Barrel length mixed with rate of twist and bullet grain is to confusing for me.


November 19, 2008, 10:24 PM
Barrel length mixed with rate of twist and bullet grain is to confusing for me.

I am just kinda looking for a cut and dry answer here.
I know the 5.56 round isn't the best thing for self defense but if it's all you had what bullet would you use if you had a ...

16 inch barrel
W/a 1:7 Twist
Like the Sig 5.56

I am looking for any advice like:
What Grain would you use?
What brand would you use?

If you enjoyed reading about "Barrel length mixed with rate of twist and bullet grain is to confusing for me." here in archive, you'll LOVE our community. Come join today for the full version!
November 19, 2008, 10:29 PM
75 grain Hornady TAP. Get the 5.56 NATO specification stuff with the T2 bullet, if you can find it. Restricted by Hornady to law enforcement only, unfortunately, but it's available sometimes. The sticker on the side should say:

75 gr BTHP/WC T2*

If it says anything else, it's not the newest NATO spec stuff. Some people try to pass off old .223 TAP as the new 5.56mm stuff, because both are packaged in a red box. New .223 TAP is in a black box.

The standard civillian 75 gr Hornady TAP is pretty good as well, it's just not as powerful, and uses a bullet with a lower coefficient of drag. The civilian bullet may also be less uniform at expanding. The meplats on the T2 bullets are the most uniform I've ever seen.

Loads utilizing 77 gr Sierra Matchking bullets perform decently, as well. Mk262 Mod 2 (or something like that) uses it, I believe, but I can't think of any other ammo off the top of my head. I prefer TAP, though.

November 19, 2008, 10:35 PM
Thanks RyanM but if it's restricted I doubt I can get any unless you PM me with some details on where.

Any other suggestions?

November 19, 2008, 10:43 PM
Ammunitiontogo used to have some, but they sold out a few days after I ordered a box. I was going to order a second one, too. :(

The plain old .223 75 gr TAP is fine. I'm probably making a big deal over nothing, on the difference between the LE and civillian stuff. And .223 from a 16" barrel probably performs about like 5.56mm out of a 14.5", so you don't really lose anything.

That's the .223 spec civilian stuff.

Also, for practice ammo, if you want something that replicates the trajectory, recoil, etc., Prvi Partizan makes a 75 gr OTM load.

I don't know how the terminal performance is (I suspect so-so) but it's good, accurate practice stuff. Wolf makes a 75 gr JHP as well, though accuracy is typical for Wolf. I dunno where to get that now. Seems like everyone's sold out.

November 19, 2008, 10:47 PM
77 grain Sierra MatchKing HPBT on sale at MidwayUSA for $96.99/500. My AR (1:8 twist) is capable of 1/2MOA with that bullet. It's not a fancy bullet but it's an accurate one and it feeds well from my Bushmaster magazines.


P.S. Are you asking about the bullet or loaded, commercially available AMMUNITION?

November 19, 2008, 10:49 PM
Cool. Thanks again RyanM.

Anyone else have any suggestions?

commercially available AMMUNITION? would be great! But I will Settle for anything.

November 19, 2008, 11:04 PM
bullet or loaded?

I prefer loaded but I do have a press. What info do you have?

November 19, 2008, 11:10 PM
with a 1:7 twist, go with 62gr or higher. 55gr is shootable but i've heard that it's not ideal. hopefully someone else chimes in on this.

November 20, 2008, 12:42 AM
What is confusing you?

The way I see it, we can provide answers to a specific question you have, limited and worded in such a way as not to confuse you, or we can teach you to fish and eliminate the confusion.

Twist rate is simply how fast the rifling in the barrel turns. It is usually worded as a ratio, such as 1:7 or 1:12. The lower the number, the faster the twist rate, because it denotes the length of barrel it takes for the rifling to complete a full twist. The 1:7 barrel, therefore, has a faster twist than the 1:12 barrel because it completes a full revolution of rifling every 7 inches, as opposed to every 12 inches. Faster twist rates are needed to stabilize longer projectiles. While not technically correct, some say faster twist rates are needed to stabilize heavier projectiles. In fact, it has to do with projectile length more than mass--it just so happens that heavier projectiles in a given caliber are usually longer than lighter ones.

And a grain is a unit of weight (not mass) equal to 1/7000th of a pound. There are 437.5 grains in an ounce. Just remember a grain is really small, and not to be confused with a gram which, is a metric unit of mass. Grain is properly abbreviated "gr." Gram is properly abbreviated "g."

In the 5.56, lighter weight bullets from 40 to 55 grains are usually reserved for varmint hunting. Most are not suitable for self-defense as they are far to frangible, and not likely to penetrate deep enough to reach the vitals of a human assailant. The exception would be some 55 gr loads, such as the M193 FMJ stuff available from Federal and Winchester, marketed as copies of the original military load for the cartridge. While not ideal, it is certainly adequate for self-defense. And I believe Federal and some other manufactures market some bonded 55 gr JSPs for defensive use as well. Generally, however, for defensive purposes, you are better suited to heavier for caliber bullet weights from 62 to 77 grains. This would include the Hornady TAP stuff already mentioned, as well as OTM and HPBT loads from Black Hills, Federal, Hornady, and others loaded with bullets such as the Sierra Matchking. These projectiles are long enough to require twist rates faster than 1:9, but they are known to exhibit terminal performance much better suited for defensive purposes than lighter loads. They penetrate deep enough to reach the vitals, while still fragmenting reliably.

November 20, 2008, 12:57 AM
wow, where did you get that info?

There are 437.5 grains in an ounce
A grain is a unit of weight (not mass) equal to 1/7000th of a pound.

!! A1 Great info !! I have always wondered these things. Thanks man!
Thats really cool.

Do you recommend a particular brand name over another for self defense with my barrel specs? or and exact grain recommendation for what I have listed?

November 20, 2008, 10:21 AM
Try different rounds with YOUR rifle. All guns can work a little differently, what works for me may not work for you.

My 1/7 carbine is loaded with 50gr Sierra Blitzking ballistic tipped JHPs. Thjey function perfectly in my rifle and are within 2" of my zero (I zero with 55gr XM193) at 100 yards.

I live in a city and need ammo that will start disintregating quickly after traversing 1 wall. Penetration is probably less than ideal but I expect 1000+ foot pounds of energy at 3000+ fps will discourage most bad activity. At any rate, I've got 30 of them in the magazine.


November 20, 2008, 10:32 AM
thanks for all your help guys!

November 20, 2008, 10:32 AM
I will suggest Hornady 75gr TAP FPD. really the same stuff as TAP, but anti flash propellant. And the cool black case:D.

wow, where did you get that info?

There are 437.5 grains in an ounce
A grain is a unit of weight (not mass) equal to 1/7000th of a pound.

I'm not MTMilitiaman, but i learned that in 8th grade.

November 20, 2008, 01:09 PM
I'm not MTMilitiaman, but i learned that in 8th grade.

I must have been in the slow classes. :(
We only learned the basics of standard and metric system. I don't remember grains and nobody offered gun 101 but I wish they did.

I will look into Hornady 75gr TAP FPD. Thanks for the advice.
Any cheap places where you buy this ammo?

Thanks again gvnwst

November 20, 2008, 01:45 PM
In reality, any 55 grain or heavier varmint or hunting load will do as well for home defense, if not better.

The heavy TAP ammo is designed for law enforcement, where barrier or glass penetration is more important.

It is unlikely you will have to shoot through a car or store window, or steel door, while defending yourself in your home.

I can assure you anybodys 55 - 60 grain soft-point, HP, or Ballistic-Tip from Wally-World in the chest will make a bad guy DRT!

And it is far more likely to blow up on sheet-rock walls and stop, then the long heavies going much slower.


November 20, 2008, 02:05 PM
To reiterate what others have said:

Barrel length is not relevant to group sizes, though it does have an effect on frag distance. 1:7 twist would indicate that you should be shooting heavier bullets. 62gr and up should be fine.

55gr ammo may actually be OK, too. Depends on the ammo and your individual barrel. Try it and see. It will certainly be OK for plinking, and will definately be ok for close in fighting drills. Once you start to move from "standing up fighting" to assuming supported positions and going for accuracy, the 55gr stuff may start to be unacceptable for practice. But the only way to know is to try it and see.

As for a "fighting" round, any of the 75gr TAP variants would do fine. The civvie .223 TAP FPD stuff was tested against the LEO 5.56 TAP T2 stuff on arfcom, and was actually found to have slightly smaller group sizes than its LE-only brethren.


November 20, 2008, 02:28 PM
Would a bullet of higher grain have a bigger effect on barrel ware, or is this unrelated?

November 20, 2008, 02:31 PM

Very high velocity is more a factor then bullet weight when it comes to wearing out a barrel.

Anyway, at todays prices, nobody is likely to shoot enough 75 grain TAP to wear out a barrel, unless the goverment is buying the ammo for you.


November 20, 2008, 02:58 PM
bullet weight does not affect barrel wear, but twist rate should. faster twist rates, if you think about it, should wear faster.

November 20, 2008, 03:01 PM
They do.

The service life of the M-16 1/7 barrel is not as long as the older 1/12.


November 20, 2008, 03:56 PM
Also, if you do go with a premium load like TAP for "serious" use and practice with something different, remember:

1. Sight-in with the TAP and leave it there.

2. run enough TAP through the gun to ensure that your gun/ammo/magazine combination will feed/function reliably. This will cost you some money.

3. Find a practice round that shoots to the same POI (preferably), or just remember that your rounds shoot to different POIs and practice as if you were shooting the TAP. That is, if you zero your rifle at 50 yds with TAP and your practice round shoots 2" higher at 50, don't practice aiming 2" low in order to put them in the black. Aim where you should aim, and just know that your group should be off by 2". You don't want to get into a scenario where you train yourself to shoot one way with your training ammo and then you need to shoot differently with your defensive ammo.

As ranges increase, this gets more and more important, and if you're doing any sort of work at extended ranges, you really want something that shoots to the same POI and has good grouping. It may very well be easiest just to use the exact same load when shooting at longer ranges, unless you're set up to reload and can dial something in that works the same way for paper-punching and costs significantly less.


If you enjoyed reading about "Barrel length mixed with rate of twist and bullet grain is to confusing for me." here in archive, you'll LOVE our community. Come join today for the full version!