SCAR Mk20 Review

[Rudy Gonsior]

Hey Guys, just wanted to share the beginning of a little project I am working on this year. Basically I am reviewing a series of semi-auto sniper systems in context to their design and function. This lack context is something that I've always though gets lost in the noise of a lot of reviews. We decided to start with the Mk20 earlier this spring but got a little tied up. The next up in the queue for semi-auto precision platforms (in no particular order):

1. Knights SR-25 ACP
2. LaRue OBR
3. JP LRP
4. LMT MWS (if I can get dig one up)

Anyways hope some of you might get something out of it. If nothing else stay for the blooper reels, sadly the editor cut the other 72 minutes of me trying my best to not be a mouth breathing retard, Lol!

 

[theLBC]

thanks! i saw that soon after it was posted and shared on the FN forums as well.
curious that your groups were so big.
did you check the barrel for tightness - some owners found them @ less than 62ft/lbs and torquing to spec tightened them up to sub moa.
i do like the fact that you shot your 5x5 quickly.

 

[schmi015]

I'd like to see an hk MR762 added to the list above and where is that range? I'd love to go shoot there.

 

[Slippery_Pete]

Saw your review. Enjoyed it. Can't wait to see more. Appreciate the info/ entertainment.

 

[GUNNER10]

Really liked your review. I too feel that the scar feels wierd to shoot.

Subscribed.

 

[Rudy Gonsior]

thanks! i saw that soon after it was posted and shared on the FN forums as well.
curious that your groups were so big.
did you check the barrel for tightness - some owners found them @ less than 62ft/lbs and torquing to spec tightened them up to sub moa.
i do like the fact that you shot your 5x5 quickly.

Yes the barrel was checked, it’s possible that the loose stock screws in the buttstock could have contributed but it seem that heat might have been the main culprit. It hovered right at that 1 MOA during zeroing early as well but that was a hasty 10 rounds just to center up on paper. I think it’s likely you’ll see a return of the Mk20, probably not the whole review but at least the accuracy portion.

 

[theLBC]

Yes the barrel was checked, it’s possible that the loose stock screws in the buttstock could have contributed but it seem that heat might have been the main culprit. It hovered right at that 1 MOA during zeroing early as well but that was a hasty 10 rounds just to center up on paper. I think it’s likely you’ll see a return of the Mk20, probably not the whole review but at least the accuracy portion.

thanks for the reply, and again for your efforts.
sure would like to see better groups. i know everyone can make claims online about how e-lite their shit is but...
i don't know any owners that can't manage sub moa consistently with 168gr or 175gr FGMM.
the only other .308 i've shot more than a few times is my '62 Winchester Model 88 (was my dad's).
perhaps because of this, i don't have habits or expectations that affects how i run it?
"recoil feels weird" is a common impression, but to me it just feels soft and ridiculously easy to shoot well.

anyway, looking forward to the rest of the reviews!

 

[556nateo]

Interesting. Just bought a mk20 myself. Shot m118 LR through it. I started with a ten round group that was, if I removed one flyer from a bad pull, sub moa.

 

[Jsp556]

Tagged for interest

 

[dgheriani]

Great video! Couple questions for you, more on your employment of the rifle than on the rifle itself.

When you shot the MEU SOC drill, were you using the offset DPP or just the scope powered down to 4x? I couldn't really tell from the video. I'm curious because I find that a rds up on the rings at 45 is too high for me to use for actually shooting (by rolling the rifle to the left) but I have them mounted there on match (bolt) guns co-zeroed to my main optic (at 600ish yards) so I can just put them on target (or close to it) drop behind the main optic and be on target. I have to run them on 45 degree offset mounts on the rifle's top pic rail to use in the "roll the rifle left" kinda way (which is what I do on gas guns).

When you shot the 21 gun salute drill, were all the target distances unknown to you or did you have a rough distance to each memorized? Or did you flash mill them?

Anyways, thanks and cool video, looking forward to more.

 

[Rudy Gonsior]

Great video! Couple questions for you, more on your employment of the rifle than on the rifle itself.

When you shot the MEU SOC drill, were you using the offset DPP or just the scope powered down to 4x? I couldn't really tell from the video. I'm curious because I find that a rds up on the rings at 45 is too high for me to use for actually shooting (by rolling the rifle to the left) but I have them mounted there on match (bolt) guns co-zeroed to my main optic (at 600ish yards) so I can just put them on target (or close to it) drop behind the main optic and be on target. I have to run them on 45 degree offset mounts on the rifle's top pic rail to use in the "roll the rifle left" kinda way (which is what I do on gas guns).

When you shot the 21 gun salute drill, were all the target distances unknown to you or did you have a rough distance to each memorized? Or did you flash mill them?

Anyways, thanks and cool video, looking forward to more.

Hey,

Yes, I shot the MEUSOC with the MRDS. There are a couple key points as to the placement of the MRDS at the 45 off the tube vs. the rail which makes it preferable for professional shooters.

1. Running the MRDS off the tube gives better situational awareness as it presents a more up right head position which became important in extremis engagements. This is the same trend you see in standard red dot sights mount on carbines. MRDS’s mount it on the rail has a tendency to keep the shooters head down along the same plane as the primary optic. Some people seem to think coming up high might be problematic, but it’s a simple switch from proper cheek weld on the primary optic into what is essentially a quick chin weld. Transitioning is a bit faster as there is less movement of the rifle, which typically occurs when rolling all the way to a rail mounted MRDS. Only down side is the additional HOB (usually in the neighborhood of 3 to 3.5 inch).

2. Additionally, MRDS mounted high actually clears lasers and UNS’s that typically either block or crowd sight pictures when mounted low on the rail.

3. Lastly if you’re trying to use the MRDS passively with NODs, you will quickly find that mounted low off the rail it’s near impossible to do.

As for the 21 gun salute, I used the 12 inch drill. Technically I know all those target or somewhere in between 150 to 600 meters but they’re all UKD and trying to remember 21 different holds is impractical. It’s just a simple understanding of the relationship between your trajectory and the size of your intended target. Thoracic cavities, which is what 66% IPSC represents are incredibly forgiving.

Added: For those interested we are planning to re-boot this review and add a bunch of other SASS/DMR platforms. COVID kinda screwed with the scheduling and we’ve had to shelf the project until this year...fingers crossed...got a lot of irons in the fire.

 

[Bigjake83]

Following

 

[longshot2000]

I look forward to reading what you have. We sell and shoot the FN Scar 20s, the LMT .308 MWS and MARS-H and the SR25 in M110 and Mk11 configurations. Most of what I have seen is in the barrel, and they are all good shooters. I think LMT and SR25 have more accuracy, but we are barrel nerds, so we are making the barrels on the KAC platform. I have been impressed with the Scar 20s in 6.5 and 7.62.

I personally also have a LaRue OBR, which I find to be quite good. I must admit to never really measuring it against the LMT or SR25, but seems to be comparable. I also have a LaRue heavy barrel Preda... something or another that Mark made. Basically an OBR barrel with more traditional frame. I like that as well.

 

[dgheriani]

Hey,

Yes, I shot the MEUSOC with the MRDS. There are a couple key points as to the placement of the MRDS at the 45 off the tube vs. the rail which makes it preferable for professional shooters.

1. Running the MRDS off the tube gives better situational awareness as it presents a more up right head position which became important in extremis engagements. This is the same trend you see in standard red dot sights mount on carbines. MRDS’s mount it on the rail has a tendency to keep the shooters head down along the same plane as the primary optic. Some people seem to think coming up high might be problematic, but it’s a simple switch from proper cheek weld on the primary optic into what is essentially a quick chin weld. Transitioning is a bit faster as there is less movement of the rifle, which typically occurs when rolling all the way to a rail mounted MRDS. Only down side is the additional HOB (usually in the neighborhood of 3 to 3.5 inch).

2. Additionally, MRDS mounted high actually clears lasers and UNS’s that typically either block or crowd sight pictures when mounted low on the rail.

3. Lastly if you’re trying to use the MRDS passively with NODs, you will quickly find that mounted low off the rail it’s near impossible to do.

As for the 21 gun salute, I used the 12 inch drill. Technically I know all those target or somewhere in between 150 to 600 meters but they’re all UKD and trying to remember 21 different holds is impractical. It’s just a simple understanding of the relationship between your trajectory and the size of your intended target. Thoracic cavities, which is what 66% IPSC represents are incredibly forgiving.

Added: For those interested we are planning to re-boot this review and add a bunch of other SASS/DMR platforms. COVID kinda screwed with the scheduling and we’ve had to shelf the project until this year...fingers crossed...got a lot of irons in the fire.

Awesome, thanks a ton for that detailed explanation, much appreciated. I'll have to go try with an offset red dot on the tube again and see if I can better make it work. Makes a ton of sense about clearing lasers/UNS/using nods. Do you go for a 50/200 zero on the red dot?

Figured you were doing something along the lines of the 12" drill. I've been meaning to try that for years but never really seem to run into a situation where I don't know the ranges to the targets so figured I'd cheat, haha. I always thought it would be really cool to have a stage at a team match that was short time, high number of targets, high round count and no lasers allowed to force you to do it in that way.

Again, thanks for your response and look forward to more videos!

 

[LRRPF52]

Hey Guys, just wanted to share the beginning of a little project I am working on this year. Basically I am reviewing a series of semi-auto sniper systems in context to their design and function. This lack context is something that I've always though gets lost in the noise of a lot of reviews. We decided to start with the Mk20 earlier this spring but got a little tied up. The next up in the queue for semi-auto precision platforms (in no particular order):

1. Knights SR-25 ACP
2. LaRue OBR
3. JP LRP
4. LMT MWS (if I can get dig one up)

Anyways hope some of you might get something out of it. If nothing else stay for the blooper reels, sadly the editor cut the other 72 minutes of me trying my best to not be a mouth breathing retard, Lol!

This is one of the only videos I’ve seen that starts to get to the heart of the matter of what I’ve been trying to convey over the past 19 years.

I remember when the Army was looking for a new Sniper Weapon System in the 1980s because of all the issues with the M21/ART II. The argument was always one between the more range-oriented guys and the ones who knew they didn’t want to go outside the wire with a bolt gun even back then. Bolt gun crowd won that argument, thus was born the "too-many cooks in the kitchen" M24 SWS, which is what I used in several units. Interestingly, we still had M21s or NM M-14s in 2 of my Scout Platoons, but with no armorer support and broken ART IIs.

JSOC and CIF Teams in SF started using SR-25s at that time, but they all had 24” barrels. JSOC had some custom 20” barrels made and installed by their armorers already in the late 1990s/early 2000s. A lot of input from those guns went into the Mk.11 Mod 0. They also were chasing 16” SR-25K carbines for all the reasons you cover, since they didn’t need 24” or 20” guns for close target sniper support for assaulters.

In my talks with guys from the STA Platoon community, they said for most of their missions, they left the M40A4/A5s in the compound and just took Mk.11s since you can fight with them.

SF tested 16” uppers with a carbine stock kit after that for what was labeled the M110K.

Most teams were using SCAR-Hs by that time for a heavier support weapon/DMR in 7.62 NATO.

What everyone has been chasing is longer range performance from a package you can still fight with.

That would look like an AR-15 sized platform in carbine format that is lightweight and easy to do CQM/CQB with, while also matching or exceeding the 7.62 NATO platforms at distance.

That’s why I really started latching onto 6.5 Grendel once I saw what a short barrel even would do past 800yds. It made me feel like I had been cheated all those years of humping an M24.

I call it the Light Sniper Concept, where you have an AR-15 chambered in something that actually reaches out with authority and retained energy on-target. I quickly lost interest in 7.62 platforms after that.

 

[theLBC]

This is one of the only videos I’ve seen that starts to get to the heart of the matter of what I’ve been trying to convey over the past 19 years.

I remember when the Army was looking for a new Sniper Weapon System in the 1980s because of all the issues with the M21/ART II. The argument was always one between the more range-oriented guys and the ones who knew they didn’t want to go outside the wire with a bolt gun even back then. Bolt gun crowd won that argument, thus was born the "too-many cooks in the kitchen" M24 SWS, which is what I used in several units. Interestingly, we still had M21s or NM M-14s in 2 of my Scout Platoons, but with no armorer support and broken ART IIs.

JSOC and CIF Teams in SF started using SR-25s at that time, but they all had 24” barrels. JSOC had some custom 20” barrels made and installed by their armorers already in the late 1990s/early 2000s. A lot of input from those guns went into the Mk.11 Mod 0. They also were chasing 16” SR-25K carbines for all the reasons you cover, since they didn’t need 24” or 20” guns for close target sniper support for assaulters.

In my talks with guys from the STA Platoon community, they said for most of their missions, they left the M40A4/A5s in the compound and just took Mk.11s since you can fight with them.

SF tested 16” uppers with a carbine stock kit after that for what was labeled the M110K.

Most teams were using SCAR-Hs by that time for a heavier support weapon/DMR in 7.62 NATO.

What everyone has been chasing is longer range performance from a package you can still fight with.

That would look like an AR-15 sized platform in carbine format that is lightweight and easy to do CQM/CQB with, while also matching or exceeding the 7.62 NATO platforms at distance.

That’s why I really started latching onto 6.5 Grendel once I saw what a short barrel even would do past 800yds. It made me feel like I had been cheated all those years of humping an M24.

I call it the Light Sniper Concept, where you have an AR-15 chambered in something that actually reaches out with authority and retained energy on-target. I quickly lost interest in 7.62 platforms after that.

certainly why it's offered in the 6.5cm version now, although i still like being able to shoot inexpensive m80 ball while ranges beyond 800 yards are not all that close or convenient, and certainly not a big priority for me personally.

 

[schmi015]

This is one of the only videos I’ve seen that starts to get to the heart of the matter of what I’ve been trying to convey over the past 19 years.

I remember when the Army was looking for a new Sniper Weapon System in the 1980s because of all the issues with the M21/ART II. The argument was always one between the more range-oriented guys and the ones who knew they didn’t want to go outside the wire with a bolt gun even back then. Bolt gun crowd won that argument, thus was born the "too-many cooks in the kitchen" M24 SWS, which is what I used in several units. Interestingly, we still had M21s or NM M-14s in 2 of my Scout Platoons, but with no armorer support and broken ART IIs.

JSOC and CIF Teams in SF started using SR-25s at that time, but they all had 24” barrels. JSOC had some custom 20” barrels made and installed by their armorers already in the late 1990s/early 2000s. A lot of input from those guns went into the Mk.11 Mod 0. They also were chasing 16” SR-25K carbines for all the reasons you cover, since they didn’t need 24” or 20” guns for close target sniper support for assaulters.

In my talks with guys from the STA Platoon community, they said for most of their missions, they left the M40A4/A5s in the compound and just took Mk.11s since you can fight with them.

SF tested 16” uppers with a carbine stock kit after that for what was labeled the M110K.

Most teams were using SCAR-Hs by that time for a heavier support weapon/DMR in 7.62 NATO.

What everyone has been chasing is longer range performance from a package you can still fight with.

That would look like an AR-15 sized platform in carbine format that is lightweight and easy to do CQM/CQB with, while also matching or exceeding the 7.62 NATO platforms at distance.

That’s why I really started latching onto 6.5 Grendel once I saw what a short barrel even would do past 800yds. It made me feel like I had been cheated all those years of humping an M24.

I call it the Light Sniper Concept, where you have an AR-15 chambered in something that actually reaches out with authority and retained energy on-target. I quickly lost interest in 7.62 platforms after that.

Oh, You mean 6ARC?

 

[Bigjake83]

Hey Guys, just wanted to share the beginning of a little project I am working on this year. Basically I am reviewing a series of semi-auto sniper systems in context to their design and function. This lack context is something that I've always though gets lost in the noise of a lot of reviews. We decided to start with the Mk20 earlier this spring but got a little tied up. The next up in the queue for semi-auto precision platforms (in no particular order):

1. Knights SR-25 ACP
2. LaRue OBR
3. JP LRP
4. LMT MWS (if I can get dig one up)

Anyways hope some of you might get something out of it. If nothing else stay for the blooper reels, sadly the editor cut the other 72 minutes of me trying my best to not be a mouth breathing retard, Lol!

Thanks for taking the time to put together these reviews, these are definitely trying times with limited supply on ammo and reloading components. I'm been putting together a review on the Seekins SP-10 for about six months now. Getting the initial first impressions on the rifle as it comes from the factory was easy but the wait times for the custom Bartlein Barrel from Craddock due to the high demand of his product has taking up a bit of time but it's showing to be well worth the wait. Here are a couple 5rd Groups with 40.8grs H4350/140 ELD/FGMM 210/ Starline Brass.

 

[LRRPF52]

Oh, You mean 6ARC?

Yes, that is the cartridge to beat for this.

It feels like shooting a 5.56 to me, and you get flatter trajectory with less recoil, so it’s perfect for CQM/CQB, while making hit probability much higher than 7.62 NATO at distance, with much better supersonic reach as well even comparing 18” barrels to 24” .308 Win.

Retained energy still favors the 175gr M118LR at closer ranges, followed by anything 123-130gr in Grendel, then the 105s-115gr in 6mm, some of which will start to overtake Grendel way downrange.

Recoil/sight picture management is 5.56 > .224 AR > 6mm Grendels (6mm AR, Turbo, Fat Rat, ARC) > 6.5 Grendel > 6.5-08s (.260/6.5CM/6.5x47L) > 7mm-08 > .308 Win/175gr.

Barrier defeat is 7mm-08 154-162gr =/> 139-142gr 6.5-08s > 6.5 Grendel 123-130gr =/> .308 175gr > 6mm Gren 115gr > .224 AR >>> 5.56x45.

You can get overlap for barrier defeat between 7.62 NATO, 6.5 Grendel, 6mm Grendel, and .224 AR depending on projectile construction and weight, but all of them are pretty impressive and substantially superior to 5.56.

The 7mm and heavier 6.5mm bullets have excellent barrier defeat due to momentum and retained energy from the higher BCs.

There is an EPR for 6.5mm but not publicly available.

You can hear the difference in impact loudness on steel between the small bores 6mm and less, vs the 6.5mm and larger. 130gr high BC 6.5mm even from the Grendel hits harder than 168gr .308 due to momentum. 175gr M118LR gives a nice big “DANK” when it hits within 600yds though. 77gr Mk.262 is barely audible sometimes in the wind once you get out there, with not much effect on target.

Then there is the whole angle of soldier’s load and practical round count he can carry. That favors:

5.56 > .224 AR > 6mm Grendel >> 6.5 Grendel >>>>>> 6.5-08 >/= 7mm-08> .308

When you stack several mags in a chest rig or PC + battle belt, you quickly see the difference.

After looking at all the downrange actual performance of the .224 AR, 6mm Grendel, and 6.5 Grendel, you really don’t see a lot of merit in any of the .308-sized cartridges, unless you’re strapped to that logistics chain and then that’s what you get.

 

[Bigjake83]

Yes, that is the cartridge to beat for this.

It feels like shooting a 5.56 to me, and you get flatter trajectory with less recoil, so it’s perfect for CQM/CQB, while making hit probability much higher than 7.62 NATO at distance, with much better supersonic reach as well even comparing 18” barrels to 24” .308 Win.

Retained energy still favors the 175gr M118LR at closer ranges, followed by anything 123-130gr in Grendel, then the 105s-115gr in 6mm, some of which will start to overtake Grendel way downrange.

Recoil/sight picture management is 5.56 > .224 AR > 6mm Grendels (6mm AR, Turbo, Fat Rat, ARC) > 6.5 Grendel > 6.5-08s (.260/6.5CM/6.5x47L) > 7mm-08 > .308 Win/175gr.

Barrier defeat is 7mm-08 154-162gr =/> 139-142gr 6.5-08s > 6.5 Grendel 123-130gr =/> .308 175gr > 6mm Gren 115gr > .224 AR >>> 5.56x45.

You can get overlap for barrier defeat between 7.62 NATO, 6.5 Grendel, 6mm Grendel, and .224 AR depending on projectile construction and weight, but all of them are pretty impressive and substantially superior to 5.56.

The 7mm and heavier 6.5mm bullets have excellent barrier defeat due to momentum and retained energy from the higher BCs.

There is an EPR for 6.5mm but not publicly available.

You can hear the difference in impact loudness on steel between the small bores 6mm and less, vs the 6.5mm and larger. 130gr high BC 6.5mm even from the Grendel hits harder than 168gr .308 due to momentum. 175gr M118LR gives a nice big “DANK” when it hits within 600yds though. 77gr Mk.262 is barely audible sometimes in the wind once you get out there, with not much effect on target.

Then there is the whole angle of soldier’s load and practical round count he can carry. That favors:

5.56 > .224 AR > 6mm Grendel >> 6.5 Grendel >>>>>> 6.5-08 >/= 7mm-08> .308

When you stack several mags in a chest rig or PC + battle belt, you quickly see the difference.

After looking at all the downrange actual performance of the .224 AR, 6mm Grendel, and 6.5 Grendel, you really don’t see a lot of merit in any of the .308-sized cartridges, unless you’re strapped to that logistics chain and then that’s what you get.

It's really hard to beat the all around performance of a 20" Grendel pushing the 123's inside of 800 yards. In all honesty I could comfortably replace all my .223's and 308's with one do it all Grendel. All my Grendels are utilizing Craddock Precision Bartlein Barrels and have exceptional accuracy with Hornady black and hand loads.

 

[PBWalsh]

Stop this gibberish about 6/6.5s, I don’t want to spend more money!

 

[FatBoy]

, unless you’re strapped to that logistics chain and then that’s what you get.

This.

I may be wrong, but it seemed to me that this was within the spirit of this eval project. What can be accomplish as issued.

What you laid out above is spot on, but with the exception of a couple pointy units nobody is seeing anything except 308Win or 5.56. Maybe the new SAW will change shit up and open up a new option but I have my doubts. I will say, serving under Clinton and going through all the Bullshit we did then, I would not want to carry a weapons system that relied on the government to have their shit together to property source and distribute an oddball cartridge.

For us at home, the 6 Grendal makes a lot of sense. A 95gr TMK is no shit.

 

[LRRPF52]

A “DoD entity” has already gone the direction I’ve been talking about for years.

The lessons-learned and discussed here are more applicable to the private sector since the big services make their decisions based on PEOs who serve for maybe 2 years at a time in various projects before moving onto another assignment, and traction rarely builds behind any of the useful programs.

The video in the OP gives many examples of the challenges faced with a 7.62 NATO platform when trying to cover down on something you can fight the close quarters and distance fights with well. With 7.62 NATO, it does a mediocre job at both due to weapon weight, recoil, bulk, ammo weight, limited basic load, difficult follow-up shots both close-in and far, muzzle blast, etc.

If we were to take all of the cartridge/rifle/optic combos and run them through the MEUSOC CQC and 21 Gun Salute drills, the 6mm AR/ARC would most likely rise above the rest, along with 6.5 Grendel and .224 AR (.224 Grendel).

A lightweight 14.5"-18” barrel AR-15 chambered in any one of the High Performance Intermediate Rifle Cartridges with high BCs would easily out-perform the larger frame guns even when you put a 20” pipe on the 7.62 NATO.

As things evolve and shooters get more time on the Grendel and 6mm AR, you will see a gravitation towards shorter barrels and suppressors basically trying to get as close to a Mk.18 as possible, but with excellent DMR performance.

There’s not a big difference in performance between an 18” 6mm AR and a 13.7”.

 

[PBWalsh]

What kinda velocities are y’all seeing with 6 ARC, and 6.5 G in 13.9/16” barrels?

 

[blbennett1288]

@LRRPF52 My understanding, was that they were staying with the large frames and going the 6.5CM shorty route. Specifically, higher twist rates and 14.5” for a do-it-all rifle package.

 

[556nateo]

Has anyone swapped out gas jets in their mk20 for suppressed use? I just picked up a couple from PMM. Would be nice to hear what others settled on.

 

[theLBC]

Has anyone swapped out gas jets in their mk20 for suppressed use? I just picked up a couple from PMM. Would be nice to hear what others settled on.

most folks from the fn forums will keep going smaller until it stops locking back, and then go up one or two sizes.

 

[LRRPF52]

@LRRPF52 My understanding, was that they were staying with the large frames and going the 6.5CM shorty route. Specifically, higher twist rates and 14.5” for a do-it-all rifle package.

There was a slide presentation from SOCOM talking about a 6.5mm SSR to complement the 6.5mm Assault Machine Gun.

The 6mm ARC is a different organization with leaner and faster acquisition capabilities/priorities, with much smarter leadership and SMEs driving systems development and testing.

 

[blbennett1288]

@LRRPF52 I am not a SME, but ballistic engines and Normalizing Factor show that a short 6.5CM (14.5”) would be more effective than a 6 ARC (18”). I guess the arguement could be made that it is “as effective” to 700 yards as the short 6.5CM.

6.5CM 140gr Hybrid
G7 0.311, 2600fps, NF=809

6ARC 108gr ELD-M
G7 0.3, 2630fps, NF=789

 

[LRRPF52]

You won’t be shooting a 140gr 6.5mm from a short barrel 6.5CM at 2600fps. You’re looking more at 2400fps for 6.5CM/14.5”.

Then there’s the magazine size and soldier’s load penalty based on cartridge size/weight.

Hornady’s data for the ARC puts a 105gr at 2550fps from an 18” barrel AR as well.

You get more rounds for less weight in the same amount of space on your gear, with flatter trajectory and plenty of energy on-target, with the ease of tracking the shot through the optic for distance, as well as running the smaller AR like an M4 in CQM/CQB where you can still fight with it with negligible handling compared to a 5.56 carbine.

If I was configuring a 6.5CM carbine for that, it would be with at least a small frame receiver set and I would shoot 123gr or 130gr, maybe 135gr. I would seriously consider a Proof barrel, use an A5 RET, slap on a Gen 3 1-10x Razor, all FDE Cerakote. I’d still be stuck with the large magazine and ammo weight penalties.

 

[blbennett1288]

You won’t be shooting a 140gr 6.5mm from a short barrel 6.5CM at 2600fps. You’re looking more at 2400fps for 6.5CM/14.5”.

Then there’s the magazine size and soldier’s load penalty based on cartridge size/weight.

Hornady’s data for the ARC puts a 105gr at 2550fps from an 18” barrel AR as well.

You get more rounds for less weight in the same amount of space on your gear, with flatter trajectory and plenty of energy on-target, with the ease of tracking the shot through the optic for distance, as well as running the smaller AR like an M4 in CQM/CQB where you can still fight with it with negligible handling compared to a 5.56 carbine.

If I was configuring a 6.5CM carbine for that, it would be with at least a small frame receiver set and I would shoot 123gr or 130gr, maybe 135gr. I would seriously consider a Proof barrel, use an A5 RET, slap on a Gen 3 1-10x Razor, all FDE Cerakote. I’d still be stuck with the large magazine and ammo weight penalties.

I am shooting my 16” .308’s at 2500fps with mild handloads. M118LR is 2450-2470fps depending on lot out of bolt and semi. 2550-2600fps out of a 16” .308 is doable with the right components and load. I have zero doubt 2600fps is doable out of a short 6.5CM. Per inch of reduction in barrel length is roughly 20-25fps

105gr and 2550fps is going to have worse ballistics and normalizing factor that what I posted. I shoot 105’s in comps out of a 6BR at 2900fps and inside of 700 I dont think there is a better combination, but running 105’s-123grs (Grendel/ARC) sub 2650fps you aren’t doing yourself any favors.

With the 6.5CM short you have 1 mil less dope, better wind bucking ability, and almost double the energy and are still supersonic at 1k.

I went down the 6.5 Grendel path with a JP. It was a solid shooter but the 123grs in a 6.5 Grendel are severely under powder in my opinion.

 

[LRRPF52]

123gr from Grendel basically gives you 175gr SMK trajectory from the .308 Win, but with half the recoil, I found. Much easier to connect when comparing AR-10 to AR-15 Grendel and see your impacts.

A 14.5” 6.5CM gas gun will spit a 130gr at anywhere from 2460-2560fps, and a 123gr optimistically at 2575-2675fps. I would shoot those instead of 140s.

In my 22” .260 Rem gas gun, I found that the 139-142gr class of bullets really push the limits of the cyclic rate when I try to load to reasonable velocities, so it really shines with 130gr VLD. I don’t recall if I really went past 2700fps with 140gr or 142gr, and .260 has more case capacity than 6.5CM.

I’m using internal ballistics models with tons of real world numbers where you can change the barrel length, charge weights, case volume, and bullet weights to determine very accurate velocity data when you change the barrel length from a known load. It has been spot-on with all of these cartridges in the real world when I confirm, usually within 15fps or less.

There are also some barrel length cutting tests with real numbers to correspond/confirm. Keep in mind that’s a bolt gun as well. Look at the 140s:

That’s where I’m getting my predictions for 14.5” 6.5CM rather than a linear assumption of x fps per inch of barrel. This is why I said you won’t be shooting 140s from a 14.5” 6.5CM at 2600fps.

We’ve had a lot of really good threads on this subject: 18” vs 22” vs 24” 6.5CM gas gun

I think a 14.5” 6.5CM tuned right in a small frame (like Colt 901, Savage MSR-10, Mega MA-TEN SF, or Remington R10 ERASR) would be great if that’s the ammo in the logistics chain. I’d prefer the 130gr or less with a really high BC.

 

[LRRPF52]

Mega MA-TEN SF before the sale to ZEV.

 

[Naaman]

Yes, that is the cartridge to beat for this.

It feels like shooting a 5.56 to me, and you get flatter trajectory with less recoil, so it’s perfect for CQM/CQB, while making hit probability much higher than 7.62 NATO at distance, with much better supersonic reach as well even comparing 18” barrels to 24” .308 Win.

Retained energy still favors the 175gr M118LR at closer ranges, followed by anything 123-130gr in Grendel, then the 105s-115gr in 6mm, some of which will start to overtake Grendel way downrange.

Recoil/sight picture management is 5.56 > .224 AR > 6mm Grendels (6mm AR, Turbo, Fat Rat, ARC) > 6.5 Grendel > 6.5-08s (.260/6.5CM/6.5x47L) > 7mm-08 > .308 Win/175gr.

Barrier defeat is 7mm-08 154-162gr =/> 139-142gr 6.5-08s > 6.5 Grendel 123-130gr =/> .308 175gr > 6mm Gren 115gr > .224 AR >>> 5.56x45.

You can get overlap for barrier defeat between 7.62 NATO, 6.5 Grendel, 6mm Grendel, and .224 AR depending on projectile construction and weight, but all of them are pretty impressive and substantially superior to 5.56.

The 7mm and heavier 6.5mm bullets have excellent barrier defeat due to momentum and retained energy from the higher BCs.

There is an EPR for 6.5mm but not publicly available.

You can hear the difference in impact loudness on steel between the small bores 6mm and less, vs the 6.5mm and larger. 130gr high BC 6.5mm even from the Grendel hits harder than 168gr .308 due to momentum. 175gr M118LR gives a nice big “DANK” when it hits within 600yds though. 77gr Mk.262 is barely audible sometimes in the wind once you get out there, with not much effect on target.

Then there is the whole angle of soldier’s load and practical round count he can carry. That favors:

5.56 > .224 AR > 6mm Grendel >> 6.5 Grendel >>>>>> 6.5-08 >/= 7mm-08> .308

When you stack several mags in a chest rig or PC + battle belt, you quickly see the difference.

After looking at all the downrange actual performance of the .224 AR, 6mm Grendel, and 6.5 Grendel, you really don’t see a lot of merit in any of the .308-sized cartridges, unless you’re strapped to that logistics chain and then that’s what you get.

How does 6.8 (spc, in particular) stack up for similar applications?

Been considering getting an alternative caliber upper as a general purpose/dmr hybrid for a small frame lower. Based on what you're saying here, now I'm thinking about 6arc or 6.5 grendel.

But the "must have" for me is that whatever I pick, it has to be compatible with a mil spec lower.

 

[LRRPF52]

How does 6.8 (spc, in particular) stack up for similar applications?

Been considering getting an alternative caliber upper as a general purpose/dmr hybrid for a small frame lower. Based on what you're saying here, now I'm thinking about 6arc or 6.5 grendel.

But the "must have" for me is that whatever I pick, it has to be compatible with a mil spec lower.

6.8 gives you more retained energy on-target within 300yds compared with 77gr, but with lower hit probability.

It does a bit better than 7.62x39 for barrier defeat, but is more of a 25-300yd rifle range cartridge, not ideal for DMR. If they had chosen .257” for the bore diameter, the .30 Remington-based SPC cartridge would have had a lot more potential in the long run. COL and case length limit it inside the AR-15 to where it’s very difficult to fit high BC projectiles in it and still work inside the AR mag well.

25 DTI (The 100gr NBT and 80gr TTSX have the best profiles for a DM cartridge, but are still really limited in BC. 100gr NBT is .393 G1 BC, which is better than the 77gr SMK, but marginally.) The 25 DTI can generate some really fast speeds with 80-90gr, but those .257” bullets are typically short/low BC.

5.56 70gr Barnes TSX and later M855A1 solved the barrier defeat within that range, while Mk.262 solved the light DMR requirements SOF was looking for without sacrificing magazine and ammo compatibility within a sub-unit already equipped with M4A1 carbines.

My opinion is that if you’re going to need a different cartridge/magazine system, the performance of the cartridge should justify the change with demonstrable increases beyond 300yds. That’s where 6mm and 6.5 Grendel sell themselves, along with the compactness and lightweight of the AR-15 receiver set.

 

[Naaman]

6.8 gives you more retained energy on-target within 300yds compared with 77gr, but with lower hit probability.

It does a bit better than 7.62x39 for barrier defeat, but is more of a 25-300yd rifle range cartridge, not ideal for DMR. If they had chosen .257” for the bore diameter, the .30 Remington-based SPC cartridge would have had a lot more potential in the long run. COL and case length limit it inside the AR-15 to where it’s very difficult to fit high BC projectiles in it and still work inside the AR mag well.

25 DTI (The 100gr NBT and 80gr TTSX have the best profiles for a DM cartridge, but are still really limited in BC. 100gr NBT is .393 G1 BC, which is better than the 77gr SMK, but marginally.) The 25 DTI can generate some really fast speeds with 80-90gr, but those .257” bullets are typically short/low BC.

5.56 70gr Barnes TSX and later M855A1 solved the barrier defeat within that range, while Mk.262 solved the light DMR requirements SOF was looking for without sacrificing magazine and ammo compatibility within a sub-unit already equipped with M4A1 carbines.

My opinion is that if you’re going to need a different cartridge/magazine system, the performance of the cartridge should justify the change with demonstrable increases beyond 300yds. That’s where 6mm and 6.5 Grendel sell themselves, along with the compactness and lightweight of the AR-15 receiver set.

Awesome, man. Thanks.
Maybe I'm just spending too much time on the forums and succumbing to the idea that I "need" a "better" caliber. One of the things I try to maintain is compatibility across applications as much as possible (hence, the small frame requirement).

I've been wanting to do a Mk12-ish build for a while, and originally assumed that 262 would be the food for it. My recent reading has opened my mind to other stuff, but it's one of those situations where there is so much information available, that it's hard to sort it all out (for me).