55 gr. ammo OK through 1:8 barrel ?


PDA






MIL-DOT
February 26, 2010, 10:08 AM
As I understand, the lighter 55 gr. ammo is more suited to slower twist barrels, like in the old 1:12 Colt AR-15's. I'm considering a rifle with a 1:8 twist, but I already have a decent bit of Lake City 55 gr. ammo, and was wondering if I'd have any accuracy issues.

If you enjoyed reading about "55 gr. ammo OK through 1:8 barrel ?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!
Z-Michigan
February 26, 2010, 10:33 AM
You may or may not have slight accuracy issues. It probably wouldn't be detectable vs. a slower twist barrel unless you test them back to back in identical rifles. Buy the 1:8 without worry.

KingTiger
February 26, 2010, 10:47 AM
Like Z said, go for the 1:8. My 16" RRA has the 1:8 twist & shoots 55 gr. fine. It really likes the GA Arms 68 gr. BTHP.

rangerruck
February 26, 2010, 10:57 AM
sure.

TIMC
February 26, 2010, 10:58 AM
As said above accuracy may be good maybe not; you will have to try some to see if your rifle likes them or not.
My Stag 1:8 model 6 like the 77 grain bergers and did not like 55 grain bullets very welll.

Canuck-IL
February 26, 2010, 11:13 AM
The weight will likely not be the issue - - there just aren't a lot of match quality bullets in 55gr. If you aren't satisfied with the results you get, try some 52gr Sierra Match or I think Berger and Nosler have some at 52 as well. 55s are usually FMJ and not really that accurate as compared to the 52, 69, 77 80 and 82s match bullets.
/Bryan

carbine85
February 26, 2010, 01:10 PM
The real issue isn't necessarily the weight of the bullet, it's the length of the bearing surface of the bullet that determines the best twist. With that in mind most lighter bullets have a shorter bearing surface and work better in a lighter twist and most heavier bullets have a longer bearing surface that work better with a tight twist. To further complicate the issue, not all rifling is made the same way. The lands of the rifling will be different from one manufacturer to another even if the twist is the same.

Bartholomew Roberts
February 26, 2010, 01:46 PM
My 1:8 16" Lilja can shoot 5rds of the Hornady steel case 55gr practice ammo into a little under an inch at 100yds. Since my best 5rd group ever is about 0.78" at 100yds, I cannot say whether the lack of smaller groups is a ammo/twist issue or a shooter issue.

My general feeling is that most people will be fine with 55gr in a 1:8 twist.

briansmithwins
February 26, 2010, 06:46 PM
My ARs with 1/7 twist get 1.5MOA or so groups with 75gr ammo. With 55gr the group soze opens up to about 2.5MOA.

BSW

MIL-DOT
February 26, 2010, 07:35 PM
Many thanks to all for the quick and useful replies. ;)

Al LaVodka
February 27, 2010, 01:47 AM
Look, European militaries primarily went to 1:7 NATO twist when they adopted the 62 grain as the most common bullet weight, leaving behind the 55 gr. and slower twists that I think started at 1:14! 1:11 or 1:12 is essentially a 55 gr. twist. My rule of thumb is that one can't use 55's in a 1:7 nor 62's in a 1:12. I am a fan of 1:9 as a more universal twist and I use 62's. The NATO twist is designed to handle up to 77 gr. specialty rounds (i.e. incendiary tracer) but supposedly still acceptably use 55's according to some, but not many. I don't think they reasonably can, especially with cheap bullets that are not made for that kind of spin. You and I are probably shooting 55's or 62's except in 1,000 yard competition (which is really what a 1:8 twist is made for -- a 69 gr. head), so, 55 gr. might be acceptable in your 1:8, but not the best, you'll have to see. However, I guarantee it'll be better than if it were a 1:7!

So, if its a find, get it! I think you'll have to end up drifting to 62 gr. fodder over time, play on words intended.

I have 55 gr. but it is relegated to use in my 1:10 Rugers and as backup for my 1:9's. I even rebarelled a 20" 1:8 HBAR AR to a 1:9 pencil carbine.

Al

Bartholomew Roberts
February 27, 2010, 05:57 PM
My rule of thumb is that one can't use 55's in a 1:7

Well, it is your rule of thumb; but it is wrong. 1:7s shoot 55gr just fine. This 10rd 0.54" group at 100yds from a 1:7.7 Krieger with 55gr Blitzking (http://www.ar15.com/forums/topic.htm?b=3&f=118&t=394748) is not mine; but it also seems to suggest that good 55gr ammo will do just fine in a 1:7 barrel.

It seems to me that before we determine that 1:7 will not work, we first need to know what standard of accuracy we need to meet and at what distance. If the standard is sub-MOA at 600yds with ball ammo, well, no barrel is likely to meet that standard but a 1:9 will give you better results than a 1:7.

For most practical type shooting (being able to hit a pepper popper out to 300m for example), nobody will be able to tell the difference between a 1:9 with 55gr FMJ and a 1:7 with 55gr FMJ.

Canuck-IL
February 27, 2010, 06:33 PM
...except in 1,000 yard competition (which is really what a 1:8 twist is made for -- a 69 gr. head)
Nobody shoots 69s at 600 let alone 1000 ... that's the domain of 80s, 82s, the occ. 90 and a precious few use 77s.
/B

Al Thompson
February 27, 2010, 06:43 PM
supposedly still acceptably use 55's according to some, but not many

M193 was fine for use in the M16A2 - required re-zeroing the rifle though.

Al LaVodka
February 27, 2010, 10:43 PM
Nobody shoots 69s at 600 let alone 1000 ... that's the domain of 80s, 82s, the occ. 90 and a precious few use 77s.
/B
LOL OK, I'll stop using 62's for 600 yards and more. And change the Squad Designated Marksman program and the whole US as well as NATO Military to boot.

:rolleyes:

Yes, a few people without crossed eyes use rounds that actually fit into mags for ALL their shooting... 69 and 70 is the max. off-the-shelf we'll limit ourselves to here. Yes, some tight-suited Camp Perry national competitors switch to 80's too, we know. But this is not a Tubb thread so no need for the soapbox -- no-one really knows what you're referring to.

Al

PS: 1:7.7 is, um, almost 1:8 and I'm glad there is agreement it'll be better than 1:7. And if a 1:7 twist was fine for 55 gr. no-one would even be asking and maybe Gene Stoner woulda used it. I will skip the backpeddling and hedging. I think some shooters CAN tell the difference -- I'd argue most young men with good eyes who don't shake.

Zach S
February 28, 2010, 07:59 AM
While heavier ammo shoots great, 55gr pills shoot fine in my 1:7 twist bbl.

Walmart had the 45gr and 55gr in the same stack last time I got ammo there, so out of 10 boxes of ammo I got five or six boxes of .45gr. Should be interesting to see how they group (or pattern)...

tkcomer
February 28, 2010, 08:15 AM
My 16” 1:9 shoots the 52gr SMKs just fine. Trouble is, it shoots them 2” left and 3” down from the 69gr SMKs. That's at 100 yards. It shoots the Hornady 55gr FMJS a little to the left also. You'd have to adjust the scope for them, so I leave the 52gr and 55gr bullets for my 1:12 AR. They're more accurate in that gun anyway. You'll just have to try 'em and see. Point of impact might be different from the heavier bullets. But they may still group good.

Bartholomew Roberts
March 3, 2010, 10:29 AM
I think some shooters CAN tell the difference -- I'd argue most young men with good eyes who don't shake.

OK then, what is the difference? Let's see some hard data for a change instead of opinion. What will the difference in group size be between a 1:9 and 1:7 barrel at a given range with a given type of ammo? I ask; because I can shoot a 0.78" 5-shot group at 100yds; but I can't tell the difference between 1:7 and 1:9 shooting 55gr.

MachIVshooter
March 3, 2010, 10:39 AM
The only problem with light bullets in fast twist barrels is bullet RPM. That is, eventually they spin fast enough that they come apart. This is not a problem with the .223, unless you use lightly-jacketed bullets meant for the .22 Hornet. I shoot 40 grain V-max's through my 1:9 Armalite every time we go for praire dogs. Guess what? They shoot just fine, even though the ideal twist for such a light and fast bullet is more like 1:12.

IMO, for a carbine that is likely to spend most of it's life shooting 55 and 62 gr. ammo, 1:9 is be ideal. But 1:8 or 1:7 work fine, too.

win71
March 3, 2010, 12:18 PM
My general feeling is that most people will be fine with 55gr in a 1:8 twist.
That's a good assessment right there. Aside from thin skinned "blitz" type bullets spinning too fast to stay together or becoming unstable, bench rest type groups suffer from improper twist rate-bullet weight.
I had that problem several years ago while working up loads in a 22-250. Some tumbled, some simply disintegrated somewhere around 70 yards out.

http://i175.photobucket.com/albums/w140/win71/cp22-250.jpg

A normal 55 gr. bullet shot out of your twist rate and rifle should be fine.

Barrel maker Shilen's recommendation of the best twist rates as far as accuracy is concerned in a .224 is as follows:
224 CF
- 7" for bullets heavier than 70gr.
- 8" for bullets heavier than 70gr.
- 8"* Ratchet rifled 4 groove
- 9" for bullets up to 70gr.
- 12: for bullets up to 63gr.
- 14" for bullets up to 55gr.
- 14"* Ratchet rifled 4 groove
- 15"* for bullets up to 55gr. driven 4,100 pfs or more
- 16:* for bullets up to 55gr. driven 4,300 fps or more

If you enjoyed reading about "55 gr. ammo OK through 1:8 barrel ?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!