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Thread: 30 HRT

  1. #21
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    I am extremely skeptical of the above chart's validity.

    First off, what are the barrel lengths used for calculation? 300blk uses a saami of 16" where most other calibers use 24". Why would anyone assume those numbers are directly comparable?

    Second, 30HRT is a wildcat. There is NO SPEC for it, so putting it in a chart along with factory 300blk is questionable. Same for the 223 77gr SMK, is that someone's handload or mk262?

    I'm coming off as a defender of 300blk I know, but that's not it. I wouldn't trust those 30-30 numbers, I don't believe 6.8 retains THAT much more energy than 30-30 or 223, etc.

    That chart is extremely suspect.

  2. #22
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    Quote Originally Posted by Noodles View Post
    I am extremely skeptical of the above chart's validity.

    First off, what are the barrel lengths used for calculation? 300blk uses a saami of 16" where most other calibers use 24". Why would anyone assume those numbers are directly comparable?

    Second, 30HRT is a wildcat. There is NO SPEC for it, so putting it in a chart along with factory 300blk is questionable. Same for the 223 77gr SMK, is that someone's handload or mk262?

    I'm coming off as a defender of 300blk I know, but that's not it. I wouldn't trust those 30-30 numbers, I don't believe 6.8 retains THAT much more energy than 30-30 or 223, etc.

    That chart is extremely suspect.
    The chart was generated using JBM's online trajectory/ballistics calculator with the inputs as specified in my reply. The MVs and BCs were taken from MFRs websites (16" BBL for 6.8 SPC and 300 BLK) except for the 30HRT and 223 data. The MV for the former was gleaned from the ARF site, but the BCs are MFR inputs. The latter chronographed by me using Black Hills ammo out of an 18" Noveske barrel and I used Sierra's BC for MV of 2500-2800 fps. Of course, all are G1 BCs.

    There are lots of widely available chrono data on the 6.8 and 30-30, but I didn't spend a lot of time compiling these numbers. As I mentioned, if you have different data than what I used for the inputs, let me know and I'll regenerate the graph.

  3. #23
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    Quote Originally Posted by constructor View Post
    The HRT will push a 130gr to over 2550 from a 16" barrel, the BLK doesn't come "close" to that.
    In the fall there will be more 30 Herrett-AR barrels on the market, we'll see what a 5R 11 twist can do.
    This is typically how these things go - someone says "The such and such wildcat is XXX fps faster than the 300 BLK." What they don't tell you is that they are comparing factory 300 BLK ammo loaded to 55,000 psi and a 2.245 OAL with hot-loaded ammo at 65,000 psi and 2.3 OAL.

    For example, loaded to equal pressure, 7.62x40mm is not the 200 fps faster than the 300 BLK as been claimed, but more like 85 fps faster.

    30 HRT - I am not exactly sure, but a quick QuickLoad simulation is looking like 150 fps faster than 300 BLK if both are loaded to 55,000 psi.

    That being said, I like the idea of the 30 HRT except it would require special magazines, and the brass should be made shorter to be more optimal for the Barnes 130 grain and the Nosler 125 grain bullet. So, if someone does a 30 SPC or 6.8-30, I hope they make this change.

  4. #24
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    Quote Originally Posted by Warg View Post
    There are lots of widely available chrono data on the 6.8 and 30-30, but I didn't spend a lot of time compiling these numbers. As I mentioned, if you have different data than what I used for the inputs, let me know and I'll regenerate the graph.
    Chrono still doesn't mean much if you're direct comparing wildcats, factory saami rounds, and over-pressure loads. 16" and X muzzle velocity doesn't mean anything unless all the rounds are loaded to standard or lesser pressures. If saami spec of the gun is 55,000psi, all that ammo has to be confirmed to be at or under before they can be compared.

    IF that 120gr 6.8 ammo example is over-pressure and that .4 BC is generous, it could start looking at LOT like that 110 300blk round on the chart. Still higher and stronger of course, it's got a larger volume, but is it enough to warrant a custom bolt, magazines, barrel, and no subsonic option? Not for me it's not. That's how I feel about the 30hrt but with even less factory support.

    rsilver's comments about equal loaded pressure are more what I was getting at.

    All that said, my problem is with charts like that that can be VERY misleading to someone who copies and pastes it somewhere without knowing those are apples to oranges comparisons. I understand you mean no harm, but that chart could easily be looked at as fact, and it is not proven to be at all.

  5. #25
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    Hornady would not print specs for overpressure ammo. I would trust their 2460 velocity as valid. The 0.400 BC would need to be checked to be sure.

    300 BLK 110 grain - is 2400 fps at 55,000 psi all day long as verified on SAAMI pressure test barrels. Hornady rates theirs at 2375 fps. 2300 fps is more of a starting load. 2400 fps is the correct number to use.
    Last edited by rsilvers; 05-24-12 at 15:38.

  6. #26
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    I understand what Rsilvers was getting at RE: overpressure.

    Here is an updated graph. I removed the 30-30, 110 gr 6.8 (since the data may be an overpressure loading from SSA) and the 130 gr 300 for simplicity. I changed 300 BLK 110 gr MV to Rsilvers recommendation of 2400 FPS. Additionally, I replaced the 150 gr HRT with 125 gr at 2450 FPS to more or less generate a confidence band for that bullet at two different velocities.



    My comparisons were not meant to compare 300 BLK to 30 HRT, rather 30 HRT to 6.8 SPC as I did not see the benefit compared to the time and hassle to reload. My prior post linking to Dr. Roberts' discussion on page one of this thread further reinforces the point.

  7. #27
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    Quote Originally Posted by rsilvers View Post
    Hornady would not print specs for overpressure ammo. I would trust their 2460 velocity as valid. The 0.400 BC would need to be checked to be sure.
    I didn't see where that was Hornady ammo, my bad. .400 does seem pretty high at least for a .270 bullet short enough to work in a 1:11" twist and fit in an AR mag. I have no idea how one would figure if it's a correct BC. I'm out of my element now, I'll shut up.

    I just didn't feel like that chart was, right. The new one looks much better, but I still have trouble with that 6.8, doesn't look correct compared to the others.

  8. #28
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    There are several ways to check BC. You can shoot it on Doppler radar. You can shoot through two chronographs. You can see if it drops more at distance than calculated. You can time the bullet at various ranges.

    My sense is that the true BC of this bullet is probably close to 0.400.
    Last edited by rsilvers; 05-24-12 at 21:10.

  9. #29
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    Quote Originally Posted by rsilvers View Post
    This is typically how these things go - someone says "The such and such wildcat is XXX fps faster than the 300 BLK." What they don't tell you is that they are comparing factory 300 BLK ammo loaded to 55,000 psi and a 2.245 OAL with hot-loaded ammo at 65,000 psi and 2.3 OAL.

    For example, loaded to equal pressure, 7.62x40mm is not the 200 fps faster than the 300 BLK as been claimed, but more like 85 fps faster.

    30 HRT - I am not exactly sure, but a quick QuickLoad simulation is looking like 150 fps faster than 300 BLK if both are loaded to 55,000 psi.

    That being said, I like the idea of the 30 HRT except it would require special magazines, and the brass should be made shorter to be more optimal for the Barnes 130 grain and the Nosler 125 grain bullet. So, if someone does a 30 SPC or 6.8-30, I hope they make this change.
    Have you tested that 30HRT load for pressure? How do you guess it's 65,000PSI? USWAG? You love to throw that 65 and 70000 psi thing around when anyone states a velocity compared to the 300 Whisper.
    65-70000 psi will seriously mess up a case in a AR.
    A 58,000psi 556 M193 load will swipe the brass and start cratering the primers. I don't know anyone that shoots a load that craters primers as a normal load. 2500fps is a normal everyday load out of an old 308 6 goove 10 twist 16" barrel from 2007. 55-58000psi ...probably
    The 30 HRT uses 6.8 mags not "special" mags.

  10. #30
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    FYI. this is what a 70,000psi proof load looks like after being fired in a AR.

    Last edited by constructor; 05-24-12 at 23:27.

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