Range Report suppressed to unsuppressed groups

[Dontmiss0311]

I'm shooting a .308 FN Patrol Bolt Rifle with a Krieger barrel, AAC Cyclone, Weaver Tactical EMDR. With the suppressor attached I'm getting groups in the .5 - .3 MOA range. When take the suppressor off the group shifts 7 o'clock about 1.5" (normal POI shift), but the group opens up to 1.5-2". Now the really interesting part...after about 10 rounds the group settles down around .5 MOA (keeping the POI shift - normal). I put the suppressor back on and over about 6-7 rounds, the impacts settle to the original zero. This is with shooting a 168 gr A-Max. When I shoot the 110 V-max the same thing happpens, but the unsuppressed groups only open to around 1-1.5" and "settles down" in about 5 rounds.

I used a torque wrench to tighten both action screws to 45 in\lbs and 65 in/lbs with the same results. The stock is a Hogue with the full length alumminum bedding block. I thinking this has something to due with harmonics/vibration in the rifle. I would think once the rifle has settled into the action and stock, that it would be settled and not shift around??

I'm looking for a possible explanation and hopefully a solution. Also, is this happening to anyone else?

 

[JSTARSZ]

Re: suppressed to unsuppressed groups

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dontmiss0311</div><div class="ubbcode-body">I'm shooting a .308 FN Patrol Bolt Rifle with a Krieger barrel, AAC Cyclone, Weaver Tactical EMDR. With the suppressor attached I'm getting groups in the .5 - .3 MOA range. When take the suppressor off the group shifts 7 o'clock about 1.5" (normal POI shift), but the group opens up to 1.5-2". Now the really interesting part...after about 10 rounds the group settles down around .5 MOA (keeping the POI shift - normal). I put the suppressor back on and over about 6-7 rounds, the impacts settle to the original zero. This is with shooting a 168 gr A-Max. When I shoot the 110 V-max the same thing happpens, but the unsuppressed groups only open to around 1-1.5" and "settles down" in about 5 rounds.

I used a torque wrench to tighten both action screws to 45 in\lbs and 65 in/lbs with the same results. The stock is a Hogue with the full length alumminum bedding block. I thinking this has something to due with harmonics/vibration in the rifle. I would think once the rifle has settled into the action and stock, that it would be settled and not shift around??

I'm looking for a possible explanation and hopefully a solution. Also, is this happening to anyone else?</div></div>I don't think you will get a exact solution but a bunch of guesses so here goes mine - first off, I am not very concerned about changes in groups as I don't shoot with the suppressor off. If you do see a change in suppressor off to on and it is consistent then it is predictable and you can compensate for that. I think you do have harmonics issues as you have stated but the other issue may be heat. When you are shooting suppressed the barrel and suppressor heat up rapidly vice unsuppressed and that changes harmonics/barrel droop. I notice that in some of my rifles that I shoot suppressors on. If you shoot longer strings say, 10-20 rounds, you may see more of a change. What you should be looking for is consistencies between off and on suppressor and make the changes accordingly.

It could be your stock as you did mention it has a bedding block that may or may not be exactly tight but you could skim bed the stock to make it tighter. But, I think you will find that it may not be the stock as the issue but the suppressor/barrel combination.

The only solution I can offer is to look for consistency with the suppressor on and off and look at how the rounds impact when the barrel/suppressor is cold versus hot to see if the change the impacts. I had the same issue with a QD mount and ended up going back to threaded suppressor because I could predict where the rounds would land on a cold bores shot within 2 MOA at 100 yards - not acceptable to me. The can would tighten up as it go hot but then I would let it cool and do it all over again and it would be unpredictable until it warmed up.

 

[nfoley]

Re: suppressed to unsuppressed groups

I had similar findings. When I removed the suppressor my groups unsuppressed opened up to 2-3" for around 10 shots. Then it would settle down and shoot back in the 1/2-3/4" area. I came to the conclusion (just my humble opinion) that shooting suppressed did something to the crown, and it would take several rounds to bring the crown back to normal. I know it doesn't make much sense, but it sure didn't make any sense that after shooting suppressed my groups enlarged after removing the suppressor.
Gemtech suggested switching to thread on style (was using the QD style), mostly because they couldn't think of a reason why it was doing this. My stock is a Manners with the mini chassis, and action screws are torqued to spec.
I will let you know if it still happens when I get the suppressor back.
I'm actually glad to see you post this - I thought I was alone in this.

 

[Dontmiss0311]

Re: suppressed to unsuppressed groups

I have tested this with a hot and cold barrel and get the same results. I was also wondering if it might have something to do with fouling on the crown. To eliminate this I cleaned the barrel after shooting it suppressed and shot it unsuppressed....same results. I am completely baffled by this. I'm going to call the guy that re-barreled my rifle and see what he has to say. I will post if I find a possible explanation. The only reason I'm really concerned with shooting it unsuppressed is for varmit hunting. However, if Indiana passes the bill allowing suppressors for hunting, then I think I'm going to drop this quest...

 

[cz777]

Re: suppressed to unsuppressed groups

ok for my understanding is the weight on the barrel which drops the group ....now opening of group is the vortexes in the suppressor bumping the bullet around plus vibrations on the barrel .....better design and materials which dampens the effects of is needed..

 

[Dontmiss0311]

Re: suppressed to unsuppressed groups

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: cz777</div><div class="ubbcode-body">ok for my understanding is the weight on the barrel which drops the group ....now opening of group is the vortexes in the suppressor bumping the bullet around plus vibrations on the barrel .....better design and materials which dampens the effects of is needed.. </div></div>

The extra weight of the suppressor changes the vibrations in the barrel and does probably cause the barrel to sag a little. Which leads to change of point of impact and change of group size. This is common. The vortexs in the suppressor gernerally tights groups up by equalizing the escaping gases around the bullet before it goes completely into "free flight". It kind of acts like the ultimate muzzle crown. If the rifle did not "settle down" into sub half moa groups then I would think there might be a need to upgrade rifle componets or do more load work up, but it shoots great when it "settles down." I'm just puzzled by the settling affect. I am familiar with rifles having to settle down after you remove the action from the stock and then put it back on. This is the same affect I am having. I talked to the guy that did my barrel work and he was puzzled by it also. He suggested bedding the action or replacing the stock. Replacing the stock is something I had in mind, but not anytime soon. Again I appreciate any help with this. Thanks.

 

[Bill Larson]

Re: suppressed to unsuppressed groups

you may have seen/understand how/why "TUNERS" and muzzle brakes work.....I have made several...various styles all threaded...none have affected things to the extent you describe......A small amount of movement in the tuner/supressor changes p.o.i. and accuracy.
How is supressor attached to barrel....??? any moveable/loose weight would affect things.....
bill larson

 

[mattj]

Re: suppressed to unsuppressed groups

Adding a can to your barrel is almost like you're shooting through a different gun as far as harmonics, etc. are concerned.

If you plan to shoot mostly suppressed, do load development (and your zero/dope) with the can on and find a good load for it.

If you're willing to do a bunch of experimentation you may be able to find a load that groups well both with the can on and off.

If you don't reload, try different ammo types and see what works best with your can (or with both can on/off depending on how much that matters to you).

 

[Dontmiss0311]

Re: suppressed to unsuppressed groups

I'm familiar with how tuners work and have a good basic understanding on how barrel harmonics work. The suppressor is a direct thread on, so there should be less room for error compared to a quick detach. I did try load development looking for a load that shot good suppressed and unsuppressed. I went through a lot of loads before I realized what was going on. When I was doing load developement I shot five rounds suppressed, let the barrel cool, took the suppressor off and put on the thread protector, and fired 5 unsuppressed rounds. I did three groups of 5 for suppressed and unsuppressed. I'm sure you can imagine how fustrated and angry I was getting with the groups I was shooting (the settling affect). It wasn't until I decided to just mess around at the range with some reloads I made for just plinking and varmit hunting with my Socom 16. 168 grain A-max with 43.5gr of Varget. I just started shooting with my FN...next thing I know after it "settles down" I'm shooting half MOA or better. I started playing with the seating depth to gain that extra tenth MOA or so (I know it's not a bench rifle, but just trying to see what I can do). I found what seems to be the load the rifle likes, but it's only after it settles. Something else I found is that taking the suppressor off for cleaning and then putting it back on doesn't have the same affect as shooting it unsuppressed. Besides harmonics, barrel whip, etc...the suppressors significantly reduces the recoil. I'm really starting to wonder if it is something with the fit of the receiver, bedding block, and stock. Like a gap or something similar. The reciever or bedding block maybe shifting around with the different types of recoil. I don't have much experience with different types of stocks and bedding, but this seems logical. What do you guys think?

 

[RTK]

Re: suppressed to unsuppressed groups

Any more news on your problem??

 

[JByrd]

Re: suppressed to unsuppressed groups

What your seeing is a speed difference. I had a load that was absolute lazer with a can and i would take can off and it was still good but not as tight as i knew rifle was capable of. I checked the speed by elevation required to my long 966 target sure enough my unsuppressed was 30 fps slower. I ran test bumping .1 grain per step and got a speed match @ .3 increase. Took it back to 100 and it was drillin like the suppressed load,shot a 10 shot group at 966 in the morning and this is it

 

[TB2Blazer]

Re: suppressed to unsuppressed groups

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: procovert45</div><div class="ubbcode-body">What your seeing is a speed difference. I had a load that was absolute lazer with a can and i would take can off and it was still good but not as tight as i knew rifle was capable of. I checked the speed by elevation required to my long 966 target sure enough my unsuppressed was 30 fps slower. I ran test bumping .1 grain per step and got a speed match @ .3 increase. Took it back to 100 and it was drillin like the suppressed load,shot a 10 shot group at 966 in the morning and this is it

</div></div>

Where are you located in north ga? I'm up in north ga as well and wondered where you were shooting 966 yards?

 

[HAZORD]

My theory for why it takes 10 rounds for a rifle to settle down and shoot accurately after removing the suppressor, is that when the suppressor is on, it causes some gases and debris back into the barrel. With a suppressor on my M1A, the brass comes out black, covered with carbon/soot etc. When fired without the suppressor, the brass comes out looking almost new clean and shiny.

If there is enough gas coming back into the chamber to blacken the brass, it will coat the inside of the barrel. Therefore it takes 10 rounds or so to burn all that crap out of the barrel so it will settle down and shoot. Shooters that fire ammo that used different powders have a similar problem, in that they need to fire a few rounds that use the new different powder through their gun before the barrel is coated with the new powder residue so that it settles down and shoots its normal accuracy with that load and powder different from the previously fired load.