Correct bullet grains wt. versus twist rate

[M&P40]

I know this is a discussion that has been had before but I am confused and would like some help. I am looking at 2 rifles chambered in .223: one has a 1:12" twist the other 1:8". From what I have read the 1:12" handles up to a 62-63 grain accurately and a 1:8" starts at 75gr and up. Some folks have posted stories about lighter bullets (55-70) fragmenting down range in a 1:8 eventually causing damage to the barrel rifling. Others have posted success stories shooting lighter bullets all day long. Is there a rule of thumb? I reload for my AR (1in9) and have lots and lots of 55 - 62 gr bullets so thats what I was planning on using. I wouldn't want to do something bad to a new rifle if I were to choose the one with the 1 in 8" twist. Is this a legitimate concern or am I thinking too much?

 

[M.O.A.]

with the 1-8 i would stick to the 70gn to 80gn bullets the 1-12 will be ok with the 50 to 62gn bullets that u have

i shoot 68 gn and there for 1in7 to 1in10

 

[PawPaw]

Some folks have posted stories about lighter bullets (55-70) fragmenting down range in a 1:8 eventually causing damage to the barrel rifling.

If you spin a bullet too fast, it'll come apart. That's basic physics. That shouldn't cause any damage to the rifling, because the bullet will come apart outside the barrel.)

One of the better online treatments of barrel twist in the .223/5.56 is posted by Chris Byrne, over at his blog. LINKY! Go read.

Short answer: There are no short answers. Every barrel is different. There are some rules of thumb, but even those are subject to being misinterpreted.

 

[jmr40]

I have shot 50-55 gr bullets from my 1:7 and 1:8 barrels with no problems. Heavier bullets are more accurate in these barrels, but the lighter bullets were OK.

 

[M.O.A.]

pawpaw that was a good read thanks for the link

 

[CPTMurdoc30]

It is more length of the bullet than weight. But all being the same a longer bullet normally weighs more for a given caliber.

 

[M.O.A.]

not the copper soilds or the tiped bullets there longer do to less mass

 

[Jeff F]

I have shot 50-55 gr bullets from my 1:7 and 1:8 barrels with no problems. Heavier bullets are more accurate in these barrels, but the lighter bullets were OK.

Thats been my experience also.

 

[Art Eatman]

OP's questions look to be well-answered, to me...