Florida Concealed Carry banner

1 - 19 of 19 Posts

·
Registered
Joined
·
10,977 Posts
Discussion Starter #1 (Edited)
One of Strelok Pro's more nifty features is the "Zero Offset."

The primary utility of it is to have multiple ammo loads for a rifle in the rifle's "library" and have the calculator automatically adjust for the corresponding different zeroes.

So, I use a specific ammo load as my "main load" and it will serve as my "base" or "benchmark" zero. So, let's say I use Berger Match 140 gr as my "benchmark." I zero my rifle with the Berger Match ammo and enter those parameters into Strelok.

Then let's say I use Hornady ELD-M as a different load. I zero my turrets and shoot a group. The group is 1-MOA low. So, I enter that as "-1.0" in the VERTICAL Zero Offset for that ammo in Strelok.

Then, I use Federal Gold Medal Match. I zero out my turret and shoot a group. The group is 0.5-MOA high and 0.5-MOA to the left. For that load, I'll enter "0.5" in the VERTICAL Zero Offset field and "-0.5" in the HORIZONTAL Zero Offset field. Now, in the future, when I switch to that ammo for that rifle in Strelok, it will automatically correct for the offset and give me accurate turret elevation and windage inputs for each distance.

Making sense? :) There's an article on this on Strelok's website. <--clicky

Continued below...
 

·
Registered
Joined
·
10,977 Posts
Discussion Starter #2
So, a couple of weeks ago, I shot at an F-class match, where they don't allow muzzle brakes. So, I removed it. I figured it MIGHT have SOME effect on the POI (point of impact). But, I didn't think it would be much. I was wrong! I used Strelok to calculate my elevation for 600 yards (based on the data I had previously entered for the ammo). But, I did not have any data for the ammo without a muzzle brake.

Strelok said I needed 14 MOA of elevation. I did that and fired the first sighter. WAY HIGH. I made an adjustment, and the elevation ended up being 11-3/4 MOA. Big difference, I thought. Though, I did not think that it was the muzzle. I thought I had made some mistake somewhere along the line.

Well, yesterday I did an experiment at the 100 yard range. I compared the zero for the ammo with and without the muzzle brake. Sure enough, the group without the muzzle brake went HIGH. Mystery solved!

So, here's how you can use Strelok's Zero Offset feature for shooting with / without a muzzle brake... or a suppressor (for example).

 

·
Super Moderator
Joined
·
26,654 Posts
Excellent alternate use of that software option intended for a different purpose. :thumsup

Still trying to get my mind around the underlying physics that cause the POI to be so much HIGHER without the muzzle brake. :dunno
 

·
Registered
Joined
·
10,977 Posts
Discussion Starter #4 (Edited)
Excellent alternate use of that software option intended for a different purpose. :thumsup

Still trying to get my mind around the underlying physics that cause the POI to be so much HIGHER without the muzzle brake. :dunno
While I'd like to claim credit for the idea... The offset IS intended for this kind of variable, too. :) Though, the software manual uses the example of a suppressor causing a shift in POI. Go to the link in the OP. And, scroll down to "Cartridge 3."

As for the brake causing such a shift... it adds weight to the end of the barrel, so that could change the barrel harmonics. There may be other effects because of the diversion of the gasses? I don't know. I wasn't surprised that there was a shift in POI. I WAS surprised at how MUCH it was.
 

·
Registered
Joined
·
3,319 Posts
Most of the discussion I read said that removing the brake could affect barrel harmonics but had a negligible effct on bullet velocity. So I think your initial intuition was probably spot on. You might try threading a piece of plain pipe having approximately the same weight and cg as the brake onto he end of your barrel and see if you don’t come back to zero, or close to zero, as an experiment to verify your hypothesis. There may be something to the blast idea as well, in that any change affecting the direction of the exhaust gases could affect barrel motion too. It’s a complicated situation from a dynamics point of view.
 

·
Super Moderator
Joined
·
26,654 Posts
Definitely changes barrel harmonics because of the mass change, and also the slight change on length, but THAT much change seems like there are other factors I'm not thinking of at the moment. If 1 MOA is 1.047 inches at 100 yards and your POI changed by 2 1/4 MOA at 600 yards, that's an ~14.13 inch change in POI. Perhaps it's not that big of a change for that distance and I shouldn't be surprised, but I am.
 

·
Registered
Joined
·
10,977 Posts
Discussion Starter #7
Definitely changes barrel harmonics because of the mass change, and also the slight change on length, but THAT much change seems like there are other factors I'm not thinking of at the moment. If 1 MOA is 1.047 inches at 100 yards and your POI changed by 2 1/4 MOA at 600 yards, that's an ~14.13 inch change in POI. Perhaps it's not that big of a change for that distance and I shouldn't be surprised, but I am.
Well... the difference in POI I saw at the 100 yard range (attributed to the muzzle brake) accounted for 1-1/2 MOA of that 2-1/4 difference at 600 yards. So, that leaves 3/4 MOA unaccounted for. But, that could be other factors, including MV and BC discrepancies, and environmental differences, I suppose.

In any case, it was an interesting and educational experiment! :)
 

·
Registered
Joined
·
6,001 Posts
What was you wind direction and speed at the 600?


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
13,346 Posts
Here is a fact. Barrel harmonics has nothing to do with it. No two barrels will have the same change in barrel harmonics and no two barrels have the same barrel harmonics off the lathe.
 

·
Registered
Joined
·
10,977 Posts
Discussion Starter #10
What was you wind direction and speed at the 600?


Sent from my iPhone using Tapatalk
I'm trying to remember... I believe 9:00 wind at 10-ish mph for the first stage. Then the rain came through and wind went to nearly zero. The POI was 2 MOA higher than Strelok calculated (based on my zero with the brake. The change was all elevation. 2 MOA UP.

But, at the 100 yard range this Sunday, wind wasn't a factor at all. With the rifle zeroed WITH the muzzle brake, when I removed the muzzle brake, the POI went up 1-1/2 MOA. Straight up.
 

·
Registered
Joined
·
10,977 Posts
Discussion Starter #11
Here is a fact. Barrel harmonics has nothing to do with it. No two barrels will have the same change in barrel harmonics and no two barrels have the same barrel harmonics off the lathe.
What is the mechanism or forces in play that cause the POI to shift so much with / without the muzzle brake? I expected some, just because anything on the barrel is going to affect ballistics. Like the guy I saw at the range, resting his barrel on the rifle rest he was using.

But, I didn't expect that much shift from a muzzle brake.
 

·
Registered
Joined
·
6,001 Posts
I'm trying to remember... I believe 9:00 wind at 10-ish mph for the first stage. Then the rain came through and wind went to nearly zero. The POI was 2 MOA higher than Strelok calculated (based on my zero with the brake. The change was all elevation. 2 MOA UP.

But, at the 100 yard range this Sunday, wind wasn't a factor at all. With the rifle zeroed WITH the muzzle brake, when I removed the muzzle brake, the POI went up 1-1/2 MOA. Straight up.
Just ruling it out because, if it was a 12 or 6 full value wind...... it could of played a role in elevation. Your test on Saturday pretty much ruled that out tho.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
10,977 Posts
Discussion Starter #13
Just ruling it out because, if it was a 12 or 6 full value wind...... it could of played a role in elevation. Your test on Saturday pretty much ruled that out tho.


Sent from my iPhone using Tapatalk
True about head / tail winds at the longer distances. But, yeah... I have to admit I was surprised (and relieved) that when I removed the muzzle and shot a group that it went a full 1-1/2 MOA up!
 

·
Registered
Joined
·
6,001 Posts
True about head / tail winds at the longer distances. But, yeah... I have to admit I was surprised (and relieved) that when I removed the muzzle and shot a group that it went a full 1-1/2 MOA up!
Well, at least you can add this to your DOPE book .


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
10,977 Posts
Discussion Starter #15
Well, at least you can add this to your DOPE book .


Sent from my iPhone using Tapatalk
I just looked at my DOPE book, and all I saw was your picture! :p :grin
 

·
Super Moderator
Joined
·
26,654 Posts

·
Registered
Joined
·
6,001 Posts
SMH


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
10,977 Posts
Discussion Starter #18
SMH


Sent from my iPhone using Tapatalk
Heh heh heh! Your emoji didn't come through, though. I figured it was a "middle finger" emoji?!? :rofl
 

·
Registered
Joined
·
6,001 Posts
No but it can be.!!!! Lol


Sent from my iPhone using Tapatalk
 
1 - 19 of 19 Posts
Top