Bolt gun issue ??

[wigwamitus]

So this is a REM700 SPS TAC AAC-SD I got last November and put in a KRG Bravo chassis.

gun in the top of the pic is the REM700 Bravo

End of 2018 thru end of Jan 2019 average groups for this setup were

0.65 inches Prone (32 x 4 rd groups)
0.98 inches RRS (18 x 4 rd groups)

(note, 4 rd groups gave me 5 x 4 rd groups out of a box of 20 which was my daily goal for the rifles I was shooting on a given day).

(in Feb 2019, I changed this to shoot 3 rd groups ... 2 "sighters" and then 6 x 3 rd groups. Trying to mix "dots" in with "groups" by doing this)

So far this year, the Bravo REM700 is
0.72 inches prone ( 15 x 3 rd groups)
0.64 inches RRS (10 x 3 rd groups)

The the last 6 x3 rd groups from prone are all over 3/4 inch, which is "out of spec" ... and last weekend, the "groups" have opened up to 8 moa !!

One shot will be 4 inches low, the next 4 inches high ... not more than 8 moa, but obviously that is a big problem ! Then there might be 2 shots in a row that are dead on the dot I'm aiming at ... then another 4 inches low ... and another 4 inches high. The windage variance is there also. About plus or minus 1 inch ... but the elevation variance is HUGE ... with plus or minus 4 inches.

Yesterday I shoot this rifle side by side with another REM700 Criterion ReMAGE 22 inch barrel, ,McCree Precision G-10 chassis. The g-10 average this year is 0.62 (10 x 3 rd groups) off the RRS. And yesterday was 0.75 avg, right on the in spec/ out of spec line.

REM700 + Criterion + McCree chassis ^^

So, something "happened" to the bravo.

I've tried replacing the scope, checking the action screws, checking the suppressor, tightening the RRS vice mount tightening the SPIGOT. Checking the scope base. Checking the scope mounts. I'm running out of things to check.

Both guns are shooting the same ammo. Which is M118LR. And yes that is less consistent than the FGMM 175gr 7.62 (or .308) I also shoot, but NOT 8 moa inconsistent !!!

==

All ideas welcome.

For today, I removed the Griffin Arms sportsman suppressor and will try groups without the suppressor. But my worry is if I burnt out the barrel. But I've never shot a barrel out before (have sold the guns before it got there) so I'm not sure exactly how a shot out barrel behaves. Does it go from sub moa to 8 moa over night ???

==

Thanks again !!

 

[diverdon]

Could the scope be loose or broke?

 

[Spblademaker]

Any chance of a carbon ring forming?

 

[wigwamitus]

... Could the scope be loose or broke?

That was my first assumption ... the scope I had on there was 5 year old L&S mk6 3-18x T3 (the reticle is new, not the rest of the scope). I called L&S and they said "send it in" and I boxed it up ... and put another scope (Burris 3-15x scr-mil) on there and same problem. Took that scope off and put brand new L&S mk5 5-25x T3 on there and ... same problem ... so I think I've ruled out broke scope !!

... Any chance of a carbon ring forming? ...

Never heard of that ... so maybe! I will google for detection process ...

This gun has about 400yds thru it since Nov 2018. Usually about 20 rds per session ... dots and groups ...

Thanks for the replies !!!

 

[maverickasu]

I was convinced optic issue until he said he changed the scope... hmmmm

carbon ring with only 400 rounds doesn't sound right...

you said you tried different lots of ammo? SHOULDN'T matter that much buuuut... idk... Are you using torque wrench to check all connection points?

Last thing, double check free float on the chasis? something logged in there? or binding up strangely?

 

[Spblademaker]

Other than loose stuff, which you’ve checked, scope, which your checked and carbon ring, I’d check the suppressor for anything wonky. Maybe the QD loosened up just a tad.

 

[wigwamitus]

Googling around for carbon rings ... after getting past the studies of the benezene molecules ... ... the short answer is ... I will clean the barrel and chamber and see if that helps.
I've fired same ammo (1400 rounds now) thru the 22 inch criterion barrel ReM700 and no groups opening up over there ... and never cleaned it. But the shorter barrel and a different suppressor, might produce a different result. Cleaning is cheap. Trying that !

 

[wigwamitus]

... Maybe the QD loosened up just a tad. ...

This suppressor is a DA ... and I do have some "anti-seize" in the threads ... but I "pounded" it tighter yesterday with a multi-tool and a small rubber hammer ... and I keep checking it and it hasn't been loose. Though last night I took it off and will try today with just a flash hider on there. So today, so far, going with no suppressor and with cleaning the barrel and chamber.

Thanks for the replies !!

 

[maverickasu]

Other than loose stuff, which you’ve checked, scope, which your checked and carbon ring, I’d check the suppressor for anything wonky. Maybe the QD loosened up just a tad.

Could he have had a light baffle strike at some point and that is causing wonkyness internally?

I assume yes but am a noob to suppressors

 

[Spblademaker]

Anything could happen. Best to remove as many variables as possible. Good luck.

 

[wigwamitus]

... Could he have had a light baffle strike at some point and that is causing wonkyness internally? ...

I had that thought also .. hence removing the suppressor.

... remove as many variables as possible ...

Yup

 

[wigwamitus]

Ok, put a brand new 7.62 nylon chamber brush on a 12 inch length of cleaning rod and stuck the other end in a drill. Slobbered a bunch of CLP on there, which was pretty thick as we as 15F outside right now. Ran the drill with the chamber brush in the chamber for maybe 20 seconds ... moving it back and forth. A bit of "dust" was visible in the air around this operation.
Then swabbed out with 6 "patches" (torn off pieces of shop towel) on a 45 acp cleaning rod ... got 90% of the loose soot out. Thought the "patches" weren't nearly as dark and dirty as the ones I see when cleaning stoner rifle chambers.
Then ran six dry bore snakes thru the barrel.

Well, if there is a real hard "carbon ring" in there, I might have to throw some KROIL in there and let it soak ... then reclean and repeat a time or so. But for today I will try this cleaning together with removing the suppressor and see if I can detect any difference.

I could remove the SPIGOT, which is used for mounting clipons and I actually have a plan to do that. A PRI receiver mounting long base is in bound to me, then I can remove the SPIGOT, though I'll have to revert to harris bipod. But I mostly shoot off the tripod anyway, so not a huge deal.

ok, so thus far for today this ^^ is the plan.

thanks again everyone ! This is a great forum, when people jump into help each other !!!

 

[wigwamitus]

One more piece of data ... magnetospeed v3 readings on both the 20 inch barrel (the bravo gun in question) and his bigger brother the 22 inch barrel McRee ... 2 days ago ... same m118lr ammo ... 20 rds each ... average MV

22 inch - 2660 fps SD 20
20 inch - 2551 fps SD 18

So that is a surprisingly low MV out of the 20 inch ... well or it is a surprisingly high MV out of the 22 inch. but previous reading on the 7.62 FGMM 175gr for the 22 inch was 2652 ... which seems aligned with real world considerations, so that indicates the 20 inch is low. Which is consistent with some carbon ring symptoms I'm seeing

http://www.snipershide.com/shooting/threads/carbon-rings.6874904/

 

[wigwamitus]

Ok, went out and fired 20 rounds and things seem better.

All rounds were prone.

2 sighters and 6 x 3 rd groups.

First three groups without the suppressor were 8, 10, 12 (I measure in 16ths) ...

Then I decided to add a different supressor (SiCo Omega) as wife was complaining about the "Loud Blunderbuss" being fired out in the yard. We live in rural area on a cattle ranch and my 100yds shooting area is right by the house. I rarely, (almost never) shoot rifles without suppressors ... so she isn't used to what real guns sound like !

Second three groups were 8, 10, 16. The 16 was aiming at a dot high up on the target board and more challenging to my cheek weld and eye relief.

So, 90% sure the issue is/was the Griffin Arms suppressor, which I've used heavily for 2.5 years and never had a problem, until last week when now I'm having a problem. I will put it on another gun, to double verify the problem, then call Griffin Arms and see if I need to sent it in.

Now, with this gun, I think I'm down to finer adjustments to the cheek piece height and the fore/aft positioning of the scope to get proper eye relief. I was stretching my neck forward to get proper eye relief. For the last three groups I cranked magnification down to 20x and that seemed to help, though the results don't show it

Any who. I will also soak the chamber in kroil and clean the chamber repeating for several days to remove any "carbon ring" that might be in there. I'm shootin' these two .308 bolt guns pretty hard these days .. 40-100 goal is 200 live fire rounds per week, every week. Over the past year I only averaged 106, but I keep trying. I have gotten down below 0.75 on all guns even off the tripod ... better than I expected to be able to do. And some days I can get strings of three groups under 0.40 inches ... so maybe 0.50 MOA is possible for me ... prone. But most things have to be working right to do anything like that consistently and I'm not there yet in the universe of getting everything working right yet. But the fun is in the journey.

Thanks for all who chimed in!

I'll update further if any significant events happen. But it seems like "broke suppressor" is the reason for the dramatic change from < 1 MOA to 8 MOA and then back to < 1 MOA again. I have no idea how I broke the suppressor. I'll discuss with G.A. maybe they can tell me what I did wrong.