I’m really confused. I went to the range today to see if I could verify just how much POI shift there was between my 12.5" suppressed and unsuppressed. I’ve done this before on this rifle with an M4-2000 and Hornady Superperformance at 565 yards and there was no discernable shift in POI. At that distance there was a pretty big spread but with and without the suppressor all rounds were hitting a 24"x24" target and any POI shift was way less than 1 MOA. I was happy with those results.
Rifle is a BCM 12.5" SS410 and DD Omega 7" upper w/ 762SD suppressor. USGI Trigger. 4x ACOG
Ammunition is plain jane Federal XM193
Range is 300 yards (Target is that little white dot out there)
This is what really threw me off. I did two separate rounds of this. I fired 10 rounds unsuppressed. Marked the target, and then ten rounds suppressed and repeated the whole thing.
Look at this ridiculous, horrid group unsuppressed.
Rifle:
Target:
Here is the suppressed setup.
Its not a sub MOA group but it is noticably better.
I used the same box of ammo for suppressed and unsuppressed. (Each trials had a separate box). There was no change in wind, no change in sunlight, no change in anything.
Educate me. What’s going on? I’d think it’d be the other way around.
Groups shrinking while suppressed is actually pretty common. I can’t provide you any citations, but the engineer in me can make a pretty educated guess.
Adding mass to the end of the barrel will – unless you somehow do something really weird with the barrel’s vibratory harmonics (like hit a resonant frequency or something) – almost always tend to reduce group size because, to put it simply, moving heavier things is harder. The amount of energy being put into the system is the same (a gun shot), but in one case, the barrel is standard, and in the other case, it has a 1lb weight hanging off the end. Because the energy hasn’t changed in either case, the scenario with the heavier mass will cause the barrel to move less. With the barrel vibrating less (and thus, moving up and down less), your bullets come out of the barrel more consistently.
Think of it like a seesaw. It’s easier to move 50 pounds on the other side of the seesaw than it is 200 lbs. So with a heavier weight on the end of your barrel, the barrel vibrates less. That’s my guess. I’d also guess hanging a weight off the end of the barrel would do the same.
(It could also be attributable to altered barrel harmonics, with the addition of a suppressor causing the barrel to release the bullet at the apex of each up/down vibration where the barrel is most still, but I highly doubt something so detailed and specific would happen so consistently across suppressed AR-15s)
Thanks for the replies. I’m no engineer - but all of those reasons make perfect sense.
I wonder why the big difference with the match ammo (lack of group size reduction) I’d assume the match grade ammo was more consistent out of the bore with and without the suppressor. The M193 benefitted much more from the suppressor than the Hornady did thus leading to a noticable group size reduction. Of course this is just a guess because the suppressor used last time was an M4-2000 and this is a .30 caliber can. Its heavier, longer, with a larger bore diameter.
I was honestly worried when I made this thread thinking people would claim I was trying to sell AAC cans or something. I’d never seen anything like it.
Just musing but I would expect the rougher surface of the M193 base would be more affected by erratic muzzle gas than the smoother base of the match bullets.
I heard the term “suppressor push” on a video from AAC.
The gasses that are being tamed in the suppressor baffles will fill the CAN at first, but they still need to expand eventually (out of the bore) just as the bullet is passing through. So the trapped expanding gasses will help push the bullet out of the suppressor. This can equal a slightly higher bullet velocity.
When shooting unsuppressed, the gasses simply escape up, down, and to the sides. They never get directly behind the bullet.
Could that along with the several other reasons mentioned help with accuracy?
It’s freebore boost, and generally increases velocity in the 20-30 fps area.
There is actually a bit of a boost from pure muzzle velocity as it exists the bore and a few feet in front of the bore as the shock of the bullet hitting standing air causes a small area of low density, permitting the bore pressure to add a few fps.
Really though, increased velocity alone does not contribute to increased precision, especially in such small gains.
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