subsonic 308Win, suppressors and accuracy

[rap36case]

I have seen articles that claim accuracy can be improved using a suppressor. I am curious under what conditions a suppressor may improve accuracy?

I have looked at the suppressors at AWC for 308Win. I also realize that subsonic velocity limits the effective range to around 200 yards. I would guess that heavier bullets such as the 210 or 230VLD would be more effective.

So what are the important facts about the use of suppressors?

 

[Laurie]

Suppressors, or as we call them in the UK 'sound moderators', are very widely used here for sporting shooting, not so much in competition. I've not seen claims that they improve accuracy, often the reverse but that's usually a fitment / alignment problem. Where the 'moddy' does tighten groups it'll likely be a result of the same effect as fitting a barrel tuner - the lump of metal on the end of the barrel alters its harmonics either for the better or worse with a particular loading, bullet weight and chamber pressure.

The tendency is to shorten the barrel significantly when a moderator is fitted . A very frequent question on the UK Varminting Forum or The Stalkers Directory forum ('stalking' being shorthand for deerstalking, our word for deerhunting) is... "What is the shortest barrel I can run a moderated [enter calibre] rifle at?" Some people are down at 14-16" with 308s and suchlike, 18 to 20 is very common. Cutting the barrel back will lose velocity but does often have a benefit in making it stiffer with beneficial effects on grouping ability.

Because many shooters have dual-use fox / target rifles, they'll use them with the moderator attached for both purposes and although F-Class rules bar them, most BR and F-Class match organisers allow them on other than at national league match level. They offer pluses and minuses in this role. The plus is that a moderator reduces recoil quite significantly, not much of an issue for 6.5X47L or 223 but useful in a heavily loaded 308 that is light for its competition class. The downside is heat - moderators get damn hot pretty quickly and produce copious mirage waves right in front of the scope.

The one point about moderator on/off is that one loading will be unlikely to perform well in both conditions because of the barrel harmonics issue. Most UK moderator users therefore tune their loads with the moderator on and are upset if they're told they can't shoot in a competition with it on. Also, the POI usually changes significantly for the same reason between conditions, so it's a resight if the moddy comes off or it's replaced by a different model.

The norm for subsonic 308 is to use a heavy bullet of around 200gn. That's not to say that 210gn Berger VLDs as an example are ideal though - the ideal subsonic bullet design differs from that optimised for a long-range supersonic flight type - shorter and blunter. Lapua makes a 200gn subsonic version of its D46 design which is quite short overall. So, the 190-220gn Sierra MKs which are short by modern bullet standards might be OK. The other issue is rifling twist rate as MVs around 1,050 fps may need something faster than normal, ie something below 1-10".

 

[6BRinNZ]

Not taking away or adding to Lauries post - with my .223 I found it improved my groups - I posted the results on a thread some time ago...in NZ suppressors are allowed in NRA sanctioned comps but the people using them are typically shooting 155s...the reduced recoil is conducive to precision.

There is barrel harmonic theory relating to having a large mass fixed on the end of the barrel dampening harmonics - I believe some of the Aussies use this approach as opposed to a tuner which is moved to find the best harmonic....suppressors could fit into the fixed large mass category.

I haven't completed any testing day to day of removing and re-adding the suppressor to see how sensitive it is to how tight it is screwed on ("tuner theory") as barrels can be extremely sensitive to tiny changes in position of a barrel tuner - but barrel tuners do not carry the mass that a suppressor does which may in turn reduce the sensitivity.

 

[rap36case]

Thank you both for your comments. I would send the rifle to AWC for suppressor and fitting, if I should decide to obtain after a gun trust.

The harmonics issue and bullet design are valid points. I expect accuracy would suffer past 200 yards with an initial muzzle velocity of 1050.

I have read of some people shooting military rounds through a can for the flash and blast concealing effects. This seems rather impractical, unless you have a can laying round.

I am thinking I will keep my Shilen 308Win the way it is now for long range and not mess with success. We can hunt with suppressors in Texas, so I'm told. I may look for an integrally suppressed 308Win for varmints and hogs.

Thanks again.

 

[Shynloco]

The harmonics issue and bullet design are valid points. I expect accuracy would suffer past 200 yards with an initial muzzle velocity of 1050.


I am thinking I will keep my Shilen 308Win the way it is now for long range and not mess with success. We can hunt with suppressors in Texas, so I'm told. I may look for an integrally suppressed 308Win for varmints and hogs.

WISE DECISION! There is a reason why serious long distance shooters don't use suppressors, moderators or whatever (besides the rules) as I believe, as many do, they are adverse to the harmonics of your Match Grade barrel. And not to disagree with some comments, but some tuners weigh as much as suppressors, but are not for long distance shooting in competition. Tuners do work nicely on higher end Rimfire Rifles (Anschutz) in competition at 50 - 100 yds. Just my .02 worth.

Alex

 

[waldo1979]

Benchmark is working on a .308 700 Action rifle for me atm. I'm going with a 24" barrel as 26" seems a bit too long for a heavy suppressor. I'm currrently using an AAC-SDN-6 w/ quick detache. If i was to do it again i'd direct thread and get a thunderbeast (a little better accuracy from talking to some guys at my range).

I actually had a problem with my quick detache where the locks ring got mucked up with carbon causing the suppressor to come flying off. No baffle strikes, it went 30 yards down range w/o any damage. Morale of the story, keep those little grooves free of carbon.

Recoil is better, noise is better, very pleasant to shoot.

 

[rap36case]

Thank you all for your input. I think AWC makes some fine products. However, I believe the working limit of a suppressor is 200yards on a rife with subsonic ammunition. I have no personal experience to base that hypothesis. The hassel, accuracy, penetration and expense has kept me from investing in these things.

I am more inclined to put an AWC suppressor on a 9mm pistol with 158gr subonic, than to put one on a rifle.

Just my impression, and thanks.

 

[mao0720]

I have seen no ill effect on accuracy with my supressor on my bolt action 308 and 243. In fact most of the time accuracy improved. this is probably mostly due to much lighter recoil, making it easier to follow through when shooting from a bipod. Yes you will have a POI change with the supressor, but it is very repeatable and predictable. I have not shot any subsonic ammo through my suppressor, and I dont plan to. Dont need to either. With my can on i can shoot full power loads without having to wear hearing protection. Yes there is still a supersonic crack, but it is very mild in the open outdoors. I highly recommend suppressors, I never want to shoot without one again.