Muzzle brake and POI shift

[Philward]

A buddy and I went to the range yesterday. He wanted to shoot his new rifle and try out the brake he bought for it. A few weeks ago we sighted the rifle in and it was shooting well, no brake at that time. He wants the MPBR method of sighting-in for hunting. Rifle is a Savage Ultralight 6.5PRC, Leupold VX3HD 4.5-14x40 scope w/B&C reticle. He mounted the brake when we got there and first shot was just as we had it set previously, 1.25 high at 100. Then he shot at 200yds and no impact on paper. 3 shots later we walked out to check target and the shots were off the target and directly below the center about 8-9 inches. Windage was good and they grouped good too just really low. I tried shooting it at 200 with same result. Then I tried the first line down on the B&C reticle and hit just right of the bull. so I dropped back to 100yds and took one shot at the target he shot first using the first line down on the reticle and that round hit right beside his first shot, same elevation just a half inch right. Then he removed the brake and fired a round at 200 aiming dead center and that shot hit 3 inches above the previous rounds that were 8inches low, so still 5 inches low at 200.

Scope sub-tensions are first point down from crosswire is 2.2moa, next is 4.8... We didn't make any scope adjustments this day. When we first shot it weeks ago it was boresighted by someone else and when I checked it scope was aiming really high and we had to adjust it by alot. i,e, looking through bore at center of target and scope was aimed at top of target.

I thought maybe the brake was causing the POI shift but even without, it was shooting way lower than it was previously. Ammo is some Norma stuff he bought, 143 or147 grain stuff.

Scope and rifle are tight and it's grouping fine so not sure what is happening. He does like shooting it with the brake to keep muzzle jump down and it does a nice job of it especially with the 6.5 not having any real recoil.

Maybe scope is adjusted to the wrong side of the tragectory path, bullet already on the downward slope? Or right at the peak of flight path?

 

[FEENIX]

A buddy and I went to the range yesterday. He wanted to shoot his new rifle and try out the brake he bought for it. A few weeks ago we sighted the rifle in and it was shooting well, no brake at that time. He wants the MPBR method of sighting-in for hunting. Rifle is a Savage Ultralight 6.5PRC, Leupold VX3HD 4.5-14x40 scope w/B&C reticle. He mounted the brake when we got there and first shot was just as we had it set previously, 1.25 high at 100. Then he shot at 200yds and no impact on paper. 3 shots later we walked out to check target and the shots were off the target and directly below the center about 8-9 inches. Windage was good and they grouped good too just really low. I tried shooting it at 200 with same result. Then I tried the first line down on the B&C reticle and hit just right of the bull. so I dropped back to 100yds and took one shot at the target he shot first using the first line down on the reticle and that round hit right beside his first shot, same elevation just a half inch right. Then he removed the brake and fired a round at 200 aiming dead center and that shot hit 3 inches above the previous rounds that were 8inches low, so still 5 inches low at 200.

Scope sub-tensions are first point down from crosswire is 2.2moa, next is 4.8... We didn't make any scope adjustments this day. When we first shot it weeks ago it was boresighted by someone else and when I checked it scope was aiming really high and we had to adjust it by alot. i,e, looking through bore at center of target and scope was aimed at top of target.

I thought maybe the brake was causing the POI shift but even without, it was shooting way lower than it was previously. Ammo is some Norma stuff he bought, 143 or147 grain stuff.

Scope and rifle are tight and it's grouping fine so not sure what is happening. He does like shooting it with the brake to keep muzzle jump down and it does a nice job of it especially with the 6.5 not having any real recoil.

Maybe scope is adjusted to the wrong side of the tragectory path, bullet already on the downward slope? Or right at the peak of flight path?

If your friend is going to hunt/shoot with the muzzle brake on, he needs to make the required adjustments with it.

 

[tim_w]

If it's for hunting I would only use cold bore shots so lots of time between shots given its a ultra light i.e. thin barrel made even thinner at the muzzle by threading. Group size (precision) do not matter as much as accuracy (POA to POI) for most

What ammo were you using (specs)? Bullet? est vel off the box?

If you are not chrono the loads you can use the box vel and hop on even an online ballistic calculator like JBM. Pick your bullet and plug in vel and scope center above bore hieght. Even my 375 cal short mag build will hold 3" over and under from 0 to almost 300 with a light for cal g1 .473 bc 260AB load.

Take the Hornady 143 ELD-X Precision Hunter Ammo with a 2960 listed fps even cut to 2900 fps to be safe. With a 1.25" high 100yd zero. You would be between 0.5-0.8" low @ 200yd and would not reach 8" low until 300yd. Point being it would be impossible to be 1.25" high @100 and over 8" low at 200.

It takes serious changes in vel and bc to have large effects inside 200 yd with cartridges that stay super sonic in that range. Hence my example of what is basically 375H&H ballistics with a light for cal G1 0.473 bc bullet compared to those g7 high bc used in 6.5.


First I would get the brake properly mounted and timed and secure it. Do not put heavy tq on it as it will distort the crown and bore at the muzzle. At the same time we don't want it breaking loose from shooting. That or leave it off.

Next let's get the specs on the ammo he will be using.

Confirm the scope mounting.

He wants to use the Max Point Blank Zero. OK what amount of spread does he want to use for max over and under?

Personally for typical hunting distances 0-300 I like 3". With a decent bc in 6.5 like the 143 Eld-x he would be able to hold dead on out to 300 and never be high or low more than 3"POI from POA. With that ELD bullet @2900 that would be a 250yd zero. Actually at 300 it would be 3.5" low but up to 280-290y depending on if it's closer to 2900 vs 2960 it will be inside 3" At 345-365yd he can drop to that first subten you stated was 2.2 moa. He would be within 0-3" in that range spread respectively.

Just need to know what ammo and a decent estimate on the vel. Then take in the field to test tweak and confirm the drops.

I am on the east coast but do hunt in TX. Have taken game out to 1k but 90% of everything has averaged to within 300yd. It also happens that with today's loads 3" to 300 yd MPBR is quite fitting as 3" with a steady well aimed shot puts you into the vitals with some wiggle room for poa poi deviation.

 

[Philward]

Here's an update: Brake mounting, there was a coned washer that came with the brake and it seems he installed that backwards. So that has been fixed and it is mounted and clocked correctly. We haven't shoot it since that day but maybe in a couple days we will. Ammo is in the picture attached. Box says 300yd zero should be 3.4"high at 100yds. I don't think this is what he is planning to shoot for hunting, he has something Hornady for that. Barrel is carbon wrapped and not thin but the stainless core is no doubt, came from factory threaded for brake.

 

[tim_w]

Glad you got the muzzle break worked out.

So basically a duplicate of the Hornady load just a bit hotter.

That sounds about right @ +3.4"@100 if your MV is 2985f/s (910m/s).

I would set a 250 zero. Should be 2.5"-2.6" high at 100 yds.

Then try shooting dead on at 100 200 250 and 300 and see if your POA to POI stays within 3" over and under. 300 should be about 3.5" That should set a good MPBR.

Post up your results when you get back out there.

 

[FEENIX]

Here's an update: Brake mounting, there was a coned washer that came with the brake and it seems he installed that backwards. So that has been fixed and it is mounted and clocked correctly. We haven't shoot it since that day but maybe in a couple days we will. Ammo is in the picture attached. Box says 300yd zero should be 3.4"high at 100yds. I don't think this is what he is planning to shoot for hunting, he has something Hornady for that. Barrel is carbon wrapped and not thin but the stainless core is no doubt, came from factory threaded for brake.

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Don't overcomplicate it unnecessarily; as in #2, your friend needs to make the necessary adjustments with MB on if he will hunt with it regardless of ammo.

If you want an actual 300Y zero, then zero it at 300Y.

 

[Shane Lindsey]

I have had POI shift from my brake not being tight or coming loose from shooting. Some of my brakes are not torqued down as I take them off to clean/hunt. Those have to be hand tightened to ensure they stay snug after a few shots.

Not clear in the first post. Did he shoot it at 200 yards the first time out? With good accuracy? Or was the first time at 200 with the brake on? Sometimes a 100 yard gun isn't the same further out.