75 Hornady vs. 77 SMK - Real world Test

[skiutah02]

Just sharing some information recently obtained at the range, but have not seen reported here or elsewhere. I developed a good load for my 20" 1/8 Windham AR using Hornady's 75 gr HPBT that I used in 600 yd FTR last summer. I acquired some 77SMKs this winter and was personally wondering which might be better. I needed to redo the load since I got a new barrel and new lot of powder, so I worked up a <MOA load for each. Ended up that the "best" accuracy node for each was the same charge with the same powder, so here is the experiment.

Using fully prepped, 6x fired LC brass that was weight sorted and H2O-capacity sorted, I prepared 17 rounds of 77SMK and 16 rounds of 75 HPBT using same powder and randomly selected cases. Nearly everything was identical except the primer was a BR4 for the 75 and a F205M for the 77SMK. After some fouling rounds on a clean barrel, I shot 10 of each, one-by-one round robin style at a target 300 yds out aiming at the same point. Did not correct for wind or adjust scope. Used a Magnetospeed chronograph to get velocities. The higher MV and higher published BC of the Hornadys showed that the calculated drop would be less for the 75s than the SMK. That did not prove to be true (see picture). The ave MV, ES and SD was with all rounds but the target was inspected and photographed after 10 of each. It is a 3" sticker for reference.

Final analysis: The 75s had more drop at 300 than the 77SMKs, even though calculations gave the opposite. Anybody else observe this?

Drew
Some detail:

300 yd
34oC
5:30-6:30 tailwind switching badly, but 5-6 mph
75 HPBT MV 2752, ES 53, SD 14
77 SMK MV 2724, ES 42, SD 13

 

[rain164845]

Your results are not valid unless both were zeroed independently at a known yardage. For instance, if you shot both loads at 100 and the 77s shot an inch higher than the 75s, you would be starting them on their way about 1moa higher. Does that make sense?

 

[stool]

sd and es too high be a test.
ya need better ammo to start with..
in my humble opinion

 

[skiutah02]

Good point, had not thought of that, but, luckily for me, yes both gave same POI at 100yds.

Your results are not valid unless both were zeroed independently at a known yardage. For instance, if you shot both loads at 100 and the 77s shot an inch higher than the 75s, you would be starting them on their way about 1moa higher. Does that make sense?

 

[skiutah02]

Generally I would agree, but the difference in POI with no comingling of shots is noteworthy? No? Simplistically, I was under the impression that a higher BC combined with higher MV should give less drop not more. Am I missing something?

sd and es too high be a test.
ya need better ammo to start with..
in my humble opinion

 

[stool]

in my opinion...the spread is too(es/sd) big for so few shots....

you need a smaller set of numbers to make a noticeable test with only 10 shots in each lot....tho 300 yds is good.

just my opinion

 

[afrench]

the Litz BCs for those two bullets are:

77SMK: .371 G1, .190 G7

75 HPBT: .357 G1, .183 G7

 

[moorepower]

E.S is huge.

 

[searcher]

You note using two different primers, each would provide their own distinct contribution to ther barrel vibe - and a different position of bullet exit. In other words, you could have loaded the SAME bullet in two groups using the two primers and ended up with the same conclusion - two differently located groups. In this case, the position of the barrel exit was likely in the "up" exit location, producing a group that went up enough to offset the differences in both velocity and coeffecient of the other. If you have ladder tested a LOT, you will surely have witynessed the effect of small inscreases of a charge actually shooting lower, then changing to left, right, etc. - all in "no wind" conditions.

 

[boltman223]

Good point, had not thought of that, but, luckily for me, yes both gave same POI at 100yds.

 

[skiutah02]

I'm trying to wrap my head around this one. I am relatively new to this, and I have explored a number of loads with differing primers effects but with this specific example if both give the same 100 yd POI are you saying that the 75 gr node is a "down node" (my term) and the 77 gr is in an "up node"? I could imagine this to be possible, but I have not read about anyone trying to gain less drop at distance by trying for not only an accuracy node, with low ES and SD, but the "up" node. I am more inclined to agree with the above poster who gives Litz's BC that seem to match my observation (i.e. that the published BC for Hornady's 75 gr is not 0.395 rather a bit lower and below the 77SMK and that Sierra published BC of 0.372 is closer to observed in the field). I would be happy to hear your thoughts and learn more.

You note using two different primers, each would provide their own distinct contribution to ther barrel vibe - and a different position of bullet exit. In other words, you could have loaded the SAME bullet in two groups using the two primers and ended up with the same conclusion - two differently located groups. In this case, the position of the barrel exit was likely in the "up" exit location, producing a group that went up enough to offset the differences in both velocity and coeffecient of the other. If you have ladder tested a LOT, you will surely have witynessed the effect of small inscreases of a charge actually shooting lower, then changing to left, right, etc. - all in "no wind" conditions.

 

[skiutah02]

Thanks for weighing in. You touch on several things that I have also observed but am still wrestling with, the most important one (to me) is that in this AR I very often find a very accurate node but the ES/SD are very high. I am trying to find the magic potion still, and prior to this test thought I might have found it as each of these loads were 21 (75) and 16 (77) for ES for 10 shots (just did an OCW the previous day) and were about <0.5 MOA at 100 yds. This is about the best I can hope to do in this rifle, to be honest. I was expecting that for this test that the ESs would have been the same but obviously they are higher. In my new Savage 308 I can find nodes that are accurate and have good ES/SD (for me anyway, i.e. ES 12 and SD 5), but the .223 is elusive for me. I appreciate everyone's input, just trying to share and learn. I do concede that the POI at 100 yds is probably not EXACTLY the same but very close (within 1/8").

As mentioned by searcher, barrel harmonics may have a lot to do with that result. I would also suggest that unless the 100 yd zero was EXACTLY the same, not just close, that that could also be a contributing factor. Very small differences in the zero will become amplified in the apparent drop at greater distance.

FWIW - 40-50 fps ES is not as bad as you might think for a small cartridge like the .223. It is definitely more difficult to obtain ES values with .223 reloads that are below 15-20 fps than it is for something like a .308, and typical .223 factory match ammo ES values fall in the 40-50 fps ES range. Sure they could be better, but those ES values are not likely to be the sole cause of the vertical dispersion between the two bullet groups. Below are some 15 round 300 yd practice targets I shot a while back with FGMM 77s. In that rifle, the ES for FGMM 77s is well over 50 fps, but they were able to hold very close to 0.5 MOA vertical at 300 yd before the wind came up during the 3rd string (the smallest of the 3 rings etched into the target faces is 1.42"/0.45 MOA).

The OPs two groups (as near as I can tell using On Target) are between 0.5 and 0.6 MOA vertical spread for each individual group. Using velocities of 2725 and 2750 fps (~1/2 the extreme spread) for the 77s, JBM predicts a difference of +/- 0.3" in drop at 300 yd. Clearly, the two groups are a lot farther apart than that, and the ES, although large, cannot account for the difference and should not negate the results of the test. A 25 fps difference in velocity alone just isn't going to change the drop at 300 yd by 3-4" for two bullets that are fairly close in BC, which is how far apart the center points of the two groups are. Therefore it seems likely that another cause like barrel harmonics, 100 yd zero, or possibly other, is responsible.

 

[jhord]

I agree with gstaylorg. .223 is tricky to get low ES/SD's from, I have tried and tried, and mostly failed. But I can get single digits from 6BR/Dasher/.308... so I know it isn't me. I would totally expect to see such a POI change from 2 different bullets at that range. It's barrel harmonics IMO. I just did some extensive bullet/powder testing on my M1A at 50 yards, (easy to get a precise aiming point, results are clear enough to draw conclusions for further, longer range testing) and saw POI changes of nearly 2" just changing powders. Same bullet, same speed, huge POI change. The same would happen with same powder, different bullets. Harmonics.

 

[effendude]

One more thing to consider when chasing ES/SD numbers: The numbers can vary a significant amount simply because you are firing them through a semi-auto rifle. The variables are many. A better test would be to slide the gas tube block forward to block the hole and essentially make the rifle a single shot. This would give you more accurage ES/SD numbers but as soon as you make the rifle functional again, you introduce all those variables inherant to an AR.

Scott

 

[skiutah02]

I agree with gstaylorg. .223 is tricky to get low ES/SD's from, I have tried and tried, and mostly failed. But I can get single digits from 6BR/Dasher/.308... so I know it isn't me. I would totally expect to see such a POI change from 2 different bullets at that range. It's barrel harmonics IMO. I just did some extensive bullet/powder testing on my M1A at 50 yards, (easy to get a precise aiming point, results are clear enough to draw conclusions for further, longer range testing) and saw POI changes of nearly 2" just changing powders. Same bullet, same speed, huge POI change. The same would happen with same powder, different bullets. Harmonics.

While I am relatively new to this area, I have been doing it long enough to appreciate that everything seems to matter . However....I was hoping that pressure and velocity might have some predictable relationship, that pressure and/or velocity with same bullet might have same/similar harmonics in a given barrel, but based upon your observation I am....sad.

 

[skiutah02]

An interesting idea, but I am not "seasoned" enough be this adventurous (yet). I'll have to remember to try this down the road...Drew

One more thing to consider when chasing ES/SD numbers: The numbers can vary a significant amount simply because you are firing them through a semi-auto rifle. The variables are many. A better test would be to slide the gas tube block forward to block the hole and essentially make the rifle a single shot. This would give you more accurage ES/SD numbers but as soon as you make the rifle functional again, you introduce all those variables inherant to an AR.

Scott

 

[XTR]

the Litz BCs for those two bullets are:

77SMK: .371 G1, .190 G7

75 HPBT: .357 G1, .183 G7

Run the numbers in JBM and use these BCs and you'll find that they hit pretty much right where they are predicted to hit.

ntexaslongshot, where did you find the Litz BC for the 75 BTHP, it's not one of the choices for the online JBM calculator. (I like having Litz BCs, they seem to be closer to reality than the advertised versions)

 

[skiutah02]

the Litz BCs for those two bullets are:

77SMK: .371 G1, .190 G7

75 HPBT: .357 G1, .183 G7

Run the numbers in JBM and use these BCs and you'll find that they hit pretty much right where they are predicted to hit.

ntexaslongshot, where did you find the Litz BC for the 75 BTHP, it's not one of the choices for the online JBM calculator. (I like having Litz BCs, they seem to be closer to reality than the advertised versions)

Great, I appreciate all of the wisdom gleaned from these responses. Drew

 

[akajun]

Uhhh, I got a sd of 7 in my woa upper with 24.1 of rl15 behind a 77smk in a lc case with a wolf primer. This was a thrown charge from a uni flow measure with a baffle and micrometer head. I have pretty much swapped over to loading my short line ammo on my Dillon and still get a sd of 13.
These are basic loads for service rifle , nothing special. They will clean the 300yd rapid fire stage and I use a 82 Berger with 24.3 for 600 and have cleaned it as well.
What is the specs on your gun? Specifically your chamber , barrel, and trigger? What ff tube are you using ?
Btw if given the choice between the two, I'd shoot the 77 smk over the 75 just due to wind alone. But if I was going to shoot 600, I'd shoot a Berger 82, or 80.5. They are good for .5 to 1moa of wind at 600 over a 77

 

[skiutah02]

Uhhh, I got a sd of 7 in my woa upper with 24.1 of rl15 behind a 77smk in a lc case with a wolf primer. This was a thrown charge from a uni flow measure with a baffle and micrometer head. I have pretty much swapped over to loading my short line ammo on my Dillon and still get a sd of 13.
These are basic loads for service rifle , nothing special. They will clean the 300yd rapid fire stage and I use a 82 Berger with 24.3 for 600 and have cleaned it as well.
What is the specs on your gun? Specifically your chamber , barrel, and trigger? What ff tube are you using ?
Btw if given the choice between the two, I'd shoot the 77 smk over the 75 just due to wind alone. But if I was going to shoot 600, I'd shoot a Berger 82, or 80.5. They are good for .5 to 1moa of wind at 600 over a 77

The rifle is mostly a stock Windham VEX-SS 20" 1/8 with a Geissele Match trigger and Magpul PRS stock. I used this to shoot F-Class at 600 for two matches last summer with the 75s. In the first match it was totally stock and the second I had upgraded the trigger and the stock. It is a free floated barrel standard and I paid a gunsmith to manufacture a mounting point for a EVO bipod on the handguard. I tried the 80 gr Amax and could not get them stabilized nor the 80 VLD Bergers, but maybe the ones you suggested might work but the chamber is a bit short for the heavies. It is a Compass Lake chamber so it was not long enough to try jumping the VLDs in the pattern they describe, but did try them jammed and about 0.015" off, and with varget or TAC they would not shoot. I weigh every charge with a Chargemaster 1500 and rezero every 20 or so rounds. One thing to mention is that I had just annealed the brass prior to this test, and before that was getting less the 20 ES. Could elaborate more if necessary. Drew