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10/20/2017 1:01:18 AM
9/22/2017 12:11:25 AM
Posted: 9/6/2005 5:57:02 AM EDT
Some of our customers at 10ring.com have been asking for 80 grain bullets for their AR's. I know a lot more about 1911's and hunting rifles, than AR's (though I have one of course!) This seems a bit heavy for a .224 bullet in a semi-auto. Will someone please give me a short primer on the rifle twist/bullet weight relationship for AR's - ideal applications for each?

Sniper Joe - if you're out there, stop on in, we haven't seen you in a while. Bob and Doc say hello.
Link Posted: 9/6/2005 6:04:12 AM EDT
the ammo oracle


usually heavier bullets need faster twist rates i.e. 1x7


i have shot 77gr. out of my 1x7 match bbl. with great results.

have stopped by your shop before, nice place


do you have instructional classes? would like to get into reloading but kinda of weary about it.
Link Posted: 9/6/2005 6:43:36 AM EDT
It's actually bullet length which is important wrt twist rate, not weight.
Link Posted: 9/6/2005 6:02:28 PM EDT
Thanks. We are working to update it so we can add more products. Regarding reloading, we do not have a class, but do teach folks in the Houston and surrounding areas - those close enough to stop by the store. The best way to start in reloading is with a single stage press, loading rifle. The reloading manuals have all the training you need in them to get started (like the Lee manual or the Speer Reloading Manual). If you are interested in getting started, send me an email at bryan@10ring.com (note what calibers you intend to load) and I will tell you what you should start with.

As to the twist, noting the last comment about bullet length having more to do with it, it makes sense then that heavier bullets will be longer as well (they can't get fatter). Is a tighter twist goign to lead to higher pressures with a longer/heavier bullet?

I hear of guys competing against .308's at long ranges with the 80 gr .224 - does a heavier/longer bullet need less twist to achieve the same stability?
Link Posted: 9/6/2005 6:15:00 PM EDT
Link Posted: 9/6/2005 6:44:49 PM EDT

Originally Posted By 10ringPres:
...As to the twist, noting the last comment about bullet length having more to do with it, it makes sense then that heavier bullets will be longer as well (they can't get fatter). Is a tighter twist goign to lead to higher pressures with a longer/heavier bullet?

I hear of guys competing against .308's at long ranges with the 80 gr .224 - does a heavier/longer bullet need less twist to achieve the same stability?



It is called the Greenhill formula. But that is an approximation equation as it doesn't take into account the shape factor. It is close enough..

On haevy bullets in the .223, yes, they DO make it practical for even 1000 yard work. It is better than most .308 Winchester loads in the wind drift department but the king is the 6mm XTC which is a modified .250 Savage AI. Very close to the .243 Winchester but better suited using 107 grain VLD in a short action length rifle.

On the pressure factor, yes, a faster twist will increase pressure somewhat but since these heavier bullets need sorrespondlingly slower propellents, it all works out EXCEPT for port pressure. Carrier weight systems are used by some to reduce damage to brass as most reloads suffer the same M4-type ejection damage where the body of the case hits the ejection port instead of the built-in brass deflector. This can leave a deep score on the brass but it harmless to the rifle.

Typical propellents are RE15, Varget, VV N135-140 and the like. And we also have the 90 grain bullets...but these, like the 80 Sierras and Bergers are single shot propositions unless you have special magazines. To achieve the high BC's, the ogive lengths prevent any seating close to normal magazine length. There is at least one magazine which allows an OAL of 2.45" but it only holds 8 and must be used with a special bolt stop, preventing the use of any other magazine. As you might have guessed, this is for CMP (nee DCP) Service Rifle competetion.
Link Posted: 9/6/2005 7:04:08 PM EDT
wheres your place at??
Link Posted: 9/6/2005 7:09:38 PM EDT
With a 1:7 twist on say a 14.5" barrel how "LOW" can you go? In other words with a 1:7 never dip below a 50 grain? - otherwise shrapnel is going to come flying out???
Link Posted: 9/6/2005 7:21:48 PM EDT
quick question on this topic

1:9 twist, 18 inch barrel - is 77 grain Sierra BTHP Matchking ok?

Link Posted: 9/6/2005 7:24:19 PM EDT

Originally Posted By TheMocoMan:
With a 1:7 twist on say a 14.5" barrel how "LOW" can you go? In other words with a 1:7 never dip below a 50 grain? - otherwise shrapnel is going to come flying out???



Pure HOOEY! I have shot 45 grain Win White Box in my Pac Nor 1:6.5 twist barrel. Over the chrono, it registers 3400 FPS, not bad since factory specs are from a 24" barrel and mine is Service Rifle legal...that is a PROPER 20".

It shoots about 1 MOA at 100 yards and functions fine. It is DEADLY on 'yotes.

I have shot 30 grainers from my 1:7" HBAR at 4010 FPS, again measured over the chrono. These are varmit special hollowpoints. Accuracy is ho-hum at 2.5" at 100 yards BUT the the holes are perfectly ROUND.

Now for some history. Back when jacketed bullets were new, some had less thanperfect jackets and cores. Spinning such a bullet too fast could and would cause problems but modern bullets can be overspun with no noticable problems. FYI, the Greenhill formula applied to those 30 grainers dictates a 1:19 twist. That they survived at nearly 3X the required tiwst should prove this myth BUSTED!

Link Posted: 9/7/2005 12:33:31 AM EDT
To answer the question about our location - our store is at 11616 Cypress N. Houston (street is four lights N. of FM 1960 W, off Jones Road in NW Houston). We are on the web at 10ring.com.
Link Posted: 9/7/2005 12:34:52 AM EDT
So, if I am pulling this together right, heavier bullets do better with a tighter twist. Lighter bullets can be shot out of a tighter twist, but will have better groups at a looser twist?
Link Posted: 9/7/2005 12:44:11 AM EDT

Originally Posted By 10ringPres:
So, if I am pulling this together right, heavier bullets do better with a tighter twist. Lighter bullets can be shot out of a tighter twist, but will have better groups at a looser twist?



Not necessarily. Most lighter bullets are of very high quality and shoot fine out of fast twist rifles. The only rule is long bullets will NOT be accurate out of slower twist barrels.

All of the light bullets are high quality. But not all of the 55 grain bullets are. And most military bullets are good for 2 MOA at best. There are exceptions but most domestic bullets are 2 MOA.

Link Posted: 9/7/2005 12:55:19 AM EDT
http://www.tanksrifleshop.com/twistcalc.htm
Link Posted: 9/7/2005 3:17:16 AM EDT
Link Posted: 9/7/2005 5:28:21 AM EDT
[Last Edit: 9/7/2005 5:32:56 AM EDT by Yojimbo]

Originally Posted By TheMocoMan:
With a 1:7 twist on say a 14.5" barrel how "LOW" can you go? In other words with a 1:7 never dip below a 50 grain? - otherwise shrapnel is going to come flying out???




I've personally shot about 1000 rounds of Winchester 45gr Valuepack ammo out of my 1/7 and it shot great. I had no prpoblems at all and as far as I could tell the was accuracy just as good as it was from my 1/9 barrel. I ended up selling my 1/9 upper after doing this because the only reason I was keeping it aorund was because I thought the 1/7 couldn't handle the lighter rounds but now I know better.

Below I've quoted from one of brouhaha's posts. People who've been here a while consider him to be very knowledgeble in .223/5.56 ammo ballistics.

"You won't find many(light bullets) that will fail due to rotational stresses.

I think the Speer TNT (40gr?) and Sierra Blitz (Also 40, I think) were the only ones I could get to fail from an 18" 1/7.

I had no problems with any ballistic tip type rounds, and I pushed them quite hard. I think I hit about 3600fps with a 40gr Vmax.

I think your best bet would be the 50gr Vmax. I've found the Black Hills load to be quite accurate in my rifles, and it's lightweight enough to really make the rabbits pop."



Also, below I've posted some pics of Ferderal Ammunition's ballistics tests using a Colt M4 with 1/7 barrel and it clearly shows that there's no issue using 40gr ammo on up.

So bascially, with proper ammo selection, the 1/7 barrel will shoot 40gr up to 77gr+ just fine.

(Pics from CavReconScout's post on the archive server)










Link Posted: 9/7/2005 12:22:40 PM EDT
Wow , nice chart. When talking twist rate you must also consider barrel length and velocity. A longer barrel can get away with less twist because velocity is increased and spin is literally faster. It takes more twist in a short barrel to get the spin up.I shoot 600 yard and some 1000 with 77 Siera's at about 2700-2800 FPS from 1 in 9 24" Krieger. No keyholes but sometimes subsonic at 1000. Going to switch to VV powder for the 1000. May even try some of the new 90's
Link Posted: 9/7/2005 12:51:38 PM EDT
The ammo oracle is all powerful. Read it when you have some spare time.
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