truly horrible accuracy problem, need help

[kevwil]

I'm really struggling with my 112 Magnum Target single-shot 338 Lapua. I'm still trying to find a good load for it, probably about 250 rounds through it so far. The only change I've made has been swapping the factory brake for an APA Fat B* muzzle brake. It appears to be concentric - cannot see it from looking through the barrel from the chamber side.

On a good day, it works well enough to get 3/4" groups at 100 yards and 5 consecutive hits at 1000 yards, so I don't think the rifle is inherently inaccurate. On a bad day, it won't even hit the paper at 100 yards. Yesterday I shot 15 rounds using a load that had been a 1" group last time, not a single hole in the target.

I've checked:

Crown has no nicks or scratches
Scope rings are tight (ARC M10 rings, 55 inch/lbs)
Picatinny rail is tight and blue locktited (EGW HD steel, 8-40 screws at 20 inch/lbs per EGW spec)
Laminate stock is factory, pillar bedded and torqued to 35 inch/lbs


I'd love some ideas on what might be wrong.

[dfrosch]

Did your scope get shaken baby syndrome?

[Smokey262]

Are you flinching?

[kevwil]

I don't think so, but I'd need some kind of super-solid mount and a carefully measured target to know for sure.

[kevwil]

Flinch is certainly a valid question. I guess I'd need to video myself to know for sure. I shot some one-ragged-hole groups with different rifles the same day, but they weren't 338LM.

[Toftwo]

Did your scope get shaken baby syndrome?

Out of curiosity what glass are you running?

[J.Baker]

Only time I've ever seen gun shift POI that much is when a scope takes a dump. Even if it's you flinching, at 100 yards you'd still be on paper unless you're shooting at playing card sized pieces of paper.

[kevwil]

Right now it's an SWFA 12x, but I had a Razor HD gen2 before.

[spaniel]

Most likely your scope took a dump. Switch to a known good scope. Sounds just like when one of my Bushnells went. Some days it would shoot, then I'd adjust it, it would do weird things, then eventually settle down and group again. Internal springs get weak.

Alternatively, some guns lose it when they get too dirty.

[Robinhood]

Have Skylar take a look at it.

[kevwil]

Most likely your scope took a dump. Switch to a known good scope. Sounds just like when one of my Bushnells went. Some days it would shoot, then I'd adjust it, it would do weird things, then eventually settle down and group again. Internal springs get weak.

Alternatively, some guns lose it when they get too dirty.

There needs to be an easy and completely definitive way to know if a scope is bad. So frustrating. And given that both scopes I've tried are well-tested on 50 BMG rifles, it shouldn't be a problem.

Yeah, I haven't done more than a BoreSnake so I'm starting a thorough cleaning now.

I'm surprised no one has pointed a finger at the stock, it feels cheap and nasty and highly suspicious. But I don't normally run laminate stocks so I wouldn't know.

[holescreek]

Your scope checked out on you. I've had it happen several times. The first time it happened to me I was knocking out good MOA groups then suddenly I couldn't hold 8 MOA. I sent that scope back for a replacement. I mounted the new replacement scope and took the rifle out again and it shot well all that day. Brought the rifle back to the range the next weekend and it wasn't even on paper. It took most of my range time trying to get it back on target and it wouldn't hold 4 MOA. Next trip out I brought a different brand of scope with me and changed it out on the shooting bench. The rifle was back to sub MOA like I just cast a magic spell on it. I sent the replacement scope back to the manufacturer and was sent yet another replacement. It's still sitting in the box on the floor of the office. Free lifetime replacements sound great until you actually have to use them (a lot).

[RustyShackle]

Time to test SWFA customer service! Hopefully they do right by you, I swore I wouldn't give them any more of my business after a bad experience about 7 years ago. Let us know how it turns out.

wishing you the best.

[foxx]

There needs to be an easy and completely definitive way to know if a scope is bad. So frustrating. And given that both scopes I've tried are well-tested on 50 BMG rifles, it shouldn't be a problem.



There is, if you have access to a good bore sighter...

Set it up, strike it hard with rubber mallet... move 10 clicks up and over to the right.... strike again....

try to reset by moving 10 clicks down and over to left again....

Should return to "Zero". Might, might not. If it doesn't, I'd say it's the scope, But, I'd say it is the scope, regardless.

[gbflyer]

Echo the scope sentiment. I have an old Bushnell 5-15 with Mildots and big knobs that I use for load development and also as a standard to check a bad one. It was on an AR I traded for. It's funny, clunky old cheap junker by most standards but it functions flawlessly and I have 100% faith in it.

[WeldNFool]

After 15-20 rounds consecutively with my 338 and my groups aren't as tight as they used to be either. 308 for plinking, 338 for 15 rounds at my leisure, giving my shoulder a rest. Eliminate the flinching by putting that beast in a gun vise like the lead sled or something. At least eliminate the flinch. I've shot my 338LM a bunch and it's still hard not anticipating that mule raring back to kick you in the shoulder when you squeeze that trigger.

[Luckyshot]

.308 for plinking? Wow! :)

[kevwil]

I just got back from the range. I took the scope off and put it on my 308 which is a 1/2 MOA rifle. After zeroing, I shot groups at zero, +2 mil, -2 mil, and zero again on the 100 yard range. All were sub MOA and one group was a 1/4 MOA bughole. The +2 and -2 mil groups were 7.2" from point of aim.

I know the SWFA is not a premier $4k optic, but I should be able to hit paper at 100 yards reliably.

[gbflyer]

One more thought: did you lap the ARC rings? It's plausible that your scope is in a bind on the .338LM but not your .308. Receiver scope mount hole "straightness" can vary significantly from one to the next. I have a flat back Savage 116 that's horrible.

[dfrosch]

[QUOTE=kevwil;395557]...The only change I've made has been swapping the factory brake for an APA Fat B* muzzle brake. It appears to be concentric - cannot see it from looking through the barrel from the chamber side...

[QUOTE]

If your scope is still good, you might look at the brake. Any copper smears?

A brake will change your POI. The factory brake could have moved POI in one direction and the APA moved it in a different direction. May still be shooting 1", just not on paper.