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Post by jkd on Nov 8, 2007 15:08:05 GMT -5
If you've not already done so, now is the time to check the zero on your PCR deer gun or slug gun for the upcoming deer firearms season. I recently purchased a Marlin 1894CB .44 mag rifle and wanted to share some learning curve experiences I had in setting up the new gun. I picked up a box of Remington 180gr JSP and a box of Winchester 240gr JSP to test in the rifle. All shots were taken seated in a folding hunting seat with shooting sticks, as will typically be the case for me when hunting from the ground. I first shot with open sights using some of the 180's, quickly got the elevation adjusted, and was shooting 1.5" groups at 50 within a few rounds. However, the front bead on the Marlin is fairly large, and basically obscured an 8" target circle at 50+. I had picked up a Bushnell 3x-9x by 32mm riflescope and see-through rings, and mounted the scope. Using the 180gr ammo, I set the scope for +2.5" at 50, which should put the round about on zero at 100 |
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Post by jajwrigh on Nov 8, 2007 18:15:10 GMT -5
Nice, informative post.
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Post by hunter480 on Nov 8, 2007 19:53:03 GMT -5
Fantastic post on many levels.
Thank you for doing some of my homework for me.
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Post by weasel1134 on Nov 9, 2007 4:43:47 GMT -5
I enjoyed reading your post lots of good info. I don't want to H.J your thread but I got to thinking if I shot 40 rounds thru my 870 that would have cost me about $96.00 and and severely bruised shoulder. I have to get a PCR as soon as I can. I will be very interested to see how everyones rifle/bullet combo performs this year. It sure must be nice to really enjoy shooting your deer gun. To everyone shooting a PCR please keep us updated as gun season gets under way.
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Post by oldhoyt on Nov 9, 2007 12:56:07 GMT -5
I don't see anything surprising about a 3" left-right impact difference when switching from 180 to 240 grain bullets. When a bullet is traveling down a rifle barrel, the muzzle is oscillating up, down and left to right. Not a dramatic amount, but it is moving in relation to the line of sight. Bullets that travel at the same velocity generally exit the muzzle at the same point in the muzzle's oscillation, so they fly to the same POI. When there is a difference in velocity, the bullet MAY exit the muzzle when the muzzle is pointing left, or right, or up or down for that matter, in realtion to where it pointed when the other bullet exited. So changes in POI should be anticipated when shooting bullets that travel at different velocities, and though you can sometimes predict elevation changes, you cannot predict left-right changes. You have to shoot to see it. By coincidence, bullets traveling at different velocities MAY exit at the same point in the muzzle's oscillation, and therefore fly to a very similar POI.
This is the cause of your 3" difference in POI between loads. The Magnus effect is valid, but won't really be seen within 50 or 100 yds. The Magnus effect only occurs in a crosswind. Think about it, a bullet spinning on its axis cannot create a difference in pressure on just one side of the bullet, unless some external force comes to bear.
I'll bet you anything, that if you adjust your windage so you hit perfectly left-to-right at 100 yds, you'll find that you're on at 50 as well. If not, the overwhelming probablility is that there is an issue with the gun itself such as forestock pressure points, the operator's shooting form, the rest, etc. or any combination of those factors.
Leave Old Magnus to the snipers that need to worry about such things.
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Post by snakeeye on Nov 9, 2007 17:50:18 GMT -5
Until I discover the lethality of the 1894 with my chosen 240s, I plan to keep my shots to ~50yds. Good post!
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Post by tenring on Nov 9, 2007 19:28:13 GMT -5
22.0/2400, 240XTP, POA/POI same at 50 and 100 yds., I'm good to go.
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Post by jajwrigh on Nov 9, 2007 21:42:06 GMT -5
I did some open sighted 50 yard work tonight and had several rounds touching with handloads in the 1894 Marlin. This is an extremely accurate guns which shoots everything I feed it well. ;D
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