How much twist for RCBS 243-095?

[Marlin Junky]

I'm thinking about rebarreling my M77 to .244 Rem. and wondering how much twist to use for RCBS 243-095. Also, are the feed rails going to be too far apart for the more tapered .244 case? The rifle was originally chamber for the .358 Win.

MJ

[reloader28]

My Rem has a 22", 1/9 twist and shoots that boolit in 3/4" @ 100yds. Love that boolit in that gun. Dont know if thats good cast accuracy or not, but I'm happy with it. Only tried 2 different loads with it and then got busy.

[BCall]

I've been shooting it in a 10" twist with excellent results. If I was building though, I'd go with a 9".

[GabbyM]

http://www.6mmbr.com/6mmbr.html#23455

You can go to this page and drop down to what twist?

It's HV J bullet loads so not much help. But they shoot 80 and 90 grain flat base VLD bullet in a 12” twist. I had a 12 in my original Ruger M77 MKII barrel. It did not like Hornady 87 grain V-Max boat tail bullets. Didn't keyhole or anything horrible but groups were not one hole at 100 yards. Hornady 100 grain flat base SP shot horrible in the 12 twist which is no surprise. What the 12 liked was Nosler 55's at 4K fps and Nosler or Sierra 70 grain ballistic tips. I have the Saeco 87 gran bullet and a pair of 243 AI rifles with 10” twist right now. I like the Saeco bullet and it should stabilize in a 12 twist barrel. Never had any RCBS 95 gr bullets.

I don't know what exactly you are planing to use the rifle for. So please excuse my meddling.
Have you looked at the 6mm BR Norma or 6 XC? They both have longer necks than a 243 Win at .241". Powder capacity is much more in line with what is needed for most applications. The Norma is different than the old 6mm BR Remington in that the neck is longer at .318” XC has a neck length of .305” and has plenty of powder capacity. The 6XC may feed better.

Something to think about if you've not already. I'm all invested in the 243AI and it's not what I wish I had gone with. With J bullet loads the barrel wear on a 243 is 21 cents per shot when you figure a $250 barrel. Plus a 150 round day will beat you up a little. With the smaller cases I'm thinking you could run near a case full of slower powder like 4831 for cast loads. Surely someone has run cast in a BR case? The Tubb XC is a tad larger than the BR and I can't see any need for more powder with a cast bullet. I'd get a 12 twist and if it wouldn't run the RCBS bullet go to the Saeco. Speer makes an 80 grain spitzer that could be used on long range antelope. What the big boomer cases will do is send the heavy 105 and 115 grain VLD bullets clean out to 1,600 yards. But so will the 6XC and the BR isn't to far behind.

6XC page http://www.davidtubb.com/6mmxc.html

When you get started on this I can send you some Saeco 87's and Lyman 84 gr Loverins to test.

[Marlin Junky]

Just for the record, I'm seeking a light weight varmint rig that'll do 1MOA or better and at least 2500 fps with HT'd alloys. Shouldn't be too hard 'cause I'm consistently getting 2300-2400+ fps and 1.5MOA (sometimes better) with my 60 year old 336A's while using 170-180 grain boolits.

I want to handle the RCBS 6mm boolit (if I stick with that caliber) so a long case neck and a 10" twist is probably required. I was thinking about having a custom reamer made and a set of standard .243 dies shortened so I'd be able to take about 0.2" in length from the body of a standard .243 case and add that 0.2" to the neck. I don't know if this is feasible and it sounds like I'd be putting a lot of stress on the brass by moving the shoulder down 0.2". Even if I drop 1/2cc in volume by shortening the case body in this manner, I still should be able to get about 38 grains of 4350 behind the RCBS boolit. I really should try burning some 4350 at 40-45K before even embarking on this venture because I don't even know how well that'll work.

MJ


P.S. Actually, I do like the 6mm Norma. Based on what I plugged into QuickLoad, it looks like 2500-2600 fps is possible with the RCBS boolit and the 4895's (or Accurate's 2495).

[felix]

My preference would be the 222 case necked up to 257. You can check that out as being the Copperhead, 222 copperhead, 25 copperhead, et. al. Somebody must have a reamer already made up. That will do what you want with aplomb... felix

[Marlin Junky]

My preference would be the 222 case necked up to 257. You can check that out as being the Copperhead, 222 copperhead, 25 copperhead, et. al. Somebody must have a reamer already made up. That will do what you want with aplomb... felix

Felix,

I doubt Wooters' wildcat can break 2500 fps with 100 grain boolits. A .250 Savage would be a better choice but I need a larger selection of molds than the single SAECO 257 (RCBS 25-120 is too long). At least in the 6mm bore, there's two choices of newly manufactured molds. I'll have to see what Veral Smith has to say about cutting .25 caliber LFN's.

MJ

Actually, I forgot to mention that BRP has a dandy looking 105 grain .243 boolit mold that casts just about the same length as RCBS 243-095.

[Dannix]

Looks like you got more than one neat project going on MJ! I look forward to seeing what you end up going for and how you like it. I've never thought of using boolits to 2500+ speeds.

What kind of range are you looking for? Just curious. I can't imagine something like the RCBS 243-095 or BRP's mold having the high B.C. around.

[Marlin Junky]

Looks like you got more than one neat project going on MJ! I look forward to seeing what you end up going for and how you like it. I've never thought of using boolits to 2500+ speeds.

HT'd, relatively low Sb alloys will stand up to 40-45K PSI (approx BHN 30). In some cartridges with a case full of slow powder this could translate to 2600-2700 fps or more with copper patched type accuracy. Then there's the whole different ball game of paper patching. Either wrap 'em in paper or lube 'em, check 'em and draw back their noses with a propane torch... name your poison... you can drive cast boolits to jacketed performance levels given your barrel can handle it.


What kind of range are you looking for? Just curious. I can't imagine something like the RCBS 243-095 or BRP's mold having the high B.C. around.

Anything from crop devastating birds at 50 yards to coyotes at 300.

MJ

[azcruiser]

think 244 rem is the same as 6mm rem I would go with 6mm REM so your brass and gun would say the same thing. If you ever sell 6mm Rem would sell easyier

[HORNET]

You know MJ, you could go retro on this and go with one of the 6mm International variants. They were originally intended for 300 meter competition but saw some use in BR guns. IIRC, Donaldson's version moved the shoulder on the .250 Savage back about 1/4" to give a nice long case neck with enough capacity to move a 100 grain j-thing about 2700 fps. There was also a version by Mike Walker that was a little different. Older bench-gun makers might have the reamers on hand. Look into the old Sierra and Hornady manuals for data. I figure one with a 10" twist would do right well with 85-90 grain HPBT's as well as cast.

[GabbyM]

I was thinking about having a custom reamer made and a set of standard .243 dies shortened so I'd be able to take about 0.2" in length from the body of a standard .243 case and add that 0.2" to the neck. I don't know if this is feasible and it sounds like I'd be putting a lot of stress on the brass by moving the shoulder down 0.2". Even if I drop 1/2cc in volume by shortening the case body in this manner, I still should be able to get about 38 grains of 4350 behind the RCBS boolit. I really should try burning some 4350 at 40-45K before even embarking on this venture because I don't even know how well that'll work.

MJ


P.S. Actually, I do like the 6mm Norma. Based on what I plugged into QuickLoad, it looks like 2500-2600 fps is possible with the RCBS boolit and the 4895's (or Accurate's 2495).

I don't know what your software says but 38 grains of 4350 under a RCBS boolit would be about 3K fps or a tad under. Or 2800 from a 22 inch barell.

As soon as you shorten a 243 what you have is the Tubb 6XC. They made that round by holding a 243 Win reamer .132" short then forming brass from 22-250. later on they changed the neck from 20 to 30 degrees. The XC holds about 7 grains less powder than a 243.

If you wanted to buy a custom reamer and modify your load dies I suppose a person could make a 6XC long neck with 243 win as parent brass. Staying with a stock 6mm Rem would be lots cheaper.

The Saeco 87 grain fits the short 243 neck just fine. I'm of the opinion you'll need a 12 or 14 twist to achieve the velocity you seek. I've never pushed mine but others loose 1 moa after 1950 fps with a 10 twist and 2 moa holds to around 2350 fps. I've a pretty nice 26" long Shilen barrel here I coudl try pushing it in . But it didn't come with a magic wand. A longer bullet is generally that much harder to push fast. But I've noticed you like a challenge.

[Marlin Junky]

I'm of the opinion you'll need a 12 or 14 twist to achieve the velocity you seek. I've never pushed mine but others loose 1 moa after 1950 fps with a 10 twist and 2 moa holds to around 2350 fps. I've a pretty nice 26" long Shilen barrel here I coudl try pushing it in . But it didn't come with a magic wand. A longer bullet is generally that much harder to push fast. But I've noticed you like a challenge.

IMHO, the actual rate of twist is not the limiting factor to HV unless it is combined with a land/groove configuration that won't "grip" (for lack of a better term) the boolit during its trip out the barrel. If I can do 1-1.5 MOA at 2400 fps with a 1:10" 4-groove 30-30 at approximately 45K PSI, then it shouldn't be too hard getting a similar volume of powder under similar conditions to launch a much lighter boolit with 10% less sectional density 200-300 fps faster.

MJ

[Marlin Junky]

You know what... this is turning out to be too much like work. I caved and bought an RCBS 22-055 on sale from Midway and a box of .22 Hornady gas checks which were also on sale. Maybe I can find a deal on a .22CF at one of the gunshows this summer.

MJ