PDA

View Full Version : Sierra 77 grain HPBT MK versus Hornady 75 grain BTHP...ballistic coefficients


RuggedTerrain40
07-01-2011, 07:09 PM
I was reading up a little on the differences between these two .223 match rounds. And based exclusively on the Hornady published ballistic coefficient of .395, it appears to beat out Sierra 77 grain BTHP MatchKings. I was reading today in the Sierra manual those have a ballistic coefficient of between .362 to .372.

Now, how can a slightly lighter bullet shoot straighter? Obviously, aerodynamics? And is this really what you see in the field at the range? I got a custom wind chart for 75 grain BTHP Hornady (not the .223 A-MAX) today from Champions Choice and they have that round listed as being good all the way out to 600 yards. Honestly, I find that hard to believe it would shoot well all the way to 600, the 75 grain A-MAX, maybe. But the 75 grain BTHP? Id have to see it to believe that.

The other Champions Choice wind charts I got were for 77 grain Sierra MK/80 grain Sierra MK. Those have 77 grain grain Sierra MK listed for 200 and 300 yards and 80 grain Sierra MK for the 600 yard stuff. When I flipped the CC wind chart over for the Hornady 75 grain BTHP and saw it listed for 600, I was mildly stunned...and honestly skeptical.

Eric

78jeep
07-01-2011, 07:43 PM
their are several folks that shoot 75's or 77's back at 600. the AMU and the All Guard Team a few years ago all got a bad batch of 80's. so they shot 77's all the way back. I believe the Marine team normally shoot 77's all the way back anyway. generally they have to come up a few clicks from the 80's they normally shoot. the 80's do help in the wind a bit more than the 75 / 77's, but I've seen 198's shot with 77's. 600 is all about reading the wind more than what bullet you have. also bare in mind these 75/77's are really hauling the mail.

78jeep

abeal
07-01-2011, 08:35 PM
You could even shoot 69s at 600. They might not handle the wind as well as the heavier rounds but you will hit the target. It is not uncommon for people to use 77s at 600.

RuggedTerrain40
07-01-2011, 08:58 PM
their are several folks that shoot 75's or 77's back at 600. the AMU and the All Guard Team a few years ago all got a bad batch of 80's. so they shot 77's all the way back. I believe the Marine team normally shoot 77's all the way back anyway. generally they have to come up a few clicks from the 80's they normally shoot. the 80's do help in the wind a bit more than the 75 / 77's, but I've seen 198's shot with 77's. 600 is all about reading the wind more than what bullet you have. also bare in mind these 75/77's are really hauling the mail.

78jeep

Yeah I have heard of people shooting 77s across the course, but never heard of Hornady 75 BTHP across the course. But you say some do it, I believe you. I guess what I should have said is I find it hard to believe the Hornady 75 BTHP would buck the wind well enough at 600 to mess with, it would be much easier to use the 80 grain Sierra at 600. My understanding of the Hornady 75 BTHP match round is it is more of a 300 to 200 yard round.

I was also reading up on the Hornady/Sierra .308 match rounds and they have higher ballistic coefficients than any 80 grain and below .223 round. For example, the Hornady 168 A-MAX has a BC of .475 and Sierra's 168 MK has a BC of .462 to .447.


Eric

raymeketa
07-01-2011, 09:13 PM
With the BCs being so close, I doubt if there is any ballistic difference between any of the bullets out to 600 yards. That tells me that whatever preferences shooters may have has to do entirely with accuracy. Two bullets with identical BC will be indentical ballistically, but not necessarily show identical accuracy.

Ray

78jeep
07-01-2011, 09:30 PM
I knew one guy that shot 75g Hornadays (not A-Max) back at 600. he was a High Master. he didn't do quite as well as the guys with 80's, but he was close. he also got his DR metal too. his load was real hot, he only got 2 loads with new brass, sometimes only one load.
all that said, most folks use 80's at 600.

78jeep

RuggedTerrain40
07-01-2011, 10:48 PM
I knew one guy that shot 75g Hornadays (not A-Max) back at 600. he was a High Master. he didn't do quite as well as the guys with 80's, but he was close. he also got his DR metal too. his load was real hot, he only got 2 loads with new brass, sometimes only one load.
all that said, most folks use 80's at 600.

78jeep


Maybe I will use 75 grain Hornady for reduced course stuff and 300 yard stuff. And use 80 grain Sierra for 600 yard line. I just found it interesting, because you hear an awful lot about 77 grain Sierra on ARs, but not as much about 75 grain Hornady BTHP...although its what CMP sells and its inexpensive but high quality factory match ammo. I mean, when I saw what CMP was selling cases of Hornady 75 BTHP for at Butner, my jaw dropped and I double blinked. Kind of had me wondering if there is not really that much difference in the BCs of the two, why not just use the Hornady 75 BTHP bought off the e-store for 200/300 yard stuff? And handload the 80s for anything farther out to 600?

Eric

HANDYMAN
07-02-2011, 12:14 AM
I use the 75 A-max at 600 and can hold the 10 ring when I do my part. I like it better than the 77gr sierra MK. I use 24gr Varget and load it just off the rifling. 2.420 col in my RRA NM.

RuggedTerrain40
07-02-2011, 12:36 AM
I use the 75 A-max at 600 and can hold the 10 ring when I do my part. I like it better than the 77gr sierra MK. I use 24gr Varget and load it just off the rifling. 2.420 col in my RRA NM.

Yeah, I believe that. The 75 A-MAX is a different AR round than the 75 grain BTHP. You ever used the Hornady 80 grain A-MAX for 600?

Eric

Gewehr43
07-02-2011, 01:03 AM
I shot alot of the BHA- 75 BTHP, before I really started reloading and yes out to 600yds-- shot very well. I tried it in a 1000yd match- not so much. :) It seemed to run out around 7-800 yds.
I do use SMK 80's now at 600yds. BTW prior to shooting an AR, I shot alot of 168 SMK's out of my M14, and when I switched I found, as a general observation, that my wind corrections were not that far off between the two.

Dave Stitz
07-02-2011, 10:13 AM
Over on the NM forum they had an informal poll. 6% used the hornady 75 gr hpbt. 9% used the 75 hornady Amax. 10% used 80 hornady Amax. 47% used the 80 smk.
Also what has not been mentioned is that the Hornady 75 & 80 Amax bullets can not be loaded to magazine length. Single load only.

Dave

Unclenick
07-03-2011, 10:49 PM
You can learn to estimate BC's from the shape of a bullet and its sectional density, and some manufacturers do that. Others just measure it over a short range near the muzzle velocity. Usually that gives a more favorable number, as most modern pointed bullet shapes tend to have higher G1 BC's at higher velocities. Sierra has a 300 yard indoor range, so they can do more thorough testing, and that's why they are able to offer the more accurate multiple BC's. It's not that other bullet makes don't have them, they just don't measure them. The reliance on estimates and short range measuring can sometimes mess you up, though. Nosler's underestimate of their own 77 grain bullet's BC is an example.

Bryan Litz's book, Applied Ballistics for Long Range Shooting, includes a long list of bullets from many manufacturers that he measured the BC's of between 1500 and 3000 fps. This is very valuable because it means you had the same equipment and the same operator measuring them all. He is able to show his estimates are accurate within about 1%.

I have the first edition of his book, which does not include the Hornady 75 grain BTHP. However, if I adjust it by the same percentage their claimed A-max BC came down in Litz's measurement, it gives the same average as Litz measured for the Sierra and Nosler, and I expect it is close. Litz added more bullets to the list for his second edition. Perhaps it is there?



Company Claim Litz Measured Average
Sierra 69 gr. MK .308 (average) .331
Hornady 68 gr HPBT .355 .331
Sierra 77 gr. MK .360 (average) .371
Nosler 77 gr. HPBT .340 .377
Hornady 75 gr. A-max .435 .414
Sierra 80 gr. MK .404 (average) .425
Hornady 80 gr. A-max .453 .452

(my proportioned estimate)
Hornady 75 gr. BTHP .395 .376

Dirty_25
07-04-2011, 09:42 PM
Sierras will shoot good far out. I was at a new range that has a Unknown distance course out to 850yrd. I was about 90% on the 650yrd target, I ran out of adjustments at the 850 target and couldn't get the right holdovers to hit it. My friend grabbed my rifle and hit the 850 5 times out of 20. I shoot a lot of the SMK 77g bullets and really like them. For a cheaper alternative I get the 75g prvi bullets from Wideners, and they are pretty accurate also.