PDA

View Full Version : AYSM 147gr FMJ Match vs. WWB FMJ NATO 9mm = 5" difference in windage???



NickDrak
05-03-2012, 05:35 AM
Does this make any sense?

I was zeroing the new 10-8 Performance sights on my new Gen4 G34 with the ASYM 147gr FMJ Match ammo @ 25yds from a bench. Printed a nicely centered group of just under 2.0" with the ASYM. I then shot a group with two of my different practice rounds. Winchester white box 124gr FMJ "NATO" and Aguila 124gr FMJ. Groups were still pretty good (approx 3" @ 25yds) But both of the 124gr rounds impacted approximately 5" to the left of where the ASYM was hitting. I followed with another nicely centered group with the ASYM.

I expected there to be a slight variation in elevation between the three different loads, but I didn't expect there to be much difference in windage....especially not 5" worth of difference at 25yds!

I finished by shooting a group of each round @ 5yds. The ASYM was impacting dead center. Both of the 124gr FMJ loads were impacting around .75" left of my P.O.A.

MEH
05-03-2012, 07:58 AM
I have seen significant difference left/right with different brands of ammo, so I don't think it's abnormal.

ToddG
05-03-2012, 08:11 AM
Just to echo MEH, it happens. Some guns and some ammo just click together that way. That's why it's important to zero one's pistol with duty/carry ammo.

Joe Mamma
05-07-2012, 07:14 AM
I've heard of thiese left/right zero shifts before. But I still have no idea why.

Joe Mamma

JHC
05-07-2012, 08:01 AM
I've seen them also. With my Glocks, IIRC, it's most noticeable with 147 gr. I don't shoot much 147 as I don't find it readily avail on the shelves were I hang out so I'm generally using 115 or 124 gr fmj by the case to training and 124 +P. But sometimes when I find some 147 and try it out at 25 yds, it impacts left of my zero with the lighter bullets. I figure it's some advanced math stuff about the imparting of the twist to the higher mass slug by the Glock barrel or slower to exit the bore and Glocks unlocking movements . . . yada yada more adv math . . . something like one of those. ;)

derekb
05-07-2012, 08:30 AM
There is a long, but very interesting, series of articles written by Tom Gaylord about his quest to determine exactly what the relationship between velocity of an airgun pellet and accuracy.

Here's the last entry, with links to earlier entries collected. (http://airgun-academy.pyramydair.com/blog/2011/12/pellet-velocity-versus-accuracy-test-part-11/)

It's a lot to read through, but he does discover some interesting things. For example, it was long believed that a diabolo pellet fired faster than the speed of sound would be inherently inaccurate due to the nature of the transonic region, but he seems to have discovered that barrel harmonics are more significant, and a supersonic pellet can be accurate.

Suvorov
05-07-2012, 09:37 AM
I haven't seen it so much on my pistols, but my M14 displays an odd shift in windage as I increase bullet weight - been trying to figure that one out for years...... :confused:

vandal
05-13-2012, 08:19 AM
I use Fed HST 147 for defense. The Winchester 124gr NATO ammo did exhibit a noticeable windage offset in my G19s.

LittleLebowski
05-14-2012, 05:24 PM
My brother's advanced Marine Scout Sniper class switched from 175gr to 173gr and saw a two foot difference in POI at 1000 yards.

Schmetallurgy
06-26-2012, 08:20 PM
I would assume, in a pistol, it's a question of dwell time and rifling torque causing any side to side play in the barrel, at either end, to affect the alignment, the direction depending on which end of the barrel is freer to move relative to the other. In a rifle, more the whip harmonics.