nice for overall length but increases blast right? I know the scar 17 uses a 16" barrel and does very well.

18" is nice but its increased weight ? And how much of an increase in long distance shooting do you get? I presume it helps a 175gr smk bullet better. And can flex to some degree of cqb if needed ?

 

[ChevyGuy91]

Barrel length effects velocity, not accuracy, and twist rate has more of an influence on what bullets the barrel likes to play with.

There is a school in TX that takes 16" OBR's out to a mile, there is a lot of chatter about it on the other forums, do a quick google search. When I get around to a 308 gas gun 16" is what I will be going with, but I will be picking up my 30cal suppressor this weekend, so blast doesn't really bother me.

 

[92G]

in .308, once you go past 20" there is very little (if any) increase in velocity. it's not like .223 where longer barrel = higher velocity.

my experience w .308 has been in 16" and 18" barrels. i have never gone past 18" because again the muzzle velocity increase is something like 100 ft/s from 18" -> 24". is that really worth an extra 3-5% in muzzle energy? not for me at least. keep in mind E = mv2, but when going from like 2600 to 2700 ft/s that's not a big jump in kinetic energy.

i feel like 18" is a sweet spot in .308. at least my 2c.

and WRT post above, my experience with barrel length is that it absolutely can affect accuracy because barrel length affects stiffness and harmonics. for this reason a longer barrel isn't necessarily more accurate, in fact can be worse especially if heat stringing is an issue.

checkout the Youtube channel from Tiborasaurus Rex, he covers these topics incredibly well.

 

[ChevyGuy91]

and WRT post above, my experience with barrel length is that it absolutely can affect accuracy because barrel length affects stiffness and harmonics. for this reason a longer barrel isn't necessarily more accurate, in fact can be worse especially if heat stringing is an issue.

I suppose I should have been more clear and said longer barrels do not necessarily make the gun more accurate.

 

[Knicks]

Im stuck between 16 and 18 as well. Im told those 2 inches wont matter unless im shooting beyond 700yds. Any truth to that?

 

[92G]

Im stuck between 16 and 18 as well. Im told those 2 inches wont matter unless im shooting beyond 700yds. Any truth to that?

I was taught that barrel rigidity and optimal harmonics are far more important than 2" of extra barrel, especially on a .308. My ruger gunsite scout has a 16" barrel and it has no issues reaching out there. My main reason for going w the 16" is that, while i have never directly compared it to a longer barrel, i was always taught that a shorter barrel is more rigid and thus heat stringing is lessened.

this is all in start contrast to a .223/5.56 where personally i love a 20+ inch barrel because it really does reward the round with velocity. I wish IWI would sell a 20 or 22" barrel for the Tavor - i would be the first one interested.

 

[Queen Bee]

Looked at Tibo's channel and a few websites including TTAG 's article on barrel length and there is little difference between the 16 and 18" for most loads.

Im looking at the sig 716 patrol vs the Dmr

The 18" dmr from what i have looked at has a better barrel overall from what im looking at but has the goofy handguards but gives more room to reach out and hold

The patrol has a really short handguard with the big fsb that i can picture my hand creep up on and get burned .

 

[mac1911]

.......it all means little if you cant shoot well.
Tossing the 308 "ar" platform around myself.....
in the end it comes down to what do you expect from it. What ammo are you going to feed it ectect. I most likely will go with a 18" target crown if/when I get one.
I only know one person with a AR 10... its a larue. Its 20" and a beast. Gun came with a 1" shot group target.
(I don't know how many groups they shoot until they get one?) From larue. He dumps the cheapest 308 he can find and gets about 3" groups at best. ........ this is the gun I am eye balling if I can buy it right.

 

[Supermoto]

if you are going to shoot off a bench, go with a heavy profile 18" barrel from a good manufacturer. If you are going to shoot offhand, go with a lightweight 16" barrel from a good manufacturer. A light profile barrel can be accurate if built properly and with a load that leaves the barrel at the right time. A heavy barrel can shoot like crap if poorly made, so I would only worried about barrel length and rigidity if you were going to buy something with a good barrel, which you aren't

 

[Queen Bee]

From what ive gathered the 18" dmr has a swiss made barrel.

 

[dcmdon]

How far do you want to shoot it?

The only real difference that matters is the extra muzzle velocity will allow a bullet to stay supersonic out further. We're talking in the 1000 yard range for a 175 gr bullet out of a bolt gun with a 26" barrel.

I am getting 2720 fps out of my 26" Savage using mid range loads of IMR 4064 and 175 gr SMKs.

2722 is pretty high for a 175 gr bullet. Its the 26" barrel that does it. I've hit things at 1000 yards with this gun.

In contrast, I've got an AR10 with an 18" barrel. I really need to chrono it to put some real data behind my conclusion, but to some degree the bullet will go transonic at a lesser distance out of the 18" barrel. When a bullet goes transonic, accuracy suffers.

I'm shooting from the hip for this number, and I'll follow it up by checking a ballistic program, but even a 16" gun should be good to 700 yards with the right ammo.

In other words, get what you want.

Don

p.s. this is why sniper rifles aimed at the police market have relatively short barrels. Since most police sniper engagements are under 200 yards, all a longer barrel adds is weight.

 

[OfficerObie59]

My guess is: .308 + 16" barrel = flames

 

[Queen Bee]

This gun is more of a bench rifle vs 200 yard cqb rifle for purpose but just not into too many bolt guns ,(preference)

Adding another grand for a scar that i have to heavily modify to make mass compliant would not be fun.

As officer alluded to im guessing a 16" 308 is going to have alot of blast and concussion which i could do without for a prone position gun.

I would like a max range of 1000 yards for this gun.

Looked at the m&p 10

 

[ColdDayInHell]

Not really interested in 308 but would buy and have tried to buy a x54 16.5" VEPR. So I'd go with 16" for size and weight. Don't think you'll notice any difference...

 

[dcmdon]

If you want to go 1000 yards you will need a lot more than 16" barrel length to keep the bullet supersonic to 1000.

One other option is to consider a different cartridge with higher ballistic coefficient bullets that will hold their speed better. You can buy/build an AR10 in both .260 Remington and 6.5 Creedmoor.

See the attached image for some real world numbers. You will notice that the difference in speed based on barrel length can vary a lot with different ammo. One thing though. The velocities they show through a 26" barrel are significantly less than I am getting out of my 26" Savage.

For example, their 175gr SMK loaded in Federal GMM from a 26" barrel is going 145 fps slower than I get with my 175 gr handloads out of a 26" barrel.

Don


***Edit. I'm now questioning my conclusion in my first statement above. I'll run some real numbers through some ballistic apps and report back.

 

[Rate_of_Twist]

This gun is more of a bench rifle vs 200 yard cqb rifle for purpose but just not into too many bolt guns ,(preference)

Adding another grand for a scar that i have to heavily modify to make mass compliant would not be fun.

As officer alluded to im guessing a 16" 308 is going to have alot of blast and concussion which i could do without for a prone position gun.

I would like a max range of 1000 yards for this gun.

Looked at the m&p 10

Um, you need to decide what you want this to do for you.... Yes, a M&P 10 will "go out" 1000 yards, but so will a m&p15-22

Where do you plan to shoot 1000 yards? Is this a competition rifle?

How is a scar even in a conversation for a 1000 yard rifle?

Do you reload?

You mention both prone and bench rifle, which one?

In previous threads you have mentioned recoil sensitivity to .223 and or 7.62x39, has this been corrected?

 

[Supermoto]

This gun is more of a bench rifle vs 200 yard cqb rifle for purpose but just not into too many bolt guns ,(preference)

Adding another grand for a scar that i have to heavily modify to make mass compliant would not be fun.

As officer alluded to im guessing a 16" 308 is going to have alot of blast and concussion which i could do without for a prone position gun.

I would like a max range of 1000 yards for this gun.

Looked at the m&p 10

Where are you going to shoot 1k?
200y is not qcb
The blast out of 16" or 18 is going to be very similar and flash will depend on the powder you use

 

[dcmdon]

queenbee -

One thing. Converting a SCAR is not a big deal if thats what you decide you want. It already comes with a very nice PWS muzzle brake. Having the stock and brake pinned in place will be less than $100 and fully reversible.

DRB - SCARs are plenty accurate to shoot 100 yards. I'm still trying to figure out if a .308 will still be supersonic at 1000 yards when shot out of a 16" gun.

 

[Rate_of_Twist]

DRB - SCARs are plenty accurate to shoot 100 yards. I'm still trying to figure out if a .308 will still be supersonic at 1000 yards when shot out of a 16" gun.

I'm not at all knocking the SCAR. Are you trying to tell me it's a bench rest / prone rifle worthy?

I don't believe a 16" 308 is still supersonic at 1000 yards, 18" is the minimum and that usually requires handholds ( I'm stating this from memory only)

 

[dcmdon]

Its prone worthy. Figure 1 MOA or slightly better with the right ammo and a Geissele trigger.

I'm inclined to agree with you re supersonic. But I'm trying to come up with a reasonable MV from a 16" gun and then I'll pllug it into a ballistics program and see where we end up.

I was astonished when I chrono'd my handloads out of my 26" savage. I got 2720 fps for my 175 SMK reloads. That is screaming for a 175.

If people can give me a day, I'll chrono the same ammo out of my 18" Liljua barreled AR10 and a 16" SCAR 17.

 

[mac1911]

I look at some of the ammo/bullet choices some of these guys use for 1000 yard shooting. Start reading about exterior ballistics and such.....my mind spins.
As I get older my eyes are getting worse. I only see a few more years with iron sights and still be able to shoot well enough to make it fun. This is why I'm looking into F class type of shooting.
Here's a brief article about 1000 yard shooting and what it takes to do well.
you can argue if this is precision shooting or not...... it still takes supersonic bullets and skill to dump 20 rounds into a 10"x ring @ 1000 yards!
http://demigodllc.com/articles/introduction-to-f-class-1000-yard-competition/

Really has me thinking is what 308 load that will fit in the mag be best for 1000 yards then what platform might best deliver this round.?
When reality sets in I'm thinking of the RRA A4 varmint 20" barrel for about 1500$ with a luepold vxIII . RRA puts a claim of 1moa. Sounds good to me. Plus I doubt I will get beyound 600 yards more than 1 or 2 times in say.......8 years!

 

[Rate_of_Twist]

Its prone worthy. Figure 1 MOA or slightly better with the right ammo and a Geissele trigger.

.

I'll disagree, especially given the 1000 yards initially stated. Yes, the SCAR's are extremely accurate battle rifles, but a 16" and a relatively thin barrel are not a great combination. I cannot imagine a worse way to spend $3k for a dedicated rifle to shoot 1000 yards

All that being said, I doubt the OP is looking for a dedicated rifle to shoot 1000 yards and my guess is the SCAR 17 is exactly what the OP is looking for. She has already expressed ad version to recoil and IMHO the SCAR 17 is probably the softest shooting 308 I've come across

EDIT: according to the FN website, effective range for the scar 17 is 700 meters

 

[Queen Bee]

recoil sensitivity was taken care of with the use of the awesome limbsaver, I won't own a rifle without one. shoot the m1a and even bolt guns in 308 without issue now because of it .

at the current time this gun will be shot from 2-400 yards till i find a longer range ..

requirements - at least 1 moa

yes we reload for 308.

i like 18'' barrels over 16''

the AR 10 platform that uses sr-25 mags that magpul makes would be idea as they have the easiest to come by 10 rounders.

id like to stay around 2K mark..

The reason i look at the sig 716 , especially the DMR is the 18'' barrel , with a piston system.. granted their barrels suck.. non CHF, Button Rifled . but its a starting point for 2K. and maybe i could find a match barrel maker that would make one later on

Ive looked at POF , and LWRC, and larue OBR's and the gorgeous 3-4K rifles out there but out of my price range.

ive got time to go out and test some rifles before i make a decision.

 

[Supermoto]

You should build one

 

[dcmdon]

I've got a lot to add here.

re build vs buy - I built an AR10 in .308. Its about as good as you are going to get for accuracy. I've got a Lilja barrel on it with a matched bolt. Mega upper and lower. Its only an 18" barrel, but the longest I get to shoot is typically 300 yards.
It is very accurate. I have not chrono'd my 175 SMK reloads out of it.
It has less recoil than any .308 I've ever shot. I've got a JP adjustable gas block on it that is set for my reloads and a SJC Lund muzzle brake. The difference in recoil between this and what would typicallly be found on a rifle like this is beyond belief. It recoils more like a .223 with a flash hider than a .308.

re scar for 1000 yards - Its definitely not an ideal 1000 yard rifle. But it does very well at 300 and there seems to be no reason to believe it won't do well at much more. The SCAR 17 has a strange ability to transcend the fact that its a piston driven gun with a skinny barrel. I'm not saying the shots won't walk if you shoot it fast. But it is surprisingly accurate.

If you must have a semi-auto a better (buy vs build) choice might be one of the RRA or DPMS varmint or predator rifles in .308. They come with heavy, accurate, stainless barrels and are reasonably priced. I know everyone here hates DPMS, but they are very accurate. You can also get the DPMS in 6.5 creedmoor, which is a better long range cartridge than the .308. It recoils less and has much better external ballistics. The RRA uses proprietary (modified FAL) mags and the DPMS uses the same ones that everyone else other than Armalite uses.

DRB - remember, the effective range is based on the speed at which standard military ball ammo either goes transonic or its KE drops below a certain threshold. Something like my handloads or Superformance match will push a heavier, higher ballistic coefficient bullet faster. So the effective range could be much more. I'm not saying its much good for more than that. Just that you should reserve judgement until some better info on the external ballistics of a fairly hot round like a Hornady Superformance Match 175gr are shot from its 16" barrel.

Mac1911 - the longest I've been able to load that will fit in an AR10 mag is 2.015". At that length, the bullet is well off the lands. (I can't remember how much) One of the things I'd like to do (someday) is check the accuracy of my lilja barreled AR with magazine length cartridges vs something loaded with the bullet just .003" off the lands. (or some otehr relelatively short jump) I guess my point here is that if you are willing to single load, you may be able to get more accuracy out of an ar platform.

 

[PatMcD]

A true "1000yd rifle" is going to be just that; good for 1000yds (and also good for 300-600), but that's about it. It's too long and cumbersome for general range shooting. The barrel wants to be 24" minimum.

Even at all the mid-range matches I attend (mid-range is 300-600yds), I never see a .308 barrel shorter than 22", and I only see one that short when it's on a M14.

If the rifle only needs to go out to 400yds, or I wanted a nice compact package, I might think about going down to 18". But if that were the case, I think an AR15 carbine (.223) fits the bill.

 

[Queen Bee]

I've got a lot to add here.

re build vs buy - I built an AR10 in .308. Its about as good as you are going to get for accuracy. I've got a Lilja barrel on it with a matched bolt. Mega upper and lower. Its only an 18" barrel, but the longest I get to shoot is typically 300 yards.
It is very accurate. I have not chrono'd my 175 SMK reloads out of it.
It has less recoil than any .308 I've ever shot. I've got a JP adjustable gas block on it that is set for my reloads and a SJC Lund muzzle brake. The difference in recoil between this and what would typicallly be found on a rifle like this is beyond belief. It recoils more like a .223 with a flash hider than a .308.


If you must have a semi-auto a better (buy vs build) choice might be one of the RRA or DPMS varmint or predator rifles in .308. They come with heavy, accurate, stainless barrels and are reasonably priced. I know everyone here hates DPMS, but they are very accurate. You can also get the DPMS in 6.5 creedmoor, which is a better long range cartridge than the .308. It recoils less and has much better external ballistics. The RRA uses proprietary (modified FAL) mags

Dcmdon, how much did the rifle cost you to build?

I am interested in it .

Ive looked at the dpms sass and repr , i think im headed down to RI to take a look at a gunshop that has the dpms repr and sig 716 patrol on hand to compare.

Not interested in a gun that uses fal mags

 

[warwickben]

Queen you brought up mag issue with the scar.
You can get a replacement lower (it's not the serial number part on a scar) that takes the the magpul 308 mags.


Dcmdon ,
You talked about bullets going transonic and effecting shot place meant.
Is this like the revers of a sonic boom . I know when some thing breaks the sound Barrier shock waves happen . Dose this also happen when the bullets slows down?

 

[Queen Bee]

How much does that replacement lower cost ?

Unless scar offers the ability to buy that lower already built into the gun..

 

[DMWB]

I haven't seen anyone mention the FNAR. Those are very soft shooting and are available in two barrel lengths. Price should be about the same or slightly less than the Sig 716. Pullman in Worcester had a nice used one for ~$1500 last I checked.