I was out this weekend at the range working on an issue with my carbine, while doing that I though I'd run some accuraccy tests.

Recently I've been having accuraccy issues even with 55gr.  So I figured I had some copper build up.  I got out my Otis & Hoppes Copper remove and scrubbed away.  Removed lots of grey gunk and some copper later on.  Beware of only cleaning with a Boresnake - its fine for light shooting - but not for heavy shooting as my patches were showing me.

Barrel:4 year old (with 8K rounds)Bushmaster M4 type (14.5") with 1:9 twist and a KKF A3 'TacBrake'

Conditions: Overcast, high humidity, cool (mid to high 60s), less than 500' ASL

Sight: 6 year old Trijicon Reflex with 6.5 moa dot (this was the biggest limit on accuraccy), sight height is 2.8".  Zeroed for 50 yards with Q3131A.

All shooting was done from a bench (elbows resting on the bench).  Stock was 8.5" long.  All groups are for 5 rounds.

At 50 Yards
South African M1A3 (1986 production):  Group size was 2", centered on the point of aim.

Black Hills 68gr Match:  Group Size was 1.5", center of group was 2.5" below the point of aim.

Black Hills 75gr Match: Group Size was 2.125", center of group was 2.5" below the point of aim.

At 100 Yards
M1A3: (SA) group size was 4"

68gr BH: group size was 2.25"

75gr BH: group size was 3" (Note in my past test I could not get a group or a pattern at 100 yards with 75gr - I think the barrel scrubbing REALLY helped here as the results from the 55gr M1A3 also improved).

I also had a chance to fire at 200 yards but I couldn't take the target home for precise measurments (I used my hands width ~4" to approximate the size) took minimal measurements
M1A3: Group size was 8-9" and it was centered on the target (pretty good imitation of Q3131A).  30 rounds fired.
75gr: BH Group size was also 8" range, but the group was centered about 8" below the target.  No evidence of keyholing was noticed for the 10 rounds fired.

BTW during my other tests I had a chance to try some PMC 55gr.  The one thing I noticed was the other rounds (M1A3/68/75) had no noticable flash - the PMC's flash was very noticable and took up half of the Reflex's field of view.

I also cannot understand why the 68 & 75 groups at 50 yards were so low.  I expected them to be a fraction of an inch low - not 2.5" low.

Edited to fix HTML codes

Interesting. I get pretty similar groups, using Federal GM Match, out of a Colt CAR-A3, which has a 1:9 twist and a 24-inch stainless barrel. Although not rigorous, I think my best groups at 100 yards are with the 69 g. The 75 g produces ragged bullet holes at 100 yards but groups well enough and similar to the 69 g. I've tested 52 g match ammo, and it produced comparable groups and the cleanest bullet holes.

Not for competition, but for combat and self-defense purposes, I think 1:9 might be able to handle 75/77gr. (6 to 8" consistent groups at 200 yards is plenty fine for me)

Oh yes...and thanks for your time testing this stuff [:)]

Forest, that is a cool post. I have been wondering about how and where other, heavier rounds would hit. I never really shoot anything but Q3131a. Very cool.

Thank you for taking the time to post this Forest.

Guys,
Your very welcome.  It wasn't my primary purpose to test the rounds that day - but I figured I had the ammo might as well collect some data.

Troy:
My Reflex is mounted using the Trijicon goosneck mount.  Standard sight Heigh is 2.6", the Trijcon Mount will mount the Reflex 0.2" higher than that - for a total Sight height of 2.8" - this insures the irons are in the lower 1/4 of the Reflex's lens.

When I ran some predicitons with the JBM online ballistic calculator I was using the 2.6" HOB - but the 0.2" difference isn't significant, especially at 50 yards.

If I run the IBSZ at 50y with M193 I get an elevation of 6.26 moa.

If I run the IBSZ at 50y (minus 2.5") with the 68 gr I get an elevation of 1.846 moa.

If I run the IBSZ at 50y (minus 2.5") with the 75gr I get an elevation of 1.902moa.  Final drop at 200y should be 10.9" which is fairly close to what I observed.

My previous calculations showed with an elevation of 6.26 both the 68gr & 75gr should be about .2" low (say a quarter inch) at 50 yards and in the neighborhood of 2" low at 200y.

I don't see how the elevation of the round would change when I didnt' touch the sights.  Its too wierd..

Anyway I just found out Fulton Armory is now carrying Black Hills.  That means I'll have better access to the ammo (good for me) and when I get a change I'll do a dedicated testing of the ammo (complete with chrony results).  I should now be able to get some of the BH 69gr, 73gr & 77gr for testing.

Ok I was out last night to check the fix to the issue with my carbine.

I was also zeroing my new TA50-2 (Compact ACOG, 3x, triangle reticule).  I figured I could also repeat some of the accuracy tests @ 50 yards to see if I could get better groups with the more precise optic.  The scope was mounted to my carryhandle and is roughly 3.5" over the bore.

Barrel was the same (note it still hadn't been cleaned since last week's tests).  The conditions were remarkably similar (almost identical) just a bit darker as it was later in the day.

At 50 yards the South African was just below a 2" group size (I'd guess 1 7/8" since my 'ruler' (multitool) was only marked in 1/4" increments).  Flash was minimal compared to other M193 rounds I've fired - but there was a group  of 'sparks' (in addition to the flame) every time I shot a round.

The 75gr Black Hills Match shot at 2.5".  The interesting thing was the rounds were centered pretty close to the point of aim (with my Reflex they hit low).  The group was slightly to the right of the centerline (about an inch).  In all I fired 20 rounds of this ammo, flash was minimal, but present; it didn't interfer with my sight picture and looked more cylindrical from my point of view.

I didn't bring along any 68gr BH on this outing

I did bring 5 rounds of Black Hills 77gr Heavy Match just to try out.  Group size was similar to the 75gr (2.5"), as was the position (though it didn't seem quite as far to the right).  No sign of keyholing.  Flash pattern was similar to the 75gr, perhaps just a bit less.

FYI the 'fix' (a new gas tube) seems to have solved the issue I was having.

I don't know why last time (with the Reflex) my heavy loads were consistantly hitting 2.5" low and this time (with the ACOG) why they are just about dead on with the 55gr.

I have always expected them to hit near the same at 50 yards.  Perhaps more testing (and use of my bipod) could resolve the inconsistancy.

Thanks Forest. Now hopefully this will debunk the idea that you need a 1 in 7 barrel for the "75gr match ammo that I plan on keeping as my SHTF ammo."

I love this site.  I've seen more rumors and falsehoods banished by this site then anywhere else.

I suppose I should try to de-Copper my 1:9" barrel, before trying to shoot 75 grain Hornadys again.  I couldn't ge them to shoot for crap.

Anytime Vinne.  BTW there was a thread on 1:7 vs 1:9 in the AR Discussion forum.  Big D indicated he could not get the 75gr BH to stabilize at 100 yards - and his was a brand new barrel (only shot to zero it).

For me it was the copper build up.  I'm sure its the case for others, but not everyone.

That was the thread I was thinking about.  I read through it yesterday and thought to myself, these guys are a smooth talking salesman's gift from heaven.  Anyways, to each their own.  I'll stick to my 1 in 9 barrels with inexpensive 55 gr for my SHTF ammo. [:D]

75/77gr ones are really good, but I think we are talking the ones that are loaded hot...and these are EXPANSIVE and not to mention not readily available. (that's as far as I know)

Me too is sticking with Q3131A / 1in9" until U.S Army or Marines adopt 75/77gr BTHP as a standard issue ammunition. I'm always considering my weapons as a general purpose weapon, not special purpose ones. (learned it)

I just don't shoot that well enough to justify it.

No my rounds are the commercial Black Hills ammo loaded to SAMMI pressure.  Otherwise they are identical.  You will get a longer fragmentation range with the NATO pressure stuff.

The stuff I purchases was $18 for a box of 50 of the 75gr, and $23 for a box of 50 for the 77gr for the blue box.  IIRC its about half of what you would pay for the new manufactured version (red box).  I have 2 shops that carry it within 30 minutes of me (one is 5 minutes away).  There are several places to mail order it including Fulton Armory and Georgia Precision.

BTW the 77gr ammo [i]IS[/i] being issued to some spec ops units (Crane has a large order in), and it was just adopted for use by certain units of the the USMC.  So the rounds are in use - they are just not general issue.  BTW you do realize the 'general issue' round of the US Army & USMC is M855?  M193 is limited issue to those reserve/guard units that still have M16A1s.

You are right general issue is M855 but in terms of fragmentation / cost M193 seems better. M193 was a general issue, not now.

I would have to get some 1/7 barrels then.

M855 works just fine in 1/9 barrels.  (The 1/7 was for the super long tracer that went with it.)

But M193 is still cheaper and frags in tissue to longer distances than M855 so it's a better choice for most civilian uses.

And the 75gr does it better, more reliably, and at longer ranges.  Not to mention $18 for 50 rounds won't send you to the poor house.

Assuming it works in your rifle.  BH 75gr blue box is marginally stable in both my 20" 1/9 Bushmater and my Dad's 20" 1/9 Bushmaster.  (Groups about twice the size of M193 vs half the size for 68gr BH.)  Based on this thread it's probably time for me to de-copper mine, but Dad's is brand new (<200 rounds so far) so it's not just that.  

Mike,
You are correct - I noticed the same differences in grouping between the 68gr and the 75gr (see first tests above).

However, the groups the 75gr is producing is fine for its intended use.  I'm not a sniper/marksman etc.  If I want precision either I'd get a 1:7 barrel or switch to the 68gr.

Its not the usual level of AR accuracy but its adequate and the terminal ballistics are hard to beat.

I was looking at 3" groups at 100yds with a 16x scope and a bipod.  I really need to get out to a 200-300yd range and see if they're still stable out there.  In the meantime, I'm going to stick with 68gr BH.  

BTW, have you seen any data on the maximum frag range (or minimum frag velocity) for these yet?  All I've seen are the "definitely better than M193" or "down to xxx at least" proclamations.

Mike I found the 75gr stable at 200y but the group size was getting fairly big (to be fair my dot was 6.5 moa and the target was only 6x9 so the dot was bigger than the target - it was hard to get a consistant point of aim).

I plan on repeating the tests now I have a Compact ACOG (magnification and a more precise reticle).

As for fragmentation range, the TAP load (higher pressure than the BH load) should fragment out to 200y from a 16" barrel (I was recently shown this link at BM [url]http://www.bushmaster.com/le/tests/hornady_tactical_ammunition.htm#gelatin[/url]).  Now the TAP runs 100fps faster than the BH load so that should put the fragmentation velocity in the 2100-2200fps range if the above data is correct.

Mike,
I have in my hands a copy of Hornady's testing of their TAP rounds.  All common AR barrel lenghts from 11 to 24".  I also had an opportunity to talk with a Hornady rep about the rounds.

Fragmentation velocity (for their listed 'Max Performance Range') of the 75gr is roughly 2200fps.  This can vary a bit due to manufacturing tolorances and twist rate from +60fps  to -20fps.  Yes a faster twist rate, FOR THIS ROUND, will help its fragmentation.  At velocities below the 2200fps it will still fragment somewhat but the 'neck' will be longer and penetration will be greater.

What is the velocity for the TAP from a 16" barrel?  Those are SAAMI spec rounds not NATO pressure so I doubt in actuality they are any faster.  Have you chronoed them personally?

Devl,
I have Chrono'd the Black Hills 75gr from a 14.5" and 20".  Their 14.5 figures 2518fps were 3fps faster than my figures.  Their 20" numbers were also in the ballpark compared to mine.

The figure for a 16" barrel (Bushmaster with a 1:9 twist) was 2616fps.  It really amazed me that you get 100fps MORE velocity by going to a 16" barrel over the 14.5" barrel (and 50-75 yards more fragmentation range).  Yet you only gain 37fps (25 yards) by going to a 20" vs the 16".

With this round it looks like a 16" barrel is the optimum choice.

Have you confirmed though that the TAP is hotter than the Black Hills?  I have some Black Hills 75 grain that runs over 2700 fps out a 16" barrel (though Black Hills says this is unusual)  I just want to know what the TAP is actually running vs what they say its running.

DevL.
I have no TAP to test - only Horady's published test results.  However, their test results on the 75gr from 14.5" & 20" barrels are fairly close to my results with Black Hills 75gr (blue box).  The differences between our testing would be 1300' of elevation (they are higher), I tested under higher humidity conditions, and they measured velocity at 21' while I measured it at 15'.

[i]Edited to fix grammer - and to say 'Your Welcome' to Kevin[/i]

Forest, thanks for the efforts...

Hi Forest. Great thread.

Do you have Hornady velocity data for the 68 gr.? I shoot BH Blue 68 gr. from an 18" barrel. If there is no 18" data, I could get kind of close by extrapolating from 14.5,16 and 20" data.
Thanks,
Ed

Ed,
I did, and like an idiot I lost it.  I will be re-running my tests soon along with some of the 'Group Buy' 77gr ammo.

Thanks Forest. Would love to come and joint you with my SPR and run some numbers sometime.
Ed