Hi all. I did a search and didn't really see the answer to my question. I understand that bullet length and barrel twist needs to be matched, so to speak, but what is the effect if the bullet is too long? I'm reloading for .308, my barrel has 1:12 twist and if I figured it right the bullet should be around 1.18" in length. The ones I have are the Barnes tipped triple shock and they are 1.41" long. They are 168 gr. I realize weight isn't what's important, I just tell you that so you know what I'm using. I haven't been able to shoot these yet, or load them for that matter, so I have nothing to go on. Any help or advice is greatly appreciated!

You seem to have a good handle on the issue.

If the greenhill formula says 1.15 and your bullet is 1.41 then you're risking not stabilizing the bullet and you might even risk keyholing at close range and beyond.

You'll have to shoot them to confirm this.

If you haven't bought the bullets yet then don't!

Find something within the calculated range.

I believe your 1/12" twist will stabilize those 1.41" bullets. Greenhill says 150/length of bullet in calibers = required twist in calibers. BUT Greenhill was modified by substituting 180 for the 150 for modern bullets. I have used 220-grain bullets successfully in my 1/12" twist .308 and these were over 4 calibers long.

quote:

I have used 220-grain bullets successfully in my 1/12" twist .308 and these were over 4 calibers long.

El Deguello, those would have been round nose bullets, right? I shoot 245gr RN casts in my 303 Brit with a 1 in 10 twist. The cast boolet is shorter than it's jacketed counterpart putting more of its mass closer to the circumference. A long boat tail bullet needs a lot more stabilizing.

When you say modern bullets, do you mean all modern bullets? I know "all" may be a bad term to use, but does that apply to most popular ones?

jwb72,

quote:

Originally posted by jwb72:
I understand that bullet length and barrel twist needs to be matched, so to speak, but what is the effect if the bullet is too long?

What you should see if the bullet is too long is that at some distance the bullet will key hole on a target. Could be right out of the barrel or could go unstable and key hole later in flight.

quote:

Originally posted by jwb72:
I'm reloading for .308, my barrel has 1:12 twist and if I figured it right the bullet should be around 1.18" in length.

This is correct by the Greenhill Formula (GHF), if muzzle velocity is going to be below 2,800 fps, A 1:12 (or faster twist) is needed to stablize a 308 at 1.18" length.

quote:

Originally posted by jwb72:
The ones I have are the Barnes tipped triple shock and they are 1.41" long. They are 168 gr. I realize weight isn't what's important, I just tell you that so you know what I'm using.

Correct again, weight isn't important and these bullet should be too long for a 308 with 1:12 twist. However, again by the GHF, a 1:12 may work for a 1.41" bullet if muzzle velocity is above 2,800 fps.

quote:

Originally posted by jwb72:
I haven't been able to shoot these yet, or load them for that matter, so I have nothing to go on. Any help or advice is greatly appreciated!

Your probably out in "no man's land". But, I've seen some rifle-bullet-twist combinations work that the GHF says shouldn't! Since you already have the bullets and rifle, my recommendation is = Experiment!

1) Measure of the barrel twist (some are not what the manufacturer says)

2) Try to maximize the velocity.

3) Shoot a target at 50 yards.

4) If OK at 50 yards, then increase the range (possibly in increments) out to farther than you ever think you'll hunt.

If those 1.41" Barns pass the test above without key holes your good to go.

I appreciate the responses. I'll just try them out and see how it works so I'll know what length to go with. Thanks again!

WHAT?
Weight of the bullet doesn't matter? To what extent?
Length of the bullet, do you mean the portion of the projo that gets etched ot the total OAL of the projo as a whole?
I admit it's been a while since I've surfed this site but you guys are speaking Greek to me here...
Projo weight doesn't matter for stabilization, since when????

Confused Pat

quote:

Posted 17 June 2009 18:10 Hide Post
WHAT?
Weight of the bullet doesn't matter? To what extent?
Length of the bullet, do you mean the portion of the projo that gets etched ot the total OAL of the projo as a whole?
I admit it's been a while since I've surfed this site but you guys are speaking Greek to me here...
Projo weight doesn't matter for stabilization, since when????

The only effect weight has is if a bullet is made from lighter material and can be driven faster for it's length. The length of the engraved portion is what counts, not the total length of the bullet.
Weight has no effect other then at what velocity it can be driven to match the twist.
The Greenhill formula does not work and the faster you stop using it to do your own testing, the better you will shoot. It was developed for cannons.
Marlin used it for the .44 and it said a 1 in 38" twist was right, yeah, sure!
If your bullet is long and you can not get the spin up high enough for stability, the twist must be faster or the bullet shorter (which means lighter--DUH.)
The only thing weight means is that the 150 gr bullet is shorter then the 180 gr and that bullet construction is different for the animal.
All copper bullets change things about bullet length but bore friction also goes up so loads need to be reduced so you just might not stabilize them.

The bullet length and twist rate are not the only variables.

The velocity helps stabilize, and a load that is stable out to one target may not be stable out to another.

A 6mmBR 75 gr Vmax 20" 1 in 14" twist barrel can get 0.1" group at 50 yards, but keyhole at 100 yards.

Greenhill works passably for middle calibers and lead core bullets. It was not designed to work with the properties of mono bullets. Go here, left hand column, seven items down.

Download a file called wload212.zip to your PC, run it using the WinGyro section, not the WinLoad section. It is much better than Greenhill and one can do a lot of "what if?" playing with it. If WinGyro says it won't fly, take it for granted that it won't.

quote:

The only effect weight has is if a bullet is made from lighter material and can be driven faster for it's length. The length of the engraved portion is what counts, not the total length of the bullet.
Weight has no effect other then at what velocity it can be driven to match the twist.
The Greenhill formula does not work and the faster you stop using it to do your own testing, the better you will shoot. It was developed for cannons.
Marlin used it for the .44 and it said a 1 in 38" twist was right, yeah, sure!
If your bullet is long and you can not get the spin up high enough for stability, the twist must be faster or the bullet shorter (which means lighter--DUH.)
The only thing weight means is that the 150 gr bullet is shorter then the 180 gr and that bullet construction is different for the animal.
All copper bullets change things about bullet length but bore friction also goes up so loads need to be reduced so you just might not stabilize them.

Phew.... Thanks BFR....
Here I thought you guys had reinvented the wheel and nobody told me about it... LoL...

quote:

Originally posted by jwb72:
Hi all. I did a search and didn't really see the answer to my question. I understand that bullet length and barrel twist needs to be matched, so to speak, but what is the effect if the bullet is too long? I'm reloading for .308, my barrel has 1:12 twist and if I figured it right the bullet should be around 1.18" in length. The ones I have are the Barnes tipped triple shock and they are 1.41" long. They are 168 gr. I realize weight isn't what's important, I just tell you that so you know what I'm using. I haven't been able to shoot these yet, or load them for that matter, so I have nothing to go on. Any help or advice is greatly appreciated!

Your 308 should have no problem stabilizing any bullet from 100 to 220gr. The rifle twist formulas are not exact so don't get hung up if your twist rate does not match exactly. In fact the only stability issue I have ever run into was with a 223 that had 1:14 twist. Would keyhole anything longer than 45gr bullets. a 1:9 barrel fixed it.
That being said, every rifle is different, so yor experience may be different than mine

quote:

In fact the only stability issue I have ever run into was with a 223 that had 1:14 twist. Would keyhole anything longer than 45gr bullets. a 1:9 barrel fixed it.

I agree...
I don't know about you, but I think .223 is about the most sensitive caliber that I own for barrel twist/projo weight (length) issues...

I'll never forget the first AR-15 I bought. It was a Match HBAR Colt w/1:7" twist rate barrel. This was also around the time when the military was getting away from the 55g projos and going to the 62g ones for the M-16. Anyway, I bought this sucker and a bunch of 55g ammo and took her to the range... The darn thing shot for crap! Really, I was lucky to print 8" groups at 100 yards!!! Boy was I upset!!!!
I figured it couldn't be me, I was a an experienced Service Rifle shooter and was pretty well accomplished w/my M1A, it had to be the gun!
Then another time at the range, I was standing there scratching my head trying to figure out WHY this "match rifle" didn't shoot for beans (shooting 55g projos again). A guy down the line saw me and came over and talked to me. I told him my problem and the first thing he asked what projos I was shooting, I told him, and he said "that's it". He went to his bench (he was also shooting an AR that day) and grabbed me a few rounds of the 62g ammo he was shooting.
I instantly grouped about 1-1/2".
Then I got into reloading .223 and w/69g Sierra Match projos, that rifle will shoot 10 round groups the size of a quarter from the bench...

I have an HK53 (w/the short 1:12" barrel twist) and it keyholes the 62g projos all the time, no matter what distance...
I've never run accoss a caliber like .223 before... My guess would be that the other small caliber/high velocity rounds (.220Swift, .25-06, etc...) would probably be just as twist sensitive, no?