Inaccurate AR-15

" If that fails I'd pull the flash hider, check the crown and try it without the flash hider in case its causing instability "

+1. I had an A2 on a rifle (basically using it as a thread protector while waiting on something else). Rifle would not shoot with the flash hider.

You can test the hand guard theory by shooting it without them. I would be surprised if you see a lot improvement.You will probably see some but not what you are looking for.
I would remove the flash hider just to see what effect it has.

I would like some feed back on the flopping around front barrel mounted sling swivel affecting groups. After all it's about barrel harmonics, nicht wahr ?

Real fast because I gotta head out to work

The front sight base is blocking the scope
View attachment 727158

If you were to focus the scope on the FSB, you would see it blocks the target from the crosshair. The only part of the target that can really be seen are the sides. When the shooter tries to align the crosshairs on the center of the target, it cannot be done because the FSB blocks the crosshair. The crosshair actually keeps sliding from side to side as the shooter tries to align it.

It pays to study the shape of the group
View attachment 727159

Notice anything? The group is not round. It spreads out from side to side and the middle is empty, right where the FSB blocks the crosshair.

The idea that the FSB does nothing because it fuzzes out is an Old Wive's Tale. Your barrel is fine. Either chop the FSB or mount the scope so the center of the crosshair is well above the FSB

I have been in the same situation as you with a PSA barrel. I tried replacing just about everything, re-crowning, free floating, flash hider, no flash hider and crowned, etc, but nothing helped. When I went back and added up the cost it was cheaper to try another barrel. When I did the groups were brought back into perspective. The barrel I chose was another cheap barrel that is being sold on AR15. I did not need the front sight so I went low pro on the gas block.

I did end up finding a way to make the barrel shoot. I cut it down to SBR length and had the gas port relocated to carbine. The barrel is a great shooter now (for an SBR). If you do decide to replace it, let me know.

On another note, you cannot see that front sight with that scope. It is strange to witness, but the sight is barely a blur in your field of view.

Go to a 1:9 twist for a lightweight 16 inch barrel. If you want the 1:7 then get a heavy 20 inch barrel. It's very aggravating not getting one to shoot decent. I've had a couple of 1:7's (lightweights) that did the same, they seem to be very finicky.

If you decide to try a new barrel, take a look at Lilja barrels.

This is why I do not buy light weight barrels. Once they heat up, the zero wonders.

Edit: Also, standard hand guards put a lot of stress on the barrel. Especially after the barrel has heated everything up.

I would get a medium profile barrel. A few ounces will go a long way to keeping the groups tighter. A decent med profile should get .7 to 1.3 MOA with most good ammo. 1.5-2 MOA with bulk ammo.

If you want small groups (consistently MOA or better) get a heavy barrel, not chrome lined, 1:8 twist. Also, free float for small groups.

It's not the barrel. It's the FSB blocking the scope

I happened to try the mounting of a scope and see through the front site and was amazed at how my front sight disappeared but reading post 29 here made a lot of sense to me and was worth thinking about so I am going to try a riser for the scope. I am not disputing the feedback I got when I mounted my scope, I always get good help on THR but this makes sense.Here's my thread for what it's worth.

Well, there's no post blocking here. LOL. To prove a point, I ran out to the range a short while ago with this silly set-up: Colt 1:9 pencil barrel, Bushnell 10x scope, off the bags, 100yds, light breeze, 52 Sierra Match bullet over 23-24 gr Accurate 2015 powder. This load has shot great for me over many years and many guns. I have shot slightly tighter (sub-MOA) groups with this carbine/4x scope in the past.

M

Well, I learned something new thanks to this thread.

cmb3366 said:

The question now is whether I shave the fsb and stick with optics, or install a new gas block.

Click to expand...

I ordered a KMR for my BCM this weekend, and will be shaving the FSB tonight or tomorrow. I can post either an inspiration or a warning, depending on how it goes.

Good call MistWolf.