QD mounts and return to zero: an anecdote

after the wacky group-measuring rant threads we've had lately, i thought I would share some groups I shot on new year's eve.

I'm still working up a load for this rifle, shooting over a chronograph and the components are lapua brass, 155g lapua scenars and VV N540 powder. (avg 2770 fps SD of 7 fps for one load)

Rifle: Knight's SR-25 (see http://thehighroad.org/showthread.php?t=375661)
Temp: 35*
Winds: mostly calm, gusts to around 10mph
Conditions: highly caffeinated

anyways, there's two things interesting about these groups. first, while i love PRVI 5.56 M193 ball for carbine classes, PRVI's "308 Match" (175g) ammo SUCKS. I was getting 6" groups last week with it at 200 yrds in 30mph gusty winds, and I thought the problem might have been the wind or myself. but no, looks like it's the ammo.

second, I've yet to sort out the larue QD mount. I've tried adjusting it several times and I just can't get rid of a tiny bit of play (maybe half a mm, forward and back, not side to side that i can tell) that shows up after the first shot or two. I'm certain it's because I've not adjusted the mount correctly.

It took me a little bit to figure out what was going on (partly because i was also inconsistently loading up the bipod), but I finally did some tests and confirmed to my satisfaction that if I push the scope assembly all the way forward on the rail before the shot, pretty much all my shots are touching (at 200 yrds). if I don't, the bullets land not quite randomly in about a 1.25 MOA group.


so... for those of you wondering how close a QD mount will return to zero on a precision rifle, when it hasn't been adjusted properly

here's 5 rounds of PRVI w/o adjusting my mount


5 rounds of load J. POA was the -0. the 3 high right are due to mount movement, but at only 100 yrds that's a 2 moa group. also, i don't think that load is nearly as good as load H.


(group 3, not pictured, was just two rounds suppressed cause some kids at the range wanted to hear what it sounded like...)

5 rounds of load H, POA was the -0. 3 touching, and i pushed the mount forward before each of those 3 shots, but did not for the other two. resulting in a 2.5" group at 200 yrds. still... not bad. the cluster of 3 measure .4" center to center



5 rounds of load H, POA was the lower right dot
5 rounds of load H, POA on the upper left dot (except one where i stupidly shot at the lower left dot... crossfire!)
again, when i pushed forward on the scope, bullets are touching the dot and when i don't, they scatter around a bit.



the sad thing is... i've got the recipes for loads A-J in my note book... all except load H. for some reason, I can't find where I wrote it down! figures i'd lose my best-shooting load so far!

yep, 1858, the play is basically the difference between the size of that lug and the space between rails, which is not much. when i push it forward, i'm just moving that lug forward til it stops against the rail.

yep, rob, it's tightened past the point it's leaving marks

got a link to the promag, krochus?

anyman, J was the worst

so what kind of groups do you get with the pro-mag? do you remove it regularly?

I'm surprised your LaRue preforms so poorly. According to those I asked it's the mount to have.

Click to expand...

like i stated in my OP, I'm fairly certain I don't have it adjusted properly. the point of my post was really "how bad can it get with decent stuff?" and the answer for me was good enough that I can still hit steel silhouettes/plates a long range even though I detach/reattach it every time i go to the range.

that's sorta why i was interested in the pro-mag performance. if anyone else has anecdotal data about how their QD mount performs, please share.

double tap

Click to expand...

i've been doing that a lot lately. i sense a disturbance in the force

1858, nope if you need tools, it's not QD.

that's something i've never understood about people who put BUIS on their guns but bolt the scope to it. ok... so your scope breaks, now how are you going to get to the irons?

stubbi, that's a FANTASTIC idea! thanks!

i talked to them this morning and am pretty sure I can solve the problem. i was basically a little apprehensive about over-tightening it, but they assured me it would be ok.


by the way, did i mention those groups were shot with a 7lb trigger?

update

saturday i shot in the rain for hours, mostly at 300 but I took one 5-shot group at 600.

These are my first and last groups of the day. It rained all day and pretty foggy (and I forgot my shooting mat) but there was no wind when i started, although there was some when I shot the last group several hours later.

I tightened the mount and shot this 8-round group: 3.7" total, but the three together are exactly half an inch.



So I tightened some more, and some more and some more and some more. It didn't seem to have much effect until the end, when I finished with a group at 600 yrds. Pretty much all of my 300 yrd groups were like the one above, give or take an inch.
even so, I still have high hopes for F-class mid-range this season.