Twist rate VS bullet selection

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Larryswn

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I have noticed that my Hornady 55G FMJBT bullets are very accurate compared to the 68 grain BTHP. By accurate I mean I can group about the size of a softball at 100 yards. Keep in mind I'm using iron sights and Im a relatively new shooter so there's some operator error at Play. But with these 68 grain bullets I have noticed I have to adjust my windage quitea bit and the group is double in size. Twist rate on the AR is 1/9 . My question is, is there any data that could help me make better bullet selections in the future based on my rifle. Concentricity on both rounds is damn near perfect. .001 max. Of course I am assuming the twist rate is the problem with the inaccuracy on the 68g. Yes I'm using a recipe and I'm near the top of the charge but maybe there's something else I'm doing wrong. The only reason I would question the twist rate is because my Hornady book specifically says certain bullets do not stabilize with such and such twist rate. My particular twist rate is not mentioned but it got me thinking........... I'm ready for lesson number six. You guys know your stuff..... seating to the lands is not an option in this rifle the throat is way too long.....
 
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Larryswn said:
Twist rate on the AR is 1/9 . My question is, is there any data that could help me make better bullet selections in the future based on my rifle.
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The twist is near perfect for the 68/69 gr match bullets and should be more accurate then most fmjbt bullets.
What powder are you using?
 
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Now,
Some 1:9's will, some won't. A sure fire way is to put your gun on a bench and shoot that load with a scope on your gun. Then you'll know for sure it's not shooting well and either need to change charge, powder, bullet, or all three.
 
BigBore44 said:
Just a friendly reminder of Code of Conduct rule #3

3. As a family-friendly board, we ask that you keep your language clean, and that starts with your chosen user name. If you wouldn't say it in front of your dear old Grandma, you probably don't want to say it here. This rule includes any inappropriate images.

The Mods monitor this rule....

Now,
Some 1:9's will, some won't. A sure fire way is to put your gun on a bench and shoot that load with a scope on your gun. Then you'll know for sure it's not shooting well and either need to change charge, powder, bullet, or all three.
Click to expand...
User name is clean but sorry about the language. Thanks for the advice.
 
BigBore44 said:
Just a friendly reminder of Code of Conduct rule #3

3. As a family-friendly board, we ask that you keep your language clean, and that starts with your chosen user name. If you wouldn't say it in front of your dear old Grandma, you probably don't want to say it here. This rule includes any inappropriate images.

The Mods monitor this rule....

Now,
Some 1:9's will, some won't. A sure fire way is to put your gun on a bench and shoot that load with a scope on your gun. Then you'll know for sure it's not shooting well and either need to change charge, powder, bullet, or all three.
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I have employed a buddy with same rifle and scope to shoot some. I spent a ton on reloading stuff and will not buy a scope yet. I prefer to get surgical with irons first.
 
I've had the same accuracy trend with boat tail bullets and Varget. Flat base bullets work good for me at 100yds. In addition to 55gr Spitzer I shoot a speer 70gr semi-Spitzer, both are sub-moa from my Handirifle with a 1:9 twist barrel. How far are you planning on shooting?
 
Tinybob said:
I've had the same accuracy trend with boat tail bullets and Varget. Flat base bullets work good for me at 100yds. In addition to 55gr Spitzer I shoot a speer 70gr semi-Spitzer, both are sub-moa from my Handirifle with a 1:9 twist barrel. How far are you planning on shooting?
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Local range is 100 max
 
According to the stability calculator at jbmballistics.com, 1/9 is too slow for the Hornady 68 gr bthp.
 
The Hornady 68 gr match bullet was most accurate using IMR 3031, in a bolt gun. Twist 1 in 9.
Most will not use IMR because it doesnt go thru a measure well. Each powder charge needs hand weighed.

With iron sights, i would test accuracy at 50 yards. Less room for sighting errors. Imo.

Twist- velocity/RPM's comes into play with short barrels.
 
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1:9 is a good twist for a 16" barrel AR and should work well with most 50-75 grain bullets. There are always exceptions to this though. Some bullets and barrels just don't play well with each other. In a longer barrel like a 24 or 26 inch bolt gun you can have issues with 50-55 grain bullets coming apart from centrifugal force because of the higher velocity. I like a 1:12 twist in a 24-26 inch barrel for 50-55 grain bullets.
 
Don't give up on them. My 1:9 shoots 69g SMKs 5 shot groups under 0.5 MOA consistently
 
The Hornady's do have a slightly different ogive than SMK's and are a little longer, but still should stabilize in a 1:9.

Don't get rid of them because you'll be sorry some day. But if you insist, send me a PM and I'll buy them from you!
 
A lot of 1-9 twist barrels will shoot the 68/69 Gr bullets just fine, but not a low speed. I am surprised they shot twice as big a group though, just like you are.

Laphroaig makes a good point, as it is bullet length and not weight that determines if it stabilizes.
 
BearingSurface_zpsbac6nfsu.jpg
There are 2 Sierra 69 gr. Hornady is the longest. Nosler 55 gr was best.
224%2069gr.jpg%20A_zps2ev93cf2.jpg
 
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They shoot well. I bought them over the V-Max some years ago because they were so much cheaper. Not as big a price difference these days.
 
I think I read somewhere ZMax bullets were being discontinued, though it may just be the ammo phased out, or a rumour.
 
someguy2800 said:
1:9 is a good twist for a 16" barrel AR and should work well with most 50-75 grain bullets. There are always exceptions to this though. Some bullets and barrels just don't play well with each other.
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That's not great advice - it's a lot more than "some bullets and barrels just don't play well" when you talk about 75grn bullets. The 75grn A-max, now the 75grn ELD-M is a massively long bullet. The Barnes TTSX 70grn is another extremely long bullet. I've never been successful in getting these to stabilize in a 1:9" barrel at 16" velocities, while alternatively, getting the 77grn SMK to stabilize is a much easier task - this isn't a "it didn't work in one or two rifles" type opinion, this is after building and rebuilding over 700 AR's in the last ~18yrs and using the 77SMK and 75 A-max as my benchmark bullets for long range precision.

Delivering these long bullets to 100yrds into a sub-MOA group isn't good proof of stability. Groups at 300 & 600yrds will give away the truth.

A 16" barrel with 1:9" twist should manage 40-70grn bullets, not including the heaviest/longest of the mono-metal bullets.
 
Tinybob said:
I think I read somewhere ZMax bullets were being discontinued, though it may just be the ammo phased out, or a rumour.
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They've been out of production for quite some time. The Z-max's in 22cal were nothing more than V-max's with green tips, so the same bullet is and will remain to be available.

You can pick up clearance boxes of the 500bullet Z-max's pretty easily in a few places. Other folks are smart enough to realize it's a V-max and charge face value on them.
 
Varminterror said:
That's not great advice - it's a lot more than "some bullets and barrels just don't play well" when you talk about 75grn bullets. The 75grn A-max, now the 75grn ELD-M is a massively long bullet. The Barnes TTSX 70grn is another extremely long bullet. I've never been successful in getting these to stabilize in a 1:9" barrel at 16" velocities, while alternatively, getting the 77grn SMK to stabilize is a much easier task - this isn't a "it didn't work in one or two rifles" type opinion, this is after building and rebuilding over 700 AR's in the last ~18yrs and using the 77SMK and 75 A-max as my benchmark bullets for long range precision.

Delivering these long bullets to 100yrds into a sub-MOA group isn't good proof of stability. Groups at 300 & 600yrds will give away the truth.

A 16" barrel with 1:9" twist should manage 40-70grn bullets, not including the heaviest/longest of the mono-metal bullets.
Click to expand...

Well I guess the bullet length and stabilization was what I was getting at, I just didn't elaborate. I've loaded for a few AR's but don't own one anymore, you obviously have way more AR experience than me. Do you every see any issues with lighter bullets coming apart at 16 inch barrel velocities? I'm surprised others don't seam to have had the issues that I had shooting varmint bullets from a 24" 1:9. My old man's 1:9 works well with most but not all 50-55 grain bullets but mine I could not get it to stop blowing apart and overstabilizing various bullets. I had a whole stack of notecards with bullets going through them sideways. Sent the gun back and it did the same when it returned so I had enough and rebarreled it to 1:12.
 
Blowing apart is a lot closer to a wives tale than it is a reality. I've not been able to "blow apart" a 50grn V-max with a 26" 1:12" 220swift, running much harder and faster than any AR ever could. Cut rifled barrels, fast twist, and 26" of tube pushing a 40grn NBT, yup - that's a shotgun, no longer a rifle, but no, a 16" AR in 5.56/223 with a 1:9" twist isn't going to spin out a 50grn V-max - nor will a 24", or even a 26" Savage 12.

I'd venture there was something a lot more interesting going on if you were able to get a 24" 1:9" 223/5.56 to blow apart 50-55grn pills. I've shot over a million 50grn V-max's through AR's from 7" up to 29", never been able to spin one fast enough to crack the egg.

Sideways tears aren't really indicative of angular destruction, however.
 
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