75 Hornady vs. 77 SMK - Real world Test

[akajun]

The two bergers I mentioned are not vld's and are more tolerant of seating depth than the vld's. However the a max's should have shot well , except for the fact that that have been known to actually come apart at 300 yds when shooting 600 if pushed too hard . I shoot the. 82's at .015 off the throat , and sone people have even shot them at mag length with good result . They are a very tolerant bullet. With the shorter cle chamber you may need to drop a few tenths of a grain of powder to get your pressure down but they should still work in your gun.
When you say geissle match, I assume you are using one if the two stage models , which are more desirable than the single stage versions for match shooting . In addition I would ditch the prs stock and replace it with a standard a2 with an adjustable butplate from Arrington and use a set of rings to adjust your scope height to your eye as opposed to an adjustable cheek piece .
After that , the only improvement you will see is from a new barrel in 1/7 from woa, cle, or keystone accuracy. If you absolutely have to use an adjustable stock, have your upper modified for a side handle and get a woa adjustable stock or one from Gary ellisio at CSS .

 

[skiutah02]

The two bergers I mentioned are not vld's and are more tolerant of seating depth than the vld's. However the a max's should have shot well , except for the fact that that have been known to actually come apart at 300 yds when shooting 600 if pushed too hard . I shoot the. 82's at .015 off the throat , and sone people have even shot them at mag length with good result . They are a very tolerant bullet. With the shorter cle chamber you may need to drop a few tenths of a grain of powder to get your pressure down but they should still work in your gun.
When you say geissle match, I assume you are using one if the two stage models , which are more desirable than the single stage versions for match shooting . In addition I would ditch the prs stock and replace it with a standard a2 with an adjustable butplate from Arrington and use a set of rings to adjust your scope height to your eye as opposed to an adjustable cheek piece .
After that , the only improvement you will see is from a new barrel in 1/7 from woa, cle, or keystone accuracy. If you absolutely have to use an adjustable stock, have your upper modified for a side handle and get a woa adjustable stock or one from Gary ellisio at CSS .

You've piqued my interest in the 82s. If I find some in stock, I'll give em a whirl, thanks. Drew

 

[afrench]

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)

from Litz's 'Applied Ballistics' book. i have the second edition, i believe.

 

[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.

I guess "up node" and "down node" have been described.

http://www.geoffrey-kolbe.com/articles/rimfire_accuracy/tuning_a_barrel.htm

Learn something everyday...

Investigating tuners these days. quite interesting. The RF crowd seems to have a head start.

Drew

 

[broncman]

In my FTR AR, I used a carrier weight similar to Tubbs. Added enough weight till carrier would reliably catch the bolt hold open stop when single firing from magazine. This helped my sd/es and my brass lived longer as well.

 

[johnfred1965]

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)

from Litz's 'Applied Ballistics' book. i have the second edition, i believe.

If you use the ballistic calculator on the applied ballistics llc site, they have the current g1 values as:Hor 75bthp g1-.357 g7-.183
Ser 77bthp g1-.377 g7-.193
I believe I read from the ballistics forum that Applied ballistics is continually testing and retesting bullets, getting the most accurate numbers for current lots of bullets. IIRC most don't amount to more than 1% difference between lots or tests

 

[mac86951]

Wow, I like the responses, but I'll give you my AR feedback from a 30,000ft view. Bullet manfs. Post a BC, usually a G1. Guess what, they're all wrong. G1 BC changes with velocity! Some post a useable average range for expected customers, others post a high average to make business competitive
Ignore the SD from velocity spread, that's another topic. Why are the two bullets impacting differently? The average BC over the range you fired, at those weather conditions meant the hornady 75gr BC was lower. All the other information like SD, etc applies to group size, not center of group.

That said, more shots to determine center of group would be needed to truly determine potential center to center differences to listed BC.

Caveat, my 20" barrel likes both 77 and 75gr bullets previously listed, but I have different loads for each.