6x45 Twist Rate

[Dr. Tad Hussein Winslow]

This cartridge is making a comeback, with Corbon making 3 loads for it, and Black Hills supposedly about to make 3 loads for it. There are also several AR15 makers who make barrels and/or complete uppers for it. Robinson Armament is considering production of 6x45 barrels for their XCR at this time (easy swap), if there is enough interest in it. If you didn't know, it's a very user-friendly "semi-wildcat", but not really a wildcat anymore as now it's standardized. Friendly in the sense that you use the same mags, same bolt, same everything, as your 5.56x45mm rifle (no swapping of anything except barrel, unlike 6.5 grendel, 6.8 spc, .30 RAR, etc.). It also uses any old plentiful .223 or 5.56x45 brass to make the brass from - no fire-forming is necessary - just expand the neck then go.

My question is this: Les Baer (and others) can and will make you a barrel/upper in either 1 in 8" twist or 1 in 9.5" twist. According to Les Baer's website, the 8 twist is for "100 gr and up bullets" and the 9.5 twist is for "less than 100 gr" bullets.

However, my question is, which of those two twists would you choose if planning to use these two rather longish bullets, creeping up on 100 grains:

1. Speer 85 gr Spitzer BT SP, and
2. Sierra 90 gr Game King FMJ BT

For a self-defense type (and possibly deer hunting) carbine, where uber-accuracy is not required, but of course good accuracy is always required???

Thanks. I'd imagine it's like 5.56x45 barrels, where there's little to no downside to erring on the side of tighter twist, but potentially a big downside to erring on the side of less twist, no? I'm thinking 8 twist, especially in light of the fact that I *might* try to use a Speer HotCor 105 and a Hornady SST 95.

Thanks.

Dang it, I forgot to make my poll!

 

[Dr. Tad Hussein Winslow]

Update -according to what I've found so far...

6x45 Barrel and/or complete upper makers:

-- AR15barrels.com
-- Les Baer
-- American Spirit Arms
-- High Standard
-- DTech
-- IDT gunsmithing in Ohio on a Douglas bbl (by special request)
-- White Oak Armanent (by special request)
-- Shilen (by special request)
-- (possibly) Olympic Arms (they may have discontinued making)

others?

 

[Ed Harris]

When I built my 6x45 years ago I only had a 9" twist, as nothing faster was available at the time. It worked OK with the 100-gr. Hornady RN bullets and 85-gr. Sierra HBPTs, but wouldn't stabilize the 105-gr. Speer Spitzer well enough to enable bullets to expand, instead they tumbled through deer like Ball ammo. Still killed them, but I would have rather had an 8" twist as used on the early 6x45mm XM732 ammo for the prototytpe Squad Automatic Weapon.

 

[Maverick223]

When I built my 6x45 years ago I only had a 9" twist, as nothing faster was available at the time. It worked OK with the 100-gr. Hornady RN bullets and 85-gr. Sierra HBPTs, but wouldn't stabilize the 105-gr. Speer Spitzer well enough to enable bullets to expand, instead they tumbled through deer like Ball ammo. Still killed them, but I would have rather had an 8" twist as used on the early 6x45mm XM732 ammo for the prototytpe Squad Automatic Weapon.

I believe that Doc. is referring to the newer 6x45mm (also known as the 6mm-223), rather than the 6x45mmSAW.

I would go with the 8" twist, the whole purpose of the 6mm is heavy bullets (for a better SD and BC). I think that the 8" would be fine for 85gr. and above, but I am just speculating as I have no experience with either 6x45mm cartridge.

 

[Dr. Tad Hussein Winslow]

is referring to the newer 6x45mm (also known as the 6mm-223), rather than the 6x45mmSAW.

Correct, lately the 6mm-.223 was standardized as the 6x45mm. It can be formed straight from .223 / 5.56 brass. Not the SAW round, but there is understandable confusion with it also starting out with 6x45....

The 6x45 is the ".20 Practical of 6mm cartridges", being formed directly from .223 brass (whereas the .204 Ruger and 6x47mm are each formed from .222 Mag case, respectively, in .20 cal and 6mm).

Nevertheless, experience with the SAW round would still likely be indicative of the 6x45 performance, when it comes to twist rates and bullet lengths, to a large extent, so that is helpful. Definitely think 8 is the way to go.

 

[Maverick223]

I'd imagine it's like 5.56x45 barrels, where there's little to no downside to erring on the side of tighter twist, but potentially a big downside to erring on the side of less twist, no? I'm thinking 8 twist, especially in light of the fact that I *might* try to use a Speer HotCor 105 and a Hornady SST 95.

Sounds like a plan...expecting a report of the new rifle when complete...with pictures...because "A thread without a pictures is like a gun without ammo. Somewhat interesting but not nearly as useful or as much fun!".

 

[M1key]

Talked with Adam Treisman of Spirit Gun Mfg. He prefers 8.5" or 9" twist rate for his proprietary (and very expensive) military/LE AR rifles and carbines.

He is very impressed with the Barnes 62gr Varmint Hand Grenade bullets (for LE/military applications) and the Hornady 85gr BTHP bullets (for hunting) ahead of H4198 or H322 powders.

 

[MetalHead]

Not so hard, 8 to 1 for High Power and other long range target shooting events, 9.5 to 1 if you expect the bullet to do something once it gets there, keep in mind that most of the bullets available are made for the higher velocity of the 243 Winchester. I have read several good arguments that the 6x45 does not need a 20" barrel as 18" offers the same bore volume as a 5.56 20", so of course the one I bought used has a 24"tube, good buy as reloading dies came with, no idea of the twist or who made it but I suspect Olympic.

 

[Float Pilot]

The 6mm-223 was developed back in 1965. Around 1983 I knew a few guys who had Mini-14s re-barrel for this cartridge. I think they had 1 in 9 or 1 in 9.5 twist rates. They used them for zapping caribou. It was an improvement over the old 55 grain 5.56mm round for game critters. And the old .223 Mini 14s could only have 55 grains or less.

Looking over the hand-loading data, it looks like you need a longer barrel like a 22 inch to get an 80- 85 grain bullet up to 3,000 fps.

I wonder how a 6.8SPC brass would do if necked down to 6mm?

 

[Maverick223]

I wonder how a 6.8SPC brass would do if necked down to 6mm?

I think it would do pretty well, a 6.5mm might be another good combination.

 

[M1key]

Someone on another forum claims 2900 fps out of a 16 incher with Barnes 62gr Varmint Grenades...

I would also be interested in the 6.5x45. I have not found much data yet...

 

[Float Pilot]

There is the 6mmAR, 6mm AR turbo and the 6mm WOA which is a 6.8spc necked down.
BUT, all the above seem to be more accuracy based than velocity based. The guys who shoot them get real hazy on solid facts when it comes to their velocity and pressures.
Plus they are all long range group shooters who have fairly long custom barrels.

 

[Maverick223]

There is the 6mmAR, 6mm AR turbo and the 6mm WOA which is a 6.8spc necked down.

That 6mmWOA seems like a neat little cartridge...I'd like it a whole lot better than its parent case.

BUT, all the above seem to be more accuracy based than velocity based.

See sig. line...accuracy isn't in a cartridge, but rather in the components (bullets, et al), barrel, action, and mostly the shooter. Case design doesn't have a bit to do with it.

 

[rc109a]

I just ordered a White Oak barrel in 6x45 with a 1 in 9 twist (18" SS). I am looking at shooting 80-100g bullets. Think this will do the job?

 

[lobo9er]

what do you think of 1in7 ?

 

[Uncle Mike]

My question is this: Les Baer (and others) can and will make you a barrel/upper in either 1 in 8" twist or 1 in 9.5" twist. According to Les Baer's website, the 8 twist is for "100 gr and up bullets" and the 9.5 twist is for "less than 100 gr" bullets.

1/8" twist-

 

[tailfeathers]

Greenhill calls for a 1in10 for bullets 90 grs and under...IF the velocity can be kept above 2800 fps...I have had my Oly 1 in 10 6x45 barrel since 1991 and I shot 85's for the most part and noticed my group opening up slightly when I went to the Sierra 90 gr fmj...Greenhill actually says an 11 twist is sufficient so I believe I could have remedied that with more load development...I believe it may be right on the edge of having enough velocity to bullet length...I think max loads are needed for heavier bullets...To try and go above 90 gr bullets would require more twist to a 1 in 9 or 1 in 8...But then you lose so much velocity it becomes futile...Its a fun cartridge though...Shoulda been adopted about 1955 if ya know what I mean...

 

[tailfeathers]

Sierra has data for the 6x45 and Lee has quite a bit as well...

 

[Maverick223]

Greenhill calls for a 1in10 for bullets 90 grs and under...IF the velocity can be kept above 2800 fps

There is absolutely no safe way to push it that fast, not with a 90gr. bullet anyway. A .223Rem. can only push a 80gr. bullet to about 2700fps.

 

[tailfeathers]

I reloaded data received from Sierra and chronied my 85 gr loads at an average 2850 fps...Remember when you open the neck for the larger bullet it holds more powder...I've reloaded for 40 years and shot service rifle for 10+ years so I've done this a few times...No pressure signs at all...

 

[Maverick223]

Perhaps I am wrong, but I can't fathom how you can squeeze that much out of one. What length barrel are you running?

 

[tailfeathers]

Its a 20" barrel...I'm wondering if the slower 10 twist is helping with velocity?...They have slowed the 6.8 twist and are getting much higher velocities out of it now...Its been a year or two since I had it out and was just about to get it out and play with it for the spring...

 

[rc109a]

So what about the optimal barrel length?

 

[M1key]

From everything I have read, concensus is that 20 inch barrels fully utilize the best the round has to offer, and no slower twist than 1:10 inches.




EDIT: I plan to build an AR in 6x45 based on a Rock River middie. All I will need to replace is the barrel. This is the cheapest way I have found to get me into the rifle I want...

I am currently looking at Black Hole Weaponry. They offer a barrel that is 18 inch, 1:10 twist, standard profile (.750), blackened stainless, polygonal rifling (poly3), mid-length gas system.

http://www.blackholeweaponry.com/st...id=42&osCsid=266e66bc8183b5f398d486e5ae5825ca

Anyone have experience with them?

 

[Maverick223]

Even a short barrel should do decently well (better than the same in .223Rem.), due to the greater efficiency of the cartridge, but I think a 20"+ bbl would be optimal, after all the primary purpose is to extend the range and velocity counts.