Suppressors POI shift

[Sumpter Steve]

Quick Question for you fellas.

My SUREFIRE 7.62K can seems to have a POI shift but settles down after about three shots. This POI shift is fairly consistant at 100 yards (see pic):

Shot # POI change (Mils)
1 (CBS) 0 (no shift)
2 .25 (low)
3 .5 (low)
4-8 .75 (low)

What would you recommend?
Should I:
A) Zero rifle for shots 4-8 when it seems to settle down and stay consistant? This would mean I would have to hold under for my CBS and shots 2&3.
B) Zero rifle for CBS and hold over for follow up shots?
C) Don't use the fucking thing and make lots of noise?

Your thoughts are appreciated.

 

[Lowlight]

Re: POI shift

Zero for the group and shoot the snot out of it for about 500 rounds, if it doesn't settle in once the carbon builds up, dump it. It may settle in when it gets dirtier.

Customer service if it doesn't straighten out.

 

[HPLLC]

Re: POI shift

That much shift (varience between CBS and settled in) would suggest your suppressor has the ability to wobble on the mount. Have you tried tightening the suppressor gorilla tight?

Some Surefire users say finger tight, the cans shoot average, but gorilla tight locking rings make for great shooting cans with the caveat that they are a bitch to remove at times.

Typically when POI shift wanders from center to 2-3MOA low that indicates the can is hanging on the mount or slightly loose. The bore should point in the direction of shift AKA down. Surefire's bores are symetrical, and that makes this more straightforward than other baffle styles as any shift should be directly related to suppressor bore attitude. (this is of course in the absence of other issues like pencil thin barrels that have residual stresses and don't shoot consistently when heated).

Certainly if you can't get better performance than that, CS would be the way to go. The minimal shift is the reason people buy Surefire.

 

[Sumpter Steve]

Re: POI shift

Thanks guys. I'll hit the range tomorrow and run a lot more rounds through it. I'll also tighten her down reeely good. It's going on my OBR which is a consistent 1/2 MOA shooter so I know it's not the rifle.

 

[wIg SpLiTtEr]

Re: POI shift

Let us know if it helped, Im interested in this feedback!

 

[jcsparky]

Re: POI shift

Yea, I have a SDN 6 I'm holding off putting on my Larue till I get the SF 762K.. Please tell me the surefire is the cat's ass..!!

 

[Sumpter Steve]

Re: POI shift

More testing today. My CBS was once again dead on except for my "shoulder" issue but then the next shot (#2) was 1/4 Mil low and shots 3-10 were all 1/2 Mil low of CBS (see pic).

I then waited about 5-6 minutes to let the can cool down until it was just warm to the touch but not hot. My first shot was 1/4 Mil lof of my POA and my follow up shots (2-5) were 1/2 Mil low of my POA (see pic). I'm thinking that this is a heat/gas issue
but I'm not sure. All shots were taken at 100 yards (prone w/rear bag).

 

[HPLLC]

Re: POI shift

When you say CBS do you mean cold bore, or "CLEAN BORE"?

In your second set of pictures it looks like you might have a cold-clean bore flier high, and the rest of the rounds are pretty well grouped.

It is not uncommon for barrels to throw fliers high with bore solvent in the bore (different velocity from lower coefficient of friction).

In the second set you have a similar first target, then a dissimilar second target (fouled bore). This implies your rifle has a cold clean bore flier ~2.75 MOA high, because that flier does not appear in your second group with the can. Rather there is a flier about 1 MOA high of center that might have something to do with First round pop and the burning of oxygen in the suppressor, while that round is only about .5MOA outside of the mean group (not great, but not horrible like the 2.75MOA Cold Clean bore), especially since you could hold ~1 MOA low (or ~.3mil) for the first round fired through the can in several minutes, accounting for FRP and eliminating the issue.

<span style="font-weight: bold"> Is your rifle shooting POI without the suppressor attached? Do you mount to a brake or flash suppressor mount? </span>

If your barrel thread is not true, that could also create a shift between suppressed and unsuppressed as the suppressor's baffle system will exaggerate the results of any miss-allignment. For a 3MOA shift, you should be able to see alignment error visually if you unload the rifle, place paper in the breach and look down the suppressor bore.

The can should have to be at least .015" out of perfect alignment for a 3MOA shift to occur. If the can weighed 40 ounces a 3MOA shift might make sense. Specs suggest it should weigh 19 ounces, or not enough to cause any dramatic shift from weight alone.

 

[Sumpter Steve]

Re: POI shift

Sorry for the confusion. I meant Cold Bore Shot (CBS) and not a Clean Cold Bore (CCB). I didn't do any cleaning of the rifle today before I fired my Cold Bore Shot (top target/last post). My bore had already been cleaned and then fouled after shooting it the day previously. I always clean and then foul my rifle with three rounds after every range session. Today the CBS was dead on for elevation then the next shot was 1/4 Mil low followed by an 8 shot group (measured 7/8") which was 1/2 Mil low. In my bottom target the first shot was taken (without any cleaning) with the barrel warm (not too hot to touch) which is similar conditions to the above target (shot #2) and their impact was the same. It seems fairly consistant that the CBS is on for elevation the second shot is 1/4 Mil low and the follow up shots (3-10) are about 1/2 Mil low of my CBS. That's why I'm guessing that it might be a gas/heat type of thing but I don't know. Thanks for all of your help/input. Steve. BTW. The suppressor is a SUREFIRE 762K (QD) has about 100-150 rounds through it. Also my rifle does shoot POA/POI without the suppressor and is mounted with a SUREFIRE muzzle break.

 

[HPLLC]

Re: POI shift

Your symptoms are strange, almost like the suppressor has a different attitude for the first round (the CBS and loosens slightly after the first shot). That major flier has no reasonable explanation IMO if not that the can shifted its alignment after this round was fired.

Take a look at your brake and your suppressor alignment.

Lowlight mentioned some brakes were made which had runout in the bore apertures. This could mean that you have a shift associated with the brake, or a shift associated with the alignment of the can.

It's harder to troubleshoot with more variables, but that seems to be what the variables are:

1. Barrel thread alignment
2. Brake aperture alignment (depending on barrel thread alignment and brake quality control)
3. Suppressor alignment (depending on the exterior surfaces of the brake and the barrel thread)

I was out shooting with my brother one day and we were using an Ops 12th model, and getting erratic fliers and poor accuracy. It turned out that the brake was about .018" eccentric or nearly touching the brake baffle on one side of the bore, because a crush washer (reccommended mounting system part) was throwing brake and suppressor alignment off. Visual inspection confirmed it was grossly missaligned without any hair splitting required.

We remounted the brake with a machined washer and accuracy returned, as well as perfect alignment.

 

[Lowlight]

Re: POI shift

Steve

This target you posted,

Looked like my Gemtech (direct connect) group before it "broke in" which was around 500 rounds. The more I shot it the better it got, but was doing the same thing.

It sort of looks liked some "first round" deviations I have seen with other cans, where that first round pop causes the round to stray. I have yet to find a real cure for these types of cans and problems.

There are some SF guys on here, Chucky maybe able to help, but I suspect the answer is, "send the rifle and can in" for analysis. Though I have seen brake issues, most of those are well over 2 years old and for the most part since addressed. However it is not to say the brake isn't the problem, maybe the next route for you is switching it out to a different brake and see what happens.

Ditto on the crush washer issue, I have seen that too, I have one right now I need to address I think the crush washers are the problem so I am moving to change those out. Not sure how your brake is timed ? Machined or washer ?

 

[Sumpter Steve]

Re: POI shift

Thanks for the input fellas. My brake is installed using SF's timing wheel and by following the directions closely. It is centered (Bottom Dead-Center) and I used the shims they provided to get it into place. I did not use a crush washer and it might just be the "First Round Pop" that I'm dealing with. I will go pickup another brake and install it as you suggest. I wonder how hard is it to get one of these brakes off after you use their "thread setter" that they provide?

 

[HPLLC]

Re: POI shift

Why not visually check alignment first? You would probably be supprised. The human eye can pick up .006" pretty easy, a lot of machinists could see .003" of alignment error (some less).

If you check the brake to barrel bore and suppressor to barrel bore alignment and there are issues, at least you would know where to start.

The brake to barrel for instance and can to barrel coinciding would suggest a bad barrel thread. That would render another mount a complete waste of time and money.

 

[Sumpter Steve]

Re: POI shift

I think that I discovered the culprit. When I went to take off the brake it was only slightly tightened down and thus came off very easily even with it being Rockset. It's now on their tight and I hope to find much less POI shift later in the week.

 

[cz777]

Re: POI shift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sumpter Steve</div><div class="ubbcode-body">I think that I discovered the culprit. When I went to take off the brake it was only slightly tightened down and thus came off very easily even with it being Rockset. It's now on their tight and I hope to find much less POI shift later in the week. </div></div> well please try this stuff clean threads with brake clearer ..let dry now prime both sets of threads muzzle devise and barrel with http://www.amazon.com/dp/B000H5YAX6/ref=...ASIN=B000H5YAX6 tighten to 25 foot pounds let dry for 24 hours ...its great for gas blocks as well etc .....

 

[HPLLC]

Re: POI shift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sumpter Steve</div><div class="ubbcode-body">I think that I discovered the culprit. When I went to take off the brake it was only slightly tightened down and thus came off very easily even with it being Rockset. It's now on their tight and I hope to find much less POI shift later in the week. </div></div>

Did you look at the alignment to see if it appeared to be centered?

I tried Rockcett and my concensus was that it was not a reliable thread sealant. I believe ASE Utra mentioned they just have people torque to a recommended spec, and that has worked for them.

It's become my opinion that torque is more important than the thread locker as a result of high temperature failure of rockcett after following flexbar engineer recommendations regarding its application (cleaning threads, application, baking in the oven for x amount of time etc).

 

[Sumpter Steve]

Re: POI shift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Griffin Armament</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sumpter Steve</div><div class="ubbcode-body">I think that I discovered the culprit. When I went to take off the brake it was only slightly tightened down and thus came off very easily even with it being Rockset. It's now on their tight and I hope to find much less POI shift later in the week. </div></div>

Did you look at the alignment to see if it appeared to be centered?

I tried Rockcett and my concensus was that it was not a reliable thread sealant. I believe ASE Utra mentioned they just have people torque to a recommended spec, and that has worked for them.

It's become my opinion that torque is more important than the thread locker as a result of high temperature failure of rockcett after following flexbar engineer recommendations regarding its application (cleaning threads, application, baking in the oven for x amount of time etc). </div></div>

Yup. I cleaned the threads (including the inside of the brake) realy well with acetone and a brush. I then timed it as per their instructions (bottom-dead-center) while using their timing wheel and the provided shims. Next I applied a liberal ammount of Rockset to the threads on both the barrell and the brake and then I re-installed the brake and timed it once again. It is now torqued down to 35lbs. and still remains aligned in the bottom-dead-center position. I'm going to allow 48 hours for the Rockset to cure but I should be able to hit the range in the morning. I'm hopeful that I will have much less POI shift. Keep checking tomorrow for my AAR. Thanks to all of you fellas for all of your help. Steve.

 

[HPLLC]

Re: POI shift

When I say "aligned" I'm not talking about brake timing. Brake timing is cosmetic and irrelevant to POI shift.

If you remove the magazine, unload your rifle, place it on safe, and put a piece of white paper in the open breech where light can hit it, you can then look down the muzzle through the bore and if you look parallel to the sidewalls of the bore on all sides you will be able to see alignment error of the brake, or the suppressor in relation to the bore if it exists. If it does it will appear in the form of less or more clearance depending on the side of the bore you are looking at. Variable clearance is evidence of alignment error.

The Surefire suppressor could be absolutely perfect to .0001" at the muzzle in relation to the mounting system when mounted to the brake, but if the barrel thread is out of true, there could be alignment error anyway. If the suppressor bore is not aligned with the barrel bore, there will be POI shift outside of intended design parameters.

 

[Sumpter Steve]

Re: POI shift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Griffin Armament</div><div class="ubbcode-body">When I say "aligned" I'm not talking about brake timing. Brake timing is cosmetic and irrelevant to POI shift.

If you remove the magazine, unload your rifle, place it on safe, and put a piece of white paper in the open breech where light can hit it, you can then look down the muzzle through the bore and if you look parallel to the sidewalls of the bore on all sides you will be able to see alignment error of the brake, or the suppressor in relation to the bore if it exists. If it does it will appear in the form of less or more clearance depending on the side of the bore you are looking at. Variable clearance is evidence of alignment error.

The Surefire suppressor could be absolutely perfect to .0001" at the muzzle in relation to the mounting system when mounted to the brake, but if the barrel thread is out of true, there could be alignment error anyway. If the suppressor bore is not aligned with the barrel bore, there will be POI shift outside of intended design parameters.



</div></div>

Interesting. Thanks for the info. I will check this alignment before I hit the range in the morning. Thanks again for your help. Steve.

 

[cz777]

Re: POI shift

use of acetone is part one after drying happens ,next is use of non-chlorinated brake cleaner wait till dry ...prime both side with rockset ...this was told to me by surefire by e-mail talk about over kill ....