Land to groove ratio
- Thread starter Richard
- Start date
C
CMaier
Guest
surface ratio..area of the land/area of the groove.
usefulness...i have no idea
usefulness...i have no idea
James, I was wondering
did he give you a reason for that ratio? I have been thinking about the different pressure curves of powders and if the L to G ratio had any effect on that. ( I'm sure it does, but I don't have the test equipment to check) It seems most shoot 4 groove cut bbls or 6 groove button bbls.
All of this might be "much ado about nothing" but I don't know.
Richard
did he give you a reason for that ratio? I have been thinking about the different pressure curves of powders and if the L to G ratio had any effect on that. ( I'm sure it does, but I don't have the test equipment to check) It seems most shoot 4 groove cut bbls or 6 groove button bbls.
All of this might be "much ado about nothing" but I don't know.
Richard
Richard
The land to groove ratio does have an effect on the pressure curve. The greater the area of the lands gets, the higher the peak pressure goes, and the quicker the pressure spikes. This effect will be on all powders to some extent. The main things to consider about land to groove ratio is that the heavier lands last longer, but cause greater bullet distortion. Thinner lands wear quicker, but can be more accurate since there is less bullet distortion. The old 8 groove Shilen barrels were very accurate, but the throats shot out quicker. Because cut rifled barrels are typically 4 groove, the grooves are a little wider than button rifled barrels with 6 grooves. This keeps the groove to land ratio close to the same between a 4 groove cut, and a 6 groove button rifled barrel. Douglas button rifled barrels have a nice groove width for a typical 6 groove barrel, just a Krieger and Bartlein maintain a nice ratio for cut rifled barrel. It's all about balancing low bullet distortion for accuracy, barrel life, and pressure curves.
Michael
The land to groove ratio does have an effect on the pressure curve. The greater the area of the lands gets, the higher the peak pressure goes, and the quicker the pressure spikes. This effect will be on all powders to some extent. The main things to consider about land to groove ratio is that the heavier lands last longer, but cause greater bullet distortion. Thinner lands wear quicker, but can be more accurate since there is less bullet distortion. The old 8 groove Shilen barrels were very accurate, but the throats shot out quicker. Because cut rifled barrels are typically 4 groove, the grooves are a little wider than button rifled barrels with 6 grooves. This keeps the groove to land ratio close to the same between a 4 groove cut, and a 6 groove button rifled barrel. Douglas button rifled barrels have a nice groove width for a typical 6 groove barrel, just a Krieger and Bartlein maintain a nice ratio for cut rifled barrel. It's all about balancing low bullet distortion for accuracy, barrel life, and pressure curves.
Michael
C
CMaier
Guest
yes it would.
tall lands tend to last forever, but accuracy goes away and does not come back.
some russian 91/30 rifles are still shooting. 80 years later( actually 116 years most were not re-bbl'd when the ammo changed in the early 1900's))
tall lands tend to last forever, but accuracy goes away and does not come back.
some russian 91/30 rifles are still shooting. 80 years later( actually 116 years most were not re-bbl'd when the ammo changed in the early 1900's))
OK, in The Spirit Of Wilbur I'm going to provide an unfounded, speculative and maybe even irrelevant "insight".......the difference is, I'ma' just forge on ahead damn the torpedoes
(cain't help myself, nuther
)"I've heard" that when the bullet obturates and upsets to fill the grooves there's a very fine line between not only width and depth, the ratios thereof, and their relationship to each other but also with the overall diameters involved. The way I grasp it is that the barrelmaker must, by figures, experience and trial and error find that combination which allows everything to squish into place, sealing against unnecessary leakage while not STRETCHING THE BULLET........
In short, the bullet WILL find it's way down the bore, at some pressure or another, but that the job of the barrelmaker is to keep it as pristine as possible.
An example.
I have a friend who fired some 30cal bullets down a .270 tube and collected the bullets. They made it to the collection box, no animals were harmed in this experiment, and the bullets were now very LOONG 270 projectiles. Some even oozed lead out the tips.....
My point (such as it is) it that it's a tricksy science..... I've managed to acquire a couple undersized "setup barrels" from rifle barrel mfgrs for use as fireform barrels and in one case I've got one set up for pressure testing. It's a 338 barrel that's 6 thou undersized from the production runs. The only way I can capture these pills is in a snowbank and we haven't had any for the last 5yrs so I don't know what the slugs measure out to but my guess is that they're "stretched"
I'll find out after the election's over and we get some snowbanks back, meantime this tight barrel does build pressure differently as Michael mentioned.
eeebedy eeebedy eeebedy that's all folks, such as it is
The old 2 groove A3 Springfield barrels were made on the same machines as the 4 groove barrels by just not cutting the second pair of grooves. So the 2 groove barrels are the majority lands. The govt couldn't tell it made any difference & I've heard several people say they thought they shot better than 4 groove.
Go figure!
Regards,
Ron
Go figure!
Regards,
Ron
Salient point.....as far as I've known you're exactly right, they just left two grooves out which left two huge lands.
That said, IIRC this DID increase pressure some according to testing, and "still showed acceptable accuracy." For a battlegun.
"Accuracy" is very much a product of environment. And in this case, mythos......I submit that these guns DID swage bullets longer.
jackie schmidt
New member
Weren't most Springfield Barrels broached? It seems I read years ago that when broaching barrels, the process was made easier with fewer lands and grooves.
One of the most accurate barrels I ever had was back in the '90's, that Glenn Newick gave me for a 25BR project. It was a 13 twist Shilen with 8 lands and grooves that was actually made in the '80's.
Ed Bernabeo still has that barrel, chambered in 25-243 improved.
In my opinion, which isn't worth much, I think the cross section of the bore in relation to the cross section of the bullet is what is important. If the barrel cross section is to small it will deform the bullet which will effect accuracy. If it is two big the bullet will not seal allowing gas to leak by also effecting accuracy.
In the case of the two grove barrels made in WW2 the wide lands made the cross section of the barrel smaller, increasing pressure. It most likely effected accuracy but they would still shoot, minute of man.
JerrySharrett
Senile Member
Over the years I have used 3-groove, 4-groove, 5-groove, 6-groove and 8-groove barrels.i never really noticed a difference in pressures and I usually shoot pretty hot. The best load I had for the 2016 Super Shoot registered 3545 on an Ohler with screens set 22' from the muzzle. At 3545 thebullets do go all the way through the paper! I sometimes blank primers with 0.062" firing pins. I always have a bolt/firing pin tool in my cart during a match!
That said, the height of the lands probably, IMO, would make a difference.
Question, how come some barrels within a family, say 4-groove 237/243 Bartleins or whoever, seem to react to pressure signs differently?
That said, the height of the lands probably, IMO, would make a difference.
Question, how come some barrels within a family, say 4-groove 237/243 Bartleins or whoever, seem to react to pressure signs differently?
Chances are the pressure was the same or very close so that you could not tell with out instruments. I think the cross section of the 3, 4, 5, 6, and 8 grove barrels was probably the same. If you think about it the lands of an 8 groove barrel won't be the same width as they are on a 4 groove, physical limitations not enough room. So if 8 groove lands are half as wide as 4 groove the cross section will be the same. That being the case the bullet will be as tight in a 4 groove as a 8 groove giving the same pressure.
Far as I remember the Springfields were pulled on Pratt and Whitneys.....old school, like 20-40 pulls/barrel. Or more.
Dunno WHY they weren't broached in one pass except that rifling broaches are labor-intensive to make and I be betcha' that out on the shop floor their useful life would have been short....
Dunno WHY they weren't broached in one pass except that rifling broaches are labor-intensive to make and I be betcha' that out on the shop floor their useful life would have been short....
BTW......not to keep flogging the horsey but I gotta' say A LOT OF MY KNOWLEDGE ABOUT VELOCITY/PRESSURE suffered a huge revision when I started weighing powder carefully.
Frankly, the barrel's role (rifling and diameter, erosion/cleanliness/age) in pressure is very minimal IME.
I'm not talking here about reamed chambers and their effects and differences but just the barrel itself.
I useta' believe stuff like "a dirty barrel could cause erratic pressures" and "copper fouling can increase pressures" and "firecracking can increase pressures" and on-and-on-and-on
now I don't.
Frankly, the barrel's role (rifling and diameter, erosion/cleanliness/age) in pressure is very minimal IME.
I'm not talking here about reamed chambers and their effects and differences but just the barrel itself.
I useta' believe stuff like "a dirty barrel could cause erratic pressures" and "copper fouling can increase pressures" and "firecracking can increase pressures" and on-and-on-and-on
now I don't.
I agree also I think chip management would be a problem. You would pack up a lot of chips over 30"
B.Larson
New member
Load Pressures
alinwa said: "Frankly, the barrel's role (rifling and diameter, erosion/cleanliness/age) in pressure is very minimal IME."
I couldn't disagree more......
take 6 different guns........
shoot 5 rounds in each gun... same load...
some will show pressure problems....... some will not......
we are dealing with friction here :
if a barrel is smaller in diameter it would take more force to get bullet down tube
ruff throat= more pressure
copper fouled barrel=more pressure
alinwa said: "Frankly, the barrel's role (rifling and diameter, erosion/cleanliness/age) in pressure is very minimal IME."
I couldn't disagree more......
take 6 different guns........
shoot 5 rounds in each gun... same load...
some will show pressure problems....... some will not......
we are dealing with friction here :
if a barrel is smaller in diameter it would take more force to get bullet down tube
ruff throat= more pressure
copper fouled barrel=more pressure