Suppressors Suppressed AR10 doing something strange

[Rancid Coolaid]

Here's the setup, Armalite AR10 upper, LARue 1.5 mount holding a 2.5-10 Trijicon Accupoint. Shooting 168-grain Hornady TAP. (Lower is Iron Ridge, great lower, I highly recommend them.) Trigger is single-stage match.

This is what I see when shooting suppressed:

Great group (>1MOA) but 4 inches low. I adjust 4 inches, and fire. Perfect group, dead nuts.
If I set the gun aside and come back to it later, it shoots 4 inches high, great group. I adjust 4 inches down and fire. Dead nuts.

Set it aside, come back to it later, fire 3-shot group, 4 inches low again.

And on and on.

Once the rifle sits (and cools - or looses pressure from the can), it shifts, always the same amount, always opposite of how it shifted last time - if once high, it will go low next time. Once I change the dope and shoot, it will stay dead nuts till I stop shooting.

I am not heating the barrel excessively, I'm not banging the whole thing against a rock, I'm not changing a thing.


I am shooting 3-shot or 5-shot groups, the rifle groups well, no problem, but point of impact jumps once the rifle sits unfired for awhile.


I will take the can off and take it back to the range soon and see if it does it again. With some luck, I can determine if this is a can problem or a scope problem.


Anyone see this before?


Same can on a bolt gun: dead nuts, no issues at all.

 

[Adician]

Re: Suppressed AR10 doing something strange

Dead nuts.

Dead.

Nuts.


To be honest, I dunno. I've never had this problem before with any of mine. Does the rail system touch the suppressor?
That's about the only thing I can think of, but yours it repeatable.

 

[KYS]

Re: Suppressed AR10 doing something strange

what ammo are you shooting?
are you sure your handgaurds and barrel nut are tightened down to spec?
Have you checked the scope mount?
are you shooting off a bipod or bags?

you should run thru those as a checklist. you could have a bad batch of ammo....

 

[jgobbels]

Re: Suppressed AR10 doing something strange

what can? How does it attach?

 

[Rancid Coolaid]

Re: Suppressed AR10 doing something strange

Hornady TAP 168-gr. Amax
Handguard and barrel nut are good to go
Scope is mounted in LaRue, torqued to spec, QD mount
Shooting from a rest, super stable.
Trigger is match, breaks about 3 pounds.
Can is YHM Phantom, screw-on

What I don't get is the precision of the groups, everything is under 1 MOA - which, in my opinion, ain't bad from an AR10 with no tuning.
I've seen what happens when a scope is loose or ammo is crap or something touches the barrel or shooting offhand; this doesn't act like that at all.


I'll take it out next week and shoot without the can, see if it still moves.


Never seen this before, hope to not see it again.

 

[microsuck]

Re: Suppressed AR10 doing something strange

You arent using a crush washer are you? The can should be shouldered up against the barrel shoulder.

 

[zenbiker]

Re: Suppressed AR10 doing something strange

I shoot a YHM Phantom on my FN but with the quick detach/flash suppressor assembly; it hits exactly 1 mil low with the can on vs. no can, but points of impact are repeatable. You're doing the right thing to check the rig without the can to confirm or rule out a scope problem; next, as previously mentioned, crush washers are a no-no; any spacers need to be the solid spacers that YHM supplies. If your can has a quick mount system, make sure there is no play. Shake the can to make sure the baffles are not loose, check the end of the can for bullet grazing. Last, pay attention to how the rifle is supported when you're shooting; if you aren't running a free float tube, the rig may be more susceptible to sling pressures/bipod pressures.

Weird that the points of impact are 4 inches; thats just about one mil at 100 meters. Man, I hate these glitches. Take a deep breath, drink a beer, recheck your gear, and go back to the range; check the rifle without the can first; keep the gun cool, and then check it with the can. Let us know. FWIW, this smells like a scope issue to me, and if your range check is the same, I'd change scopes (or go to irons) and repeat.

Best of Luck,

Wes

 

[Rancid Coolaid]

Re: Suppressed AR10 doing something strange

No crush washers.

Pictures of me shooting it will accomplish nothing, I ain't a mall ninja, the Marine Corps taught me how to shoot pretty well.

Yea, hoping to get to the range tomorrow for some additional testing. No rattles in the can, no baffle strikes, no play when screwed on.

I too am leaning toward scope issue - which sucks, I really like the scope.

 

[KYS]

Re: Suppressed AR10 doing something strange

what scope are your using?

FYI - do not drink a beer then go to a range. thats just dumb. I have never seen a YHM mount come with spacers, so dont use them. No thread on can will have washers they depend on the shoulder of your barrel threading to line up. If your baffles are loose then you have a VERY defective can.

I will bet money on a defective scope or bad ammo.

 

[sinister]

Re: Suppressed AR10 doing something strange

What reticle?

An Accupoint with a triangle isn't going to be nearly as repeatable as crosshairs.

 

[smokshwn]

Re: Suppressed AR10 doing something strange

If it is truly doing the same thing that consistently, I can't seem to steer myself away from something wrong at the barrel nut/barrel/receiver interface.

 

[Rancid Coolaid]

Re: Suppressed AR10 doing something strange

Range today, report to follow.

It is Trijicon Accupoint with triangle but I use the triangle tip as the aiming point on the bench.

Am taking 2 ammo types today, see if it replicates with can on and off and see if it replicates with 2 different ammos.

No spacers or washers, can goes straight onto barrel threads, sits on the shoulder.

 

[zenbiker]

Re: Suppressed AR10 doing something strange

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kyshooter338</div><div class="ubbcode-body">what scope are your using?

FYI - <span style="font-weight: bold">do not drink a beer then go to a range</span>. thats just dumb. I have never seen a YHM mount come with spacers, so dont use them. No thread on can will have washers they depend on the shoulder of your barrel threading to line up. If your baffles are loose then you have a VERY defective can.

I will bet money on a defective scope or bad ammo. </div></div>

Crap, I never thought anyone would interpret it that way. Yeah, for whoever thinks it's cool to go the range drunk, what he said. However, if you need one while you're figuring out the problem, AND you're not going to the range, driving, operating heavy machinery, etc., well, go ahead and have a cold one.

Geez.

Spacers: right, should be none on YHM screw on or quick connect. SureFire uses them to index the quickconnects on its system, but are adamant about no crush washers.

I'm still betting scope OR LOOSE SCOPE MOUNT (just occured to me).


Regards and luck,


Wes

 

[Rancid Coolaid]

Re: Suppressed AR10 doing something strange

Curiouser and curiouser!


Here is a picture of the day's shooting (full disclosure.) Groups were all 3-shot except first which was 5 shot (without can. Ammo was a mix of Hornady TAP 168 and Black Hills 168, some groups fired with can on, some with can off. All groups were fired from bipod (so my movement is an issue) and a jackass decided to plop his fat ass down next to me with a 300RUM with a brake, that opened up a few groups with fliers.

Details to follow.

First rounds down range were Group #3. These were cold barrel, cold shooter shots with no can (weapon is zeroed with can.) Aiming point was dead bull.

Next group fired was with can, group#5.

Next fired was group #8 WITHOUT can

All other groups were fired with can (mix of Black Hills and Hornday.)

So:

1. Worst group ,as measured by "OnTarget", is Group 8 (without can) and is 1.932 MOA.

2. Best group fired was Group#4 at 0.516 MOA (all groups are max spread, center-to-center.)

3. Both ammo types were fired with and without can, no real change in POI due to ammo (that I can tell.)

4. Not one click on the scope all day. No dope changes at all.

5. Usually shoot lefty, shot all these righty.

6. All aiming points are the bull's eye closest to the respective group - except the first group, whose aiming point was center bull.


Analyze away!

I'm baffled. The first group without can (cold shooter cold bore) was 7 inches high and 1.5 inches right. Follow-up groups were all within 2 inches of dead center - even the next group fired without the can.

The scope is a Trijicon accupoint and I did my best to keep the top point of the post dead-center on the bull. Some of the nice groups are probably luck, some of the crap groups are probably more skill.

I checked the scope, all screws are good, the base is secure. I put a bore sighter (cheap BSA with arbor in the bore) and watched the clicks on the scope appear on the grid, all moved as it should, no jumps, no delayed movements.


Obviously the rifle is capable of great accuracy, but my first group always ends up other than where I want it, suppressed or not.

I did not see the "jump high - jump low" problem, just the initial group, then everything was dead on.

I didn't let the rifle sit for an hour like last time, shot groups, then let the rifle sit for 10 minutes or so, then shot next group.

Anyone? Anyone?

 

[KYS]

Re: Suppressed AR10 doing something strange

It has to be the rifle. I would send it in to a smith and have them work it over. You could have a bad barrel. Manufacturers are not impervious to getting some bad tubes and the metal be flaking or fouling badly.

 

[Stealth-X]

Re: Suppressed AR10 doing something strange

The way I see it, the real problem in troubleshooting this is that you're getting good groups. If you had something touching or loose or inconsistent, then it would be very strange for something to change only between groups. The expected result would be crap accuracy. Since the gun is shooting consistently good groups, it would seem to be something that changes between your groups. Assuming you are shooting consistently, the only thing that comes to mind is the mag, but I can't see how that wold change poi much. Maybe a different feed angle or spring pressure, but in the end, it's seated in a chamber well enough to shoot good groups so that would seem to negate that idea.

I think we need some Mensa types for this brain teaser.

Good luck,
Nate

 

[sinister]

Re: Suppressed AR10 doing something strange

1 -- Get the rifle on to sandbags (both fore <span style="font-weight: bold">and</span> aft).

2 -- Shoot 10-shot groups. Nobody can tell where the center of your group is with three shots. You need to see how the rifle builds its groups.

3 -- Use a higher magnification scope with crosshairs. You aren't going to have a consistent, single aiming point using a chisel point.

4 -- Is this a rifle with free-floated barrel? Is it a chrome-lined service barrel or a heavy AR-10T barrel?

5 -- Horizontal isn't bad but you have consistent verticle spread. Your eyeball needs to be in the same place for every shot.

 

[zenbiker]

Re: Suppressed AR10 doing something strange

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sinister</div><div class="ubbcode-body">1 -- Get the rifle on to sandbags (both fore <span style="font-weight: bold">and</span> aft).

2 -- Shoot 10-shot groups. Nobody can tell where the center of your group is with three shots. You need to see how the rifle builds its groups.

3 -- Use a higher magnification scope with crosshairs. You aren't going to have a consistent, single aiming point using a chisel point.

4 -- Is this a rifle with free-floated barrel? Is it a chrome-lined service barrel or a heavy AR-10T barrel?

5 -- Horizontal isn't bad but you have consistent verticle spread. Your eyeball needs to be in the same place for every shot. </div></div>

+1. You've got some crucial information here, but it still doesn't totally answer the question.

A few questions: How many rounds do you have down the barrel? Is it free float or rigid? When the can is not mounted, are you using a flash suppressor that screws on? Give us a little more info about the mounting system. I've had similar issues in a rifle with a loose muzzle brake/flash suppressor.

Mount a known scope in place of your Trijicon, reshoot from a solid rest. See what happens. I'm with you, that cold bore group is way the heck out in right field, and then the POI doesn't seem to vary whether the can is on or not. <span style="font-weight: bold"><span style="font-style: italic">Last, check the barrel nut for tightness</span></span>. Good Luck, looking forward to seeing what you find out.

Regards,


Wes Haddix

 

[cwshooter]

Re: Suppressed AR10 doing something strange

I can't explain the 4" swing. What I see on the target would lead me to think about parallax, and consistency during recoil.
All of your groups, with the exception of 8, are consistent with ar-10 type accuracy, it's just that the point of impact appears to shift a bit.
FWIW, my last 2 DPMS 308s have shot best with some left hand rearward pressure on the stock into my shoulder, and a little forward and down pressure on the grip.
I agree that some testing with a higher magnification scope of known consistency could demonstrate a lot, and that 3 shots doesn't give enough information.
Plus we're dealing with two brands of ammo, and a bipod.

 

[KYS]

Re: Suppressed AR10 doing something strange

I can hold a 1" group with my LWRC Repr, easily at 100 yards.

I would ditch the ACOG.... go to a scope.

 

[zenbiker]

Re: Suppressed AR10 doing something strange

Rancid, did you just get this can? If so, how does the current accuracy compare to the rifle before having the can? Does the can use threads already on the barrel for a flash suppressor or did a 'smith have to turn them? <span style="font-style: italic">How hard was it to remove the existing flash suppressor and how did you do it? </span> Can you post a pic of the rig? Any chance you twisted the barrel and gas tube, even a little?

I'm also curious about the vertical stringing in most of the groups. This rig, with this ammo, with a well trained shooter driving it, off a solid rest, should drill round groups. Vertical strings are a bad sign.

 

[zenbiker]

Re: Suppressed AR10 doing something strange

Any updates yet?

 

[Rancid Coolaid]

Re: Suppressed AR10 doing something strange

Nothing new yet.


Shot the can on another gun, no problems at all.


Will get it to the range this week and shoot lefty (my usual stance) and see if the vertical stringing goes away.

My primary concern is still that first high group, and I have yet to explain that.

More to come

 

[dieselten]

Re: Suppressed AR10 doing something strange

accupoint triangle will easily allow for some POI shift. As the light changes you will hold more or less of the tip in the bull as the tip gets brighter or duller. Changing shooting position between lefty & righty will also change POI. I didn't notice the type of silencer but if it is YHM QD or AAC 762SD with click mount it can change POI depending on how much you initially tighten it.

 

[Rancid Coolaid]

Re: Suppressed AR10 doing something strange

On the range today (rainy in Houston), all groups shot lefty, nothing was over 1MOA, most groups had multiple rounds in the same hole.

All seems to be fine!

....which sucks, because now I'll always wonder when the yips will return.

 

[Witch_Doctor]

Re: Suppressed AR10 doing something strange

I dare say Rancid it was the Indian and not the arrow. I wouldn't worry about the yips coming back unless you decide to switch-shoot again.