Posted: 3/19/2017 9:39:58 PM EDT
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Lately I've been having some trouble with my FN SPR A5M 308 holding zero. Historically this rifle has been lights out for me, I've had it probably 5 years now, maybe 3000ish rounds through it now, still groups great. Highlights of my rig are:
FN SPR a5m 308 rifle 24" barrel USO 5-25 scope (which I dislike) Surefire 762SS suppressor Federal 175 fgmm ammo Pic for reference: 
Last weekend: I shot a 1 day match, the rifle was equipped with a Leupold mk4 6.5-20 m5a2 scope at that time. Confirmed zero the morning of the match..... carry the rifle to the first stage, a plate rack at 450 yds from prone position, literally could not hit anything. After a couple stages I deduced I was hitting .5-.75 mil low but wasn't able to salvage any kind of decent finish. Go to the range when I get home from the match..... bam, my groups were hitting .5 mil low at 100 yds which explained why I wasn't hitting anything in the match. But fishy as I zeroed literally 30 minutes before the first match stage. Today: I swapped my USO 5-25 onto the rifle to see if it was a scope trouble. I also cleaned the bore, shot a couple fouling rounds, then get on paper at 25, once pleased I back up to 100 yds and fine tune the zero. Note, I haven't messed with the EREK function, just turned knobs to adjust POI, then loosened knobs and spun back to zero. Here is that confirmation 3 rd group: 
Then I adjust my knobs back to zero, fired 3 more rounds to confirm no change. Here is that confirmation group: 
Satisfied, I pick the rifle up, place it in the back seat of my pickup and drive to 275 yds where I plan to shoot an 8" plate off the tailgate. Get all PRS bagged up, super solid position and send my first 3 rounds, all absurdly high. Note, my dope is spot on, I've used it for forever and the plate was huge. Frustrated I send 5-10 more rounds and discover I'm hitting roughly .5 mil high..... Annoyed I go back to the 100 yd line where I check my zero and get this group: 
You can see it's just over 1.5" high, right at .5 mil in the reticle. This shift happened in less than 20 rounds. The rifle and suppressor barely even warmed up. For what it's worth, I had my 6cm PRS rig there with me and shot a bit out of it. Zero was perfect, dope was spot on and groups were respectable. Something is up with the FN SPR. Any ideas what is going on here? What should I be looking for? The rifle is not bedded from FN. Could that be the culprit? It's never a been a problem before, but maybe with the age on the rifle tolerances have worn. Everything I can check feels tight. Any help is appreciated. |
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Have you tested without the can? If its not the scope/mount, its likely the suppressor. If its a QD can, the attachment systems can wear over time.
I would also remove / retorque the action screws The only way it could be a bedding issue is if you are using a rest at one spot then switch to a bipod which is flexing on the barrel. Otherwise shitty bedding seems to simply open up group sizes in my experience. |
| First thing I'd do (because I've had issues with this in my brief time of long range shooting) is check the torque values on everything that's threaded. Action screws, base screws, rings-mount & ring screws and make sure they're all loctited. I had my chassis screws worth themselves loose from thermal contraction on a cold day (large shifts in aluminum...), just to say for an anecdote. See if you can repeat the change in POI without the suppressor on (obviously you may have a shift from that alone). |
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Thanks guys! The can being the culprit didn't really crosss my mind as I've been shooting this rifle suppressed almost 100% of the time.
Makes sense the locking mechanism could wear however. Also pulling the can to see what happens is simple, in the meantime I'll check torque on all screws. I'll keep this thread updated as I make progress diagnosing the issue. |