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Interesting group during max charge work-up

 
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  #1  
Old 08-16-2013, 08:42 PM
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Interesting group during max charge work-up

I'm not sure if this is unusual or not. I just got a Magnetospeed (which I REALLY like) and decided to run a max-load work-up on my 22-250. Basically, an excuse to try my new toy. The rifle is a Cooper M54 Varminter. Powder used was Varget, pushing 50gr Sierra BlitzKings. I was really only shooting to look for pressure signs and test out the chrony, so I shot 3 foulers at 100 and went on to record:


36.0 ----3770 ft/sec ----No pressure signs
36.3 ----3793 ft/sec ----No pressure signs
36.6 ----3819 ft/sec ----Primer slightly flat
36.9 ----3834 ft/sec ----No pressure signs
37.2 ----3885 ft/sec ----Primer slightly flat
37.5 ----3930 ft/sec ----[BOOK MAX] Primer slightly flat
37.8 ----3980 ft/sec ----Primer is flat, very slight bolt stick


The interesting thing was the shot distribution (picture below). The two shots in the black were 36.0 and 36.3. The only bad load was 37.2, which apparently shoots left


Even at 100 yds, I was surprised at the lack of vertical stringing with a 200fps difference in velocity. Maybe this is normal for a speedy round like 22-250? I am certainly questioning the usefulness of my OCD powder trickling method.


In any case, I am going to work up some rounds in the 36.6 to 37.2 range and see what I get when I stretch out a little. Historically I have been running 35.8 and it will shoot 1/2 MOA at 100. Maybe I can get a little more speed out of her. Groundhogs beware.
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  #2  
Old 08-16-2013, 08:52 PM
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Re: Interesting group during max charge work-up

Here is the Magnetospeed attached. I have read some reviews on having POI shifts with the unit attached. For whatever reason, I had no change on this rifle.
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  #3  
Old 08-16-2013, 09:51 PM
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Re: Interesting group during max charge work-up

Quote:
Originally Posted by varmintH8R View Post
Even at 100 yds, I was surprised at the lack of vertical stringing with a 200fps difference in velocity. Maybe this is normal for a speedy round like 22-250? I am certainly questioning the usefulness of my OCD powder trickling method.
My 22-250 will do exactly the same thing. I find a few good loads at 100 and then run them to 300 yards and it's quickly apparent which loads are going to work best. Oddly enough, my most consistent load at 100 with my first 22-250 absolutely fell apart after about 150 yards (high ES).

Extensive testing in my rifle showed that I usually had a sweet spot of about .3 grains where all groups would shoot same POI at 300 yards. I simply set up my powder dump to throw in the middle of the sweet spot and check every 5th throw on a scale to make sure it's still throwing accurate. The majority of my best 300 yard groups were shot with loads that were put together with just a powder dump. I still trickle my 300 WSM and 6.5 Creedmoor loads because I only load 20-50 at a time, but my 22-250 hasn't been fed trickled loads in a long time.
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Old 08-18-2013, 08:07 AM
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Re: Interesting group during max charge work-up

I think the differences you're expecting are lost to invalid testing for them.
You're just finding your max load, shouldn't assume anything else from it.
Remove the chrony, incremental test/ladder at 300yds, raise expectations, and I think you'll see differences like any other gun.
Just my opinion
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Old 08-18-2013, 12:04 PM
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Re: Interesting group during max charge work-up

Quote:
Originally Posted by varmintH8R View Post
I have read some reviews on having POI shifts with the unit attached.
I'd like to know what the final word is on that. I have always had suspicions that allowing the projectile to pass too closely to any object during it's flight could affect it's trajectory, from that point forward. I'm thinking that "waves" of air pressure eminating from the bullet itself (from the side, and/or slightly ahead of it) hit the object and reflect back to the bullet, altering what otherwise would have been a "clean" trajectory. That would seem to be what is applicable in this case. I'm sure anything more than 5 or 6" away (unless shooting parallel to a long wall, or something) would have a negligible effect, but that magnachron device looks like it is within an inch, and it is there for multiple inches of the flightpath. It makes sense that as the "closeness" to the object doubles, the effect on the passing bullet would square.

Take a scenario where you are in a fixed position and spot a nice deer at 600yds, but there is a large tree at 75yds. Looking through the scope, you see that your round will just barely miss hitting the tree. Will the round be off-target at 600yds, if you take the shot?
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Old 08-18-2013, 12:32 PM
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Re: Interesting group during max charge work-up

Quote:
Originally Posted by Mikecr View Post
I think the differences you're expecting are lost to invalid testing for them.
You're just finding your max load, shouldn't assume anything else from it.
Remove the chrony, incremental test/ladder at 300yds, raise expectations, and I think you'll see differences like any other gun.
Just my opinion
Mike,

I (almost) totally agree, and think much of that is reflected in my original post. You are correct that in giving even negligible credence to the shot distribution is a worthless exercise. I am probably a little guilty of that... I will definitely work up some loads in a structured way and stretch it out. I certainly don't expect the same result in regards to group distribution at distance.

The caveat of "almost" totally agreeing with you is due to your comment of "raising expectations". I'm not sure how to read that in the context of the original post? A personal shot over some perceived ignorance on my part? Thought it was an interesting inclusion in your otherwise technical response.

Browninglover's response is also appreciated as his direct experience seems to line up with mine. Differing charge weights in 22-250 don't add up to much in the way of POI shifts at 100 yds. That leads me to an answer to my question: is this unusual or interesting? Answer: not really.
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Old 08-18-2013, 12:40 PM
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Re: Interesting group during max charge work-up

Quote:
Originally Posted by Max Heat View Post
I'd like to know what the final word is on that. I have always had suspicions that allowing the projectile to pass too closely to any object during it's flight could affect it's trajectory, from that point forward. I'm thinking that "waves" of air pressure eminating from the bullet itself (from the side, and/or slightly ahead of it) hit the object and reflect back to the bullet, altering what otherwise would have been a "clean" trajectory. That would seem to be what is applicable in this case. I'm sure anything more than 5 or 6" away (unless shooting parallel to a long wall, or something) would have a negligible effect, but that magnachron device looks like it is within an inch, and it is there for multiple inches of the flightpath. It makes sense that as the "closeness" to the object doubles, the effect on the passing bullet would square.

Take a scenario where you are in a fixed position and spot a nice deer at 600yds, but there is a large tree at 75yds. Looking through the scope, you see that your round will just barely miss hitting the tree. Will the round be off-target at 600yds, if you take the shot?
THAT is an interesting concept and way outside of my technical competence. Most of the POI shifts I have read about using the Magnetospeed were generally attributed to a change in barrel harmonics. To my uneducated mind your theory has merit and I would be interested in what others have to say.

I intend to try this Chrony on a bunch of different rifles, and will post any findings on POI change. My intention is primarily to back-check proven loads for ES and get another data point for working out drops. I have seen many claims of POI shifts with no effect on group size, but until I have WAAAAAY more experience with this unit I am not going to use it for load development purposes.

It is definitely closer than 5" from the flight path ... Job #1 is quadruple checking my set up so that I don't become "that idiot" who shoots it off
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