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Posted: 12/8/2005 9:21:58 AM EDT
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I need some help. I am a shooter on a budget. As such, my equipment is inexpensive. My rifle is a Model 1 Sales 20" barrel .223 chamber 1-9 twist. My scope is a NCstar 3x9 (actually 3x 8.11) with P-4 sniper reticle. It is calibrated on the top turret 100, 200, 300, 400, and 500 yard settings. So, I am looking into getting the most out of my equipment. The rifle consistently shoots 2 MOAs at 100 yards. The scope seems to hold zero if you keep the screws tight. OK, so here is my question. Using JBMs website and ballistic calculations, and also calling NCstar to see what they found testing my scope, it appears the bullet path (Winchester 55gr FMJ) corresponds almost exactly using a G7 drag function. At my range, I only have 100 yards to work with... If this G7 functions does seem to duplicate reality, then that also means velocity drops off much faster then described with the G1 function model. It is my understanding the true effectiveness of the .223/5.56 round is fragmentation. That fragmentation primarily ends at 2600 fps (www. ammo-oracle.com). Also, my rounds go below the speed of sound before 500 yards. I calculated the BC for my rounds from JBM using posted velocities from both Winchester, Federal, and Remington. As an example .223 55 gr listed BC .255 at G7 is .125, .223 62 gr listed BC .301 at G7 is .124. With my rifle, fragmentation ends at 75 yards not around 150 as a G1 would indicate.... So, does this bullet path, and velocity drop off make sense? It is important too me to understand the limitations of both my equipment, and ammunition. Thanks for your help... OH, also I am going to try some Black Hills 77 gr with my rifle. I have read that it is a 50-50 proposition if my barrel will stablize the rounds. The Sierra 77 gr has a length of .985. I have shot 69 grs which actually gave me my best groups out of my rifle, and I understand the 69 gr has a length of .980. So, I dont expect the 77 grainers to stablize, but maybe.... Thanks, |
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I have a 1:9 twist, 16", chrome-lined bushmaster and it stabilizes the 75 gr BH OTM out to at least 300yds. I haven't had the chance to properly test it byeond that. If you are on a budget, the 75 gr is much cheaper than the 77, which is used by high power rifle enthusiasts. I have a Burris ballistic plex scope that is probably similar the the NCstar you are describing. I have tried mine with several different ammo types and all I can say is: you won't know until you test it yourself. Actually, the ballistic plex allows me to make hits on man-sized gongs at my local range out to 500 yards with XM193. As for whether or not your G7 drag function make sense, I have no idea. I am assuming that the Winchester is similar to the BH 55 gr which goes approx 2750 fps from a 20 in barrell(XM 193 goes about 3250 fps form a 20"). Personally, I use the 55 gr for most of my practice for cost reasons but I also practice a bit with the 75gr and I know how to adjust my BUIS and all my different optics for each loading. Hope you find this helpful. Oops! I accidentally pulled the velocity of the 75gr instead of the 55gr. actually velocity of the 55gr is 3250 fps. Sorry for the error. I will try to be more careful next time. |
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Thanks for the input. Problem for me is I don't have a range beyond 100 yards to verify. If the G7 drag model is true. Doesn't it also mean my fragmentation range is significantly less then published? With that drag function the velocity drops under 2600 fps around 80 or 90 yards with XM193 and 75 with reqular Winchester 55 grain (not the Q3131a)... Again, I appreciate your help. Thanks, |
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I think it would be difficult to conclude that the bullet path corresponds to a G7 drag function on a relatively short 100 yard range. I suspect you would need some real world data out to at least 500-600 yards. I also think that the bullet manufacturers know what the correct BC is for each bullet that they manufacture. I wouldn't put much stock in the turret caps on the scope either. My experience tells me that you need to chronograph your ammo, and then determine your actual come-ups at various ranges out to say 600 yards (or more). For instance, the .308 cap on my Leupold LR scope is totally out of wack when compared to the actual performance of my .308 handloads. I think the best way to go about it, is to get some real world data, and then have some custom turret caps made up...if that's an option for your scope. Good luck. |
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