No, the 338 ARC is .445" Grendel/7.63*39 parent. The spectre is .421".
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338 ARC
- Thread starter Parham4020
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I,m wondering if 8 twist is sufficient if you want to shoot say 300 gr SMK subsonic?
Here is 300 gr SMK at 300 meters in minus 5 degrees Celsius from a 7 twist barrel:
It’s not making a round hole, and if you look at several bullet holes in the same group, they’re entering whit different angles through the paper
At this point they don’t group well either..
A 10mm Auto is too short to be the parent case of the .338 Spectre, which has a case length of 1.250.
338 Spectre | The Ballistic Assistant
www.theballisticassistant.com
No the 338 ARC is .441-442" the 338 Spectre is .421 to .422" head area diameter. Grindel vs 224 Valkyrie, 6.8 SPC, 10MM Mag pistol, or 30 Remington, cut to length. With a short case their water capacities are very close. With in a grain or two, with only .019" to .020" different in head diameter. How deep the bullet is seated will make a big difference in either case.
No its Starline 10 mm magnum, which are perfect... no trimming just anneal for best results and run through your 338 Spectre FL die $68 per set. Use on all sub loads up to 300 gr SMK then switch to SR cases the highest velocity for supers. They are so cheap ya don't care of ya lose a few.View attachment 8548093
A 10mm Auto is too short to be the parent case of the .338 Spectre, which has a case length of 1.250.
338 Spectre | The Ballistic Assistant
The 8 twist is on the low end for subs with long 300 gr match bullets...a 7 twist should work according to Berger stability calculator.
But that doesn’t matter if you're have trouble.
So try a shorter bullet like the 250 SMK to see if things improve.
Hornady’s 307 gr sub is likely much shorter and will stablize in a 8 twist. But none are available, yet.
Has Hornady said publicly if they were going to release that bullet as standalone component in 2025 ?
Hornady will release components after they get factory ammo up and running. They always do ...just way late and huge shortages, just like all the rest of their cartridge introductions.. Their projected prices for cases is pretty high for such a tiny case.
The SR Spectre brass and 10 mm Mag brass have basically the same case volume#1 & #2.
They all have the same solid head thickness 338 Spectre, 10 MM Mag, 224 Valkyrie, and the 6.5 Grendel.
I used the same collet to mill all the fired cases including the 6.5 Grendel, so the diameters of the fired cases are close enough for one collet to fit both.
So logically the brass head hardness, and alloy, plus firearm design will be the only factors in ability to take pressure, since they are all the same thickmess in the solid head.
They all have the same solid head thickness 338 Spectre, 10 MM Mag, 224 Valkyrie, and the 6.5 Grendel.
I used the same collet to mill all the fired cases including the 6.5 Grendel, so the diameters of the fired cases are close enough for one collet to fit both.
So logically the brass head hardness, and alloy, plus firearm design will be the only factors in ability to take pressure, since they are all the same thickmess in the solid head.
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You'd think not, but it took forever to get 6 ARC brass as a component when it came out... Supply chains and whatnot back then, but still.
The Berger stability calculator uses the miller formula which is not intended for subsonic speed. It’s useless for that application according to Litz. I have not tried the 250 gr SMK or the Scenar/Lockbase, but I have tried to cut down the 300 gr SMK in the lathe. I chopped off 6mm of the tip, ending up with a bullet that looks like Hornady subX in the front.
At this point they make round holes again. Here at 100 meters
And here at 190 meters
I hope Hornady have tested the 338 Sub X thoroughly in 8 twist with Doppler radar before thy released it? Litz says subsonic flight is not yet fully understood, so I guess it’s all trial and error. I have examples of solids from Peregrine bullets that won’t fly straight in 7 twist that Peregrine says are stable in 9 and 8 twist.
All this .338 arc talk made me order a 300 blk barrel and superlative arms gas block. Oops
10 mm mag brass is available I just bought 500 rds, and formed it, and so is SBR SR brass.
The 10 mag brass has been great for subs and really cheap. So I'll use it for subs and moderate loads. The SR SBR brass appears to have a bit more strength so far, and is less than half price of Hornady.
Hornady has not been great brass either and I avoid it as much as possible. So you're right none of this brass is Lapua but it will do, for the intended purpose of the round, mostly subs. Mine is very accurate with a variety of reloads, especially 300 gr SMK.
The 165 gr Maker super expanding bullet hit 2100 fps for a super load along with cheap 200 gr Speer at subs to 1900 fps with SR brass. The pistol brass will not make 1900 fps more than once, so 1750 or maybe 1800 fps would be a good max for it.
So I'm finding out what this brass will handle. May try some cut down 224 Valkyrie brass to see how it works for supers. But for subs the pistol brass works fine...so far in my experience.
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I checked the primer pockets on all these loads they appear as new after 1 firing with subs, and moderate loads, where they are giving excellent accuracy, with pistol primers, then checked the next batch from 2 days ago...all is good on the first loading, 300 gr SMK, 300 gr Maker, 272 gr FMJ plus a bunch of 200 gr Speer.
Out of all the loads I tried I lost 6 cases with too much case expansion on top loads with both primers
Like the 165 gr Maker at 2136 fps one was too loose and the others were a one shot more with the no go gauge, with the SR.
I noticed no case head expansion at all when miked at the case head, with AA 1680 cases came out very sooty as powder gas came back along the case toward the shooter...even felt it.
But velocity was still 1160 fps with the 200 gr Speer. It had large velocity variations and less accuracy...not the powder for light 200 gr subs.
Not very efficient here but I haven't tried it with the 300 gr bullets where it's lower pressure may help you with primer pockets, and the extra bullet weight will help build pressure for a better burn.
I have 50 338 ARC cases coming to check them against the 338 Spectre, for capacity and strength...most likely about equal, but I'll find out.
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Since I have 224 Valkyrie and 6.5 Grendel cases lying around....I decided to make 338 Spectre cases out of them.
The 224 Valkyrie is easy, trim to length, lube, & run through the 338 spectre FL die.
The 6.5 Grendel is a bit more involved for the average reloader.
Cut to length. Turn the sold head to size, blend out and recut extractor groove, lube, size in the FL 338 Spectre die.
Anneal and resize. It goes pretty quick with a lathe once set up.
So the 224 Valkyrie is really easy.
Both chamber in the rifle at the same die setting as the 338 Spectre brass.
For what it's worth, pressures jump pretty fast in this tiny case, so even tougher, harder case headed brass, might not increase velocity much but hang in there longer for a few more firings.
The 224 Valkyrie is easy, trim to length, lube, & run through the 338 spectre FL die.
The 6.5 Grendel is a bit more involved for the average reloader.
Cut to length. Turn the sold head to size, blend out and recut extractor groove, lube, size in the FL 338 Spectre die.
Anneal and resize. It goes pretty quick with a lathe once set up.
So the 224 Valkyrie is really easy.
Both chamber in the rifle at the same die setting as the 338 Spectre brass.
For what it's worth, pressures jump pretty fast in this tiny case, so even tougher, harder case headed brass, might not increase velocity much but hang in there longer for a few more firings.
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The 338 ARC and the 338 Spectre are almost identical, as I suspected earlier.
I jumped on the Spectre to check out these small cased 338s while waiting for 338 ARC reamer, brass etc.
Well the 338 ARC brass arrived, so let's compare it to the 338 Spectre I now have been shooting is very accurate.
Hornady brass is $104 per hundred, Spectra brass is $46 per hundres for SR primer or a bit cheeper for LP primered cases.
Here they are side by side.
The 338 Spectre holds 29.4 grs of H2O,
The 338 ARC holds 30.5 grs of H2O, probably increase a grain when fired, depending on chamber.
Maybe the ARC will have 25 to 40 fps more velocity with supers...but the difference is insignificant...but with good barrels the ARC should be accurate.
The Spectre has been around a long time over 10 yrs I believe.
The Spectre has a 6.5 twist and I have fired bullets from 160 to 350 grs in it.
Hornady has an 8 twist, that may make a difference with the long heavy 300 gr match bullets at sub velocities. Maker already makes a variety of sub and super expanding bullets for the 6.5 twist.
Their 165 gr super expanding is running 2100 fps in the Spectre 16" barrel and supposed expand around as low as 900 fps.
I jumped on the Spectre to check out these small cased 338s while waiting for 338 ARC reamer, brass etc.
Well the 338 ARC brass arrived, so let's compare it to the 338 Spectre I now have been shooting is very accurate.
Hornady brass is $104 per hundred, Spectra brass is $46 per hundres for SR primer or a bit cheeper for LP primered cases.
Here they are side by side.
The 338 Spectre holds 29.4 grs of H2O,
The 338 ARC holds 30.5 grs of H2O, probably increase a grain when fired, depending on chamber.
Maybe the ARC will have 25 to 40 fps more velocity with supers...but the difference is insignificant...but with good barrels the ARC should be accurate.
The Spectre has been around a long time over 10 yrs I believe.
The Spectre has a 6.5 twist and I have fired bullets from 160 to 350 grs in it.
Hornady has an 8 twist, that may make a difference with the long heavy 300 gr match bullets at sub velocities. Maker already makes a variety of sub and super expanding bullets for the 6.5 twist.
Their 165 gr super expanding is running 2100 fps in the Spectre 16" barrel and supposed expand around as low as 900 fps.
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I've wanted to see a NAS3 case for the 6arc for some velocity gains. With the 6 arc gaining steam that could be a future possibility and converting it to 338 arc wouldn’t be too much trouble.
Looks like CMMG is going to adopt it. Would be awesome if they did velocity testing with the factory subsonic load at the different barrel lengths.
I know I'll catch some shit for this, but I actually like the "compliant" version with the magpul SGA stock. Just wish it would fold to be more compact in a deer blind.
I know I'll catch some shit for this, but I actually like the "compliant" version with the magpul SGA stock. Just wish it would fold to be more compact in a deer blind.
Slightly off topic, but if it folded, it wouldn't be compliant.
Now back to your regularly scheduled programming.
I like the 338 Spectre for accuracy and super consistent velocities.
Just new formed 10 mm mag brass or 338 Spectre SR primed brass, loaded in a Dillion progressive, with just a powder measure.
Single digit S/D is the norm.
Outstanding for an AR 15 mag feed autoloader.
Especially when most all bullet powder combinations are like this... it's what is needed to keep from vertical stringing as range increases.
I have a 338 ARC reamer coming Friday, I could rechamber to 338 ARC.
The only problem is brass is pretty weak for supers as another has alluded to in 338 Spectre.... but for moderate supers and especially subs this barrel is a shooter.
Just new formed 10 mm mag brass or 338 Spectre SR primed brass, loaded in a Dillion progressive, with just a powder measure.
Single digit S/D is the norm.
Outstanding for an AR 15 mag feed autoloader.
Especially when most all bullet powder combinations are like this... it's what is needed to keep from vertical stringing as range increases.
I have a 338 ARC reamer coming Friday, I could rechamber to 338 ARC.
The only problem is brass is pretty weak for supers as another has alluded to in 338 Spectre.... but for moderate supers and especially subs this barrel is a shooter.
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These are loaded on a Dillon progressive press with auto powder dispenser, Lee dies and a Lee factory crimp die
10 mm mag brass is sized and loaded in the Dillion, no triming. 338 SR brass is better for high pressure loads and just run it through the Dillion progressive press.
Range day again, for the 338 Spectre....
Loaded it with slightly modified 338 ARC brass and 224 Valkyrie brass.
Both of these brass cases take pressure better.
The 200 gr Hornaday 338 Marlin Express is a low velocity bullet performing in 1800 to 2800 muzzle velocity area according to Hornady.
Seems to work here, but you'd have to check it to see if it's right for you.
The 200 gr Speer at inching up to 2000 fps from this small case with Valkyrie brass, with excellent accuracy and super low S/D for a mag feed AR 15.
There is a lot to like from a case that shoots everything good with low S/D, about best I've ever had in an AR 15.
Spectre brass is a bit weak but cheap, and a non issue with subs, and run supers slower, with cheap lead bullets, or copper bullets, or 300 gr match bullets are accurate.
The diameter of this chamber is a bit oversized, but it doesn't hurt accuracy, but it will be working the brass with sizing.
Can change it to 338 ARC with little effort, since they are almost identical.
Close to a 200 gr 35 Rem in power with 200 gr supers with better BC and penetration.
A fun little cartridge.
Loaded it with slightly modified 338 ARC brass and 224 Valkyrie brass.
Both of these brass cases take pressure better.
The 200 gr Hornaday 338 Marlin Express is a low velocity bullet performing in 1800 to 2800 muzzle velocity area according to Hornady.
Seems to work here, but you'd have to check it to see if it's right for you.
The 200 gr Speer at inching up to 2000 fps from this small case with Valkyrie brass, with excellent accuracy and super low S/D for a mag feed AR 15.
There is a lot to like from a case that shoots everything good with low S/D, about best I've ever had in an AR 15.
Spectre brass is a bit weak but cheap, and a non issue with subs, and run supers slower, with cheap lead bullets, or copper bullets, or 300 gr match bullets are accurate.
The diameter of this chamber is a bit oversized, but it doesn't hurt accuracy, but it will be working the brass with sizing.
Can change it to 338 ARC with little effort, since they are almost identical.
Close to a 200 gr 35 Rem in power with 200 gr supers with better BC and penetration.
A fun little cartridge.
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Here it is 375 / 338 Spectre! ...a 270 gr Speer seated out to give maximum powder space.
A velocity of 1500 to 1550, would be expected max.
The 375 still has a decent sharp case shoulder and would be a fun sub gun in an AR 15.
Now all ya need is a fast twist .375" barrel and a reamer.
The barrel extension and mag mods may be necessary.
Almost there!
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I've formed a case and seated a 400gr Maker.Here it is 375 / 338 Spectre! ...a 270 gr Speer seated out to give maximum powder space.
A velocity of 1500 to 1550, would be expected max.
The 375 still has a decent sharp case shoulder and would be a fun sub gun in an AR 15.
Now all ya need is a fast twist .375" barrel and a reamer.
The barrel extension and mag mods may be necessary.
Almost there!
But validating the case capacity to push a 400gr subsonic bullet is the real test. Get a reamer made. Have dies made from a die reamer and blanks. Validate the case size will work with powders to accurately push a 400gr Maker. That's the real deal. And not cheap.
I have shot the 350 gr Maker in the 338 Spectre, they came in at 824 fps with the powder I chose, a bit under what was predicted.
The 350 gr 338 is 1.975" long, if the 375 400 gr is shorter it may not be a problem at 2.300" for mag max is about 2.310" .
You can run cutout mags if necessary.
The 338 300 Maker was captured at 961 fps on this one.
I do not plan in hunting with the subs I shoot but just have fun with them, and share the information, that might be useful to others, with whatever they are doing.
But this is my hobbie, so I actually do a lot of tinkering
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Mag length won't be a problem in a bolt gun. I'm more concerned about the particular case capacity and powder combination that will be able to propel a 400gr at 1000 and not have a narrow operating window that spikes into pressure real fast. Lil'Gun is more forgiving in a 375 Raptor case than it is in a Spectre case. I've found Lil Gun to pressure spike in the Spectre which is how I blew primer pockets in the soft brass. I could easily neck a Spectre case up, send a dummy round to a reamer manufacturer and have some dies and a barrel chambered. But who knows if the case capacity of the Spectre case will support an easy, multi powder, heavy bullet subsonic cartridge.I have shot the 350 gr Maker in the 338 Spectre, they came in at 824 fps with the powder I chose, a bit under what was predicted.
The 350 gr 338 is 1.975" long, if the 375 400 gr is shorter it may not be a problem at 2.300" for mag max is about 2.310" .
You can run cutout mags if necessary.
The 338 300 Maker was captured at 961 fps on this one.
I do not plan in hunting with the subs I shoot but just have fun with them, and share the information, that might be useful to others, with whatever they are doing.
But this is my hobbie, so I actually do a lot of tinkering
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