Help with POI shift!!!

[T3ninja]

Hey all,

Here's the story. I just picked up a Browning Max LR in .300 Win. I'm not new to reloading, but this is my first belted Mag. I'm somewhat familiar with some POI shift due to heat, stock contact etc.

So as of now I'm still working to fine tune this load for my rifle which is 215 Berger 73.9 RL-26 .010 from lands. This is giving me consistent 1" groups @ 175 yards. Acceptable to me for a hunting rifle.

Here's my problem. I've shot this rifle 4 times (12 rounds) @ 450 yards. The first 2 rounds of each 3 shot group are perfect, within 1.5-2" of each other, the 3rd is ALWAYS 6.5" high! Approx .4 MIL. I'm not happy about this but since it's consistent I can compensate for it. My question is, at my altitude 950' I'm hitting .4 mil high, will this correlate to the same thing at say 9k' elevation? I'm going to be running this load at everything from 100 to 1k, so I'll have info for everything in between. I understand these will be useless at elevation, and will need to be updated accordingly.

Being RL 26, Do you think that the 3rd round heats up enough in the chamber to cause part of this vertical? I have a magneto to put on but it changes my POI so much I don't do any accuracy testing with it, especially at distance since it will probably cause me to miss the target completely.

Thanks in advance

 

[WeiserBucks]

Have you checked the action to stock interface? Action screws ? I don't know if RE26 is a potential issue, I use H1000 exclusively in my WM .

 

[T3ninja]

Yep, I've checked all screws, everything is tight. I tried H1000 and absolutely couldn't get it to shoot.

 

[Rick Richard]

If it is consistently jumping up on the third shot, then it is due to barrel/chamber heating up and causing pressure somewhere. If you can't live with this, then I would have it bedded. Just my opinion.

 

[T3ninja]

The rifle is factory bedded, pretty nicely done in fact. It's not so much that I can't cope with the shift. It's more about the elevation change. I can compensate for this at my altitude, but I have a CO elk hunt planned this year and the area in scouting and planning to hunt is 8500-9500 FT. My main question is, right now, it gives me a .4 mil change. Would this still be .4 mil at the higher elevation? Not sure I'm wording my questions right.

 

[WeiserBucks]

In theory the shift should be repeatable, but I wouldn't trust a hunt on it .

 

[Rick Richard]

The rifle is factory bedded, pretty nicely done in fact. It's not so much that I can't cope with the shift. It's more about the elevation change. I can compensate for this at my altitude, but I have a CO elk hunt planned this year and the area in scouting and planning to hunt is 8500-9500 FT. My main question is, right now, it gives me a .4 mil change. Would this still be .4 mil at the higher elevation? Not sure I'm wording my questions right.

It will be different than at your current elevation. How much? Use a ballistic calculator such as the Berger online app and input your parameters and it will provide POI chart.

 

[entoptics]

...It's more about the elevation change...My main question is, right now, it gives me a .4 mil change. Would this still be .4 mil at the higher elevation? Not sure I'm wording my questions right.

It really depends on what's causing the POI shift. If it's truly due to a heat in the chamber making the 3rd round cook off at higher velocity, then you'll have to compensate for the velocity differences at different altitudes.

If it's being caused by the rifle heating up and shifting in the stock, or some other issue that's actually changing the point of impact and not the bullet velocity, then the POI shift could be consistent across elevation changes.

0.4 Mils at 450 yds seems like an awful lot for it to just be a hot round shooting faster.

Regardless, I'd figure out what the heck is causing the issue and address it directly. Kentucky windage usually isn't ideal in the middle of a hunt...

 

[T3ninja]

I'm still fairly new to this rifle, only about 100 rounds through it so far. I bedded the base/rail to the receiver followinbrg "Broz" video on long range only. All screws are tight, action/rings/base, even the muzzle brake is tight. I'm not sure what, other than hearing of the barrel would cause the 3rd round to go high. All rounds are single loaded in the chamber for maybe 15-20 seconds and fired less than a minute apart. I'm not changing position or the position of the rifle. Shots are prone with bipod and rear bag. Ambient temp is approx 65-70* light wind, 2-3mph.

Yes I think .4 is EXTREME. I would think if it was a heating issue, it would be more gradual. I'm Certain it's not me or technique. I don't mean to come off arrogant.

 

[HobieH3]

Try the magnetospeed at short range to see if you ARE getting a velocity change. Don't worry about the target, just hit the berm!

 

[Remmy700]

As mentioned prior shoot a few shots over a chrono with this load and see what the velocity is doing. Also in real thin sporters I try to shoot and let sit for 2-3 mins when doing three shot strings if u are popping off three back to back rather quickly the chamber heat can be causing your issue. I also like to wait till I am all setup and on target then gently slide bolt forward chambering a round vs chambering a round and then getting gun back on target and all settled. Keeps the bullet from sitting in a warm chamber unnecessarily.

 

[nmbarta]

How are you sizing your brass?
FL? Bumping the shoulder?
Is this with new brass or fired brass?
I just ask because four groups would not be enough for me to determine it to be consistent.
Heating issues that cause poi shifts are somewhat sporadic in my experience and are difficult to compensate for. Your ammo and chamber are probably not going to be the same temp as they were during your testing.
I've had a couple smiths that bed the chamber portion of the barrel when bedding the action, I think the jury is out on this, but the couple rifles I've had that were done this way did shoot. I don't know if this would help with heat shifting or not, but might be something to try.
I imagine that you've already made sure that your barrel has plenty of clearance from your stock.

 

[nmbarta]

You may want to try a ladder test as well.
This method can help you determine the top and bottom end of your accuracy node.
If your already right at the top of your node, a slight increase in velocity can put you outside of the node which will explain why the shift in poi doesn't match the change in velocity.
Then you can choose the load that's in the middle of the node, which will be more tolerant of slight changes in velocity.

 

[Remmy700]

I just got done writing the same thing u beat me to it lol, what he said!