Barrel twist question?

[PNW_Steve]

Hey Everyone,

I am looking at re-barreling my Ruger M77. It is chambered in .243win and has 1:10 twist barrel.

I thought about going to 6mm Creedmoor then got to considering a .243 win barrel with a 1:8 twist and the chamber cut to accommodate the newer 100 -115 grain bullets.

I know how to figure out the heaviest bullet that I can run with a given twist but I am clueless when it comes to figuring out what the lightest bullet would be??

Can anyone enlighten me?

Thanks.

S.

[pietro]

.

The first thing that needs to be understood is that bullet weight does not directly have anything to do with what rifle twist you should be using.

The bullet length is what dictates your barrel rifling twist.

A general rule of thumb with weight, is that the longer a bullet is, the heavier it becomes.

Ergo, heavier/longer bullets like faster rifle twists than lighter/shorter bullets do.

.

[Outpost75]

The construction and quality of the lighter bullet matters. Old school 55-grain M193 Ball and the sturdy Nosler solid-based softpoints of that weight shoot with normal accuracy in 1:7" barrels as used in the M16A2 and M4, but sporting "varmint" class bullets of fragile construction, such as Sierra Blitz or Hornady SX will come apart in the air.

In a target-grade barrel of good quality firing "good" bullets the accuracy of common 6mm sporting bullets of "deer" vs. "varmint" construction is not going to be important in an 8" vs. 10" twist.

[uscra112]

I've had the experience of light bullets literally fragmenting when fired through a fast twist barrel at what I would consider normal velocity (for a slower twist). They'd make a hole in a 25 yard target, but never reached one at 50 yards, never mind 100. .

[Earlwb]

Well in my experiences, firing 50 to 55 grain .22 bullets in a rifle with a rifling twist for heavier bullets, 77 grains for example, didn't really affect much of anything except for accuracy. Maybe for the purist the bullet leade to the rifling would cause some inaccuracy to creep in though. The longer heavier bullets are up close to the start of the rifling while the shorter lighter bullets are farther back from it. You see something like this with the old military guns where the guns were setup for heavier weight, longer, round nose bullets. But you try using shorter pointed bullets instead. The long gap of the bullet leade to the rifling can affect accuracy. sometimes quite a bit but I haven't seen it be bad enough that you couldn't go deer hunting with one. For example 8x57 designed for 220 grain round nose bullets but you are using 150-160 grain spitzer bullets. Or a Carcano 6.5mm setup for 160 grain bullets but you are using 90-100-120 grain spitzer bullets. Of course I have not needed to shoot deer or pigs beyond 100 yards so it wasn't a big deal for me.

Now with the .22's don't fire bullets meant for 22-20, 22 Hornets, etc. in a high velocity 22 though. The low velocity light weight bullets are too lightly constructed to handle the higher velocity stresses. The high velocity and rifling twist will spin the light weight bullets so fast that centrifugal force will tear the bullets apart. I did this once myself using 22 Hornet bullets in my 22-250 AI rifle and none of the bullets made it to the target. That was way back before the internet existed. I didn't figure it out until I saw some bullet fragments on the target sort of like birdshot. Then I remember reading about it in one of the old bullet reloading manuals if that time period.

[PNW_Steve]

Thanks everyone for the replies.

Good effort but no joy. It sounds like trial and error will be the solution.

Thanks again.

[M-Tecs]

My experience in 8 twist 6mm with light bullets is limited but with 55 grain and 70 grain V-max I have had great results.

In 22 cal I do shoot a lot of 40 grain V-Max in fast twists. The V-max or Nosler BT's hold together a shoot very well over spun. Some other bullets not so much. My Speer 52 grain HP's would vaporize at about 35 yards.

[MostlyLeverGuns]

Some of the light .243 bullets do not take the speed very well. Even in a .243 with 1-10 barrel some of the 'bargain' house brand bullets don't get to the target. My Nosler 55 gr and Sierra 60 gr have not had the same problems. A .243 with a 1-8 makes a lot of sense, with the availability of 243 Win 'stuff' much higher than 6mm Creedmoor 'stuff'.

[MT Gianni]

It all depends on what you want the cartridge to do. The 243 IMO, will not be improved on much by 55 gr bullets and 110+ weight bullets. IMO, If you want heavier bullets go to a larger diameter, 260 Remington, 7mm 08 or such. Both of the latter cartridges will push a heavier than standard bullet faster than the creedmors and beat them in every way but in a gun forum or magazine.

[white eagle]

.

The first thing that needs to be understood is that bullet weight does not directly have anything to do with what rifle twist you should be using.

The bullet length is what dictates your barrel rifling twist.

A general rule of thumb with weight, is that the longer a bullet is, the heavier it becomes.

Ergo, heavier/longer bullets like faster rifle twists than lighter/shorter bullets do.

.

and just because its supposed to shoot this or that bullet does not mean it will
there are just some contrary rifle's just like people

[farmbif]

1-10" is very common twist rate in many factory 243 win.
I went through the array of different weight bullets for 243 win years back when I got an old savage. turned out to be a real tack driver and I came to conclusion that 100 grain bullets at right around 3000 fps is just a very effective load for just about anything. ive still got a bunch of .243 bullets including some of the real light ones and only load and shoot hunting bullets 95 or 100 grains in the the 243. somewhere ive got a .243 bullet mold but have yet to even try it

[Kraschenbirn]

Dunno 'bout anything heavier but my early (1971) M700 (1-10 twist) handles 105 gr. jacketed quite well. Used those for many years in my coyote loads...MOA accuracy and less pelt damage than than lighter, "varmit-type' bullets.

Bill

[Tripplebeards]

I’ve asked the same question on many forums and searched for anyone posting groups and answers. Never found ANY real answers like you. Well, here’s my 1 in 8 twist with light bullet targets…




I did a 12 load ladder test with two different powders in my one and eight twist bear creek arsenal 243 upper last Friday morning. I was in a crunch for time so I shot a follower load in all 36 rounds in 45 minutes. The barrel was pretty hot when I tested the loads needless to say. The last group which was of 42.2 grains of H4895 (which is 2/10 of a grain over max)shot the tightest load of .3”. Only one of the 12 loads shot over MOA!…which was the first load I tested. Maybe I took a few shots to foul the barrel to settle down?…or a few shots for me to settle down? Lol. This was trip number three to the range testing it in the last week. I tried 55 grain CT Nosler ballistic tips earlier in the week. I had a few tight groups. They pushed pretty hard. Book said around 4100 FPS with a 24” barrel. The 60 grains were around 3817 FPS at 42 grains of h4895. Still no cloverleaves so I will be trying the 42.2 grain load of h4895 with 60 grain Seirras again with a cold barrel and also working it up and down to 42.1, 42.3, and 42.4 grains watching for pressure signs. I received the Seirras off PIF and am almost out. Anyone have any I could trade or buy? These are the only 2 light offerings I have or I’d test more. If you have anything else under the 70 grain mark I’d love to test some. I do have a couple of 70 grain noslers I will test when my 60’s are gone. I think I only have a dozen or so 60’s left. My plan was to use the rig as a coyote lazer out to 400 yards and not have to take my crosshairs off fur. I have a cmc single stage 2.5 competition trigger in it.



Here is my Friday morning 12 load test with 60 grain Seirra varmint HPs…







Here are the best 55 grain Nosler 100 yard groups. The only thing about the noslers is the up-and-down latter test weren’t as consistent as the Sierras. I would have a few large groups, then small. I believe my loads are a few tenths of a grain over max book loadings. Once again no pressure signs. All my 243’s seem to shoot best at about .2 grains or a hair more over max book loads.








Long story of how I got this upper… The first 1/8 twist 243 BCA 20” upper i shot I received at best a high .6” group with one or two loads out of 29 plus loads I tested. It also wouldn’t repeat the same .6” accuracy with either load. BCA had a MOA guarantee at the time so I sent it back since most loads were 1.5” plus groups with 55 & 60 grain bullets I tested it with. I waited a half of a year to get this replacement back. They were waiting for new 243 tooling I was told. Also was told my barrel didn’t pass the the MOA testing when I sent it back. I kept calling and bugging them asking if the new tooling arrived. They found 4 uppers a little over a month ago that had been there The whole time. All 4 uppers were tested and failed MOA testing. I was told I’d get a call in a few days to be told when the the ETA of the new tooling would arrive. Two weeks went passed with no return phone call. I received a little over two and a half weeks later an saying the 243 chambering was discontinued and they were wanting to know how I wanted to proceed with either a refund or pick an upper out if their inventory in another chambering. I called and raised heck since BCA told me they set my upper aside back in December when I sent it in…but it mysteriously disappeared! I saw a ( I’m sure it was mine) 243 up for sale in January…the day after I had a phone conversation asked them to hold onto my original upper till the new tooling arrived instead of sending back to to me. I didn’t see the point of wasting my time and money…and theirs since I wasn’t in a rush to get a replacement. They were of out of stock on the the 20” 243 uppers for two months and a 20” 243 upper showed magically popped up in stock the following day after I told them to hold on to it…and then they were out of stock a few hours later. Anyways, after I received the email that they were not producing the 243 chambering anymore and they had none in their inventory left to offer me BCA wanted to know if I wanted a different caliber upper or a refund. I called up asking for my original upper again to see if they might have found it. I was told it was still “missing” but they magically found two more 20” 243 uppers in their warehouse coded different. The reason they were coded different is because the receivers were milled not forged. I was sent a photo of one of the uppers for clarification. I had to explain the the BCA long tern employee who sent me the photo of it what was different about their product. It was an upper that was never offered for retail sale. They used a milled receiver instead of a forged along with the new style hand guard. I already had the milled receiver on my 22” upper and liked it better then the forged they offered originally for retail sale. Both uppers once again were tested for accuracy by their new BCA marksman with their “accuracy devise” . I was told one shot 2 MOA and the other would not function. They finally got it functioning a half week later but said it shot larger than 2 MOA. I had to argue with them to send me the first one of these last two tested. They didn’t want to sent it to me because it shot over MOA…even though they do not offer a MOA guarantees any more on any of their products. I told them I didn’t care because it was the last one that cycled properly and I told them I would get it to shoot tight groups. I also them thr parts were worth more than the original $298 I paid for it. They sent me the upper, a test target their in house marksman shot with FMJs that were closer to 1.5”…or a little larger group, and a $50 coupon for the inconvenience because it did not pass MOA testing along with the 6 month turn around drama. Well it sure sure shoots better than MOA! I was told by the customer service representative that they used bulk FMJs and a random powder charge to test the uppers. I told them that any FMJ 243 bullet used for testing was their issue. I tried 90 grain Seirras years passed in my target rifle chambered in 243 that shoots .3” or tighter groups with just about anything. I struggled to find a good load with the FMJs. Most shot 1.5” or larger MOA with most loads. They told me they bought bulk no name FMJs and picked a random powder and loaded it up. No wonder non of the uppers tested shot MOA. I figured they tested them with match grade ammo. I was also asked to report back with my testing and accuracy findings. I sent in my same photos last week. They told me the utter uppers were “ discarded and destroyed“ because they didn’t meet MOA accuracy. I am sure that was a tall tale as well. I asked if they we still around because I sure would take the other defective uppers off their hands.lol