Were metal/GI mags hurting my accuracy?....Sure looks that way.

#1
While I've had no shortage of guns that shot excellent groups, it seems that lately a few of my guns weren't shooting up to my standards and I seemed to be chasing zero's all the time. This came to a head the other day when I had a Hodge barreled gun that was throwing 3-4" groups uncharacteristically. I wasn't sure if it was how I was getting on the gun; bad day or what.

I decided today after work, I would take out my stubby tripod setup that is pretty rock solid and double check my groups again on a new day. I tried shooting 2x different ways with the setup and I was throwing rounds up, down, and all around that I wasn't calling. Remembering that some of my best groups from other guns came from 20 round mags off my pack because I could get lower so I tried that...still no good. However, I've had some bad 20-round mags mar up my bullets too so I decided to try a gen 3 Pmag just for grins. Low and behold...the group was about 1/2 the size and right about where it should be (despite a pretty hot barrel, hot temper, and sliding fundamentals). I had some less-than-perfect trigger presses but all my shots were right where I called them. My center dot never left the "X" ring and neither did my impacts.





Happy to have figured that out, I shot the gun off my pack at my 2/3rd IPSC steel in the fence line. In speaking with Jim, he said his barrel magic in 14.5" shows numbers close to 16" guns. I can say that this 14.5" Hodge barrel chrono's the exact same as a 16.5" HK barrel and spits out 77gr TMK's at about 2600fps.

807y with a 14.5" chrome-line barrel and factory Black Hills ammo...
9.5 Mils of elevation with wind holds varying between 1.7 and 2.1 Mils, I went 14/25 on the steel.


 
#4
If I had to take a wild guess; it's because the one specific 30-rounder needs to be cashed out and 20-rounders have given me trouble before. Stupid me did not note which mag that was so it's still floating round in my training mag bin. Perhaps feed lip spread or a change in the feed angle that's causing trauma to the projectile.


I've read people doing all sorts of voodoo and wonky shit when they were going for the tiniest of groups with AR's. I know some would throw off their first round and group with the remainder as the first was manually loaded while the others were cycled at full speed. I've also seen multiple instances where guys would track their dope based off which side of the magazine the round came off. I don't know if there's any truth in these gestures; just noting how deep some have gone down this rabbit hole.


I have several irons in the fire at the moment and while this is fairly low on my list, I have shot some groups with a couple other guns between GI and PMag and noted little to no difference. It has not escaped my notice that I've had some WTF type moments with some other guns lately...all of which have worn that same scope at one time or another. There's definitely some funky stuff going on with that SFP floating dot in the FFP optic It still may likely be another factor and the stars just happened to align when I changed mags.

As I showed another member earlier; here's the original 100y test-fire/zero group from this past winter after it was assembled:



It was wearing this optic at the time:

 

Yondering

Regular Member
#5
I'm pretty skeptical too, and have to wonder if it's really a scope problem.

If it is a magazine problem - maybe your bad magazines are dragging on the bolt carrier enough to affect lockup; early unlocking can have a small effect on accuracy.
I doubt it's anything to do with the magazines damaging the bullets, but you could always chamber some rounds with those mags and pull them out unfired for inspection. Enough damage to cause that much accuracy difference would have to be really obvious.
 

RobbieRob

Newbie
Network Support I
#6
Different platform, but perhaps the same principle.

With my bullseye 1911 Dave Salyer recommends using the same 1 or 2 magazines for a match since small changes in a magazine can affect the zero on my pistol. Joe Chambers said something similar.... something something...he always uses the same magazine in his ransom rest despite the spring being weaker than Hillary's 2020 election campaign.

The Barrett .50 increases in accuracy when you handload the rounds into the chamber vs. letting the magazine feed it.

I don't shoot service rifle anymore, but perhaps some looking at the usrifleteam forums has something on the subject.
 
#7
The plot thickens...

In trying to figure some things out (double checking ammo and optics) I found that with 2 of my SPR's the above short tripod setup is a complete No-Go. Whether it's the Proof Research in a Pinch Lock using an ARCA adapter or a Centurion Mk12 barrel w/ a Daniel Def bolt-up rail in the saddle/clamp, they both can exhibit a solid 5-6 MOA impact shift low from zero if support is given to the rear/buttstock of the gun. And it's repeatable. Funny that whether it's getting into the gun and loading the hell out of the bipod or free recoil off the pack...POA/POI remains consistent.


Meanwhile yesterday, I got multiple hits on target (granted a fairly sizeable target) at a 1680y with a 6.5CM Accuracy International...shooting factory Fed ammo (22.5 mils elevation, 6 mils wind)...standing using a tripod (2nd round hit). So it's not like I can't shoot. These damn "precision" AR's though are trying my patience.
 
#8
What optics are you using? Some are very picky about head position. Putting a bag on top of the tripod, to shoot off of, would be another way to test the clamp.
 

Yondering

Regular Member
#9
The plot thickens...

In trying to figure some things out (double checking ammo and optics) I found that with 2 of my SPR's the above short tripod setup is a complete No-Go. Whether it's the Proof Research in a Pinch Lock using an ARCA adapter or a Centurion Mk12 barrel w/ a Daniel Def bolt-up rail in the saddle/clamp, they both can exhibit a solid 5-6 MOA impact shift low from zero if support is given to the rear/buttstock of the gun. And it's repeatable. Funny that whether it's getting into the gun and loading the hell out of the bipod or free recoil off the pack...POA/POI remains consistent.
About that - if you're going for precision, why is your tripod clamped so far back towards the receiver? Normally you'd want to start with that out at the front of the handguard for stability and adjust as needed. That may change your POI shift as well.
 
#10
About that - if you're going for precision, why is your tripod clamped so far back towards the receiver? Normally you'd want to start with that out at the front of the handguard for stability and adjust as needed. That may change your POI shift as well.

Because the WHOLE POINT of a tripod setup is to put the support under or closest to the center of gravity on a precision rifle. What you're describing is a bipod method where you still need additional rear support.

The concept works just fine with AR's in traditional standing, sitting, or kneeling tripod use as one would do with a bolt gun. Case in point, here was my day shooting an 416 out to 755y with a 4x standing, off the tripod:





Needless to say, the "stubby" tripod in the prone is not working as intended (at least with some guns), but it was worth a shot to try and modify it to the prone without the need of a rear support. Or at least I would need a different center hardware/attachment to get the gun lower and not creating tension in having to build my position up to get on the gun in the prone.
 

Yondering

Regular Member
#11
I get it for a tall tripod as your latest pics show for standing or sitting, and have used that myself. Your earlier pics look like a prone setup though, and a tripod mounted close to the receiver doesn't work nearly as well in that position.
 
#12
TL;DR: GI mags on the cusp of giving up the ghost might be adding to group size.

Pretty sure I have this figured out...at least some more repeatable data.

After putting this on the back-burner, I had a gun experience 2x failures to feed. I marked it as such and took several of my GI mags in rotation out to shoot some groups. I shot 5-round groups until I couldn't stand it with various GI mags and noted the results with the numbered mags (1-9) and used a brand spaking new Gen 3 Pmag as a control. To avoid user/support error; all groups were shot bagged off of a bench.

About 1/2 of the GI mags measured no demonstrable reduction in accuracy. Those that did were set aside for further group testing. For those that did, I calculated an aggregate group size. Later I measured the magazine lip spread. The magazines that had the widest magazine lip spread were also the ones exhibiting the widest accuracy dispersion. Spead measured between 0.454" to 0.491"....all Colt/OKay/NHMTG bodies w/ magpul followers. The magazine that was involved with the failure to feed exhibited some of the widest feed lip spread and widest groups. [I am not for certain, but I suspect that this occurring off of one side of the mag and not the other. When the failures occured, rounds were coming off the right-side of the gun, and no defects can be seen on the right feed ramp...but there was more copper deposit on the right feed ramp. I had pulled some chambered rounds and noted some heavy V-shaped gouges in some projectiles but it is not consistent.] This would be consistent with the groupings in that when I was able to do a full 10-round string, at least half or more would be consistent with my shot call and within my margin of error, but there would always be a few unexplained flyers...typically with odd vertical dispersion.

Probably my best example where I know all 10 shots, my crosshair never left the "X" much less the X-ring.



Done again with a nearly identical (but different) gun and different optic; same ammo lot.
suspect GI on the left, fresh PMag on the right




Thanks for listening...
 

Yondering

Regular Member
#13
Did you find any damage on the tips of the bullets (i.e. bent or flattened tips), or measure the runout? Maybe the bad magazines are causing rounds to hit the feed ramps hard enough to cause runout (essentially bending the case neck/shoulder area) so the bullet starts crooked down the barrel. Excessive runout definitely affects accuracy, and could be what you're seeing. Pull out a few of those chambered rounds and roll them on a sheet of glass if you don't have a runout gauge; watch for the tip of the bullet wobbling around as it rolls.

That V-shaped damage is pretty common when extracting a live round from an AR; it's caused by the bullet dragging on the barrel extension lugs. You can prevent that by holding the round straight with your finger (counteracting the ejector spring force) as you extract it.
 
#14
The to feeding failures were the bullet running straight into the feedramp and then getting shoved straight back into the case. Needless to say there was some case deformation. The damage on the bullet this time is not the normal scratch I'm used to seeing; more like a deep sliver of the bullet like you took a vege peeler too it and got part way.