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Posted: 3/31/2021 5:23:51 PM EDT
I want to build an AR15 DMR/Precision/MK12ish rifle that will host a nice scope and maybe accompany me on some hunting trips. I haven't pulled the trigger on a suppressor yet, but eventually there will be that too.

I know that all the rage was 18" barrels for the longest time, and that was always my plan. But my plan never came together. I think it would be an attractive rifle, and I can't stop thinking that this is the way to go.

Talk me into or out of a 20" dmr.
Link Posted: 3/31/2021 5:41:39 PM EDT
[Last Edit: 42tula] [#1]
You lose like 50 fps on a 18” barrel vs a 20”. If you get a can, 18” barrel is long enough that with the can the fps of the projectile is within 20 fps difference and sometimes almost identical. No reason to get a 20” when a 18” can do everything the 20 can do and it handles better...unless you’re making a 20” clone. Just my opinion, and I’m sure someone will come along shortly to correct me.
Link Posted: 3/31/2021 5:47:17 PM EDT
[Last Edit: Houlagan72] [#2]
What kind of ranges are you talking?
If it's 300 yds. or less you might be able to get away with a 14.5/16 barrel.
Unless you want a 20" barrel, then get that.
A 20" barrel gets a little long with a suppressor if thats a concern.
Link Posted: 3/31/2021 6:09:17 PM EDT
[#3]
Link Posted: 3/31/2021 11:08:32 PM EDT
[#4]
With a 16" barrel you are good with 77 TMK out to 400. That is full terminal ballistic capability. With a 6.5 Creedmoor you can use 130 grain instead of 140/143 and have the same wind calls out to 800 yards as a 22 or 24 inch barreled gun shooting 140/143 grain loads.

Key to all those loads is hitting 2700 FPS.
Link Posted: 4/1/2021 2:03:52 AM EDT
[#5]
18" rifles are my favorite...







Link Posted: 4/1/2021 5:35:17 AM EDT
[#6]
20" barrels are fine. I climb in and out of rangers with a 20" barrel and an Ultra 7 and an 18" barrel with an Ultra 9 when we go pig hunting. Sure, you can make it more compact by going shorter and the performance difference shouldn't be that great, but it's just a couple more inches
Link Posted: 4/1/2021 11:55:26 AM EDT
[#7]
20" rifles are very efficient in .223. I lose more velocity per inch going shooter than 20" than I gain going longer.

My personal belief is that 20" government profile barrels got it backwards. The heavy (.730") section should be under the handguard, the narrow section ahead of the front sight post.

Outstanding barrels are available in 20" "service rifle" profiles for NRA/CMP competition, IMO they are too heavy for any other use. Having their profile changed by turning them to .750" or .800" under the handguard makes more sense.

In normal times White Oak Armament sells them for $220.00. These are not normal times and inventory gets consumed within a day or so of availability.
Link Posted: 4/1/2021 1:06:13 PM EDT
[#8]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By borderpatrol:
20" rifles are very efficient in .223. I lose more velocity per inch going shooter than 20" than I gain going longer.

My personal belief is that 20" government profile barrels got it backwards. The heavy (.730") section should be under the handguard, the narrow section ahead of the front sight post.

Outstanding barrels are available in 20" "service rifle" profiles for NRA/CMP competition, IMO they are too heavy for any other use. Having their profile changed by turning them to .750" or .800" under the handguard makes more sense.

In normal times White Oak Armament sells them for $220.00. These are not normal times and inventory gets consumed within a day or so of availability.
View Quote

White Oak was my plan either way. If I have to wait out this panic I will, but I think I can put together most of the rifle in the time being.

My uncle found an AR at a gun shop that was some guys home build. He looked it over and realized that the store was asking less money than the some of the parts so he bought it. It had a heavy 20" barrel and a free float quad rail. It was enormously heavy, but shooting it was really wonderful. I don't want anything that heavy, but it turned out to be a really excellent rifle.

Distance is always the tough one for me to answer. In a perfect world, 500yds. Problem is there are so few ranges around me that I hardly ever get to go out and mess with real distance.
Link Posted: 4/2/2021 12:11:41 PM EDT
[#9]
500 yards is easy with 75+ grain match ammo.
Link Posted: 4/3/2021 10:58:02 PM EDT
[#10]
If your going to hunt hogs or deer and such with it I'd go with a 16-18" just because it's easier to carry/maneuver. Especially if you're going to include a suppressor at some point. If you're going to predator hunt where you may be stretching it out I'd choose the 20" to get the better performance.  

I went with an 18" on my first Grendel because it was supposed to be a hunting rifle first and a paper puncher second.  My next rifle is more of a paper puncher first and hunting second so I went with a 20".
Link Posted: 4/4/2021 8:12:19 AM EDT
[#11]
I went with 18" for mine.  It's a little less weight for carrying around, and still gives excellent performance.
Link Posted: 4/4/2021 8:14:11 AM EDT
[#12]
I have come to the conclusion that 20-22” barrels are kinda Bastard length for me. Not enough velocity gain to warrant the extra length over 16-18” barrels that are much more maneuverable. With today’s twist and bullet selection the 20” barrel is more of a hindering factor than a compromise. Just my 0.02’s worth. But if you’re building a true retro style mod. Then you need to stick to it.
Link Posted: 4/4/2021 2:24:44 PM EDT
[#13]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By sparkyD:
I have come to the conclusion that 20-22” barrels are kinda Bastard length for me. Not enough velocity gain to warrant the extra length over 16-18” barrels that are much more maneuverable. With today’s twist and bullet selection the 20” barrel is more of a hindering factor than a compromise. Just my 0.02’s worth. But if you’re building a true retro style mod. Then you need to stick to it.
View Quote

This here
I had an 18in setup that shot friggin amazing with 77gr ammo. Took it out to 900 on steel. I still felt like it was too long for my liking and sold it. Building a 16in gun now that I feel will be every bit as capable.
Link Posted: 4/4/2021 5:02:42 PM EDT
[#14]
I have a 20" ar with a larue stealth barrel and it shoots really well.  That being said, I got a steal of a deal on an 18" JP barrel a long time ago ( effort I got the 20") and its still my go to precision 556 rifle.  Don't get me wrong, I love shooting a classic fixed stock 20" ar...but every JP barrel I have just shoots amazing.  Id like to 1 day try a "better" barrel brand, but every time I think about it, I just get a JP.
Link Posted: 4/6/2021 3:26:31 PM EDT
[#15]
Unless you have a specific need for the rifle to fit in something like a patrol squad rifle rack, then the reason to either get or avoid a 20” barrel is really akin to Ford vs Chevy.  You can get an 18” barrel to perform similar to a 20” barrel, just like you could get a 20” barrel to perform similar to a 22” barrel.  16” is generally pushing the limits on potentially not being long enough if you want to push a round out to longer ranges consistently if you intend to shoot past about 700-800yds or more, but you can still lob them in there.  I have an 18” SPR that I built that I could regularly get to 1,000yds with it and make hits on IPSC steel, but environmentals like wind played a major factor in that.  There are recorded sniper kills by Ranger snipers at over 900m in Afghanistan using a Mk12, which has an 18” barrel and Mk262 77gr SMKs.

Handloading ammo can help tailor a round to any barrel, but fastest is not always most accurate so when considering complete powder burn and velocity differences for barrels, that’s not the whole story because the most accurate load you use may not see any detriment in velocity or performance by reducing barrel length.  

That said, it’s my understanding that the Mk262 Mod 1 load was optimized specifically for the 1:8 twist rate 18” barrel SPR platform that is the Mk12.  If you want that specific load, you have a blueprint for what is needed for that.  That doesn’t mean it won’t perform in a 20” barrel, and everyone’s mileage will vary.
Link Posted: 4/6/2021 7:45:52 PM EDT
[#16]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By UnaStamus:
That said, it’s my understanding that the Mk262 Mod 1 load was optimized specifically for the 1:8 twist rate 18” barrel SPR platform that is the Mk12.  If you want that specific load, you have a blueprint for what is needed for that.
View Quote


I'm not sure that's correct... the only difference in the Mod 0 and Mod 1 that I've ever seen is the addition of a cannelure on the bullet. Had nothing to do with twist rate. I've not read anything that stated the Mod 1 was more or less accurate and it had more to do with preventing bullet set back.

If you have info to clarify I'd be interested.  
Link Posted: 4/6/2021 9:55:42 PM EDT
[#17]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By DevL:
With a 16" barrel you are good with 77 TMK out to 400. That is full terminal ballistic capability. With a 6.5 Creedmoor you can use 130 grain instead of 140/143 and have the same wind calls out to 800 yards as a 22 or 24 inch barreled gun shooting 140/143 grain loads.

Key to all those loads is hitting 2700 FPS.
View Quote


I am seeing 10 shot groups under 1 moa at 600 with Berger 77 hybrids. I definitely wouldn’t use that on game at that range.
Link Posted: 4/7/2021 7:58:41 PM EDT
[#18]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Bowhntr6pt:


I'm not sure that's correct... the only difference in the Mod 0 and Mod 1 that I've ever seen is the addition of a cannelure on the bullet. Had nothing to do with twist rate. I've not read anything that stated the Mod 1 was more or less accurate and it had more to do with preventing bullet set back.

If you have info to clarify I'd be interested.  
View Quote

The comment was not an analysis of the Mod 1 over the Mod 0.  I think you read too much into the Mod 1 portion of it.  I said Mod 1 because the Mod 0 isn’t manufactured anymore.    
The comment was in relation to the fact that the 77gr SMK 5.56 load that Black Hills Ammunition makes for the US military was developed to run in the Mk12 rifle.
Link Posted: 4/8/2021 12:47:51 AM EDT
[Last Edit: Bowhntr6pt] [#19]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By UnaStamus:

The comment was not an analysis of the Mod 1 over the Mod 0.  I think you read too much into the Mod 1 portion of it.  I said Mod 1 because the Mod 0 isn’t manufactured anymore.    
The comment was in relation to the fact that the 77gr SMK 5.56 load that Black Hills Ammunition makes for the US military was developed to run in the Mk12 rifle.
View Quote


That said, it’s my understanding that the Mk262 Mod 1 load was optimized specifically for the 1:8 twist rate 18” barrel SPR platform that is the Mk12.

Perhaps I did, I was referring to the above statement and the 1:8 twist portion.

Just clarifying that Mk12's are 1:7 twist not 1:8 and a cannelure is mainly what differentiates Mod 0 from Mod 1 ammo and it was added as a measure to prevent bullet set back.

I thought maybe there was more to the Mod 1 development reference barrel twist thus my post.
Link Posted: 4/10/2021 9:49:29 AM EDT
[#20]
Like others have said 2 inches isn’t going to make or break a 600 yard shot. What does make a difference between a MK 12 and M16 is the barrel profile. The M16 barrel has it’s thinnest point behind the gas block under the hand guard. Where the MK 12 it’s thinnest point is infront of the gas block. That mass does a couple things, one being that it takes longer to heat up and it also make the barrel stiffer. Those two things play a big part in accuracy as they help mitigate point of impact shifts.

The loss in velocity between an 18 and 20 inch barrel is relatively small, however bullet choice also plays a big part. If you are shooting a 40 grain bullet at say 3500+ fps it will lose velocity faster than a 77 grain bullet that starts at like 2700 fps, lighter bullets tend to loose velocity faster than heavy bullets.

So at the end of the day it really comes down to what are you going to be using it for and what bullet/ammo are you planning on using. If you are planning on this for a parrie dog gun or a hog/coyote gun or is it just to ring steel at distance.

So barrel length isn’t the only factor that needs to be addressed. My opinion is I don’t need a 20 in barrel on an AR because my 18 inch works every bit as good as a 20 inch.
Link Posted: 6/21/2021 12:40:08 PM EDT
[#21]
I have a 20" barrel on my DMR type rifle and I like it alot.
Link Posted: 7/7/2021 8:28:04 PM EDT
[#22]
I always tended to prefer my 20in FN upper, regardless of the rather small performance gain over the 16inch bbls I have when using 77gr loads.
The VERY noticeable lower muzzle blast is a big part of the appeal for me, plus it just "points" better for me.
Link Posted: 8/2/2021 5:44:12 PM EDT
[#23]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By borderpatrol:
My personal belief is that 20" government profile barrels got it backwards. The heavy (.730") section should be under the handguard, the narrow section ahead of the front sight post.
View Quote


Agreed.
Link Posted: 8/2/2021 8:00:57 PM EDT
[#24]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Bowhntr6pt:


That said, it’s my understanding that the Mk262 Mod 1 load was optimized specifically for the 1:8 twist rate 18” barrel SPR platform that is the Mk12.

Perhaps I did, I was referring to the above statement and the 1:8 twist portion.

Just clarifying that Mk12's are 1:7 twist not 1:8 and a cannelure is mainly what differentiates Mod 0 from Mod 1 ammo and it was added as a measure to prevent bullet set back.

I thought maybe there was more to the Mod 1 development reference barrel twist thus my post.
View Quote


Uncrimped bullets are more likely to move forward upon being fed from a magazine.

Similar to a Kinetics bullet puller.

If you have at least .003" of neck tension the bullet should stay put, if it moves it will be minimal.

The Armed Forces have to make unilateral decisions based on the worst case scenarios. Uncrimped ammo in a belt fed machine gun is just asking for trouble. The same could be said regarding full auto mag dumps from an M4.

I stopped crimping high power rifle ammo 35 years ago and have never had one problem because of it.

Revolvers and lever action rifles are a different animal.
Link Posted: 9/4/2021 8:32:26 PM EDT
[#25]
If you live out west where you don't worry about thick forests and have the ability to shoot far go with the 20 and get that tiny boost in velocity. Everyone talks about guns needing to be handy and light and I agree that is a big advantage but if you plan on shooting prone or off a bench the majority of the time it doesn't matter if your gun is light and handy.
Link Posted: 9/12/2021 11:33:25 AM EDT
[#26]
Well, I think there needs to be more information given about what the rifle is going to be used for before a clearer answer can be given.

It's been fairly well established that for every inch of barrel removed (at least for 223/556) you loose about 25 fps at the muzzle. Like other stated lighter bullets shed velocity faster than heavier bullets. So if the OP is intending on shooting lighter bullets then it makes sence to have as much barrel as,possible.

If the OP wants it to ring steel at 800+ yards but doesn't have a range that he can shoot past 300 yards it kind of makes a mute point about several things about which barrel length would be better.

What kind of hunting is the OP looking to do? If the OP is looking to hunt deer, proghorn or hogs, that would require differnt bullet selection than varmint hunting or prairie dog shooting. Is the OP going to be getting in and out of a vehicle, then barrel length may come into play.

Like,others have said if the OP is sitting at a bench or laying prone then barrel length has very little play in the equation. But if one is hiking through dense brush or woods then barrel length does come into play.

While I'm no expert on suppressors, I do understand how they work, I highly doubt that a suppressor will add velocity to a bullet being fired through one. Any gain will most likely be within the standard deviation of the ammo being fired.
Link Posted: 9/18/2021 11:16:11 PM EDT
[#27]
I don’t have an issue with a 20” hunting. We do a lot of walking and climbing over fences and 2” shorter wouldn’t ever make a difference
Link Posted: 12/21/2021 9:15:30 PM EDT
[Last Edit: LeadBreakfast] [#28]
Love 20" barrels, so smooth, quieter at the ear, build enough velocity with heavy, high BC pills to reach way, way out which is awesome practice for practicing wind holds and precision shooting for cheaper than larger calibers. They're also a joy with a can.  The only downside is maneuvering them in tight spaces - say, in and out of a vehicle quickly when doing something like coyote hunting.

ETA: really not a huge issue without a can but with one...woof. Thinking about making a 20" a day rifle and going shorter but adding the can for my night/thermal rifle. 20" with a can is just a bit too much for anything but static positions, bench, or target work IMO.
Link Posted: 12/21/2021 9:47:10 PM EDT
[Last Edit: MRW] [#29]
Link Posted: 12/28/2021 8:08:03 PM EDT
[#30]
I have a 20” Compass Lake SAM-R for my target AR.  If it’s good enough for the Marines….

I like the extra velocity.  My cans go on my Tikka 24” T3x 6.5CM or 16” Hbar AR in 5.56, or 5.56 SBR.  I’m less concerned about OAL vs velocity & target reach at the range, since i’m a high-drag, low speed, paper-punching non-tactical FOG (friggin ol’ guy).  The SBRs are specific for under 200 yards, but i seldom use them, truth be told.

YMMV, if you’re an Uber-tacticool young-un.

Hope it helps with your choice—works for me, but my ARs run from 11.5” SBR (Form 1) to 20” Hbar.  I have AR pistols, too, but they don’t count.
Link Posted: 12/30/2021 9:15:54 PM EDT
[#31]
If it is the “look” you are going for just do it.

I have had multiple 20” guns. I enjoyed my 16” guns much more, even shooting at 600 yds. I enjoy shooting my sbr’s even more.

I no longer have a 20” gun.
Link Posted: 1/22/2022 11:07:42 PM EDT
[#32]
I've owned 20's in the past.. found myself rarely shooting them. I've got one 18" ar now and it's great, perfect length with a can
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