Correct bullet grains wt. versus twist rate

M&P40 · March 13, 2011, 06:55 AM

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. · March 13, 2011, 07:00 AM

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 · March 13, 2011, 07:05 AM

Quote:

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 · March 13, 2011, 07:25 AM

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. · March 13, 2011, 07:58 AM

pawpaw that was a good read thanks for the link

CPTMurdoc30 · March 13, 2011, 08:03 AM

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. · March 13, 2011, 08:05 AM

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

Jeff F · March 13, 2011, 08:10 AM

Quote:

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 · March 13, 2011, 09:54 AM

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

March 13, 2011, 06:55 AM	#1
M&P40 Member Join Date: May 25, 2009 Location: New Castle, PA Posts: 95	Correct bullet grains wt. versus twist rate 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?

March 13, 2011, 08:03 AM	#6
CPTMurdoc30 Senior Member Join Date: February 27, 2008 Location: Stafford VA Posts: 969	It is more length of the bullet than weight. But all being the same a longer bullet normally weighs more for a given caliber. __________________ Solving Virginia's Ground Hog problems 50gr at a time.....

March 13, 2011, 07:00 AM	#2
M.O.A. Senior Member Join Date: January 29, 2011 Location: south indiana Posts: 555	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

March 13, 2011, 07:25 AM	#4
jmr40 Senior Member Join Date: June 15, 2008 Location: Georgia Posts: 10,809	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.

March 13, 2011, 07:58 AM	#5
M.O.A. Senior Member Join Date: January 29, 2011 Location: south indiana Posts: 555	pawpaw that was a good read thanks for the link

March 13, 2011, 08:05 AM	#7
M.O.A. Senior Member Join Date: January 29, 2011 Location: south indiana Posts: 555	not the copper soilds or the tiped bullets there longer do to less mass

March 13, 2011, 09:54 AM	#9
Art Eatman Staff in Memoriam Join Date: November 13, 1998 Location: Terlingua, TX; Thomasville, GA Posts: 24,798	OP's questions look to be well-answered, to me...