Jump to content
308AR.com Community
  • Visit Aero Precision
  • Visit Brownells
  • Visit EuroOptic
  • Visit Site
  • Visit Beachin Tactical
  • Visit Rainier Arms
  • Visit Ballistic Advantage
  • Visit Palmetto State Armory
  • Visit Cabelas
  • Visit Sportsmans Guide
Sign in to follow this  
Big Bore

.30HRT, another TJ winner!

Recommended Posts

Another but less well known .30 cal for the AR-15 platform is the .30 HRT originated by Marty ter Weeme of Teppo Jutsu.  It is a 6.8 SPC case, necked up .308.  You make it by running the 6.8 case through a .30 Herrett sizer die (Hornady dies have a tapered expander so no need to neck them up to .30 first), and trimmed to a maximum case length of 1.610 (TTL to 1.605).  I have just started working with it but am getting 2594.4 fps with a Hornady 110 gr. VMAX and will start work with the 110 gr. TTSX next week, followed by 125 gr. Nosler Ballistic Tips.

Three shot groups at 100 yards with a 2400 fps load gave me .177 inch groups while at full throttle,  the 2600 fps load gave me 1.095 inch groups.

You can either have a barrel made from SBR or you can have any .300 BO barrel rechambered.  I am not interested in shooting sub-sonics, that's what the .338 Spectre (another TJ innovation) is all about, and used a Wilson 7.62 x 40 barrel as the host.  Big mistake.  I did not take careful enough readings and the chamber would not clean up so my smith had to set the barrel back and index a new barrel extension to make everything line up, but he did it (I'm sure cussing me every step of the way) and it works like  dream.  Thanks Thomas (Paladin Machine Shop Service). 

My barrel was CAR gassed and a 1:12 twist.  Too slow for subsonic use but works just fine for what I need since I will not be going over 125 gr. 

When converting another barrel to .30 HRT, first make sure you get the twist you want and the gas position you want.  And if buying from Wilson, make sure you get what you order because someone there is not on the ball.  In my case, I am glad they were not.  I ordered a 16 inch lightweight midlength 1:12.  I got it, turned it around to Thomas, and when I got it back, only then did I notice that it was not a midlength gassed barrel like shown on their web site, and as described on their web site, but rather a CAR gassed barrel.  HAZAA for me because CAR gassed is what I wanted in the first place, but since Wilson did not list a CAR gassed 7.62 x 40 barrel, I settled for the midlength.  Worked out great for me but it might not for someone else.

Of course, you need a 6.8 bolt and mags.  ARP has a great 6.8 Super Bolt and my PRI and CP (old company CP) mags work perfectly.

Also, keep an eye on the gas port.  Most 30 HRTs seem to like .086 gas ports.  Mine from Wilson had a .076 and would not run at all.  Once I got to .082 it ran with IMR 4198 but nothing else.  I went ahead and took it to .086 and it still will not run with H110 or IMR4227 (feeds and ejects fine but bolt will not lock back), but runs like a scalded dog with IMR4198 so that's what I am sticking with, however, with IMR 4198 I could have stopped with .082 so am a little over gassed at .086.  It still runs fine with standard CAR buffers, H, 2H, and even 3H buffers plus the 3H buffer corrects for the slight over gassing some.  At .082 and with IMR4198 a standard buffer is all you need. 

So, if you are looking for a .30 caliber that will go faster than any other .30 cal out there except for the .30 RAR (which as we all know, is not exactly a true AR-15 upper) and you do not mind a little wildcatting, the .30 HRT is quite an interesting round.  It bests the .30 BO and the 7.62 x 40 by quite a bit with all bullet weights, and of course, if you want to go subsonic, get a 1:8 twist and shoot anything you want.  And if you want to push 240 gr. SMKs faster than subsonic, you can do that too, or any other bullet weight you want.  While 110 gr. bullets might suffer from the mythical over stabilized condition, they are reported to shoot just fine in the 1:8 as they do in a 1:10, 1:11, or in my 1:12.

Good shooting!

th_HRT-1.jpg

2373 fps

th_HRT-2.jpg

2594.4 fps

Share this post


Link to post
Share on other sites

After some more playing, it seems that the ejection is best with a 2HB using the .086 gas port along with IMR4198.  I found that a maximum charge capacity, not pressure, is 28.5 gr. for 2605 fps and MOA groups.  However, the ES with all loads is more than I like, between 30 and 50 fps, plus, anything over 27.5 gr. is compressed and at 28.5 gr. I have to use a drop tube, trickle, and vibrate to get the powder level down far enough to seat a bullet and it still comes up over half way up the neck resulting in a lot of compression.

I switched over to H4198 and using a drop tube the powder comes up the bottom of the neck, so H is more dense than IMR.  Another load work up is in order with H4198 and we'll see if it gives me the velocity I want along with acceptable accuracy and a lower ES.  If it does, I can likely work up to at least 29 gr., possibly 29.5 gr. and see what happens.  If, and I know it's a big IF, I can top this out at 2700 fps with acceptable accuracy and no pressure signs with that little 110 gr. TTSX bullet, this doll baby is going to be a screamer.  And if H4198 does not do it, I may just try some magnum primers and work up again.  I have found that often the addition of a magnum primer is similar to adding a full grain of powder, so if that is the case here and pressures allow, that might just get me to 2700 fps. 

A nasty cold is keeping my old butt at home this week so with Christmas coming up and my son coming home, I doubt there will be any range time for load work up until after the first of the year.  Stupid cold... 

Share this post


Link to post
Share on other sites

Definitely give magnum primers a try...the magnum primers give me better velocity

out of my 6.5mm PCC wildcat when using ball powders like H335. Just use common

sense and start a little lower on your charge weight when using magnum primers.

If your your using some of the faster stick powders like H4198 or RL-7, use caution

as you will reach peak pressure sooner vs. non magnum primers with the same

charge, so you will have to reduce the charge slightly when using the faster

stick powders with the magnum primers.

Hope this helps...YMMV.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...