6.5 TCU bullets sideways

[joeb33050]

The 3 shots the gun decided to fire yesterday were 15/IMR4227 and a 140gr Rem PSP. All went through the target sideways-keyholing.
1. Does anyone know the twist on a TC 6.5TCU barrel?
2. Is my load too slow?
3. What's wrong?
Thanks;
joe b.

[contendernut]

I think its a 1:9.  Sounds like you need to pick up the velocity to keep from keyholing.  Or switch to a shorter bullet.

[B_Koes]

I know that T/C barrels were made with 1-9" & 1-8" twist rate barrels.  I may be mistaken, but some reloading manuals even list a 1-10" twist.  It is probable that you have one of the slower ones (not 1-8") which for the most part be insufficient to stabilize a 140gr bullet.  A 1-9" twist may occasionally stabilize a heavy bullet, but it may depend upon the velocity of the load as well.  It sounds like you either need to find a lighter (and therefore shorter) bullet or buy a barrel with a faster twist.  You could try bumping up the velocity and see if it starts to stabilize...experimentation is the key here and that takes time.

[helobill]

B_Koes,
Isn't that backwards? I might be wrong, but I thought it meant 1 revolution in 8" of travel versus 1 rev in 10" , wouldn't that make 1 in 8" faster than 1 in 10"? Or is twist like golf and everything is backwards (golf spelled backwards is flog which is what it sometimes feels like)?
Just a Helo pilot trying to figure this out.
Bill

[IronMonkey]

120s will shoot great, but anything over is too heavy for the TC factory barrels unless you have a 1:8 twist barrel which is not common.  I would stick with 120s or lighter and just push the velocity a little.  Dan

[thomas]

My 10" 6.5 TCU has no problems with the 140 or the 160 grain bullet.
I would first check the crown for damage.
Very unusual for the 6.5 TCU to key hole.
and I would call TC but I believe All TCU 6.5 have been made with a 1-9 twist Except for the  early ones  (1-8) Might be wrong so check with TC
Key holing should not be a problem with your TCU
Tom

[contendernut]

I think the problem is not necessarly the 140 gr bullet, but the velocity of it.  If I read Joe's post correctly, he is using 15grs IMR 4227 for a reduced load.  Is this correct Joe?

[Clev]

Tc has only made two twists that I know of. First was a 1-10 the newest is 1-8. If it is a 1-10 twist you will never make a 140 gr bullet stablize in that barrel. Your other problem may be the bullets. Rem. bullets. It isn't that they are long but those bullets have a vary short drivingband(part of the bullet that is in contact with the lands) the rem. bullets are only .264 from the crimping grove down to the base, so there is not much there touching to stablize the bullet. Pumping up your load may help but don't be suprised if it doesn't. I own a few pistols in the 6.5 caliber If someone asks me about the 6.5's and they are thinking about buying on 6.5TCU, 6.5BR,or 6.5PPC I tell them no to buy anything with a slower twist than 1-8. unless they only want to shoot 120's and down. Don't give up on this barrel go buy some more bullets like Sierra or Hornady that are 140's and give them a try. Clev

[Graycg]

Hello Joe,
  I've missed you at Trail Glades, but I've been underway keeping things safe for months....  Doesn't look like I'll get back there anytime soon.  Hope Wednesdays are still good for you.

Regards,
  Graycg, aka CDR Gene Gray, USCG

[joeb33050]

As near as I can measure, the twist is 1 turn in 9".
Lyman 266649 cast of WW weigh 157 gr. and are 1.175" long without the gas check. These stabilize with 14/IMR4227.
Remington 140 gr. PSP weigh 141gr., and are 1.225" long. They do not stabilize at 50 yards with 15/IMR4227.
Greenhill says that a .264" barrel with a 1 in 9" twist will stabilize a bullet of 1.16" length.
The cast bullet is .015" over this length, the jacketed bullet is .065" over this length.
It looks like I'm on the stability border. I'll try more IMR4227.
Does anyone out there have IMR4227 loads for the 6.5TCU?
Thanks;
joe b.

[B_Koes]

Tc has only made two twists that I know of. First was a 1-10 the newest is 1-8. If it is a 1-10 twist you will never make a 140 gr bullet stablize in that barrel. Your other problem may be the bullets. Rem. bullets. It isn't that they are long but those bullets have a vary short drivingband(part of the bullet that is in contact with the lands) the rem. bullets are only .264 from the crimping grove down to the base, so there is not much there touching to stablize the bullet. Pumping up your load may help but don't be suprised if it doesn't. I own a few pistols in the 6.5 caliber If someone asks me about the 6.5's and they are thinking about buying on 6.5TCU, 6.5BR,or 6.5PPC I tell them no to buy anything with a slower twist than 1-8. unless they only want to shoot 120's and down. Don't give up on this barrel go buy some more bullets like Sierra or Hornady that are 140's and give them a try. Clev

Mark,

I swear that my 14" 6.5TCU is a 1-9" twist.  I used to think like you (only 8" & 10" twists).  Either my cleaning rod experiment was off or there are actually three twists in existence.  With all the bastardization that TC has done to their barrels that wouldn't surprise me a bit!

[B_Koes]

B_Koes,
Isn't that backwards? I might be wrong, but I thought it meant 1 revolution in 8" of travel versus 1 rev in 10" , wouldn't that make 1 in 8" faster than 1 in 10"? Or is twist like golf and everything is backwards (golf spelled backwards is flog which is what it sometimes feels like)?
Just a Helo pilot trying to figure this out.
Bill

I agree with everything you said.  I don't know where you could have inferred different from my previous post.  Regardless, 1-8" = fast  1-10" = slow(er)

[helobill]

B_Koes,
My apologies, I guess I read your post wrong, or read something into it.
Helicopter Bill