I think I might have found it. Thank you AR15.com
https://www.ar15.com/content/page.html?id=647 Author: Forest
Last Updated :: 7/15/2010 12:48:35 PM EDT
FAQ by Krochus with additions and comments by Marty ter Weeme of Teppo Jutsu
30 HRT FAQ
Introduction to the 30 HRT
The 30HRT or Herrett Tactical Rimless is a wildcat cartridge based on the 30Herrett of TC contender fame. But rather than forming cases from rimmed 30-30wcf you form cases from 6.8spc (remember 30rem or 30-30rimless is the parent case for SPC). While this cartridge is a wildcat with no factory ammo or SAAMI pressure spec it's a somewhat domesticated wildcat in that there is plenty of load data and reloading dies readily available from most major manufacturers.
History of the 30 HRT
The original team that developed the 6.8 x 43 SPC cartridge looked at a variety of calibers using the same case during their development phase. Versions ranging from .223 caliber (reminiscent of the .219 Donaldson Wasp) up to .308 caliber were explored. The ideal cartridge in terms of the team's performance requirements was a 7mm cartridge similar to the old .280 British in terms of exterior ballistics, but this would require an intermediate case size not suited for the AR-15. Seeking to be able to offer a cartridge that better matched their performance requirements that also fit the AR-15 platform, the team chose the 6.8 x 43 version based on the .30 Remington case. This version offered the exterior ballistic performance, while sized to fit the AR-15 and not sacrificing too much magazine capacity.
After the 6.8 x 43 SPC made its debut, the wildcatting community naturally took to coming up with its own versions. In the past, .30 Remington wildcats had been tried in the AR-15 before, most notably the 7 x 40mm. Among the "new" wildcats tried were the aforementioned .219 Donaldson Wasp, with limited success. Comparing the case size of the 6.8 x 43 SPC to other cases suggested that the shortened .30-30 wildcats developed by Steve Herrett would be a natural progression. Among these, the .30 caliber version, known as the .30 Herrett, seemed to be the logical choice. Not only would it allow use of the plethora of .308 caliber bullets, but it would still fit the SPC magazines and offered a decent starting point for load development due to plenty of .30 Herrett load data being available.
Another aspect that made the .30 Herrett version of the 6.8 x 43 SPC attractive was that this version would allow taking existing .300-.221 Fireball barrels and cleaning up the chamber to the new cartridge. This was particularly useful for some of the .300-.221 Fireball AR-15 barrels with carbine length gas systems as that length gas system is not ideally suited for use with the 240-grain Sierra Match King subsonic load in the original Fireball chambering. By going to the larger SPC case, more powder capacity is available for a slower burning powder, making it possible to get full reliability with the 240 SMK loads AND a carbine gas system. As such, the .30 Herrett version seemed ideal and this wildcat of the 6.8 SPC (and originally of the .30-30) was given the moniker .30 HRT for Herrett Rimless Tactical.
Later, with the advent of various piston operating systems for the AR-15, the desire was to use these piston systems with the .300-.221 Fireball. Initially, no commercial piston systems were offered with the pistol length gas system, which would prevent retrofit of many of the .300.-221 Fireball barrels to piston operation. Furthermore, several of the piston systems appear(ed) not to be able to function with the .300-.221 Fireball, even with loads that will rip the rims off a case if used in a traditional DI system. The larger .30 HRT offered the right amount of gas volume to operate the piston systems, both in supersonic loads (like the 110 Vmax) as well as subsonic loads with the 240 SMK.
Below are pictures of a 16" barrel AR-15 with Adams Arms piston system and YHM suppressor mount. This system will run anything from the 110 Vmax loads to the 240 SMK loads, including suppressed. The ability to switch the amount of gas to the piston system is ideal for this set up.
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Comparisons to 7.62x39mm
The natural and most obvious comparison to make with this round is to the 7.62x39 Russian as bullet diameter and case capacity are both almost identical. While it's obvious the x39 wins in availability of ammo,uppers and barrels there are several distinct advantages the 30HRT holds in comparison.
- Much wider, cheaper, more modern and available bullet selection with almost universally higher BC's
- A case shape that's much better suited to the AR15 magazine and mag well resulting in a much more reliable upper.
- A much stronger bolt, the reduction in case taper also helps here
- Stronger and all round better brass to work with. SAA and Hornady 6.8 cases are very good cases comparable to lapua 7.62x39cases only they last over 3x as many loadings
- Three and Four combine to allow even the cautious handloader to really outstrip the velocities possible from the Russian cartridge. I'm not going to share specific load data but 200fps over what 7.62x39 can do with the same bullet weights is very achievable.
- This one's debatable but IMO the more pronounced shoulder on the HRT provides more positive headspace and lends to a generally more accurate cartridge although I'll admit you might really end up splitting hairs to prove it.
What is the trim length for the brass?
The official length is 1.610”
How do I resize the brass?
More important than trim length is shoulder set back as this cartridge head spaces on the shoulder. Experienced reloaders will know what this means, but for those that do not – you have to set up your dies such that when you full length size the brass after firing, you do not push the shoulder back down the case. If you were to do so, the case would still chamber, but likely FAIL upon firing. Not a huge issue, just a pain. I have had several do this, before I got my dies dialed in properly. Sometimes the shell holder can make al the difference needed …. I run my dies all the way down to where the fully contact the shell holder and this works for me but again; there are variances in shell holder thickness which can cause problems.
Making 30HRT cases (by Krochus)
Case forming is a pretty straightforward process. Lots of lube and if available the use of a form/trim die can greatly simplify things.
For me the case forming process takes a few distinct steps:
- Run a NEW (used cases have a very high failure rate due to neck cracking on initial fireform) 6.8spc case into the form/trim die and cut off the excess with a hacksaw and them chamfer
- Size this partially formed case in your 30Herrett die
- Finish trim to 1.695" (I prefer to trim shorter)
- You might get by without this step with new cases but I prefer to anneal before loading
- Load and fireform using a mid to full powered loading
Using the above method I've got cases that are on their 7th full powered load with no signs of brass thinning or excessive stretching.
What bullets can I use?
As stated above, just about any .308 diameter bullet, ranging from 110 grains to 240 grains is what we have found out there. Cast lead could be used, but we would recommend limiting the number of cast lead bullets as the lead may foul the gas system. Seating depth can be a bit of a challenge with some of the heavier bullets. NOTE that the crimping groove on many .308 caliber bullets was designed with a totally different cartridge in mind. Therefore, the crimping groove will likely NOT line up with the case mouth when seating to an overall length that fits in the magazine (or chambers).
What about crimping? Bullet set back?
Crimping is recommended to prevent set back of the bullet due to recoil or during the feeding process. I tend to put a light crimp on my loaded rounds with my CH dies and have not encountered an issue … yet.
Propellants and loads
Powders that are well suited to 7.62x39 seem to work equally well in the HRT. There's lots of 30Herrett data available but much of it is fairly low pressure in difference to not stretching TC contender frames. I personally use 7.62x39 data as a starting point for my loads. However I make no claims whatsoever as to what actual chamber pressures are. It's up to the individual handloader to work up their own loadings.
Typical powders include Hodgdon H110, Winchester Win296, Norma N200, Alliant Reloder7, IMR4198 and VVN110.
What bullets can I use?
Just about any .308 diameter bullet, ranging from 110 grains to 240 grains is what we have found out there. Cast lead could be used, but we would recommend limiting the number of cast lead bullets as the lead may foul the gas system. Seating depth can be a bit of a challenge with some of the heavier bullets. NOTE that the crimping groove on many .308 caliber bullets was designed with a totally different cartridge in mind. Therefore, the crimping groove will likely NOT line up with the case mouth when seating to an overall length that fits in the magazine (or chambers).
Where do I get dies?
The .30 HRT is loaded using standard .30 Herrett dies with a shell holder made for the 6.8 SPC round. This is convenient as any major reloading supplier stocks or can easily order .30 Herrett dies.
Can I load these using a Dillon progressive?
You sure can. The fine folks at Dillon can help you with specifics.
Velocities and External ballistics
Thus far I've worked up what I would call two distinct varieties of loadings, Short range 30-30 replicating thumper loads and lighter faster bullet loads that you could think of as 7.62x39 +p+. All loads reflect a 20" bbl
using my AA1680 125g Sierra proHunter spitzer loading @ a MV of 2625fps based on a 200yd ZERO
@100yds.. +2.0 .. 2310fps... 1481ft lbs
@200yds.. - 0-.... 2018fps... 1130 ft lbs
@300yds.. -10.6.. 1737fps... 838 ft lbs
IPSC PF: 328.12
My other load is a 150g REM RN intended for 30-30 over a charge of H335 @ a MV of 2350fps
@100yds... -0-... 1933fps... 1245 ft lbs
@200yds.. -8.0.. 1568fps... 818 ft lbs
IPSC PF: 352.50
What type of velocity can I expect?
Velocity will vary from rifle to rifle and obviously also depend on the bullet that is being loaded. Some of the velocities recorded from a 16” barreled upper are as follows:
110 grain bullet – about 2500 fps
125 grain bullet – about 2200 fps
168 grain bullet – about 1800 fps
240 grain bullet – about 1000 fps
What is the shortest possible barrel?
The typical short barrel upper will have a 10.5” barrel; you can’t go much shorter than that and still have the gas system work.
What lower, stock, other parts can I use?
The .30 HRT was designed to work with as many mil-spec components as possible and requires no special parts other than the barrel. Any of the lowers out there that meet mil-spec should readily accept the .30 HRT. The only dedicated items required that are not "standard .223” are the bolt and magazines.
Magazines
The .30 HRT, unfortunately, will NOT work with standard .223 Remington caliber GI/Mil Spec magazines. Specific, dedicated magazines are needed and magazine capacities vary for the different size magazines. As mentioned earlier, with the market acceptance of the 6.8 SPC there are now many options for magazines. Essentially any quality 6.8 SPC dedicated magazine will work with the .30 HRT. Stick with quality manufacturers such as PRI, Barrett, and CP Products and you should be good to go.
Where can I buy an upper?
At this time we know of several folks offering this caliber including White Oak Armament.
External 30 Herrett links
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Below: 125g Sierra Pro Hunter loaded into a C-Products 10rd 6.8 SPC mag. The loaded length shown reflects the limitations of the rifling engagement for my upper and not magazine length.
