Surefire ICAR

#51
My polymer 7.62x39 mags have the same width up top as the Six8 PMAGs. They’re both right around 1.010”.

The orifice for the standard AR-15 upper that mates to the mag well is .920”.

NFA 6.8 upper orifice is 1.020” wide.

My 1st Gen MGI QBC upper seems to have standard mag well orifice. I think the 2nd Gen opened up, but I sold the one I had.

iu


They even tried an M14 mag well back in the day, but it didn’t work.

iu
 
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#52
This was the 1st Gen, which is what I got back in 2007.

iu


I actually dipped my toes in the water with 6.5 Grendel first using this in 2009, as I could just drop the barrel in and give it whirl.

I modified my MGI Gen I upper by machining off the 3 & 9 o’clock rails, cut vent slots in it, and profiled the locking lever shafts to be flush with the top of the handguard. Cerakoted it all Coyote Tan.

I later just installed my 1st 16" Grendel barrel in a normal upper.
 
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#54
It might mean I'm a poor, but the ICAR/Six8 developments weren't that interesting to me as long as it was just expensive or boutique manufacturers because they won't really generate a spread of the standard. When PSA jumped in, things got a lot more interesting, if anyone can create a defacto standard through sheer production and distribution numbers it's the folks that basically killed the AR-15 mil-spec "list" by making compliance to it a basic given.
 
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#55
I think I got my New Frontier Armory blem receivers for around $120.

The blem lower was $41 if I recall.

Combine that with PMAG support and it’s not much different than standard parts.

Even their normal retail prices are nothing crazy like a lot of billet sets.

Looks like the lower is $139, upper is $128.

Six8 PMAGs were around $40 each.

We’ll see what the ICAR PMAGs go for, but they’re PMAGs.
 
#56
Proprietary bolt and extension to "solve lug breakage issues". He also said they had zero magazine related issues going to the larger and dedicated mag. I think the rifle will still have a Proof barrel for production. Some other aftermarket parts but a majority is being made in house.

Magpul shows the mags for $40 on their site. https://magpul.com/pmag-25-icar-gen-m3-window.html?mp_global_color=118
 
#57
#58
LRRPF52 said:
This was the 1st Gen, which is what I got back in 2007.

iu


I actually dipped my toes in the water with 6.5 Grendel first using this in 2009, as I could just drop the barrel in and give it whirl.

I modified my MGI Gen I upper by machining off the 3 & 9 o’clock rails, cut vent slots in it, and profiled the locking lever shafts to be flush with the top of the handguard. Cerakoted it all Coyote Tan.

I later just installed my 1st 16" Grendel barrel in a normal upper.
Click to expand...
reminds me of that guy that sawed his lower in half because he was so :mad:🤬🥵
 
#63
LWRCi and New Frontier Armory are already poised to provide the market with options.

It never made sense to me that LWRCi didn’t offer a 6.5 Grendel version of their carbines after they put all the work into the Six8.

Now with a barrel/bolt change, they can capitalize off these magazines.

PSA will drive the price points down as well.

I’m wondering if KAC will jump on-board since they already have an E3.3 bolt/barrel extension solution for this ecosystem of cartridges.

End users will be asking for both the 6mm ARC and 338 ARC full systems utilizing the ICAR PMAGs.
 
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#64
LRRPF52 said:
LWRCi and New Frontier Armory are already poised to provide the market with options.

It never made sense to me that LWRCi didn’t offer a 6.5 Grendel version of their carbines after they put all the work into the Six8.

Now with a barrel/bolt change, they can capitalize off these magazines.

PSA will drive the price points down as well.

I’m wondering if KAC will jump on-board since they already have an E3.3 bolt/barrel extension solution for this ecosystem of cartridges.

End users will be asking for both the 6mm ARC and 338 ARC full systems utilizing the ICAR PMAGs.
Click to expand...
If they could increase the 175gr velocity via pressure that might be true but I'm not yet sold on the 338 ARC... Unless the 338 really expands better than the 30 cal (which I'm not sure it will as I had a friend shoot a deer with a 350L sub and didn't find any blood). I'm hopeful Hornady standardizes the 375 Raptor so we can get legit supersonic and subsonic performance albeit from a large frame
 
#65
rlsmith1 said:
If they could increase the 175gr velocity via pressure that might be true but I'm not yet sold on the 338 ARC... Unless the 338 really expands better than the 30 cal (which I'm not sure it will as I had a friend shoot a deer with a 350L sub and didn't find any blood). I'm hopeful Hornady standardizes the 375 Raptor so we can get legit supersonic and subsonic performance albeit from a large frame
Click to expand...
338 ARC is mainly a subsonic interest for me and I think most everyone who will be getting into it.

Using Nosler ABLR projectile design though, it would be brutal even at the speeds they’re advertising. ABLRs expand down to 1300fps.
 
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#66
LRRPF52 said:
What’s going to happen moving forward I think is that the market will respond with:

22 ARC Rifles
6mm ARC obviously
6.5 Grendel Rifles/Carbines
338 ARC pistols/carbines

PSA just announced a 338 ARC pistol that looks like a Honey Badger.

All 4 of these cartridges are supported with SAAMI specs, dedicated PMAGs, and now an expanding range of rifle manufacturers using the larger mag well AR-15 receiver set.

If it feeds 338 ARC, it will also feed 30 ARX. The only diameters left to mess with in this range are:

20 Grendel
25 Grendel
270 Grendel

Without 2.500” COL, the 25 Grendel doesn’t make sense if you’re wanting to shoot the 131-138gr high BC bullets. I mocked it up already years ago with the Black Jack 131gr ACEs.
Click to expand...
I wonder how fast a 25 Grendel with a 2.5 coal could spit out a 131 ace with an alloy case. Probably would be a Goldilocks round in terms of weight/performence
 
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#69
I don't see it on their site, but I hope Magpul is planning on producing 10 or 12 rd ICAR mags in addition to the 25rd version. My 6 ARCs aren't set up or used for berm hosing duties, when shooting from a bench or mat, or hunting I almost always use a shorter more compact mag (maybe why I've had zero real issues with ASC and Duramags). It would be one thing if I could use an adapter or something to run a standard AR mag in the ICAR magwell if needed, but if I'm stuck with only the new design as an option, I want the size options.
 
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#70
Gtscotty said:
I don't see it on their site, but I hope Magpul is planning on producing 10 or 12 rd ICAR mags in addition to the 25rd version. My 6 ARCs aren't set up or used for berm hosing duties, when shooting from a bench or mat, or hunting I almost always use a shorter more compact mag (maybe why I've had zero real issues with ASC and Duramags). It would be one thing if I could use an adapter or something to run a standard AR mag in the ICAR magwell if needed, but if I'm stuck with only the new design as an option, I want the size options.
Click to expand...
and I'm hoping they go the other way as well, with a true 30 and perhaps even a quad-stack 60 like the ATI/Schmeisser mags.

magpul could do a lot worse than license that design from Schmeisser, I've used the AK and AR 60s plenty and not once had an issue with them, unlike the surefires.
 
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#71
Gtscotty said:
I don't see it on their site, but I hope Magpul is planning on producing 10 or 12 rd ICAR mags in addition to the 25rd version. My 6 ARCs aren't set up or used for berm hosing duties, when shooting from a bench or mat, or hunting I almost always use a shorter more compact mag (maybe why I've had zero real issues with ASC and Duramags). It would be one thing if I could use an adapter or something to run a standard AR mag in the ICAR magwell if needed, but if I'm stuck with only the new design as an option, I want the size options.
Click to expand...

There are 5, 10, and 20 round Six8 PMags, so it seems likely. And if not, there are folks in Grendel community who have converted these mags to work by just filing down the internal ribs a bit by hand.

 
#72
putput30 said:
I wonder how fast a 25 Grendel with a 2.5 coal could spit out a 131 ace with an alloy case. Probably would be a Goldilocks round in terms of weight/performence
Click to expand...
From a 24” barrel, it’s already hard to get a 130gr to do 2500fps with Grendel.

I do think somewhere in that cartridge configuration is the Goldilocks, and is what got my interest when that bullet came out.

I ordered a sample pack of 131gr ACEs and mocked one up in Grendel in 2019:

Left to Right:
140gr Berger I think, 140gr A-MAX, 131gr .257” ACE, 6mm AR, 123gr SST Factory Grendel load

95c4e29c-e3d1-48b0-96c7-2d746df6ac68.jpg


Hornady recently responded to a question about 25 Grendel where someone asked if they could get their new 25 cal high BC bullets up to 2700fps, and they said they tried, couldn’t do it.

So you would need the hybrid or high-strength steel case to to do it.

It would beat or match most of the 6.5 Creedmoor loads when I ran the numbers, so it’s a very efficient combo.

But you end up with mags that are only .3” shorter COL than 6.5CM and .308 Win.

Here’s the 140gr Berger loaded out a little longer at 2.430” with SNJ/Shank-Boattail placement:

7a79edd7-0f44-475f-98f8-48c2d90509f9.jpg
 
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#73
BrianRobeson said:
So I take it we still have no idea whether the bolt will be beefed up or not? Would be amazing to handle closer to bolt gun pressures with 6 arc.
Click to expand...
PSA’s Sabre and Mixtape bolts appear to be knock-offs of the KAC E3.3 bolt with Fosberry Shotgun style lugs and extensions.

I’m still waiting for Surefire bolt/extension details.

Here’s the PSA Mixtape showing their “E4” bolt design. Go to 1:15

 
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#74
Gtscotty said:
I don't see it on their site, but I hope Magpul is planning on producing 10 or 12 rd ICAR mags in addition to the 25rd version. My 6 ARCs aren't set up or used for berm hosing duties, when shooting from a bench or mat, or hunting I almost always use a shorter more compact mag (maybe why I've had zero real issues with ASC and Duramags). It would be one thing if I could use an adapter or something to run a standard AR mag in the ICAR magwell if needed, but if I'm stuck with only the new design as an option, I want the size options.
Click to expand...
There’s a 20rd Six8 PMAG that is perfect for bench.

Seems like a logical SKU evolution in the future if they haven’t planned it already.
 
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#79
Spd37 said:
PSA Youtube short video states they are using larger bolt head, barrel extension, and ICAR lower.
Click to expand...
The bolt visible in the PSA video looks just like a KAC E3 bolt with the Fosberry shotgun style lugs, didn’t look larger overall than a standard 5.56 bolt. This seems to indicate that the barrel extension will also be standard OD, but with corresponding teeth for interface with the lugs. PSA also said they’re using dual ejectors.

This is what a KAC 5.56 E3 bolt looks like:

iu


In the PSA video, the walls in the valleys between the lugs and the bolt face were very thin, indicating standard bolt head diameter.
 
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#82
Spd37 said:
Video clearly states increased lug diameter and barrel extension. I think its different than the KAC bolt
Click to expand...
I think he’s referring to the lug root area, after having heard descriptions of it from other people.

Go to post #73, screenshoot the video at 1:17. It looks just like a KAC E3 with a larger face to accommodate the .441” diameter cartridge family. Pay particular attention to the walls formed between the bolt face and the lug valleys. They are not as thick as 5.56 E3 bolts.

That leans towards standard diameters for outside bolt head dims, and barrel extensions that will fit in standard extension tunnels.

Once we get hands-on, we’ll be able to confirm or deny.

Surefire said they’re using the Six8 receiver set dimensions, which have a standard extension tunnel ID.
 
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#84
LRRPF52 said:
The bolt visible in the PSA video looks just like a KAC E3 bolt with the Fosberry shotgun style lugs, didn’t look larger overall than a standard 5.56 bolt. This seems to indicate that the barrel extension will also be standard OD, but with corresponding teeth for interface with the lugs. PSA also said they’re using dual ejectors.

This is what a KAC 5.56 E3 bolt looks like:

iu


In the PSA video, the walls in the valleys between the lugs and the bolt face were very thin, indicating standard bolt head diameter.
Click to expand...
Any fear of the dual ejector set up weakening the bolt from an engineering and durability standpoint?
 
#85
XLR308 said:
Any fear of the dual ejector set up weakening the bolt from an engineering and durability standpoint?
Click to expand...
Drilling more holes through a high-stress part can’t help, but they are axial to bolt thrust and far enough from the lug roots to not matter. KAC wouldn’t do it if their engineers had not tested all that, and they have excellent engineering staff.

The main areas to look at with AR-15 bolts are the lengths and widths of the lug roots, the cam pin hole, then all the metallurgy with source alloy, how it was formed (Canada has been big on forging bolts for decades on the Diemaco guns, for example.), how it’s machined, how it’s heat-treated, and then batch-tested vs non-destructive testing with HPT and MPI.

The more knowledgeable, successful companies who are known for making bolts that don’t break think the Army’s retarded HPT non-destructive test protocols are counter-productive, so they don’t do them on programs of record overseen by more competent people.

Another thing KAC did was reduce the ID of the cam pin hole and OD of the cam pin, increasing bolt wall strength around the cam pin hole. Lugs and cam pin walls are the 2 main failure nodes on AR-15 bolts. I’ve only broken 5.56 bolts, and they broke at the cam pin hole after over 10,000 rounds of extreme high-volume training sessions, packing 500+ rounds per day.

On Grendel bolts, little changes to the geometry help to gain back lug root strength by modifying radii in certain locations, and chamber pressure is much lower than 5.56 NATO, so even with more normal-looking bolt dimensions, you can have a perfectly-strong bolt that will last.

We also have to acknowledge that the AR-15 bolt was engineered around the .222 Remington cartridge, which is 50,000psi SAAMI MAP. .223 Rem is 55,000psi SAAMI MAP, but did not exist at the time (1957).

I think the KAC/Fosberry bolt lug and extension tooth cross-sectional geometries are a great way to approach the lug root and tooth strength for both components, and they are easy to machine. That should have been the design set-up from the start really.
 
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#86
LRRPF52 said:
Drilling more holes through a high-stress part can’t help, but they are axial to bolt thrust and far enough from the lug roots to not matter. KAC wouldn’t do it if their engineers had not tested all that, and they have excellent engineering staff.

The main areas to look at with AR-15 bolts are the lengths and widths of the lug roots, the cam pin hole, then all the metallurgy with source alloy, how it was formed (Canada has been big on forging bolts for decades on the Diemaco guns, for example.), how it’s machined, how it’s heat-treated, and then batch-tested vs non-destructive testing with HPT and MPI.

The more knowledgeable, successful companies who are known for making bolts that don’t break think the Army’s retarded HPT non-destructive test protocols are counter-productive, so they don’t do them on programs of record overseen by more competent people.

Another thing KAC did was reduce the ID of the cam pin hole and OD of the cam pin, increasing bolt wall strength around the cam pin hole. Lugs and cam pin walls are the 2 main failure nodes on AR-15 bolts. I’ve only broken 5.56 bolts, and they broke at the cam pin hole after over 10,000 rounds of extreme high-volume training sessions, packing 500+ rounds per day.

On Grendel bolts, little changes to the geometry help to gain back lug root strength by modifying radii in certain locations, and chamber pressure is much lower than 5.56 NATO, so even with more normal-looking bolt dimensions, you can have a perfectly-strong bolt that will last.

We also have to acknowledge that the AR-15 bolt was engineered around the .222 Remington cartridge, which is 50,000psi SAAMI MAP. .223 Rem is 55,000psi SAAMI MAP, but did not exist at the time (1957).

I think the KAC/Fosberry bolt lug and extension tooth cross-sectional geometries are a great way to approach the lug root and tooth strength for both components, and they are easy to machine. That should have been the design set-up from the start really.
Click to expand...
Was just curious as I remember all of the mud slinging and shit talk about Grendel bolts breaking in the past although I know there have been dimensional and metallurgical changes to improveme them.
Whether that was bad heat treat, dimensional difficiencies or metallurgical it still gets drug back up from time to time especially with individuals pushing the pressure boundaries of the system.
 
#87
With well-made Grendel bolts, there is a different radius on the back of the lugs, since the barrel extension has a 45˚ relief cut to the bearing side of the teeth for debris clearance and ease of unlocking. They blurred it out here on the call-out, but you can see the 45˚ reference and arrow to that specific location I’m referencing:

barrel-extension-blueprint.jpg


There are also different radii on the sides of the lugs to add root strength, as well as within the bolt face inner wall. Not all companies have done this of course, but the Rexus Grendel bolts have key strengthening features that are not present on others.

Alloy selection, processes, and heat-treating contribute to additional strengthening properties.
 
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#89
MaximusDecimusMeidius said:
So, if a pmag is about 2.260" on the coal and a geissele 6arc mag is about 2.310" on the coal, what could a steel mag that fits in the new receiver size be if made from steel? Is the ICAR PMAG about a 2.300" coal?
Click to expand...
The Six8 PMAGs have an internal raw maximum length of 2.327-2.330”, so you could load to 2.310-2.315”.

If someone makes a metal magazine (this was in the works but was abandoned several years ago), you could get closer to 2.400"

Raw internal length in my New Frontier lower is 2.478”.

Stainless magazine wall thickness is .020”-.025”, so you have to stack all that with clearance.
___________________________________________________________________________________________________________
So from the rear of the mag well limit to the front of the inner mag well, using a stainless steel mag body looks like this:

[ .010” clearance + mag wall thickness .025” + raw internal mag COL + .025” + .010” clearance ]

2.478” - .070” = 2.408"

So that actually brings some longer bullets into play if you went with a steel magazine.

If you set the high BC 131-138gr bullets just slightly back into 2.400” COL in a Grendel case, it will nearly match 147gr ELD-M in 6.5CM.

135gr Berger and 138gr A-TIP have insane BCs in the .25 cal.

Even with the 134gr ELD-M, Doppler Data is showing 1 mil drift at 600yds, assuming 2600fps. You will need at least a 24” barrel to get to that speed. You can get to 2500fps with 24” barrel and 2.285” COL with 130gr VLD in Grendel already.
 
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#90
LRRPF52 said:
The Six8 PMAGs have an internal raw maximum length of 2.327-2.330”, so you could load to 2.310-2.315”.

If someone makes a metal magazine (this was in the works but was abandoned several years ago), you could get closer to 2.400"
Click to expand...
Longer mags and a higher chamber pressure ceiling would bring 130gr 6.5G back into play. There also wouldn't be much point in pushing back the 6ARC shoulder.
 
#91
Cascade Hemi said:
Longer mags and a higher chamber pressure ceiling would bring 130gr 6.5G back into play. There also wouldn't be much point in pushing back the 6ARC shoulder.
Click to expand...
I'd think a 6mm or 25 cal would be just right. At the 2.4" COAL the 6mm probably shines better at long range while still giving great short range performance with lighter bullets
 
#92
LRRPF52 said:
The Six8 PMAGs have an internal raw maximum length of 2.327-2.330”, so you could load to 2.310-2.315”.

If someone makes a metal magazine (this was in the works but was abandoned several years ago), you could get closer to 2.400"

Raw internal length in my New Frontier lower is 2.478”.

Stainless magazine wall thickness is .020”-.025”, so you have to stack all that with clearance.
Click to expand...
Would loading bullets out that far work with standard SAAMI leades?
 
#94
rlsmith1 said:
I'd think a 6mm or 25 cal would be just right. At the 2.4" COAL the 6mm probably shines better at long range while still giving great short range performance with lighter bullets
Click to expand...

Could go either way but you're right. One issue I see is getting a 6G chamber and dies made. ARC pretty well killed all of the Grendel wildcat demand.
 
#95
115 DTACS loaded to 2.400" out of a 6ARC case loaded to 60k psi ...

.620 G1 BC of a 115 DTAC with a 20" at 60k psi I don't know what the velocity would be at that pressure level and barrel length

a man can dream
 
#96
MaximusDecimusMeidius said:
115 DTACS loaded to 2.400" out of a 6ARC case loaded to 60k psi ...

.620 G1 BC of a 115 DTAC with a 20" at 60k psi I don't know what the velocity would be at that pressure level and barrel length

a man can dream
Click to expand...
2625fps, give or take. LVR, CFE, and 2520 look the best. 4064, Varget,, RE15.5, 8208, and AR-Comp work but give up 100fps. RE15 looks really promising, 105% case fill very close to 60k. I have the most experience with 2520 so that is where I'd start.
 
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#97
Cascade Hemi said:
Longer mags and a higher chamber pressure ceiling would bring 130gr 6.5G back into play. There also wouldn't be much point in pushing back the 6ARC shoulder.
Click to expand...
Looking back at my 140gr Berger VLD dummy round loaded to 2.430”, I’m thinking about the 130gr Nosler RDF loaded long.


FOR ANYONE READING THE FOLLOWING, THESE LOADS WERE A PRESSURE EXCURSION EXPERIMENT, NOT NORMAL LOAD DEVELOPMENT
In my initial CFE223 pressure ladder tests from 2012, I got the 123gr A-MAX up to 2698fps from a 16” AA Enfield-rifled Grendel barrel with SAAMI chamber. I was just incrementally loading in steps of .3gr to see where it would finally depart from the trend, not that I was looking for a crazy high-end to load to.

16” 6.5 Grendel AA Barrel, SAAMI Compound throat chamber, Button-Rifled, ER Shaw
123gr A-MAX
Lapua brass
COL 2.272-2.277”
CFE223 Loaded Nov 2012
60˚ F Range Temp in Shade

31.1gr 2489 fps
31.4gr 2520 fps 47,302psi
31.7gr 2572 fps
32.0gr 2553 fps

32.3gr 2572 fps 52,075psi
32.6gr 2598 fps
32.9gr 2612 fps
33.2gr 2640 fps Slight cratering on primer
33.5gr 2698fps Slight cratering on primer

Keep in mind the 123gr A-MAX has a much shorter boat tail than a 107 SMK, 108 Scenar, 123gr Nosler CC, 123gr SMK, or 123 Scenar, so it’s easy to get a lot of powder behind the 123gr A-MAX, now ELD-M.

3d1c74c0-0939-4827-9cea-65f5c63a4651.jpg


The Fort Scott 123gr TUI has a listed .571 G1 BC, and is 1.300” long. It doesn’t look like anything in that picture. It’s really secant with a pointed tip. Their 24” test barrel showed 2538fps with that ammo, which means the monolith is eating up case capacity, and you have to be careful driving it into the lands.

6.5GRENDEL123GR-80_467x600.jpg
 
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#98
LRRPF52 said:
Looking back at my 140gr Berger VLD dummy round loaded to 2.430”, I’m thinking about the 130gr Nosler RDF loaded long.


FOR ANYONE READING THE FOLLOWING, THESE LOADS WERE A PRESSURE EXCURSION EXPERIMENT, NOT NORMAL LOAD DEVELOPMENT
In my initial CFE223 pressure ladder tests from 2012, I got the 123gr A-MAX up to 2698fps from a 16” AA Enfield-rifled Grendel barrel with SAAMI chamber. I was just incrementally loading in steps of .3gr to see where it would finally depart from the trend, not that I was looking for a crazy high-end to load to.

16” 6.5 Grendel AA Barrel, SAAMI Compound throat chamber, Button-Rifled, ER Shaw
123gr A-MAX
Lapua brass
COL 2.272-2.277”
CFE223 Loaded Nov 2012
60˚ F Range Temp in Shade

31.1gr 2489 fps
31.4gr 2520 fps 47,302psi
31.7gr 2572 fps
32.0gr 2553 fps

32.3gr 2572 fps 52,075psi
32.6gr 2598 fps
32.9gr 2612 fps
33.2gr 2640 fps Slight cratering on primer
33.5gr 2698fps Slight cratering on primer

Keep in mind the 123gr A-MAX has a much shorter boat tail than a 107 SMK, 108 Scenar, 123gr Nosler CC, 123gr SMK, or 123 Scenar, so it’s easy to get a lot of powder behind the 123gr A-MAX, now ELD-M.

3d1c74c0-0939-4827-9cea-65f5c63a4651.jpg


The Fort Scott 123gr TUI has a listed .571 G1 BC, and is 1.300” long. It doesn’t look like anything in that picture. It’s really secant with a pointed tip. Their 24” test barrel showed 2538fps with that ammo, which means the monolith is eating up case capacity, and you have to be careful driving it into the lands.

6.5GRENDEL123GR-80_467x600.jpg
Click to expand...
What’s your go to bolt for Grendel? JP ?? There a bolt carrier you like with a cam path that’s more conducive to the Grendel?
 
#99
Bravo6niner said:
What’s your go to bolt for Grendel? JP ?? There a bolt carrier you like with a cam path that’s more conducive to the Grendel?
Click to expand...
My current preferred bolts are Rexus Ultrabolts. They have thicker walls around the lug root ring, and larger radii between the lugs and the bolt head. They also have the added radii behind each bolt lug to increase strength on the back end of the lugs, with more connection to the bolt head.

Bolt bodies are machined completely in one operation (which produces more consistent and accurate tolerances) from tough AISI 9310 VAR (Vacuum Arc Remelt) steel and finished with a tightly-controlled proprietary QPQ heat-treat process to accurately control cast depth and core hardness. Extractors are produced from mil-spec 4140 PH steel and are mil-spec shot-peened and manganese phosphate coated.
Click to expand...

Over the years, I have used:

AA Standard Grendel bolt from 2009
AA Hard Use (many)
Maxim (many)
LaRue
Monster Logo group buy (many)
Just got Rexus Ultrabolts last year

The ones with the highest round counts are my first AA, my Maxim with Lilja 17.6” MLGS, and Monster logo in the 12” CLGS suppressed. LaRue comes after that, 18” MLGS.

18” MLGS tend to be hard on bolts, as are 16” CLGS.

12” CLGS Suppressed with high back pressure cans are hard on bolts too, but I’ve been using Bootleg carriers. I built 2 like that with identical cores, namely barrels, bolts, and Bootleg carriers.

I’ve only used standard cam pin paths in standard dimensioned carriers all along. The LMT Enhanced bolt carrier with extended cam helix would be something to consider for short barrel/suppressed configuration. Bootleg seems to deal with that just fine for me so far. I dropped a Bootleg in the 17.6” MLGS as well.

RLGS/longer barrels will be the least-harsh on bolts, just like with 5.56x45. I have yet to break any bolts or extractors. I also use squared receiver faces to ensure balanced lug engagement with the extension.
 
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6mm ARC for 1k yards build
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SOLD Seekins 6ARC Gasser Rifle with extra parts - Seekins, Proof, Triggertech, JP
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Need some troubleshooting help: Bad Gas Block or Out of Spec Bolt Catch
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