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Posted: 12/28/2009 9:35:15 AM EDT
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I have a decent blasting load for the AR with 55 gr Horn fmjbt and 23.8 gr of H335. The rifle is a Double Star lower, 16" BCM middy, w/ MIllet 1-4 scope. I got some 60 gr Spitzers to work up a hunting load.
I was surprised at the different POI for the 60 gr compared to the 55gr. I thought maybe my cheap scope mount was causing trouble so I fired 3 rounds of the blasting ammo. The blasting ammo hit where it was supposed to. Here is the last target at 100yds. http://i700.photobucket.com/albums/ww7/cactus_jack/60spitzer.jpg I expected the 60 gr to print lower than the blasting round, but not 4". With the H335 at the lower end and Varget at the higher, I thought the velocity would be within 100fps or so. I guess a chrony would help me out here. I can go up a bit on the Varget charge, but am pretty close to the upper limit. The ballistics stuff has me baffled. The printing to the right was unexpected. My son was shooting some of the groups and he ALWAYS shoots a bit to the right with this rifle. I think it's something different with our eyes . He shot the 26.4 gr group, and then I shot the rest on this target. My Varget rounds are still to the right. So am I stuck rezeroing for each load? That's a pain, Anyone loading spitzers over Varget? What was your results? I am quite impressed with the Spitzers. I know 3 round groups are nothing to brag about. The 40 cents a bullet gets expensive with larger groups. Thanks, Fred |
| I'm loading 23.6 grains of 2230 at Sierra's recommended height. Now, that said. My son is an Army Sniper. With every load and change of environment you HAVE TO find a new zero. They call it the " DOPE " . With every change of load, wind change, temperature change, cold bore vs warm bore, distances, elevation, angle of shot, rain and snow. They have the zero recorded in a book. Your going to need to record the same thing for various loads. Good target turrets are a neccesity too.... or at least nice to have. |
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Quoted:
Thanks Smith, I guess its not rocket science. Zero scope adjustments for the blasting ammo since thats what I will usually shoot. For Spitzers: move POI left 2" (8 clicks) move POI up 3 3/4" (15 clicks) Pretty damn simple. Sorry to take up your time. Fred I see your new to Arfcom... Welcome ! The only stupid question you'll ever have is the one you don't ask. For all the help I've received in forum. I'm all too happy to help. Anytime. david. |
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Quoted: Quoted: The reason for the POI shift isn't velocity but barrel time. Especially at 100 yards. Interesting! Can you elaborate? I said ballistics stuff had me confused. The rifle begins moving back as soon as the bullet starts moving forward. With most rifles, a heavier bullet tends to cause the muzzle to pitch up more before the bullet exits the bore, making them shoot higher. But on the AR15, the nearly straight line action negates most of this. But depending on how the rifle is held, different loads can have different POI. The secondary issue is barrel vibrations. But this is minor compared to gross rifle movement. |
| Barrels have different POI charatoristics. Not all barrels shoot all bullets straight down the middle and high or low. Example, I had 3 bolt guns with heavy barrels in .223, I was shooting them at the same time. I would shoot 3 rds of the same load in each rifle. I had a few different loads from 52gr Match up to 77gr Match. All was 1x9 twist. All 3 of the rifles shot tight groups, 2 of the rifles had POI shifts like you have pictured, but 1 had a very close to same POI. The lower priced and thought of rifle shot the best. I have ARs, but have not done as a stringent test as this, but I know they will do the same. |
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The reason for the POI shift isn't velocity but barrel time. Especially at 100 yards. Interesting! Can you elaborate? I said ballistics stuff had me confused. The rifle begins moving back as soon as the bullet starts moving forward. With most rifles, a heavier bullet tends to cause the muzzle to pitch up more before the bullet exits the bore, making them shoot higher. But on the AR15, the nearly straight line action negates most of this. But depending on how the rifle is held, different loads can have different POI. The secondary issue is barrel vibrations. But this is minor compared to gross rifle movement. Unless you have a KRISS, which I don't and probably no one reading this does either. |
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The POI discussion makes sense to my simple mind. It probably also explains the different POI between me and my son.
As for my bullet selection, that was an uneducated guess on my part. I have seen what my 55 gr blasting load does to untreated 3/8" steel targets (NOT recommended). It almost blasts through it. I figured a 60 gr projectile around 3000 fps with any expansion at all would be devastating to most game. I will use the AR mostly for hogs. I will work up a heavier load. That's a good excuse for some more range time. Thanks, Fred |
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