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Old November 2, 2009, 06:58 AM   #1
rattletrap1970
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Savage 12BTCSS 1 in 9 Twist (Hates 55 gr)

Hey there.

I just picked up a Savage 12BTCSS in .223, the rifle has a 1 in 9 twist. I loaded up 6 batches of ammo. The ammo was prepped as follows:
All brass is matching head stamp, length trimmed to (1.740 - 1.739), matching weight (within 1gr), neck sized, chamfered on the neck ID, OD, primer pocket and inside flash hole, primer pockets are trued.

2 types of bullets used, Sierra 69gr HPBT Match, Hornady 55gr FMJ w/cannelure
Sierra seated to .009 before lands.
Hornady seated to bottom edge of cannelure

3 types of powder used, IMR4895/Accurate 2460/Varget

Loaded 20 rounds of each (120 rounds)
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The 69 gr will hold 1" groups at 200 yards. In some cases 3 rounds touching with one .375 to left and another .375 to the right. (I'm assuming those were my fault). Anyway, no appreciable difference in accuracy that I could tell with the 3 powders. I'd say I could use any of the three and do just fine.

The 55gr bullets looked like I hit the target with a shotgun. And the spread was equally crappy with all three powders.
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So, everyone says the 1 in 9 is good for 55gr and up.. I just don't see it. I know every gun has it's preferences, but I find it odd that the 55 gr bullets suck that much. 69 gr bullets work fantastic but they are "allegedly" on the edge of being too heavy for that twist. I'm wondering if I should try some 77 gr HPBT. Anyone have any experience with this twist and this weight?

Last edited by rattletrap1970; November 2, 2009 at 08:11 AM.
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Old November 2, 2009, 09:17 AM   #2
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There are many better bullets than the Hornady 55 fmj....Even the Hornady 55 SP is much more accurate imo.
Or try a 52 SMK...

Of course there are other variables.
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Old November 2, 2009, 09:27 AM   #3
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Generaly speaking your 1 in 9" twist is for the heavier bullets. Light bullets usually require a slower twist.
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Old November 2, 2009, 09:33 AM   #4
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Pongo..welcomr to the forum

rattletrap1970.....what was your load data on your best group of 55?
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Old November 2, 2009, 09:52 AM   #5
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I just went middle of the road with the loading data for the 55 gr bullets. Just about centered between starting and max. I didn't even bother measuring the group with the 55 gr bullets. I may just use the 55 gr bullets to fire form my brass.
I want to give the 77 gr bullets a try but I didn't want to buy a box just to find out they suck. But it certainly looks like the rifle prefers heavier. I'm wondering how heavy I can go before accuracy falls apart. Definably want to try 77 gr and 80 gr just to see if they will stabilize well. They would be a nice alternative to use for longer shots to buck the wind better.
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Old November 2, 2009, 09:56 AM   #6
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Well, if your looking for precision...precise data would help.

Typically a 1-9 will stabilize up to a 69gr. 55 should do very well but each firearm is unique.

Of course, this is all covered in your manual.

Last edited by PBKing; November 2, 2009 at 12:56 PM. Reason: stand corrected
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Old November 2, 2009, 10:06 AM   #7
rattletrap1970
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Oh I have precise data, just not off the top of my head at work.

I keep impeccable records. I made an Excel spreadsheet to keep track of the Weight of brass, bullets, seating depth, neck size bushing, neck size depth, powder weight, the micrometer settings on my dies so I can dial back anytime, chronograph data, etc. I also weigh each loaded round, average and do a standard deviation.

I've always been a fan of the 69 gr HPBT the only reason I even bothered with the 55gr bullets was because someone gave me a whole bunch of them. I don't have any huge interest in trying to make them work. I was just surprised they didn't.
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Old November 2, 2009, 10:41 AM   #8
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Sorry your having the issues, pm me if you decide the 55gn are a waste of time, I may be interested.
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Old November 2, 2009, 10:45 AM   #9
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Thank you PBKing Re: welcome to the forum.

‘The bearing surface of the bullet is the determining factor for twist rate,,,not weight.’

That is absolutely correct but heavy bullets tend to have a longer bearing surface and it is true each firearm is unique.


Rattletrap1970. Try a reduced load and see if the group improves. In my opinion a 1-9” twist is a fast twist for a .223 and lighter (shorter bearing surface) bullets can deform with a combination of high velocity and fast twist.

Again generally speaking.
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Old November 2, 2009, 11:03 AM   #10
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I'd be MORE than willing to trade the 55 grainers for a fairly equal amount of 69 gr or 77 gr (or hell 80 gr even).
HPBT match any manufacturer
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Old November 2, 2009, 11:13 AM   #11
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Rattletrap1970,

Your 9" twist is fine for 50-55 grain bullets, but the powders you've chosen all are optimal for heavier bullets, being a bit slow for the 50-55's. Stoner developed the AR for IMR4198 with those lighter bullet weights. It's true he used a 12" twist, and the military has now gone over to 9" twists in their 5.56 guns, but that powder continues to produce excellent accuracy with those weights. It's manufacture was recently moved from Canada to Australia, but it should still be an excellent option. Reloader 10X is another reasonable choice. The problem with the slower powders is they have trouble igniting and burning consistently without more acceleration resistance to work with. It's not a stability issue. My match mouse gun has a 7 1/2" twist and shoots the 53 grain Sierra MatchKings under 1/2 moa all day long.

Bearing surface has nothing to do with rate of twist. The dominant factors are bullet length and, to a lesser extent, mass. The length is the lever arm by which air resistance turns the bullet. Mass is proportional to how hard it is to turn the bullet off course at a given spin rate. How dense the air is affects how much air resistance is presented at a given velocity to a given bullet shape, so temperature and barometric pressure are factors as well. In ballistics it is standard practice to speak of drag rather than of overcoming air resistance, but I think the latter is easier to visualize.

If you would like an Excel file for twist rate estimation, you can download one from my file repository. Find the file name and put the cursor on the right end of the line and a small down arrow triangle will appear. Click on that to download it. I included an air pressure vs. altitude estimator below the twist calculator if you scroll down to it. You enter the bullet caliber, length, weight, and muzzle velocity, and also your barrel's twist rate. Also temperature an air pressure if you want something other than the Army standard meteorological conditions. It will tell you the stability factor for your bullet with the twist you have, and also what an ideal twist would be.
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Last edited by Unclenick; November 2, 2009 at 11:48 AM.
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Old November 2, 2009, 11:28 AM   #12
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Hmm, I'll take one more whack with a different powder. I would like to have a reliable accurate load for varmint bullets on the off chance I ever do any varmint shooting.

I think I will stick with the heavy bullets for now and pick up some actual varmint bullets. Then I'll work up a load for them.

The offer for the 55 grainers still stands. I'd love to trade for some heavy HPBT 69 to 80 gr
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Old November 2, 2009, 12:10 PM   #13
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I think you'll find the faster powder does the trick, though I should also point out that FMJ's are notoriously difficult to manufacture for accuracy. It is hard for the jacket dies to keep the gilding metal symmetrical when forming a point from behind. Forming a uniform cup shape for a flat base from the front, as is done for hollow points and soft points, is much easier. This is why match bullets are hollow points.

Putting a cannelure into a bullet without unacceptable distortion of the aerodynamic shape is also problematic. It is why match bullets have smooth sides. Hornady and Sierra seem to have figured out how to make cannelures that don't destroy aerodynamic precision, but many bulk bullet makers have failed to do so, and I always find a way to obtain and test a small quantity before committing to a quantity of them.

Buy one box of the 53 Grain SMK, Sierra #1400, that I mentioned and some 4198 (either IMR or H) and see what you can come up with by way of accuracy? It think you'll be pleasantly surprised, and that combination will tell you the potential of your loads and gun in that bullet weight range. Afterward, you can substitute 50 and 55 grain bullets and get a comparison to that standard. Whatever you land on with that 53 grain bullet with your 4198 choice, for other flat base designs, figure about .3 grains less powder for a 55 grain weight, and about .5 grains more for a 50 grain weight, assuming the same COL's.

If you haven't done so already, read through Dan Newberry's OCW load development method. His round-robin technique provides a good systematic approach to load development.
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Old November 2, 2009, 12:20 PM   #14
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I really appreciate all the input. I've been reloading for a long time and it never ceases to amaze me how much more I have to learn.
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Old November 2, 2009, 12:55 PM   #15
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Quote:
Bearing surface has nothing to do with rate of twist. The dominant factors are bullet length and, to a lesser extent, mass. The length is the lever arm by which air resistance turns the bullet. Mass is proportional to how hard it is to turn the bullet off course at a given spin rate. How dense the air is affects how much air resistance is presented at a given velocity to a given bullet shape, so temperature and barometric pressure are factors as well. In ballistics it is standard practice to speak of drag rather than of overcoming air resistance, but I think the latter is easier to visualize.
Thank You for contributing to my continuing education.
I stand corrected.

Thanks

Last edited by PBKing; November 2, 2009 at 01:09 PM. Reason: Back to researching internal and external ballistics
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Old November 2, 2009, 03:01 PM   #16
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trade

I don't have anything to trade


I've had good luck with h335 and h322 in my ar's with a 55gn, 1x9 twist. But it does seem to like 62gn's slightly better, although I never get "shotgun" patterns with the 55gn.
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Old November 2, 2009, 09:14 PM   #17
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There is a second potential problem with the slow powders and the light bullets, and that is secondary pressure spikes. You can see them on a number of graphs on RSI's web site. I linked to one for the image below. Some have argued these are a measurement system artifact, but I don't believe so. For one, they always clear up when the bullet weight is raised or the powder is changed to a faster one. Texas gunsmith Charlie Sisk had some images up on, I think, the 24 Hour Campfire forum or that were linked to there from another site, of .338 barrels he'd blown the muzzles off of with repeatability by intentionally creating these spikes.



What happens is the bullet is so light, relative to the powder burn rate, that the initial peak pressure scoots it down the barrel faster than the powder burn can keep up with the rate of volume expansion behind it. In the resulting reduced pressure, the powder's burning rate becomes very slow. But since about half the powder in a bottleneck cartridge is shot forward when the bullet is, the powder also has a lot of inertia. So, it catches up with and slams into the bullet. The resulting temporary high pressure zone revives the powder burn, adding pressure to the inertia, and the bullet upsets, creating an elastic bulge in the barrel before it gets moving again. If the upset is strong enough, the barrel steel can be bulged or even burst, but in most instances it just causes a traveling wave that gets back to the strain gauge near the chamber and looks like a pressure spike on the instrumentation, even though there is no actual pressure spike at the chamber end. For that reason, no pressure signs in the case result. The distortion local to the bullet can, however, throw the bullet shape out of symmetry and cause poor accuracy; especially if the reflecting bulge happens to coincide with the bullet exit.
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Old November 3, 2009, 09:02 AM   #18
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Hmm. I've been hearing H335 mentioned a lot. What load are you using with the H335 and those 55 gr heads? Again, I'm using a 26" barreled bolt gun, but I doubt it will make a difference. Just nice that I don't have to have the added worry about cycling function and such.

I don't mind taking a whack at this again. At the very least I will accomplish one (if not two) things: 1. I will have a load for 55gr that works and 2. I will have fireformed a butt load of brass.

The graph is interesting and the reasoning certainly seems plausible. Thanks for that info.
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Old November 3, 2009, 10:09 AM   #19
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The h335 was 23.9 for the 55gn fmj. The h322 was 21.9gn. But please don't take that as gospel, I only have a short time reloading. Those loads are below max I think the max on the h335/55gn is 25gn. The backstop at my range is around 150' and I got good groups with that load. I'm not loading for match shooting, just fun and small game.
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