I was wondering how many people are using the hornady 75 gr A-Max with a 1\9 twist barrel. I have a Remington 700 .223 with a 24" 5r barrel and am trying to get this heavy bullet to shoot well.
I’ve tried a few different powders; blc2, benchmark, imr 4064, varget, and xbr 8208. Varget and xbr seem to shoot the best.
Hornady load data is very conservative and I can’t seem to find any other data for the 75 gr A-Max.
I am looking for fastest fps but with 3\4 to 1 moa groups. Any other powder recommendations. Anyone have a favorite load with this bullet. Last time i was at the range 23.5 gr of varget was good groups but only 2650 average fps. I tried it today in 20-25 mph winds and it gouped poorly. Probably due to the wind. 25.0 gr of varget at 2810 fps did a little better handling the gusty winds. Xbr at 23.1 grs did okay as well at 2782 fps.
If it was keyholing then it wouldn’t be hitting paper at 100 yrds. Plus I would have baffle strikes. No keyholes with mine. Worst groups, I’m able to get averages of 1-3/4"with blc2at 100yrds and with the varget I was getting about 1" with best groups, but the bullet was going too slow for long range, about 2550-2600. I’m trying to find a combo where I can push 2850+ fps and still have 1 moa groups or a little better.
Molon’s target looks better than a 25 yard target I fired years ago with 68g match handloads through a bolt action rifle with 1:12 twist barrel. The same load would shoot under 3/4 MOA at 200 yards when fired through an AR-15 with 1:8 barrel.
I believe a 1:9 twist barrel is suitable for bullet weights of 52g to 69g and a 75g bullet would stabilize better through a 1:8 or faster twist barrel.
Every barrel is a law unto itself. I think Molon said that, but am not certain. This is one of those things that while most here, myself included, are going to look at 75gr projectile, it being a longer round,and go the slowest twist that it is going to likely work with is a 1/8(though not always, have one that does not like 75gr Hornady BTHPs at all) but at the same time, it is possible that the 1/9 could work, and I have seen it. Only way you will find out is to try.
Mathematically, a 1/9 twist should be fast enough for the 75/77 grain bullets. The rifles I’ve tried them in all shot well, if not brilliantly.
I have wondered what the “spread” is for barrel twist. If we take a “1/9” barrel, woudl we find that the twist in a production lot, or from one maker to another, varies from 1/8.9 to 1/9.1, or is it more like 1/8.5 to 1/9.5?
I’ve used the Greenhill Formula to determine optimum barrel twist a few times and it did not work out. I’ve only been able to develop decent loads by getting a general idea of where to start, then trial and error. I have not had any luck with 75g projectiles fired through a 1:9 twist barrel.
Yeah… we too have had good luck with 75, 77, and even 80 gr bullets out of a 20" 5R Rem 700. I’d push your load up into the 23.5ish area with XBR, DEPENDING on how deep you’re seating them. i.e. if you seat them deep step off a few tenths. Other than that, the slower powders like Varget will get you better velocity. I just don’t mess with Varget for .223 due to metering with my higher volume of ammo production.
I would try it. I have a 1/9 chrome-lined barrel that shoots very well. With a clean, copper-free bore, I shot ~.75moa with my 77gr SMK XBR hand loads. I only shot 10 rounds, so this may not be the case with a lot copper fouling.
I shot 50rds today and had better accuracy with faster velocity. I only shot xbr today but am going to try a few more loads with varget.
Best grouping was with xbr 23.8 grs with the 75 gr amax seated to the recommended length of 2.390". I am one grain over recommend max powder charge but that remington has a long throat so I’m not concerned about pressure spikes. With that bullet I have to load it to COAL of 2.455" to seat it right off the lands and grooves. Average velocity was 2841 fps at 12’ in front of muzzle. 75 degrees with moderate rain produced about 1" groups. 100% humidity with winds 10-12 mph steadily.
Only other loads I’m going to try is 25.0-26.0 of varget to see how that shoots.
I’ll post some pics when I get to my computer since it’s hard to load photos from my phone.
I’m fairly happy with the xbr once I got it up to speed.
I did say that, but I was referring strictly to accuracy (from an adequately stabilized twist); whereas the currently discussed issue pertaining to the 75 grain A-MAX with a 1:9" twist is gyroscopic stability. The 75 grain A-MAX is significantly longer than the 75 grain BTHP; length (and specific gravity) are going to be two of the important factors in determining adequate stability with a particular twist.
Again, the OP referred specifically to the 75 grain A-MAX and it will not adequately stabilize with the same twist that the common 75 grain BTHP bullet will. The 75 grain A-MAX can not even be seated to magazine length without the ogive of the bullet extending below the case mouth. This is what happens when you seat the 75 grain A-MAX to magazine length . . .
OK, mathematically, a 75 grain A-Max, .224" in diameter, in a 1/9 twist barrel, gives us a Sweeney Stability Index of 0.897.
Lower values are less-stable. The SSI for a 55 fmj in a 1/12 twist is 1.0. The SSI for an M855 in a 1/12 twist is 0.827.
And as a further data point, a 55 fmj, in a 1/14 twist, has an SSI of 0.854.
So, a 75 A-max, in a 1/9 barrel, is more stable than a 55 fmj in a 1/14 barrel, which we know to be right on the ragged edge of stability. It is a lot more stable than the known bad combo of M855 in a 1/12.
If the A-Max is not stable in a 1/9 barrel, there is something more than simple twist rate going on.
