Thread: Supressor Fitted - major change to point of impact?

After some advice regarding major change in the point of impact when a supressor is fitted.

I fitted a Gunworks supressor to a rifle which is zeroed 1" high at 100 metres. The point of impact holds the vertical alignment pretty much the same, however, the pint of impact has dropped 3" lower.

I've never encountered such a major variance previously.

Any suggestions or comments would be appreciated

2inches low on 7m08

thats quite normal. all depends on the gun and barrel harmonics, one of mine have 2" horizontal and 4" vertical.

What you need to check for is consistancy. I had one gun where POI was different each time I removed and re-fitted hte suppressor. I could feel it binding at one point when screwing it on so sent it back to get the internal sleeve bored out a bit. That fixed it.

You need to shoot a 3 shot groups with it on, then remove and shhot anotehr 3 shot group, then re-sit and shoot 3rd s shot group to confirm POI is same.

Originally Posted by Mauser308

Suppressor acts as a break, reduces the recoil and the muzzle jump. Hence the POI is lower, and with a RH twist often to the right an inch or so. Worst I've seen is 5" down, 3" right.

The bullet leaves the barrel before the muzzle has a chance to "jump".

4" at hundred is about normal.....50quid to knob of goat shit if you read the bit of paper that came with your suppressor IT WILL TELL YOU THIS....

I tested this yesterday. With suppressor off, it missed the A4 paper altogether at 100m. At 50 it was 2.5" left and 0.5 " high. So extrapolated out it should be about 5" left and about 0.5" high. More testing to be done, I'll take a A3 sheet next time.

For me I really want to understand this as one day I'm going to forget my suppressor! So I want to know exactly how many clicks each way to get it right.

Originally Posted by Timmay

The bullet leaves the barrel before the muzzle has a chance to "jump".

Not quite.

There are a number of factors that can combine to cause this.

-The reaction in force starts while the bullet is still in the barrel- technically while the bullet is still just starting to move. As the projectile accelerates down the barrel, the rifle starts to move back and up under load. Now 4" at 100m (close enough to 4moa) is the same angle of movement / deflection as 20 thou (.02 inches) at the end of a 20 inch barrel which is very small. It takes about half a second for the barrel to lift about 6 inches under recoil meaning it takes about 1/600th of a second to rise .02 inches. With the muzzle velocity being about 2800fps, the bullet will take about 2 thousandths of a second to reach the muzzle.

The gas does not hit the suppressor baffles until the projectile has passed so the muzzle brake effect is not what causes this as this does not start until after the bullet has left the barrel. (It is worth noting that the air in front of the bullet is pushed through into the suppressor while the projectile is still in the barrel, but whether that is enough to start the suppressor action- I have my doubts due to the volume of that in relation to the volume inside the suppressor. (Bore volume on a 7mm08 with a 20 inch barrel is about 19.5ml and the suppressor will have a volume about 280ml ratio 1 part to 14)


-One factor to take into consideration is the over barrel suppressor will make the barrel more rigid by supporting in two places with the tube

Or the small amount of weight added to the end of the barrel could be putting slightly more pressure downwards on the barrel "preloading" the muzzle. Barrels are not unbending and do flex. Even a small amount of weight theoretically could apply resistance to the upwards acceleration by starting from an ever so slightly lower start point.


At the end of the day, a downwards POI shift is common in suppressors. this is normal and it wont really matter why this happens, as long as it is known about and the "zero" is checked.

The main point is did the group size improve? Stay the same? get worse? As long as it is not the latter of the three, adjust the scope and all will be well.

Greetings,
My .308 Bergara break open shot over 300 mm high with the suppressor on. Go figure.
Grandpamac.

Why would you shoot it ever with the suppressor off?

Originally Posted by Timmay

The bullet leaves the barrel before the muzzle has a chance to "jump".

Actually the whole rifle moves about 2-3mm before the bullet leaves the barrel - hence why follow-through is so important. As @timattalon pointed out - the laws of physics are absolute.

Originally Posted by grandpamac

Greetings,
My .308 Bergara break open shot over 300 mm high with the suppressor on. Go figure.
Grandpamac.

My 1st SUP was on a Mini 14 Ranch rifle
Was Robbie's 1st Ranch rifle SUP build
That shot either 14 inches high or 16 inches high (can’t remem exact) with SUP off
Cost me a few Deer too as I often had in in bum bag and had to remember to aim for the knee if shooting without and 50% of time forgot in the quickness of tight bush shooting
Pretty sure it was 14" and that was at 50m
I got Robbie to redo with Duralumin later - and never tried it without as it was a huge diff to carry over the 1st SUP (re weight)
I imagine it would have been vastly diff/less

Any weight you add to your barrel will usually have some kind of effect on harmonics, and thus POI - and sometimes even group size.

A person need only look at a "barrel tuner" device, or the browning BOSS system and similar to see that literally anything attached to a barrel can have dramatic changes in both POI and *consistency with an already established load.
Anyone who doubts this can tape a fishing sinker or something near the end of their barrel and test their zero

I’m fortunate with my .223 and DPT suppressor it shoots same POI regardless of suppressor on or off.

For my other centrefires there is typically a 3 inch shift in POI but my rifles are all zeroed with suppressor on because that’s how I hunt/shoot them.

Worst I have experienced was with a 7mm RM and a suppressor build by a guy in Auckland.

The thing was long, heavy and when I zeroed the rifle the POI was over a foot low at 100 mtrs.

I remember donging a possum on the head with that suppressor!

Sounds like an early PES