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Posted: 12/1/2007 9:58:06 AM EDT
| Sorry if this has been covered but after several searches and reads I'm still confused. I have a 11.5 upper with 1/9 twist. I have always used 55 grain with this upper. After reading several threads it would seem that 55 grain would be a poor choice for defensive ammo. Most of the threads deal with 11.5 1/7 barrels so I'm confused as to what the best ammo would be for a 1/9 11.5". Thanks in advance! |
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I would want to use a lighter bullet with the short 11.5" barrel; especially if you only have a 1/9 twist. 55gr would be ideal....maybe 62gr on the heavier end of the spectrum. When you get into heavier bullets, short barrels, and the 1/9 twist...you will start to have stabilization issues at range. Of course, you did mention self-defense, so I'm assuming we are talking very short distance in this situation. Maj |
| I use an 11.5" upper for my duty rifle and use 55 grain soft point bullets. I am staking my life on them and have no doubts that they will do the job. My upper is also a 1/9 twist. It has been accurate out to 150 yards with no problems. If you are used to 55 grains, stick with what you do the best with. Like was mentioned earlier, if it is for self defense, any shot you make would probably be under 100 yards, and most likely under 50 in an urban environment. |
I would think that a 1/9 twist, coupled with the rather short barrel (11.5") would prove to be very difficult to stabilize a heavier round. Maybe somebody can elaborate if I am wrong? Maj |
| With the 11.5" barrel, velocity is the enemy. Although heavier bullets are generally considered better stoppers (with 14.5" or longer barrels), you need to stick with 55 gr. bullets with short barrels so you still have enough velocity for the bullets to fragment. And even with 55 gr., don't expect much beyond 100 yards. |
The heavier bullets will fragment at lower velocities than standard 55 FMJ, which is why they are suggested for short barrels. Again, this info is covered in the tacked info. Seydou |
| Where do you see this? Everything I see in these threads state that barrels have to be 14.5" or longer for 69 grain or heavier bullet weights to fragment. Every source I have ever seen said 2600 to 2700 fps is the minimum velocity threshold for fragmentation. And you will not get that velocity with an 11.5" barrel and heavier bullet weights. |
From the "Ammunition Forum FAQs (This is a must read before you post)" tacked topic at the top of the forum: www.ar15.com/content/page.html?id=173 Seydou |
| Maybe YOU should read the information you just quoted again. The table clearly shows fragmentation data for 14.5", 16" and 20" barrels, NOT 11.5" barrels. There is no way heavier bullets fragment at the slower velocities an 11.5" barrel produces. I'm not trying to start a fight here, but your information is not correct. |
If you look at the chart you will notice that for the heavier OTM bullets the minimum velocity for fragmentation is much less. 2400/2300 fps You will lose about 40 fps for each inch of barrel length, so about 120 fps from 14.5 to 11.5 So you should still get fragmentation out to about 75 yds. Disclaimer: Figures are approximate and I am sure Zhukov or someone else more knowledgeable than I am will be along shortly to correct me if I am wrong. FTR my post was not meant to be argumentative, so no worries. |
It clearly has a small influence. It increases the RPMs of the bullet due to greater velocity. VERY short barreled pistols can exhibit yaw due to the short barrel... the Rohrbaugh pistol comes to mind. Not hat any of this applies here where we are discussing 11.5" 1/9 twist 5.56 barrels. |
Which is why I worded it the way I did, you nit-picker. 
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Thanks for all the replies. Very interesting. Everthing I have read on 11.5 barrels is about 1/7s. How would I test to see if the 75s would stabilize in my 1/9? Test at 100 yards? 200 Yards? 50 Yards? What about 62grain? Any advantage over the 55? I always had thought 55 was the best for a 1/9 but that was before what I call the "new" loads came out. My old barrel was a 1/12 11.5. |
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To test for bullet stability, simply shoot at a paper target and look for "keyholes". If none at 50yds, try 100 then 200, though these will be beyond the frag range(at least the 200 will, the 100 may not be with 5.56 TAP). IIRC there is no significant advantage of 62gr ball over 55gr ball other than better barrier penetration. Your barrel should stabilize everything up to 68/69 and maybe also the 75/77. Seydou |
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