AR shooting HIGH when adding suppressor ?? - Page 1

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[ARCHIVED THREAD] - AR shooting HIGH when adding suppressor ??

Posted: 3/6/2015 5:49:46 PM EDT

Added a suppressor to my 18" SS WOA barrel (Gemtech Trek Ti).

I had anticipated it shooting LOW, that was not the case, it was 5-6" High. And this is from a rifle that was a tack driver.

Once I adjusted the scope, its back to being a tack driver, only quieter. lol

But does that seem odd that it was HIGH and not LOW when adding suppressor? No other changes were made to the AR, even the ammo was the same Hornady 75 gr BTHP.

Posted: 3/6/2015 5:59:00 PM EDT

[#1]

No, barrel harmonics could cause POI shift up, down, left, right or any combination of that.

Posted: 3/6/2015 5:59:35 PM EDT

[#2]

Fpni

Posted: 3/6/2015 6:05:29 PM EDT

[#3]

Ok. I figured it would just be low. It pulled a lil to the right but a couple clicks brought it back, was just surprised how HIGH it was.

Oh well, was fun to shoot. lol.

Posted: 3/6/2015 6:05:31 PM EDT

[#4]

Yep: cans will cause a POI shift.

The only questions are how much and in which direction.

Posted: 3/6/2015 6:15:45 PM EDT

[#5]

It causes a noticeable downward poi on my AR's. And only about a 1/2 MOA shift up on my bolt gun.

Posted: 3/7/2015 12:22:36 AM EDT

[#6]

Maybe the barrel concentricity of the threads just a little bit upwards? Were you using the same rest that you use when you are firing them as you do when they are unsuppressed? I don't know all of mine usually shoot low on their hosts and they are Ti as well.

Posted: 3/7/2015 12:43:49 AM EDT

[#7]

My HVT QD causes a considerable shift on my M1a. I think it's been up as well.

Posted: 3/7/2015 8:25:48 AM EDT

[#8]

Several factors come into play with cans and POI changes.
First the weight of the can makes the barrel sag a bit. This is why a lot of people see a downward drop in POI and happens more with light barrels than heavy.

Second the barrel harmonics change because the barrel is heavier with a can on it. This can shift POI in any direction.

Third, if the can has asymmetric baffles the uneven gas pressure as the bullet goes thru a baffle can push it off center slightly.

Posted: 3/8/2015 9:53:35 AM EDT

[#9]

I'd add to this that you will generally see slightly higher velocities with the suppressor attached over the same barrel length with no suppressor. I've not heard of anyone doing a study as to why, but every chronograph comparison I've seen shows the increase.

The amateur engineer in me thinks that the suppressor acts as a longer barrel would in that it adds some (albeit reduced) acceleration pressure while still in the suppressor.

All things being equal, you would then expect it to be a little higher than when un-suppressed.

Just my 2 cents.

SMS-ret

Posted: 3/8/2015 2:14:27 PM EDT

[#10]

Quote History

Quoted:
The amateur engineer in me thinks that the suppressor acts as a longer barrel would in that it adds some (albeit reduced) acceleration pressure while still in the suppressor.

All things being equal, you would then expect it to be a little higher than when un-suppressed.

Just my 2 cents.

SMS-ret

View Quote

I am a physicist and this is exactly what happens.

Posted: 3/8/2015 7:02:11 PM EDT

[#11]

Quote History

Quoted:

I am a physicist and this is exactly what happens.

View Quote View All Quotes

View All Quotes

Quote History

Quoted:

Quoted:
The amateur engineer in me thinks that the suppressor acts as a longer barrel would in that it adds some (albeit reduced) acceleration pressure while still in the suppressor.

All things being equal, you would then expect it to be a little higher than when un-suppressed.

Just my 2 cents.

SMS-ret

I am a physicist and this is exactly what happens.

Ok what about when you get a poi shift down?