Flat-base vs. boat-tail
This is a discussion on Flat-base vs. boat-tail within the Cartridges & Calibers forums, part of the Sniping Related category; Ok, we all know that boat-tail rounds are more accurate than flat base bullets because the tapered end of a boat-tail cuts down size of ...
Flat-base vs. boat-tail
Ok, we all know that boat-tail rounds are more accurate than flat base bullets because the tapered end of a boat-tail cuts down size of the base of the bullet and therefore the size of the vacuum behind it. (I don't know how/why that all works, but it is a generally accepted concept)
That being said, why use a flat based bullet in a rifle (especially a fighting rifle)? Everybody wants more accuracy out of their rifle. The older military 55 grain (M193) 5.56 and the newer 62 grain (M85, I think) 5.56 are flat base bullets. My department makes us carry Federal 55 grain TRUs, which are also flat-base. Outside match grade bullets, most of the rounds (at least for 5.56) I find are flat base. Why don't these ammo makers use boat-tails and therefore increase accuracy? Are flat-base bullets more stable at shorter engagement distances? Are boat-tails somehow more expensive to make? Whats the deal?
Well, at very long distances, a boat tail's wind fighting abilities may be significant. However, at the range that most LE shots occur, how important is wind drift going to be?
There are a lot of issues involved here. The most important is probably terminal ballistic performance by the bullet. I think the TRU round is pretty good in that department.
I have a number of older military surplus rifles, (Eddystones, 03A3's Mausers, etc). Not all of them shoot well with a boat tail round. Don't forget, a flat base bullet has a larger bearing surface to engage the lands with. For some rifles, that is an important factor in accuracy.
Boat tail are NOT necessarly more accurate, they buck the wind better at long range. As said above each rifle has its likes and dislikes.
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CalFed, I agree totally. Most LE shootings (riflewise) are going to be inside 50 yards, probably less. But accuracy, at any range, is highly important (especially in the LE world) due to backdrop and the possibility (however likely or unlikely) of having to take a precision shot to put a bad guy down.
It was my understanding that boat-tails are more accurate across the board, not just in wind-fighting conditions. I may be wrong though. And I never thought of flat-base bullets engaging more of the rifling. Interesting.
I've never heard that BT's are more accurate across the board, although I must admit that I'm a tyro on this subject.
They do typically buck the wind better and maintain velocity better. But those are only a factor at longer ranges--much longer than we are talking here. I would wager that the difference in accuracy, wind drift and velocity maintenance inside a couple of hundred yards are negligible--and may well be overcome by more urgent factors like terminal performance.
I'm not certain that the extra bearing surface would be a major factor, but don't forget--light .22 caliber bullets already have precious little bearing surface as it is.
But, I guess I will change my question to this then: What benefits do flat-base bullets have over boat-tails. There must be a reason that one is used over the other in the afore-mentioned fighting cartridges...
The two 5.56 loads you cited the M193 and the M885 are both loaded with boat tail bullets. The boat tail lessens the drag of the bullet and makes it more aerodynamic, so it retains its velocity better and is less affected by wind. (It gives it a higher B.C.) The military uses them because they have a longer effective range. One of the reasons they switched from the M193 55gr BTFMJ was they found they by increasing the weight from 55 grains to 62grains they could gain an extra 50 or so yards effective range. They had to go with faster rifling twist to stabilize this bullet though.
Flat based bullets are very accurate, especially at shorter ranges. Itâ€™s my understanding they are very popular with the bench rest crowd. They wouldnâ€™t use them if they were less accurate. They just lose their energy faster due to their lower Ballistic Coefficient. If you are shooting at 100 yards that isnâ€™t a big deal. The trajectory of a flat base bullet wonâ€™t be as flat. They are every bit as accurate, especially at shorter ranges.
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Don't confuse flying better with shooting better. Boat Tails reduce BC, which will give the bullet more range and help it to buck wind better. However, this doesn't mean the bullet is more accurate. At long range, the wiggle room that the BT gives in doping wind is a real asset. As was pointed out above, flat tails are used by benchrest shooters because they can (or believe they can) get more accuracy at shorter ranges.
I can't tell you which is more accurate. I can say that I read an interview with Joyce Hornady in which he said that both boat tails and hollow points inhibit accuracy, yet BTHP is what is used in match ammo. Of course, the meplat in, say, a 168gr BTHP is not really a hollow point, it is present because of the way that the bullet is manufactured. I think the boat tail is there to increase BC.
It's all been said here, go to a 300yd BR shoot and see what they're shooting, you'll see a lot of flat base bullets.
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