Is 14.5 too short for a DMR?

[BP 3papa 7sierra]

So, I've got this AR with a 14.5 barrel. The lower is already sbr'd so no worries about pinning the muzzle device. It consistently shoots 1"or less with the 8x scope that's on it. My question is, is this barrel too short to press into service in a DMR role? And, besides the suppressor that's in jail, is there anything I should be thinking about upgrading?

 

[BP 3papa 7sierra]

Or is this more of a "recce" rifle?

 

[TonyTheTiger]

DMR is a pretty loose term that means different things to different people. Just like the word carbine. Call it what you want and do with it whatever you want.
All that said, I've got a 13.7", 14", 14.5",14.8" and 15" that all see more long range than any of my >16" guns do, to include pretty good hit % beyond 700 yards. Made a first round hit with the 14.5" Core at 780yds last weekend even.

 

[WindstormSCR]

14.5” is not too short for 5.56. It’s not optimal, but it certainly isn’t bad at it. The main thing it will do is limit your effective range to about 500m, vs 700m with a proper Mk12 style upper with 77gr OTMs. The velocity loss is the primary reason there

 

[BP 3papa 7sierra]

All good points, I just see so many posts with 18"-20"barrels shooting sub moa. Then again, I guess it's all relative to what your want to do with it.

 

[TonyTheTiger]

I just see so many posts with 18"-20"barrels shooting sub moa.

Accuracy has nothing to do with barrel length, but extra velocity definitely makes long range easier.

 

[LRRPF52]

18” SPR Mk.262 Doppler Radar data, 2750fps 2.7” optic height
700yds 1289fps 284ft-lbs 6.2 Mils drop 2.4 mils drift

14.5” SOPMOD Mk.262, 2633fps
700 1218fps 254ft-lbs 6.9 Mils drop 2.5 mils drift

This is the kind of info I have and put out in my DM courses, showing the marginal-at-best practical differences between an 18” gun and a 14.5” gun.

The only advantages you get are .7 Mils flatter and .1 mils less drift at 700yds. 700yds is really pushing it even for 77gr. You can get hits, but they are hard to hear or see even at 400yds sometimes in full value winds.

You’ll probably never see me spec out an 18” 5.56 SPR-type rifle again. 14.5” with a better BC bullet is about as long as I would go nowadays, and I lean more to 12.5”-13.9” for the .224 bore carbines, suppressed.

73gr ELD-M will match the velocity at 700 of the 77gr SMK, with 6.5 Mils drop/2.3 mils drift, from a 14.5”.

300yd performance is pretty good with them all.

The one area I really like the 16” and 18” RLGS suppressed is how smooth they are cyclically. Total pussycats to shoot.

14.5” MLGS or ILGS is there too with the right gas port.

 

[BP 3papa 7sierra]

So, I guess really it just comes down to training with it to get proficient at my particular expected ranges and speeds. Quit trying to wedge it in some category and build my gear up for its intended use.

 

[camocorvette]

I've got the same scope on a 16". It's not terrible. I had a DMR rifle in the Army. It was a clapped out m4. It was the same rifle I was issued a year before I went to LRM. So anything is a DMR if you've been designated the Marksman.

Use the weapon within its capabilities. Recognize it's weaknesses. You wanna call it a DMR go for it. That swimmer dude says he a girl so...

 

[camocorvette]

Taken everything above. If I was to think "DMR" or just a short carbine that is accurate at medium to longer range.

I would think accurate barrel of whatever brand and medium contour. 1 moa with quality ammo. A longer forend to mount a stable bipod. 20 rounders and a very nice 2 stage trigger.

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AR15-Two Piece Free Float M-LOK Handguards from Midwest Industries, a U.S. manufacturer of quality tactical rifle accessories. Quality components, competitive pricing, and top notch customer service.

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Maybe a handguard similar to that for your gun could be a good upgrade.

 

[Bakwa]

Anything is a DMR if it's designated into such a role.

We like labeling things so we can appropriately compartmentalize and organize how things should be placed in our minds. Militaries will label things, and because of their limited tools there will be a relatively small number of things they could be referencing with any given term or label they use. That does not preclude that the terms they use may have a broader meaning or possess examples beyond what a given military would use the term for.

For example:
A DMR within the US military might be a term reserved for MK12's, SAM-R's, URGI w/1-8 ATACR, etc,.... but that's because these guns and setups are the ones typically being pushed into these roles within the context of the US military.

The Taliban might push a sharp shooter with a Lee Enfield into a DM role, making that Lee Enfield a DMR. But I wouldn't call the rifle by itself a DMR.

In northern Vietnam the VC would in many cases push SKS's into DM roles over AK's not because SKS's are DMR's but because it was thought that SKS's were more accurate than AK's.

OP, what you have is a good looking general purpose rifle that could very well be pushed into a DMR role, recce role, or even a CQB role.
Is it the best for any of those, probably not. But it could fulfill any of those roles well.


P.S.
So far as upgrades, the weakest part of that system looks to be your optic.
Vortex is great for competition guys and hobbyist, but many lose zero more often than they should and I've seen an unusually high failure and return rate with their products compared to others in similar price ranges. This is particularly the case with Chinese Vortex. Their warranty is excellent though. lol.
Keeping the spirit of what it seems like you're going for, I'd eventually get a more rugged LPVO or a RDS with magnifier.
Train on your rig though. To many people get caught up in spending money on the perfect kit and forget that training is always most important. I'd rather be a monster on a bone stock SKS in a firefight or competition or whatever than a Gecko45 mall ninja with the coolest rifle and gear but no training.

Cheers!

 

[generalzip]

People always go straight to velocity when talking about performance of a rifle vs barrel length. Obviously the shorter barrel will hurt your ballistics some. What often gets left out is the things you can’t see in a table or graph. Longer barrels have 4 main advantages:

1. Velocity. This will reduce drop, wind drift (slightly), and energy on target. These items are easily quantifiable and up to you to decide the best balance.

2. Rail length. The longer the barrel the longer the rail can be. This has 2 effects. Mounting options for your accessories and hand placement. It’s nice to not have shit all bunched up and unable to properly hold the rifle. The other advantage is it puts you bipod further out. This creates a more stable platform. Why do you think all these PRS rifle chassis seem to be getting longer and longer? There’s a stability advantage to make fine adjustments while aiming prone.

3. Balance and “pointability”. A longer barrel will balance the rifle better (suppressor helps with this too). It creates a rifle that will simply “point” better. This makes the rifle more stable off improvised positions and off barricades. You simply need to shoot a long vs short barrel at range to feel the difference. Heavier contours add this effect as well.

4. Gas system. The rifle length has systems just shoot softer. Plain and simple. They enable you to watch your shots and misses better which is hard enough as is with a .223 past 400.

I did not discuss the disadvantages of longer barrels but they are fairly obvious. All this said I own .223 rifles from 10.3” to 29.5”. They each serve their purpose and you need to be realistic as to what you’re going to use it for. If you live in the mountains and most shots are over 300 yards I’d 100% lean toward an 18” barrel. If you live with most woods And your shots don’t exceed 150 yards I’d get a 12.5”. If you want a decent “do all rifle” I think 16” in a lightweight contour is about as good as it gets. If you plan to suppress, the 14.5” is a good all around option but I would not likely use it in a DMR role for the reasons mentioned above. I have a 16” larue (1-6 razor) and 18” compass lake upper (3-20 ultra short) for those roles.

 

[powerspc]

Accuracy has nothing to do with barrel length, but extra velocity definitely makes long range easier.

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[fdkay]

The 5.56 and the M16 were designed around a 20" barrel for a reason.
It is a marginal load that actually works better than most would think, when used within design parameters.
Bullet technology has come a long way and while the effectiveness of the 5.56 is bullet and velocity dependent, new bullets have extended the range.
Can you get hits at extended ranges? Absolutely.
Is it terminally effective at those extended ranges? Not really, even with the 77 grain bullets. As a previous poster mentioned, you have less than 300 ft lbs of energy at 700 yards, you are talking less energy than some .380 loads at the muzzle.
If this is a range toy, no one cares, if it is for serious social work, then you have some considerations.
Will it make for a bad day? Yes. Will it kill someone, yes SOMETIMES.
Things to consider: what is the AO?
Is this primarily a CQB weapon that might be pushed into extended ranges?
OR
Is the intent extended ranges?
If it is a CQB weapon with capabilities to reach out, it is fine.
If it is intended to shoot what qualifies for extended ranges with the 5.56, then I would strongly consider an 18 0r 20" barrel, will it improve velocity and energy tremendously? No. But when you are dealing with such a tiny bullet, with so little energy at distance, every little bit helps.

 

[rlsmith1]

That’s why you should convert to a 6.5 Grendel. It’s pretty much a 308 in an AR15 platform

If you want (or need) 308 energy, train and run a 308. Great points about energy on target

 

[LRRPF52]

That’s why you should convert to a 6.5 Grendel. It’s pretty much a 308 in an AR15 platform

If you want (or need) 308 energy, train and run a 308. Great points about energy on target

I’ve been running DM courses dating back to 1996, when we (Recon Platoon) put one on for our Battalion in Korea. We had an excess of NM M14s in the HHC Arms Room that could be kicked out to the line companies for select marksmen, so our PL recommended that to LTC Milley, who blessed-off on it.

While working with coalition partners in Scandinavia in prep for events like we’re seeing now, from 2005-2016, I remember several courses where we had guys with SPRs and 7.62x51 auto-loaders, including Hk417s.

Even at 200m, unless you could rapid-hammer the head on the steel poppers, they wouldn’t fall with 5.56, whereas the 7.62 NATO rifles would send the 200m poppers flying head-over-heel.

We did another drill from one of the berms where on a shot timer, you had to barely pop up into minimum exposure and clear a plate rack at 100m. The 7.62 NATO platform was very difficult to manage and get a low time with because of muzzle climb.

I remember thinking, “Man I wish I had my little 16” Grendel here right now.” The Grendel has no problem putting down steel poppers at 300, and is almost as fast as a 5.56 DM carbine at the fast TGT-to-TGT drills. I had only been working with 6.5 Grendel for 3 years at that time (2012), and used my .260 Rem gas guns more for LR work. That’s about when I shifted to spending more time with the Grendel.

With 18” SPRs in any chambering, they are great to shoot from the prone bipod-supported, but get kinda hard to manage from other positions, which is where 75% of my DM courses tend to focus. It can be done, but the forward weight increases your figure 8 wobble a bit.

 

[LRRPF52]

DM is a duty position and skill set, not a platform.

 

[rlsmith1]

I’ve been running DM courses dating back to 1996, when we (Recon Platoon) put one on for our Battalion in Korea. We had an excess of NM M14s in the HHC Arms Room that could be kicked out to the line companies for select marksmen, so our PL recommended that to LTC Milley, who blessed-off on it.

While working with coalition partners in Scandinavia in prep for events like we’re seeing now, from 2005-2016, I remember several courses where we had guys with SPRs and 7.62x51 auto-loaders, including Hk417s.

Even at 200m, unless you could rapid-hammer the head on the steel poppers, they wouldn’t fall with 5.56, whereas the 7.62 NATO rifles would send the 200m poppers flying head-over-heel.

We did another drill from one of the berms where on a shot timer, you had to barely pop up into minimum exposure and clear a plate rack at 100m. The 7.62 NATO platform was very difficult to manage and get a low time with because of muzzle climb.

I remember thinking, “Man I wish I had my little 16” Grendel here right now.” The Grendel has no problem putting down steel poppers at 300, and is almost as fast as a 5.56 DM carbine at the fast TGT-to-TGT drills. I had only been working with 6.5 Grendel for 3 years at that time (2012), and used my .260 Rem gas guns more for LR work. That’s about when I shifted to spending more time with the Grendel.

With 18” SPRs in any chambering, they are great to shoot from the prone bipod-supported, but get kinda hard to manage from other positions, which is where 75% of my DM courses tend to focus. It can be done, but the forward weight increases your figure 8 wobble a bit.

Just had to throw in the "I wish I had my Grendel"

Thanks for the info and always fun to see pics out in the wild. Here's a pic of last weekend shooting steel at 525 (far fence line) and energy on target was real but not enormous (shooting 223 power 75 gr loads). 13.9" barrel suppressed was great

 

[Winny94]

DMR, Recce, etc arent specs - theyre uses. The specs change based on the situation. A "recce" in the pacific northwest is not a "recce" the desert. Same for "DMR". Pick your use, and build/buy to that use. Call it whatever you want, it doesnt matter. If it works, it works - name doesnt matter.

 

[bigjake83]

So, I've got this AR with a 14.5 barrel. The lower is already sbr'd so no worries about pinning the muzzle device. It consistently shoots 1"or less with the 8x scope that's on it. My question is, is this barrel too short to press into service in a DMR role? And, besides the suppressor that's in jail, is there anything I should be thinking about upgrading? View attachment 7833491

OP,

There's nothing wrong with having a 14.5" DMR setup, that said you need to get a "Match Grade" 14.5 barrel and free float it.

 

[WindstormSCR]

If someone asked me for a specific recommendation for a rifle to fill a modern DMR role, with minimal retraining, my answer would probably be a 14.5” SOCOM profile 6mm ARC build, with a heavy duty muzzle brake/suppressor QD (probably a Lantac Dragon)

Gives ~850m reliable terminal effect, bucks wind better than most other options, but isn’t a liability in odd positions or CQ, mags are the same, ergos are the same.

The MCX Spear with a slightly heavier accurized barrel would also be an excellent contender for that role

 

[Winny94]

If someone asked me for a specific recommendation for a rifle to fill a modern DMR role, with minimal retraining, my answer would probably be a 14.5” SOCOM profile 6mm ARC build, with a heavy duty muzzle brake/suppressor QD (probably a Lantac Dragon)

Gives ~850m reliable terminal effect, bucks wind better than most other options, but isn’t a liability in odd positions or CQ, mags are the same, ergos are the same.

The MCX Spear with a slightly heavier accurized barrel would also be an excellent contender for that role

Mags are the same as what?

 

[WindstormSCR]

Mags are the same as what?

Meant same form factor as AR mags, not 100% the same, but requires no re-configuring of load-bearing equipment

 

[fdkay]

If someone asked me for a specific recommendation for a rifle to fill a modern DMR role, with minimal retraining, my answer would probably be a 14.5” SOCOM profile 6mm ARC build, with a heavy duty muzzle brake/suppressor QD (probably a Lantac Dragon)

Gives ~850m reliable terminal effect, bucks wind better than most other options, but isn’t a liability in odd positions or CQ, mags are the same, ergos are the same.

The MCX Spear with a slightly heavier accurized barrel would also be an excellent contender for that role

All those great numbers you see are from a 24" barrel.
You cut 9.5" of barrel off, you are cutting the legs out from under it.
Same thing with the Grendel, Bill Alexander talked about how great it was for distance shooting, all the great numbers were from, you guessed it, 24" barrels.
I'm not saying they aren't good cartridges, but they are NOT short barrel friendly.
There is no free lunch.

 

[WindstormSCR]

All those great numbers you see are from a 24" barrel.
You cut 9.5" of barrel off, you are cutting the legs out from under it.
Same thing with the Grendel, Bill Alexander talked about how great it was for distance shooting, all the great numbers were from, you guessed it, 24" barrels.
I'm not saying they aren't good cartridges, but they are NOT short barrel friendly.
There is no free lunch.

My own experiences with helping a friend build and load develop for a 16” 6mm Arc would tend to disagree. Yes it doesn’t perfectly match the numbers from a 24” barrel, but per Hornady (6mm ARC’s creators) 6mm ARC arose out of a DOD contact/project for better results out of a 16” barrel, not a 20-22” heavy barrel. Currently at work, once I get home I’ll dig up my notes from load development and post numbers. I don’t think the loss of 1.5” would be particularly detrimental

 

[drewthebrave]

If someone asked me for a specific recommendation for a rifle to fill a modern DMR role, with minimal retraining, my answer would probably be a 14.5” SOCOM profile 6mm ARC build, with a heavy duty muzzle brake/suppressor QD (probably a Lantac Dragon)

I'm inclined to agree here, as my ideal "do everything" rifle would be a 14.5" chambered in an intermediate cartridge like 6 ARC, 6.5 Grendel or 6.8 SPC. My 14.7" 5.56 is a fantastic little gun, but I really do love the way my Grendel thwacks plates at 600 yards.

 

[WindstormSCR]

All those great numbers you see are from a 24" barrel.
You cut 9.5" of barrel off, you are cutting the legs out from under it.
Same thing with the Grendel, Bill Alexander talked about how great it was for distance shooting, all the great numbers were from, you guessed it, 24" barrels.
I'm not saying they aren't good cartridges, but they are NOT short barrel friendly.
There is no free lunch.

Still not home (second shift be like that) but on lunch so I figured I would provide some supporting material for my commentary. Here’s Ryan Cleckner’s commentary on the cartridge out of an 18” Rec-7: https://gununiversity.com/6mm-arc-review/

 

[fdkay]

Still not home (second shift be like that) but on lunch so I figured I would provide some supporting material for my commentary. Here’s Ryan Cleckner’s commentary on the cartridge out of an 18” Rec-7: https://gununiversity.com/6mm-arc-review/

I'm not denying that the 6mm ARC has benefits.
All of Hornady's data on their webpage is for 24" barrels. The article you list, which you also point out, is an 18 inch barrel.
That is a difference of 3.5" of barrel length from the OP's 14.5" barrel.
If hornady touts that it was designed around a 16" barrel, why do they use figures for 24" barrels?
I'll give you a hint, it's to mislead.
Also note Ryan has concerns about the magazines.
But, as I said in my earlier post, more oomph is better and the 6 arc, Grendel and 6.8 spc all provide more.

 

[WindstormSCR]

It’s not necessarily to mislead so much as all the barrels used in test rigs by major manufacturers for sample testing and spec QA are 24” custom jobs because of the pressure transducers, etc.

For magazines E-landers have been dead-nuts reliable for my friend so far, but they do require a small breaking in period.

Edit: link a friend sent me off the Hornady site to barrel vs velocity data

 

[generalzip]

Yes the 6 arc and other rounds are better for long range. The advantage for 5.56 is affordable ammo to train and it uses the same common ammo around the world. If you’re just shooting steel and paper for fun and have plenty of money sure get a 6 arc or 6.8 or whatever.

 

[fdkay]

View attachment 7834261It’s not necessarily to mislead so much as all the barrels used in test rigs by major manufacturers for sample testing and spec QA are 24” custom jobs because of the pressure transducers, etc.

For magazines E-landers have been dead-nuts reliable for my friend so far, but they do require a small breaking in period.

Edit: link a friend sent me off the Hornady site to barrel vs velocity data

"All barrels"???
When I look at the nosler site and look up .22 nosler, the show info out of an 18" barrel. They provide all of the Same data.
They don't have to use a 24" barrel, the transducer is not that far in front of the chamber.
They use a 24" barrel to increase velocity.

 

[rlsmith1]

And I had written off the 6 ARC... I love my 6 Creed though

 

[WindstormSCR]

And I had written off the 6 ARC... I love my 6 Creed though

It fits a very specific niche, for those that love the small frame AR and want the most they can get out of it (non-subsonic).

Personally I’d rather have my 6.5CM MDRX, the follow ups aren’t as snappy as you might get with 6 Arc (at least with my skills), but the energy, velocity and effective range make up for it, and it ends up about the same length.

For those willing to pack large frame ARs, things like the MCX Spear will be the optimal choice over 6 ARC as the .277 Fury offers all the trajectory advantages without trading off an ounce of power to the short barrel (it’s pretty damn nuts)

 

[generalzip]

It fits a very specific niche, for those that love the small frame AR and want the most they can get out of it (non-subsonic).

Personally I’d rather have my 6.5CM MDRX, the follow ups aren’t as snappy as you might get with 6 Arc (at least with my skills), but the energy, velocity and effective range make up for it, and it ends up about the same length.

For those willing to pack large frame ARs, things like the MCX Spear will be the optimal choice over 6 ARC as the .277 Fury offers all the trajectory advantages without trading off an ounce of power to the short barrel (it’s pretty damn nuts)

I have a 6.5 MDRx. Incredibly underrated weapon. Great for suppressed and getting in and out of vehicles. It replaced my 12.5” 6.8 for hog and coyotes at night. The MDRx has been very reliable so far. Don’t think I’ve had a malfunction yet. I have noticed it reaches pressure much faster than most bolt guns however and the recoil is a bit violent compared to a tuned AR10 but those trade offs are nothing compared to how well balanced this rifle is. It’s heavier but with the weight in the rear it feels 2-3 lbs lighter than it really is. It’s accurate enough. Hit a fox at 250 yards in the dome off my front porch.

 

[WindstormSCR]

I have a 6.5 MDRx. Incredibly underrated weapon. Great for suppressed and getting in and out of vehicles. It replaced my 12.5” 6.8 for hog and coyotes at night. The MDRx has been very reliable so far. Don’t think I’ve had a malfunction yet. I have noticed it reaches pressure much faster than most bolt guns however and the recoil is a bit violent compared to a tuned AR10 but those trade offs are nothing compared to how well balanced this rifle is. It’s heavier but with the weight in the rear it feels 2-3 lbs lighter than it really is. It’s accurate enough. Hit a fox at 250 yards in the dome off my front porch.

if you’re getting excessive recoil try turning the gas down a notch, when unsuppressed I’m usually running one setting below ‘N’ hasn’t caused me any short strokes and stops it beating the brass to death

 

[generalzip]

I’ve adjusted the gas. It’s still violent compared to an AR10. Likely due to the higher bolt mass and piston system vs DI. It’s by no means terrible it’s a 6.5cm after all. Just a bit more than 6.5cm AR10s I’ve owned

 

[Naaman]

So, I've got this AR with a 14.5 barrel. The lower is already sbr'd so no worries about pinning the muzzle device. It consistently shoots 1"or less with the 8x scope that's on it. My question is, is this barrel too short to press into service in a DMR role? And, besides the suppressor that's in jail, is there anything I should be thinking about upgrading? View attachment 7833491

With what I've been learning over the last several months about rifles, I'm starting to think that the choice between 14.5 and 16 depends on if you absolutely must have a specific muzzle device. If you are content with a standard A2, seems like 16 may be the better way to go, even if only for the little bit extra velocity.

However, if you're dead set on something like a KAC or SF flash hider, then the pin/weld (or sbr stamp) may be worth the reduction in length.

More than barrel length, however, it seems that barrel profile is the attribute to look at -- not for "range" but rather precision/consistency (which has the side effect of making hits at any distance more likely, assuming the shooter has good DOPE).

Others who know more than me about all this seem to have already stated as much above, so maybe I'm just being redundant.

But if starting from scratch, I would probably go with a "medium" contour (like the SOCOM or Criterion Core) mid-length gas, 14.5" with a twist rate appropriate to my chosen ammo. I like 1:7 (maybe I'm a "fudd" in that sense), but a lot of mfrs are making 1:8s as their standard/general purpose offerings. I've been curious about the 7.7 twist and may eventually do a build based on one some day.

 

[LawnMM]

1" or less, eh? At what distance? Calling BS on that one.

I'd start with a free floating handguard instead of that damn delta ring and take a Dremel and cut that front sight post off.

But please, throw up a photo with a couple Birchwood Casey plasters at 100yds, say three of em, give em five rounds a peace, before you change anything.

An inch or less with a delta ring handguard and no bipod, I've just gotta see this! Video the whole thing and if all 3 are an inch or less I'll send you a box of ammo.

 

[WindstormSCR]

With what I've been learning over the last several months about rifles, I'm starting to think that the choice between 14.5 and 16 depends on if you absolutely must have a specific muzzle device. If you are content with a standard A2, seems like 16 may be the better way to go, even if only for the little bit extra velocity.

However, if you're dead set on something like a KAC or SF flash hider, then the pin/weld (or sbr stamp) may be worth the reduction in length.

More than barrel length, however, it seems that barrel profile is the attribute to look at -- not for "range" but rather precision/consistency (which has the side effect of making hits at any distance more likely, assuming the shooter has good DOPE).

Others who know more than me about all this seem to have already stated as much above, so maybe I'm just being redundant.

But if starting from scratch, I would probably go with a "medium" contour (like the SOCOM or Criterion Core) mid-length gas, 14.5" with a twist rate appropriate to my chosen ammo. I like 1:7 (maybe I'm a "fudd" in that sense), but a lot of mfrs are making 1:8s as their standard/general purpose offerings. I've been curious about the 7.7 twist and may eventually do a build based on one some day.

You’re in the right direction.

Barrel Length often dictates velocity, but not always, powder burn rates and loadings play a big factor too. But this is accurate enough for factory ammo

Barrel profile dictates overall stiffness and ability to absorb heat before imperfections in the metal begin to cause PoI shift as the metal expands. more barrel, more mass, less energy per cm3 per shot.

Twist rate is dictated by the type of projectiles you want to use. the longer the bullet, the faster you need to spin it to gyroscopically stabilize it. using 5.56 as an example 1:8 is perfectly fine for 55gr and 62gr, but the heavy and long 77gr projectiles work best with the faster 1:7 twist rate. however the faster you move the bullet, the less twist per distance you need to achieve the same rotational velocity, so if you could magically increase your velocity to 3800 fps, you would require less twist rate. This is why magnum calibers have slower barrel twists than “standard” calibers, and why subsonic centric cartridges have such fast twist rates.

a fast twist rate isn’t always good. spin a bullet too fast and it will rip itself apart from the rotational forces, known as “shedding the jacket”

 

[Naaman]

You’re in the right direction.

Barrel Length often dictates velocity, but not always, powder burn rates and loadings play a big factor too. But this is accurate enough for factory ammo

Barrel profile dictates overall stiffness and ability to absorb heat before imperfections in the metal begin to cause PoI shift as the metal expands. more barrel, more mass, less energy per cm3 per shot.

Twist rate is dictated by the type of projectiles you want to use. the longer the bullet, the faster you need to spin it to gyroscopically stabilize it. using 5.56 as an example 1:8 is perfectly fine for 55gr and 62gr, but the heavy and long 77gr projectiles work best with the faster 1:7 twist rate. however the faster you move the bullet, the less twist per distance you need to achieve the same rotational velocity, so if you could magically increase your velocity to 3800 fps, you would require less twist rate. This is why magnum calibers have slower barrel twists than “standard” calibers, and why subsonic centric cartridges have such fast twist rates.

a fast twist rate isn’t always good. spin a bullet too fast and it will rip itself apart from the rotational forces, known as “shedding the jacket”

I didn't know that about twist vs velocity. Thanks for the tip, man.

I had read about "over stabilizing" a bullet and always figured it meant something like spinning it so fast that the imperfections cause it to wobble instead of spinning concentrically (like a bad football throw vs a good football throw).

Didn't know about shedding the jacket.

 

[generalzip]

There’s no bullets worth shooting in a DMR role in 223 you’re going to blow up from a 7 twist. There’s no reason today to not use a 7 twist to be honest. And @WindstormSCR, magnum calibers usually use faster twists not slower. This is because they generally have longer COAL lengths due to longer mag size and they also have the freebore and the ass behind them to launch heavier, longer bullets at usable velocities to where the longer heavier bullet makes sense. Longer heavier bullets need a faster twist.

For example a 308 it was very common to have a 12 twist. Then as time went on and higher Bc, longer bullets came out that moved to 11.25 and now 10 twist. A 300 Norma mag uses most commonly a 9 or even 8 twist for 230-250 grain bullets.

For .223, a 7 or 8 twist will work for pretty much any bullet you’d mag feed so there’s no practical difference. I own 7, 7.7, and 8 twist ARs with no practical difference between them. Some barrels like certain bullets more than others. For a bolt 223 absolutely use a 7 twist so you can shoot the longer 80-88 grain bullets

 

[WindstormSCR]

There’s no bullets worth shooting in a DMR role in 223 you’re going to blow up from a 7 twist. There’s no reason today to not use a 7 twist to be honest. And @WindstormSCR, magnum calibers usually use faster twists not slower. This is because they generally have longer COAL lengths due to longer mag size and they also have the freebore and the ass behind them to launch heavier, longer bullets at usable velocities to where the longer heavier bullet makes sense. Longer heavier bullets need a faster twist.

For example a 308 it was very common to have a 12 twist. Then as time went on and higher Bc, longer bullets came out that moved to 11.25 and now 10 twist. A 300 Norma mag uses most commonly a 9 or even 8 twist for 230-250 grain bullets.

For .223, a 7 or 8 twist will work for pretty much any bullet you’d mag feed so there’s no practical difference. I own 7, 7.7, and 8 twist ARs with no practical difference between them. Some barrels like certain bullets more than others. For a bolt 223 absolutely use a 7 twist so you can shoot the longer 80-88 grain bullets

I use the slower or faster twist comment in a relative sense to bullet density. An example of that would be a heavy bullet for .308 win (eg 175gr) needing a faster twist than the same bullet fired from a 300 win mag. The relative density of the extremely long for caliber bullets used by .300 PRC and .300NM are even lower and make for a poor comparison to illustrate the relationship. to make the .300 NM comparison you would illustrate that at .308win’s lower velocities you’d need an even faster twist rate than 1:8 to stabilize the projectiles used in 300NM (assuming you could even make a chamberable loading) at which point 147gr M80 ball through the same barrel would likely begin to shed its jackets.

as for 7 vs 8 twist for 5.56, velocity plays a critical role in determining how effective 1:8 is at stabilizing 77gr ammunition, with shorter barrels needing the faster twist to compensate for reduced velocity.

 

[generalzip]

Velocity plays less of a role than you think in determining twist rate. Elevation, bullet length and temperature play much more of a role.

The density of all bullets is the same. They are all made out of lead. I believe you may be referring to sectional density. As sectional density increases yes the required twist rate will increase because the bullet generally gets longer.

I’d suggest you got to berger stability calculator and play around with the numbers. You’ll start to see what I described above. You’ll soon realize velocity doesn’t not play a role with 77 grain and less bullets in a .223. Especially when talking about 1.5” of barrel length.

For bolt guns your point is valid. For an AR you are generally limited by mag length before you surpass the need for anything faster than an 8 twist. All that being said is still choose a 7 or 7.7 twist because it doesn’t hurt anything.

 

[rlsmith1]

It fits a very specific niche, for those that love the small frame AR and want the most they can get out of it (non-subsonic).

Personally I’d rather have my 6.5CM MDRX, the follow ups aren’t as snappy as you might get with 6 Arc (at least with my skills), but the energy, velocity and effective range make up for it, and it ends up about the same length.

For those willing to pack large frame ARs, things like the MCX Spear will be the optimal choice over 6 ARC as the .277 Fury offers all the trajectory advantages without trading off an ounce of power to the short barrel (it’s pretty damn nuts)

I’m excited for the 277 Fury especially if big army picks it up. First real significant improvement in performance in a long time

 

[fdkay]

I’m excited for the 277 Fury especially if big army picks it up. First real significant improvement in performance in a long time

They are not going to pick it up, or any other cartridge for that matter. They have never had any intention of replacing the 5.56
At 80,000 psi and 3000 fps, you are going to burn your barrel up in short order. Even the Army can't replace thousands of barrels every year.
The Army comes up with theses stupid RFP's just to generate money for their friends in the weapons industry.

 

[generalzip]

They are not going to pick it up, or any other cartridge for that matter. They have never had any intention of replacing the 5.56
At 80,000 psi and 3000 fps, you are going to burn your barrel up in short order. Even the Army can't replace thousands of barrels every year.
The Army comes up with theses stupid RFP's just to generate money for their friends in the weapons industry.

Facts. Only use for this round in my eyes is as a hunting cartridge for hogs and the like. Even then there are existing options that get the job done for much cheaper.

 

[rlsmith1]

After 60 years, it seems like we are in the right timeframe for a new cartridge. They did pick up the MRAD in 300 NM which torches barrels too but also made sure to have 308's for each system. I could see them doing something similar for the NGSW. If we truly care about "near peer" conflict then we need to make some type of a change. Or accurize the systems and soldiers we have to give headshot capabilities at distance.

Would it be prudent to make a huge switch given current global events? No, but that hasn't stopped .gov before...

I have no military background so I could be wrong but that's how I see it with the public info available. And I'm rooting for military to adopt something newer than the 308 so I can shoot it for even cheaper!

 

[fdkay]

After 60 years, it seems like we are in the right timeframe for a new cartridge. They did pick up the MRAD in 300 NM which torches barrels too but also made sure to have 308's for each system. I could see them doing something similar for the NGSW. If we truly care about "near peer" conflict then we need to make some type of a change. Or accurize the systems and soldiers we have to give headshot capabilities at distance.

Would it be prudent to make a huge switch given current global events? No, but that hasn't stopped .gov before...

I have no military background so I could be wrong but that's how I see it with the public info available. And I'm rooting for military to adopt something newer than the 308 so I can shoot it for even cheaper!

There is a significant difference between a specialized weapon system like the MRAD and a front line, select fire, assault rifle issued to the troops en-mass. 1000 of one, 250,000 of the other.
Full auto fire, even with cartridges like the .308, which is known to be easy on barrels, burns them out in short order.
apples to oranges comparison

 

[rlsmith1]

Then I'll add they seem to be investing in soldier level tech much more too. Our defense companies have to make money so they can kick it back to politicians somehow!

You may be right and the boring 308 will stay in the beltfed weapons for a while

 

[eastexsteve]

So, I've got this AR with a 14.5 barrel. The lower is already sbr'd so no worries about pinning the muzzle device. It consistently shoots 1"or less with the 8x scope that's on it. My question is, is this barrel too short to press into service in a DMR role? And, besides the suppressor that's in jail, is there anything I should be thinking about upgrading?

If you mean "designated marksman rifle" it depends upon what you will be shooting out of it, and how far. The first thought that comes to my head is a SHTF type DMR rifle. As such, I would be using M855s in it, and look for the effective range to be out to 600 yards or so. For anything more than that, i would be looking for a longer barrel or more rifle altogether.