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55gr. vs 75gr. vs 77gr. Login/Join 
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Picture of GroundedCLK
posted
Soo... looking for some clarification.

Long story short... On this balmy 21 degree day I took my AR out topped with my new optics.

Started at 25 yards with 55 grain XM193 ammo and zeroed it there - once I was pretty close I then switched over to 75 grain TAP ammo. The POI was very close as I expected, didn't believe there would be a huge shift at these distances. Once this was complete I took it out to 50 yards and went through the same steps until it was zeroed for 50 yards.

Then just tried it at 100 yards and as expected it was 1.5" high, but this is where the question comes in.

I shot it at all three distances with the 55 & 75 grain ammo (couldn't find 77 grain), the POI shift was very minimal at all. Is there really a huge benefit to one or the other?

Grouping was close(only shot two groups, it was cold):
1.1" at 100yards with 55gr.
.89" at 100yards with 75gr.

Rifle:
BCM Recce 14.5" 1/7 twist
 
Posts: 1511 | Location: New Hampshire | Registered: January 12, 2005Reply With QuoteReport This Post
Freethinker
Picture of sigfreund
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Benefit of what?




“Most men … can seldom accept the simplest and most obvious truth if it … would oblige them to admit the falsity of conclusions … which they have woven, thread by thread, into the fabrics of their lives.”
— Leo Tolstoy
 
Posts: 35841 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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Picture of GroundedCLK
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quote:
Originally posted by sigfreund:
Benefit of what?


Since I am not taking this rifle to war is there a benefit of using the higher grain/more expensive ammo?

From reading I have seen a lot of different opinions about energy transfer with the heavier rounds to better accuracy.
 
Posts: 1511 | Location: New Hampshire | Registered: January 12, 2005Reply With QuoteReport This Post
Freethinker
Picture of sigfreund
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Yes, different types of bullets (FMJ, soft point, open tip, etc.) cause different wounding effects and perform differently through barrier materials, if that’s what someone is looking for. Bullet velocities also make a difference for those purposes. I do not rely on M193 for defensive purposes.

For accuracy, heavier bullets in a specific caliber (e.g., 0.224") are usually affected less by the wind, and therefore are more favored for long distance shooting.

In comparing the two rounds you fired, though, what really makes a difference in accuracy is the quality of the bullets and loads. The Hornady 75 grain open tip match bullet is manufactured to much higher standards than the typical 55 grain FMJ bullet used in XM193 loads. In my experience with the two loads you mentioned, the Hornady 75 grain TAP groups far, far better than the M193 stuff I’ve fired. In fact, I strongly suspect that the relatively small size difference between your two groups was merely due to chance. Single groups don’t demonstrate much of anything unless they’re really bad. Before making any significant decisions (like buying a pallet of the one you settle one), you should fire many more groups for evaluation.

If you’re only plinking and the M193 load is accurate and reliable enough for your purposes, then there’s no reason not to use it. That’s all I use for one training course I fire, but the maximum range is 25 yards and the hit zone is relatively large. On the other hand, when I shoot another course with a 2 inch circle target at 100 yards, I use a premium load. At 100 yards the bullet weight isn’t very important, if at all (I get very good groups with Hornady 55 grain TAP ammo), but bullet and overall load quality does matter a lot.

Added: Bullet weight per se does not determine accuracy one way or the other unless we get into reading the wind and other longer range issues. When I tried some IMI with 77 grain OTM bullet I was initially very dissatisfied, but again I only fired a couple of groups. When I went back to it, I got much better results. Other weight bullets, though, like the 69 grain Sierra Matchking and as I mentioned the Hornady 55 grain A-MAX (TAP) performed very well. Even if we know exactly what bullet we’re using, there are many other factors that go into making a load that will produce consistent accurate results.




“Most men … can seldom accept the simplest and most obvious truth if it … would oblige them to admit the falsity of conclusions … which they have woven, thread by thread, into the fabrics of their lives.”
— Leo Tolstoy
 
Posts: 35841 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
The Persian
Picture of PPGMD
posted Hide Post
BC determines long range performance more than anything else, typically the higher the weight the higher the BC but that isn't always the case. Berger and Nosler both have slightly lighter bullets than the 77gr SMK with higher BCs.

So if you are looking at a precision load I would be running a load that uses one of the above bullets. Probably the most commonly available at the SSA Mk262 or the Blackhills Match 77gr SMK.

If I was looking for a defensive load it would probably be the Hornady TAP 5.56 75gr. It has better terminal ballistics than most other common loads.


-------
Take your time, I'm hourly.

Mr. Doom and Gloom
"King in the north!"
"Slow is smooth... and also slow.

The opinions posted by this user are his own. And do not represent the opinions of his employer or sponsors.
 
Posts: 19553 | Location: At the wall | Registered: February 13, 2008Reply With QuoteReport This Post
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