question on odd results

[Bayouhunter1960]

With the new barrel I recently installed this was my initial 100yd group using Nosler 120gr BT and 4 loads of AR Comp in .3gr increments. My initial group was fair but I wanted to test dampening the barrel harmonics.
I had a scrap piece of honeycomb shaped synthetic rubber that was left over from mounting motor controllers on an engine room bulkhead (I work on oil field supply vessels). Due to the amount of vibration the installing technicians used this material to dampen vibration to the electronics.
It was a tight fit but I inserted the rubber between the end of the hand guard and the barrel.
First group is without the dampening material.
Second group is with the material inserted in the hand guard. Due to barrel tension the shot about an inch higher but the same load tightened up substantially. This I think supports Lemonaid?s third method.

[Lemonaid]

Interesting results!
More like method four though. Putting upward pressure on the barrel -- Similar concept to full length barrel bedding in bolt action rifles.
Method three, deresonator is a rubber like doughnut that slides over the barrel.
For more info see about minuet 29 on this video JRB made.

https://www.youtube.com/watch?v=uoBXTrngLxg

[imaguy3]

Interesting results!
More like method four though. Putting upward pressure on the barrel -- Similar concept to full length barrel bedding in bolt action rifles.
Method three, deresonator is a rubber like doughnut that slides over the barrel.
For more info see about minuet 29 on this video JRB made.
https://www.youtube.com/watch?v=uoBXTrngLxg

I'm familiar with the donut... don't think it'll fit... Also not really doing anything with my muzzle device... pretty much limits me to tweaking the load...

[Lemonaid]

I'm familiar with the donut... don't think it'll fit... Also not really doing anything with my muzzle device... pretty much limits me to tweaking the load...

Only other free advise (worth every penny!) would be to try a different bullet. I'm getting very good results with the Sierra 120 Pro Hunter and 120 Sierra Match King.
I haven't tried the Barnes 120 Match Burner but the price is right. Next ammo order I make will include some to try out.

https://www.midsouthshooterssupply.com/item/0003530234/6halfmm-point243-diameter-120-grain-match-burner-lead-core-boat-tail-100-count

[A5BLASTER]

That’s exactly the reason I use imr 8208. It’s 100 degrees out now. It is not unusual for it to be 25 during hunting season.

Where? Not in louisiana.

[Bayouhunter1960]

After seeing the group tighten with the dampening rubber under the end of the barrel I cut another piece that would wrap around the barrel putting tension on the sides of the barrel also. Thinking more would be better I found out it that more is not always better. Since there is almost no way to insure the exact tension on each side of the barrel my next 5 groups shifted to the right a bit. I plan on staying with the one piece directly under the barrel as that seems to be the best on this rifle. I saw similar results on my 20? Lilja and will hunt with each this year using the single piece under the barrel.

[URL=http://s1203.photobucket.com/user/Bayouhunter/media/DE0E47CD-9E70-458F-B125-7EDB46A78E56.jpg.html][/URL

[imaguy3]

good consistent MV and low SD but bad groups usually means the timing of the bullet's exit is off. Try that load but varying OAL by 0.010 delta's...

I was skeptical that changing OAL could affect a group size by inches.. but darn it if it did...

Load I'm settling on...

28.3gr IMR 8208xbr
123gr SST
Federal Gold Medal Match AR primer
Hornady brass
Seated to 1.636" base to ogive, giving me a cartridge oal of 2.215".

2475fps at the muzzle from a 16" barrel.
6.68 SD over a 5 shot group

5 shot group size

[grayfox]

Timing, as they say, is everything.
Glad you found something!

[Bayouhunter1960]

Congrats that’s is a fine group. I haven’t loaded the123sst to that length, 2.230” has been the my shortest load to date.