Need ammo suggestion for carbine 1:8 twist

[Buck1122]

Hey folks,

I am new to the forum but not new to shootings. Ordinarily, I strictly shoot .308s but I have bought a smith a wesson m&p carbine with then1:8 twist barrel.

I will be shooting both with and without a suppresor but hopefully will not need to change ammomduemto the can. I plan oshooting no further than 600 yards max.

Question : what is the best bullet weight to sight in and shoot with? The heavier the better is my philosophy so I'm thinking anywhere from 70-77 grains.

Next question, I will be shooting with a red dot sight co witnessed withnthenstandard a2 front sight. If I want to be able to shoot from 100 to 300 without having due massive dope adjustments what should I set my initial zero at? Unfortunately their are no 50 yard ranges around so I might have to use the outdated 100 yard zero. What do you guys suggest? Also, I will have back up sights so I plan on setting the front sight flush with the base of the sight....what should I set my rear sight at? 8/3 and then plus 2 or 3 for longer range shooting?

I've read the posts and charts by the master on this site with all the bullet poi/poa charts imjustbneed to know what will work best with my set up.

Thanks for the help bros.

[El Cid]

I am by no means an expert, but my understanding is the bullet weight has more to do with distance than twist or zero. A 1/8 should shoot most bullets well. I use 55gr for most training and practice, but have not noticed significant shifts in impact with 69, 70, and 77gr. FWIW I zeroed with 77 after using 55gr to get mostly dialed in at 100yds.

After taking Defoor's advanced carbine I can tell you I personally am now using 70gr TSX for close work and 77gr for beyond a couple hundred yards.

I've also switched to a 100yd zero and would hardly call it outdated. Bottom line is what works best for you may not be the same as others. It depends upon how you use your rifle. My recommendation would be to take a class (I highly recommend Defoor's) and find out what works best. It's all theory until you try it. Good luck!

[Low Drag]

The rate of twist impacts the stability of the bullet, e,g. making if fly true and accurate. Take note of a football thrown with that perfect spiral pass Vs a wobbly one.

Generally, generally, the heavy bullets in .223/5.56 need a higher rate of twist (1:7) be cause they are longer. Longer bullets require a higher rate of twist than light (short) bullets like the 55 gr and lighter. The NATO M855 round has a steel core so it is long when compared to a typical 62 grain bullet.

A 1:9 twist is paired with a 68 or 69 gr bullet.

Now all this is great to learn and apply, but if you're not trying to wring out 1 MOA of accuracy or less (1" at 100 yards) (to the peanut gallery - yes I know 1" at 100 yds is not quite 1 MOA but it's close enough) - meaning 5" groups at 500 yards the rate of twist and bullet weight/length really is not a concern.

A 1:8 twist rate is a "compromise" with a bias towards the heavy / long bullets. And as a bonus for you "over spinning" a light bullet will not have a negative impact on accuracy, however not spinning a heavy bullet fast enough will make things go down hill fast.

[chewie]

Originally Posted by Low Drag

The rate of twist impacts the stability of the bullet, e,g. making if fly true and accurate. Take note of a football thrown with that perfect spiral pass Vs a wobbly one.

Generally, generally, the heavy bullets in .223/5.56 need a higher rate of twist (1:7) be cause they are longer. Longer bullets require a higher rate of twist than light (short) bullets like the 55 gr and lighter. The NATO M855 round has a steel core so it is long when compared to a typical 62 grain bullet.

A 1:9 twist is paired with a 68 or 69 gr bullet.

Now all this is great to learn and apply, but if you're not trying to wring out 1 MOA of accuracy or less (1" at 100 yards) (to the peanut gallery - yes I know 1" at 100 yds is not quite 1 MOA but it's close enough) - meaning 5" groups at 500 yards the rate of twist and bullet weight/length really is not a concern.

A 1:8 twist rate is a "compromise" with a bias towards the heavy / long bullets. And as a bonus for you "over spinning" a light bullet will not have a negative impact on accuracy, however not spinning a heavy bullet fast enough will make things go down hill fast.

i've been lurking around some posts like this one. thanks for the info. as i go out to purchase my first serious rifle, it's info like this that will help me make decisions on the specs i'm searching for.

[Buck1122]

Thanks for the info. I'm pretty well versed in shooting and ballistics but have never owned a carbine with the 1:8 twist rate. I'd like to go with the heaviest weight round I can get so I can shoot as far as I can. Keep in mind that will be shooting with a full,size thunderbeast 30p-1 can on the end which may or may not help accuracy out of the weapon.

Anyone on here that shoots the same type of set up I'd love to hear what works best for you. Sounds like anything from 60 grain all the way up to maybe a low 70gr round may work well. The 77 grain round may do ok at short range but at 500 yards it may be looking like wobbly thrown football.

I don't need sub mo accuracy but I do want to be able to shoot at least 1 moa at up to 250 yards and then maybe 2-2.5 moa at anything past that.


Really, I'm just using this rig to keep my m4 skills up to qualification standards

[MistWolf]

Best thing to do is buy a variety of ammo types and see what delivers good enough accuracy for the job at hand. At 50 yards or less, for training purposes, ammo selection isn't very critical. My 16" carbine with it's 1:8 twist does very well up close with the Federal 55 gr FMJ.

While I haven't shot the carbine for groups at 100 yards or more, I have a 20" precision AR with a 1:8 twist that does about 2.5 MOA with the 55 gr Federal but groups tighten up significantly when using quality bullets of the 75-77 gr variety.

Buy some of the least expensive bulk ammo you can lay your hands on and test it for function, reliability and practical accuracy and run that. Remember a 6 inch group at 100 yards is 3 inches at 50, 1.5 inches at 25 and .6 inches at 10

[lifebreath]

1/8 should shoot everything fine.

[kmrtnsn]

Originally Posted by lifebreath

1/8 should shoot everything fine.

What he said. From a 14.5 -16" barrel you should expect excellent performance from all bullet weights between 55 and 77 grains out to 450-600 meters. Get a good 50/200 meter zero on your rifle, learn your offsets and holdovers, and you should be good to go.

[shootist~]

A 200 Meter zero is usually 2" high at 100. It works well at 300 Meters on 12" steel by going to the top edge or a hair over. Half the Dot is over the top of the gong at 300 which aids in seeing the target at that distance. 50 Yds is close and IIRC about 1/2" low - easy enough to verify at the range.

[Buck1122]

Thanks for all of the input guys....perfect timing as USPS just delivered a whole pack of 30rd PMAGS.

I think I will try everything from 62gr all the way up to 77gr and see how it does. Whatever seems to get the best grouping I am just going to go out and buy a case or 3 of it.

[MrFJones]

I too get great performance out of the 69 grain SMK. Good luck.