[Quentin]

Originally Posted by Vincine

1:7, 1:9, 1:12, etc?

Clearly I don’t know much about this stuff, but wouldn’t/shouldn’t the rifling twist rate smoothly increase from where the bullet enters the barrel to where it exits the barrel?

If you mean a variable twist that starts slowly to get the bullet spinning then gets faster as the bullet travels down the barrel - well that has been done but the machinery to do it is complex. So barrels with a variable twist would be every expensive. Good idea, just hard to implement.

[Vincine]

Originally Posted by Quentin

If you mean a variable twist that starts slowly to get the bullet spinning then gets faster as the bullet travels down the barrel - well that has been done but the machinery to do it is complex. So barrels with a variable twist would be every expensive. Good idea, just hard to implement.

Yes, that’s what I meant. Did it work? I guess it was easier to do on the big guns. I’m figuring maybe rifle bullets are too teeny tiny to benefit as compared to the mass of 16 inch shells.

[Quentin]

Yeah I could see variable twist being beneficial on large shells, more mass to get spinning down the barrel so anything to smooth it out is good. But for rifle barrels how to get the mandril out of the small bore after hammer forging and similar problems with button rifling. Just how do you get the durn thing out of a small barrel once the variable rifling is done.

[canebrake]

Originally Posted by Quentin

Yeah I could see variable twist being beneficial on large shells, more mass to get spinning down the barrel so anything to smooth it out is good. But for rifle barrels how to get the mandril out of the small bore after hammer forging and similar problems with button rifling. Just how do you get the durn thing out of a small barrel once the variable rifling is done.

I bet this conundrum could be solved with the new manufacturing process called hydro-forming.

Hornady’s custom shop offers a hydraulic case-forming kit for "Wildcat" rounds.



Fluids are not compressible and work as the mandrel in Hydraulic Forming. This requires the die to be the "shape" the final product takes with regard to the external dimensions. Some modifications would be required to develop a variable mandrel with a fluid core. Once the desired shape is achieved, the fluid can be drained and the metal part of the mandrel can collapse and be removed.

OK, here's the deal. I need $250,000,000.00 of venture capital to start this process development.

Any VC Angles out there?

[Vincine]

Interesting.

Originally Posted by canebrake

I need $250,000,000.00 of venture capital to start this process development.

I once received a bid for a rubber band powered business card. It popped into a cube when pulled out of its envelope. They wanted a few thousand for the first one and then would charge me half a cent each for the rest.

I told them I didn’t want the first one, but I’d buy the others.

They wouldn’t work with me on it! Imagine!

[spacegun]

The 1:7 is ussed primarily in NATIONAL MATCH rifles for the 80 gr
sierra. Yes they have to be loaded single shot. To long for the mag. NM will use 69 -80 gr bullets accross the course. Some manufactures are finally seeing the light and using the faster twist more often in the A4's. Everone likes the heavy bullets instead of those little 55 pills. Ask the military guys what they shoot. They love the Seirra 77gr. Use the 1:6.5 twist for the 90 gr bullets out to a thousand.


QUOTE=Sniper03;534039]Quentin,

Just to explaining the 1:7 issue. The reason I kept the 1:7 specs at 77 grain max. Is that most all 1:7 ARs and military M-4s are tactical weapons and used for military. LE and similar weapons. Therefor to shoot the 80 grain bullets would in all probability require hand or single round loading due to the AOL of the round. Didn't want someone going out with a defense weapon thinking the 80s would feed without any problems in a critical situation. Like the guy that would load his magazine with some 80s and never check it to see if they would feed. Most of the guys that shoot the 80 Grains out of the 1:8 are varmint shooters doing some long range work. And feed a round one at a time or from the special single round sold follower magazines that are available or just hand load one round at a time in the chamber. If all that makes sense? You are correct about the 1:7 twist being able to shoot them for sure! Thanks for reminding me I should have explained that in the tread.

03

03[/QUOTE]

[jslone0103]

man i have ben really having trouble getting my ar 15 to shoot a decent group at 100 yards .. i have tried 77 g 62 g 55 grain bullets and the gun is just a basic ar15 m4 set up manufactured from Delton out of N Carolina... i have changed scopes and litteraly shot round after round and the bullets hit to the right one shot and maybe right on the next and then low the next lol its jsut all over the place.. i am using a wever scope mount on a picitnany rail .. could this be a problem???? is it improper scope set up or is my 1x10 twist barrel not cut out for the load im using?????

Please help needed .....

[spacegun]

I didn't know anyone made a 1x10 for an AR15. 1x9 is the slowest I have heard of. I beleive we used a 1x12 twist for bench rest and varmit barrels in the past. But that was for 52 gr bullets only.
I don't think your problem is in your scope set up. Try another one from another set up to verify that. Process of elimination. Don't worry about sighting it in to hit center of target. Where it hits the target is not important. You are trying to eliminate what could be the problem.
I just returned a new A4 upper today from a major manufacturer. 1x9 twist would not stabilize a 62 gr. Shot 4" groups at 50 yds from a quality bech rest with a 10X scope. 55 gr would shoot about 1 1/4. Something isn't correct here. Manufacturer thought so too. Every barrel isn't perfect. A good company will take care of your problem. A bad one won't.

Originally Posted by jslone0103

man i have ben really having trouble getting my ar 15 to shoot a decent group at 100 yards .. i have tried 77 g 62 g 55 grain bullets and the gun is just a basic ar15 m4 set up manufactured from Delton out of N Carolina... i have changed scopes and litteraly shot round after round and the bullets hit to the right one shot and maybe right on the next and then low the next lol its jsut all over the place.. i am using a wever scope mount on a picitnany rail .. could this be a problem???? is it improper scope set up or is my 1x10 twist barrel not cut out for the load im using?????

Please help needed .....

[gunnut07]

I draw a Straight line down my cleaning rod and line it up with a known mark on the rear of the receiver. I then place a has mark where I start then I push gently till the mark makes it back to the reference mark on the reciever then make another hash mark. Push the patch though the barrel and withdraw the cleaning rod measure the space between the two hash marks and that is your twist rate.

Also you didn't point out that Barrel twist is more set on bullet length not weight. That said most of the time a bullet that is longer per a given caliber is normally longer.

[Darth AkSarBen]

I shoot the 6.8 SPC II caliber for my AR-15. I have 2 uppers in this caliber. One is a 16" long barrel with 1 i 11.25 twist with 5R rifling, and the other is an 18" barrel with 1:11 twist with 4 groove rifling. Both hold to about a dime at 100 yards. Both have the improved chamber, meaning, when Remington submitted the drawing to SAAMI for the 6.8 SPC caliber they did not have the corrected bore drawing and the resulting first rifles created and used for testing for that matter, were with a shorter "free bore" on the bullet before it engaged the rifling. That, and along with a 1 in 10 twist created pressures that would not allow for the full capability of the caliber that the original designers had in mind. It was found out later that the rate of twist needed to be opened up to minimum of 1:10 and preferably 1:11 or 1:12 twist. At 1:13 some studies found that it did not stabilize the 130 gr 270 caliber bullet well but did for the 100 to 115 bullet. So, 1:13 was the maximum looseness of twist and 1:10 was pretty much set as the maximum tightness of twist. It seems that the tighter the twist on this caliber, and I would be guessing it was for a lot of other calibers as well, was that it created more pressure spikes in the beginning to get the bullet mass twisting and the fact that it had to make that twist during the time the bullet was in the barrel.

It was amazing what changing the leade in the rifling was from 0.050" to 0.100" would do as well as they (originally) had a steep 60 deg slope where the new (and now) chamber reamers have a slope of about 33 deg. It was a mis-calculation on the drawing and it struck down the 6.8 SPC as not as great as was bragged to be, but that was with the original chambering. Now, it has proper spec chambers, called either 6.8 SPC II, or merely 6.8 x 43mm . Now it is capable of spitting out a 110 or 115 gr bullet close to 3000 fps with no more pressure signs than the previous loadings at reduced powder charge to accommodate rifles in the original chambering design. Few rifle manufacturers use the old specs as they realize that the newer twists and chamber were what the cartridge had for original intentions. Tighter twists on this caliber amounted to larger pressures. When I hand load, I generally end up about 2 grains above maximum recommend charge in the books, and yet have no case pressure or other signs of excessive pressure, like flattened primers and extreme brass flow. Reloading is always, a world of caution, and to develop the best load for this caliber does not always mean extreme speed. Right now I have a load that sends the 100 grain bullet into small dime size groups at 100 yards. It was not the fastest, but it is the most accurate.