Barrel accuracy with/without suppressor

[gatordev]

So I know there's all kinds of crazy physics involved with the barrel when a gun fires, and there's things like harmonics, barrel whip, barrel "droop" depending on the heat and profile, etc. I also understand some guns like or don't like certain kinds of ammo. Given all of that, I've been noticing some interesting effects of using a suppressor on a couple of different rifles and thought it might be something others would like to see. Or maybe not.

After finally depleting my supply of PPU M193 ammo over the last year, I'm now moving everything (non-precision) back to Federal M193 since I have a "solid" supply on hand that's accumulated over time. While confirming zero this weekend, I found something interesting with my Noveske N4...as well as something I've noticed in the past with my Colt 6921 SOCOM barrel.

Below is a picture to show what I was seeing, but here's the breakdown... I was zeroing the N4 and after some issues with my rear bag (in red), I settled down into a very comfortable group for the ammo being shot (in yellow). Since I was happy with that, I moved on to putting my SF 556RC on the gun. This was mostly just a test to see what POI shift would occur with this ammo/gun.

I was a bit surprised to see the results (blue):

http://i840.photobucket.com/albums/zz322/gatordev/Public%20pics/N4.M193.drawing_zpsuffxufem.jpg

With this ammo and my not-that-special skill, it definitely looks like the group tightened. So, maybe the can helped counter whatever various barrel harmonic/whatever was occuring?

What I find interesting is that I haven't seen the same result with a Mini on the same gun. And on my Colt, putting the Mini made it worse (this was with the PPU stuff on another day, but the Colt really seemed to like the PPU stuff). The full-size 556RC did NOT have the same poor results on the Colt, either.

I guess it makes sense...you're making the barrel longer by some certain length, depending on the suppressor, and that affects the results, one way or the other, depending on the barrel, but it was interesting to see. Apparently on the Noveske and the Colt, the Mini is adding just the right amount of "wrong" to the equation, while the RC is making everything awesome.

Or is there more at play here?

[alamo5000]

While I am not a suppressor owner just yet I know some of the old timers and precision shooters tried everything from adjustable muzzle devices to barrel tuners to get the harmonics right in line with whatever round it was on whatever barrel it was.

Adding over a pound of weight onto the end of your barrel is going to make a difference.

As for the 'accuracy' game...to get groups.. what kind of optic were you using and at what distance? How were you shooting? (IE position) Prone? On a bench? How is your optic mounted? QD or something else? I ask because I shot a group like that before...a 'string' if you will...only to find out my scope mount was slightly loose.

When my suppressor gets here you better believe I will be taking the scientific approach with it but in your case there are too many unknowns to say with any certainty what is happening.

If you want to get down to brass tacks about it get a solid rest and a consistent aim point. I bought some circle dot stickers at Target that I put on my shoot n see targets so that I have a clearer point of aim.

Once you eliminate all the variables... IE loose QD mount or whatever then start shot logging. Take one shot and then look through your spotting scope. Mark it's position on a piece of paper. Then do shot 2 and log it...on to 10 shots. This way you know not only where it hits but what order each shot is hitting. Do that two or three times and you can map out your shots. Do it without the suppressor and then with the suppressor and you will know what the effect is.

[Former11B]

It is not unusual for a suppressor to tighten up your groups. More than likely there will be some POI shift (you're hanging weight off the barrel, some physics reaction will occur). Velocity increase is probably negligible. And just a thought: you might also provide a more stable platform when shooting suppressed due to lack of muzzle blast if you are unconsciously moving/jerking when shooting unsuppressed. I like to shoot with my brothers suppressed (younger teens). They shoot better because they're less intimidated (not saying you are!)

[gatordev]

As for the 'accuracy' game...to get groups.. what kind of optic were you using and at what distance? How were you shooting? (IE position) Prone? On a bench? How is your optic mounted? QD or something else? I ask because I shot a group like that before...a 'string' if you will...only to find out my scope mount was slightly loose.

It was with a MK6 with a bipod and a rear bag on a bench with a Larue mount shot at 100 yards. I'm not really sure why you think it's a string. It's 4+ MOA ammo out of a chrome-lined barrel (and a target that's bouncing back in forth in the wind), so the fact that they're moving around within a 3" area isn't out of the ordinary.


If you want to get down to brass tacks about it get a solid rest and a consistent aim point. I bought some circle dot stickers at Target that I put on my shoot n see targets so that I have a clearer point of aim.

I think you may be mistaken in that I'm trying to solve a problem. I'm very happy with the results, suppressed or unsuppressed. This was more of a theory or "why" question. I know it happens, and I can guess (added weight is dampening the the barrel in some way, in this case a good way), but wasn't sure if anyone knew more specifics.


It is not unusual for a suppressor to tighten up your groups. More than likely there will be some POI shift (you're hanging weight off the barrel, some physics reaction will occur). Velocity increase is probably negligible.

I'm with you on velocity. Seems like sometimes it's noticeable, but often it's not, depending on the gun. Like I said, I was just wondering if there's a "why" for it tightening up the groups. All that said, I continue to be impressed with the lack of the POI shift with the Noveske barrel and "bulk" ammo. M193 seems to be pretty consistent. Geco .223, however, has a pretty significant drop on this gun, but it's logged and at least I know the drop.

[SINNER]

I experienced the same but more drastic change on a good friends gun. He claimed it would not group without a can on the weapon. I refused to believe that the can could improve his groups by such a significant amount. After about 60 rounds both with and without the supressor on, the gun clearly shot better with the can. Knowing something was not right I went to the next logical thing, the flash hider/mount. We removed that and the gun shot the best group of the day.

Later inspection of the 51t flash hider with a alignment rod showed one of the three prongs was visibly closer to the bore. So in the end the flash hider was causing a slight deflection of the round exiting the barrel and the can partially corrected the issue. He replaced the mount and other then the slight impact shift the grouping remained consistent.

[GOST]

I experienced the same but more drastic change on a good friends gun. He claimed it would not group without a can on the weapon. I refused to believe that the can could improve his groups by such a significant amount. After about 60 rounds both with and without the supressor on, the gun clearly shot better with the can. Knowing something was not right I went to the next logical thing, the flash hider/mount. We removed that and the gun shot the best group of the day.

Later inspection of the 51t flash hider with a alignment rod showed one of the three prongs was visibly closer to the bore. So in the end the flash hider was causing a slight deflection of the round exiting the barrel and the can partially corrected the issue. He replaced the mount and other then the slight impact shift the grouping remained consistent.

Makes sense, I've seen some muzzle devices mess up groups.

[gatordev]

Later inspection of the 51t flash hider with a alignment rod showed one of the three prongs was visibly closer to the bore. So in the end the flash hider was causing a slight deflection of the round exiting the barrel and the can partially corrected the issue. He replaced the mount and other then the slight impact shift the grouping remained consistent.

Yeah, that definitely makes sense. I know another issue can be the torque of the muzzle device, which I've always found interesting. I find it amazing how something seemingly insignificant can affect a large piece of steel, but it does.

[JGifford]

Yeah, that definitely makes sense. I know another issue can be the torque of the muzzle device, which I've always found interesting. I find it amazing how something seemingly insignificant can affect a large piece of steel, but it does.

It causes flaring at the muzzle, like a trumpet, when you pass 25 ft of tq. It becomes noticeable past about 30 ft tq.

[Slippers]

It causes flaring at the muzzle, like a trumpet, when you pass 25 inches of tq. It becomes noticeable past about 30 inches.

Do you mean feet? 25 inches is not much past finger tight.

[gatordev]

I'm guessing that's what he meant. I believe the spec on the M-16/4 is 20-30 ft-lb. If it's supposed to be inches, I'm in big trouble!

Now that I think about it, would the same spec be good for other barrels? I'm in a medium-term build up of a LR bolt gun and I need to throw a brake on it (once I actually buy the brake).

[Slippers]

Yes, 20 ft. lbs should be fine on a bolt gun. If you're worried, talk to the barrel and/or muzzle device manufacturer.

[JGifford]

Do you mean feet? 25 inches is not much past finger tight.

Yes, I'm sorry. I meant feet, and edited to that effect. I've been dealing with optics lately...