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Posted: 7/2/2006 7:24:32 PM EDT
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I shot both today, WW white box loose bulk pack- 40 round boxes from Wal Mart 55gr and American Express 62gr. Both shot close to the same size groups, with the 62gr looking a little smaller. The wind did seem to blow the 55gr more. This is out of a 20" HBAR barrel with a 1/9 twist. Will a 69gr show more of a difference than just going to the 62gr from 55gr? Should I also try a lighter bullet - 45gr? Are the varmint loads too fast- 3600fps, for an AR15, or will any .223 ammo work? I know in a Garand you have to be careful about the bullet weight. Is an AR15 as picky? Jim |
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Yes and no... heavier match bullet is worthless in a slow twisting barrel and that goes the same with light bullet going down fast twisting barrel. While it may not answer your question... it shine some light on the matter. A "faster" twist - one full turn in a smaller number of inches is what is needed to stabilize long heavy bullets. The gyroscopic effect has to work harder on a long skinny object. Think twist rate (IE: 1:9) is the lenght in inches it takes for a bullet to rotate a full circle. So in a 1:9 twist, it takes 9 inches to rotate a full cicle. Examples for .22 history.... 1:16 - . 22 lr 40 grain; .22 Hornet 45 grain bullets. 1:14 - most .22 centerfires with 50-55 gr bullets, will handle up to 60 grain flatbase spitzer. 1:12 - early M16 barrel for M193 55 grain boattail in cold climate. 1:10 - used it in Mini-14 for a while, usually ok for SS109 62 grain and 68 grain. 1:9 - early .223 target barrel for 68-69 grain BTHP. 1:7 - current GI barrel for M856 tracer, a 9" is enough for M855/SS109 ball. "Overstabilization" of a light bullet in a fast twist is a bugabear seen only with very extreme differences. A very light bullet in a very fast twist might not be real accurate. You can actually blow up a bullet in flight by driving it too hard and 9" twist will often be more accurate with cheap FMJ econo-ball than a 12". I hvae 9" twist barrels that's great for everything from 50 to 68 grains and that is enough for me, but I am not a long range shooter. The only way to know for sure is to shoot them. An "understabilized" bullet will soon become an UNstabilized bullet and will not hit anything. I use to run a match 20" 1:9 with 68 grain without issue... it was a tick driver. These days, with 80 grain being what's perferred for 500+ yards, my 1:9 is slow. ~nb |
What distance? Wind difference between these two bullets at anything less than 200 yds is totally negligible.
It's not a question just of bullet weight. It is one of the total consistency of the load, and whether your rifle likes that load. In general - consistently loaded ammo with match grade bullets (like Black Hills) will almost always shoot better in any rifle than cheap off the shelf standard loads without match bullets.
Sure. Why not?
There are not factory .223 loads that actually are 3600fps that I know of. If you are speaking of the 45gr Winchester varmint load that states "3600 fps" on the box... that's BS. Maybe in a perfect world, with a lapped 26" test barrel in a vaccuum. My testing out of a 20" AR showed about 3350fps with this round. Any commercial .223 round is pretty much safe for your AR15... as long as the bulle weight can be stabilized by your barrel twist.
No. But your barrel twist determines your range of bullet weights. Read the oracle. www.ammo-oracle.com/ |
I'd buy a box of 55gr American Eagle, a box of 55gr Winchester Whitebox (WWB), maybe some 62gr WWB,and a box of Reminton 55 grain. I would also buy a box of each of Black Hills Blue Box load I could find up to 69gr and maybe a 75gr as some 1:9" twist barrels are actually 1:8.7" barrels and some are 1:9.2" barrels. Each barrel is different, so you have to find the one your rifle likes. TS ETA: Basically what FALARAK said. |
I read it, and it's very useful. I get the impression that my 1 in 9" twist rate is a compromise. I also understand that anything over 69gr may not stabilize, and I can go down to 45gr. Is there any one weight bullet that twist rate seems to like best, or is it just trial and error until I find "it"? Thanks, Jim |
In general - no. It is difficult to match a specific twist rate alone to a specific bullet weight.... and determine that load will be the best. There are too many other factors involved. Especially if you are buying factory ammo and not reloading. For instance - your barrel may shoot the 69gr SMK really well, but maybe only at a given velocity. If you buy the BH 69SMK load - your barrel might not shoot that load as well. Overall - however - I can offer some proven projectiles.... from my experience. 1:7 77 SMK 75 Horn match 69 SMK 68 Horn match 52 SMK 52 Horn match 45 gr winchester varmint 1:8 77 SMK 75 Horn match 69 SMK 68 Horn match 52 SMK 52 Horn match 45 gr winchester varmint 1:9 77 SMK *** might not stabilize 75 Horn match *** might not stabilize 69 SMK 68 Horn match 52 SMK 52 Horn match 45 gr winchester varmint 1:10 69 SMK 68 Horn match 52 SMK 52 Horn match 45 gr winchester varmint 1:12 52 SMK 52 Horn match 45 gr winchester varmint As you can see - the 52gr loadings will work in any common twist, and often shoot really well, especially at 300yds and less. A 1:9 is not a "compromise". It is just a middle of the road twist rate. If you are gonna pony up for serious match ammo - then I would also get a match stainless 1:8 or 1:7 barrel to complement that, and I love the 77SMK for that. However, for your rifle, I would stock up on BH 52gr Blue box and practice, practice, practice. |
I've never used any 52gr loads as I thought is was either a BS load or a match-type load for 1:12" twist rifles. I'll have to buy a box on my next gun shop trip. I have found that my 1:8 and 1:7 carbines do not like the 68gr BHBB round. The only Black Hills available to me are 52gr moly, 55gr FMJ, 55gr SP, and 68gr OTM. TS ETA: they like the 45gr WWB VP too. |
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The bottom line is you have to try any particular loading in your rifle.I have done some testing with various BH ammos and some comercial stuff. Much of the BH ammo shoots well but I have settled on Win 45gr Varmint as my "test" ammo. In three or four Bushmaster 1/9 chrome lined barrells it has wound up at the top of the heap or tied with some other higher priced stuff . Same goes for my 1/9 stainless bushmaster varmit special upper. From the way I read the info available theory alone indicates the "perfect" weight bullet for the 1/9 should be the 69gr. When I compare the groups I get with 69gr fed gold metal (considered by many to be a top performer) and various BH 69gr loads vs the Win 45gr Varmint I can see no load that beats the Varmint.Haveing the ability to go to Wall-Mart and buy a box of 40 for $14 is a plus in my book I now have the Bushmaster varmit special and I just bought myself a Rock River NM so I have to spend some time at the loading bench to see what I can whip up. The Win Varmint load is what I will work to beat. |
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