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-   -   Why Cant i have a two shot grouping ? (http://www.firearmstalk.com/forums/f30/why-cant-i-have-two-shot-grouping-84964/)

Tenderribbs 02-23-2013 05:48 PM

Why Cant i have a two shot grouping ?
 
Because if I can , I can shoot a 1/2 MOA all day but dadgumit , every time that third shot will make it a 1 1-2 MOA . I've tried putting another shell below my 3 shots in my magazine in hopes of helping seating the same every time no luck .heres what I'm shooting....
1 by 7 DPMS with 16in barrel with DPMS upper and lower the ammo is u55 grain FMJ /BT and 23.5 of H-335. .
Theory-1the heat from the barrel by the third shot is heating the barrel
Theory 2 - I'm a bad shot
Theory3 - go To a heavier bullet
Theory 4 - this is what I need y'alls help with.
Any recommendations are appreciated

cottontop 02-23-2013 06:00 PM

Get a bolt action rifle and then you can shoot 5 shot sub MOA groups all day long.
ct

trip286 02-23-2013 06:06 PM

Try letting the barrel cool at least five minutes between each shot and see what you can do.

The heat from even one single shot can throw off the POI on the next shot, and the effect of heat is cumulative.

The object of shooting groups is not to judge the combat accuracy of a rifle, but to judge the cold bore accuracy, so that an experienced cold bore shooter (such as a hunter or long range marksman who normally wouldn't engage in CQB) will know within a set margin exactly where their first cold bore shot will land.

JTJ 02-23-2013 06:08 PM

2 is a couple, 3 is a group. Bump your load up to 24.8 grains H335 and watch your overall length.

trip286 02-23-2013 06:10 PM

And ct, many of today's modern semi's will hold accuracy on a level easily comparable to modern bolt actions. Many, MANY, ARs are capable of sub MOA accuracy, yet "sub MOA" is still a marketing tag line for selling bolt action hunting rifles.

And even then, I've rarely seen a shooter more accurate than their tool. It happens though.

Tenderribbs 02-23-2013 06:38 PM

I'm sure we all wished our talents would exceed our weapons ability but as you say it's far and few. I have a recipee for A 77 g nosler with varget that shoots sub MOA so I'm just curious what would cause this phenomenon . Thanks

Tenderribbs 02-23-2013 06:40 PM

That makes sense so your saying the heat does affect the bullet the third shot?

trip286 02-23-2013 06:42 PM

Just to point out, I wasn't taking a dig at you or your rifle. That was more directed towards the idea that "this is better than that" kind of rifle.

locutus 02-23-2013 06:53 PM

If you want to get an idea of the true accuracy of your rifle, at a minimum, shoot 5 groups of 5 shots and average them.

An even better indicator, and the one used for high dollar SuperMatch guns is 10 groups of 10 shots.

3 shot groups are all you need for big game hunting loads, but to work up long range target or varmint loads, 5 or 10 shot groups will tell you much more about your load and your rifle.

trip286 02-23-2013 07:13 PM

Quote:

Originally Posted by Tenderribbs (Post 1150471)
That makes sense so your saying the heat does affect the bullet the third shot?

I'm saying it can, and it's possible that it can affect it quite significantly. One shot will warm the barrel. If the second shot is fired before it cools, then a third is fired in the same interval, then the third shot could be leaving from a bore that is twice as warm as the second shot, and 4 times as warm as the first.

Just an example, to try and put it into numbers. These aren't accurate numbers, and I've conducted no study to get exact figures or percentages, but with many hours behind machine guns, semis, and bolt actions, I'll stand behind thus theory of mine until or unless someone proves me wrong beyond any shadow of a doubt...

Let's say your first shot is fired from a bore at an ambient temp of 70 degrees. That shot hits exactly where you meant it to, but it raises the temp of the bore by 5 degrees.

Now your second shot is fired from a 75 degree barrel. It is only slightly off from the first POI, but if you fire it before the heat from the first shot dissipates, you may have just raised the temp of your barrel to 85 degrees. Twice the increase from the first shot, because the effects of friction (which is what's causing the heat) accumulate over continued application.

Let's relate that to inches, for the sake of simplicity. Again, I'm making up theoretical numbers for illustrative purposes.

If your second shot is fired from a note that's five degrees warmer than the first shot, it may be off a half inch. If the third is fired from a bore 10 degrees warmer than the second, this translates into FIFTEEN degrees warmer than the first, and it may be off your mark by upwards of an inch and a half! And in a different direction!

This is why thicker profile barrels are more popular for marksmanship competitions. The greater surface area dissipates heat faster and the profile adds rigidity.


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