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The Green Mountain Carbine Barrel
by Hank Strong

Marksmanship and the Long Rifle are synonymous. In our minds and in our country's development, the two are inseparable. This is reflected in our early military history and continues in our present day muzzle loading matches. But the Long Rifle has draw backs. In close quarters or heavy brush it is awkward to handle. If the barrel were shortened, improved handling and reduced weight for the rifleman would result.

Native Americans recognized the problems associated with a long gun since they lived off the land, they learned to hunt in close. They wanted a short barreled rifle that was easy to carry and quick to point. The Plains Indians liked a short barreled rifle for its handling characteristics on horse back. Coincidentally, by the 1850's the US Army had adopted a carbine styled rifle for Calvary use for similar reasons. Today the muzzle loading hunter has a requirement for the same type of rifle for the same reasons that our forefathers had.

Deer hunting is one of the fastest growing sports in the nation. In the last few years, hunters discovered that a muzzle loader can extend their hunting season, and do it in a very effective way. A carbine is a natural choice in a tree stand or for hunting heavy brush. Over the last three years we have tested most of the muzzle loading carbines on the market. The results have been very favorable. With the right load they are accurate and hard hitting, but one question always came back to us. What do you lose when the barrel is shortened on a frontloader? Accuracy? Muzzle velocity? And how short could a barrel be cut off before disadvantages showed up. Because of the company's reputation for producing accurate rifle barrels, we decided to ask Green Mountain's owner, Branch Meanly, for help.

Early last year we thoroughly wrung out Green Mountain's Long Range Hunter barrel or the L.R.H., as it is more commonly known. This is a 28" replacement barrel that will fit most rifles that have a snail ignition system. It is undoubtedly the most accurate and versatile barrel available. Accuracy with one, two or three bullet types is one thing and isn't that uncommon among the new fast twist barrels. The L.R.H. shoots most any sabot combination or conical at 100 yards, delivering 1 to 2 inch groups. That is accuracy and versatility!

Branch recognized the advantages of the carbine for the whitetail hunter and shared our interested in the research. So he graciously agreed to prepare four of his 28" L.R.H. barrels to our specifications. To check the incremental changes, we cut them down in two inch steps. The barrels have a 1-28" twist with 8 lands and groves and .005 to .006 deep rifling. The four barrels were to be mated to a Hawken stock from Thompson-Center with their standard lock and triggers. Early in January four barrels arrived from Branch in lengths of 26, 24, 22 and 20 inches. The next step was to select the sighting system that would be used on the barrels.

A few years ago no self respecting muzzle loader would have allowed a scope on a rifle. Today, that has changed. Muzzle loaders are recognizing the advantages a scope offers. It eliminates the short sighting radius problem associated with a carbine. And under low light in the dense fall foliage it enables a hunter to distinguish between a buck or doe. It also can help those whose eyes are no longer perfect besides, the test was of the barrels, not our eye sight.

We selected a 2X7 variable power Simmons 44 Mag because of our experience with the scope at the range and in the field. We installed Warne quick disconnect mounts on the barrels. They offer advantages over other removable mounts we have used. The base is a slotted one piece rail and the rings fit into the base. This is stronger than the two piece mounts frequently used. It is dovetailed so that the rings can be slid on or off as desired. The rings are designed with a thumb screw lever on a separate spring loaded plate. When the lever on the rings is tightened, it firmly secures the rings to the rail. By loosening the lever, the scope can easily be removed and installed on another barrel. The Warne system also allows the use of a scope with a large front bell, like the Simmons 44 Mag. Several loads we intended to test would generate recoil that is similar to shooting a .338. So it was important the mounts be strong enough to withstand the recoil. Neither of us wanted to wind up wearing a 32mm eye piece! The front and rear shoulders on the base help to hold the scope in place. The detachable mounts also minimized the effort needed to re-zero each barrel.

Chronographs are usually not associated with muzzle- loaders, but a dedicated shooter can learn a great deal from one. The Pact 1 chronograph will calculate the standard deviations in a string of fire for the shooter. Standard deviation is the average difference in muzzle velocity between shots in a string of fire. Armed with this information, we can make one of several judgement calls if the groups are too large. Some examples; if the muzzle velocities become erratic it could mean that the rifle was loaded incorrectly. Too much pressure used in seating the bullet will crush the powder and increase muzzle velocities. A dirty bore will gradually increase muzzle velocities with each succeeding shot. A bore left damp from cleaning will cause hang fires and inconsistent muzzle velocities. If the group spreads and the muzzle velocities are close, then it could be fouling in the bore. These can all adversely affect accuracy. Shooters may blame the rifle or chalk's it up as a bad day at the range.

All bullets have a certain velocity range that they will operate accurately within. That range will vary depending on the bullet and bore design. A chronograph enables the shooter to establish what that range is and build an accurate load. In the C.V.A. Stalker, we recently tested, we lowered the velocity on a Lyman 350 grain cast bullet from 1486 fps to 1299 fps. The group went from 2.8" to 1.27" at 100 yards. Muzzle velocity and ballistic coefficient, when run through a personal computer, will give you the trajectory and down range energy.

Two of the bullets selected for the test in the carbine barrels had been fired from the L.R.H.. They grouped very well at 100 yards, so they were a natural for the test. The 225 grain sabot from Buffalo Bullet and the 350 grain cast 45-70 Lyman bullet were chosen. Both were Pushed by 80 grains of RS grade Pyrodex. We believed that the charge would provide a high enough muzzle velocity for a 100 yard shot and not blow the group apart. The two bullets offered the hunter a choice of a heavy or light load and that was important. The heavy load would be capable of taking everything from whitetail to Elk. The light load would be primarily for whitetail and would create a mild recoil. If such a load could be effective for a carbine, it would cut across gender lines and appeal to young and old alike.

After the rifle was on paper at 100 yards, each string would consist of seven shots. We selected the number seven because the highest and lowest muzzle velocity could be thrown out when the standard deviation was computed. This still left 5 shots for computing a valid standard deviation and average muzzle velocity. The bore was cleaned between shots as we normally do. This procedure has eliminated problems and produced better groups. All the strings were shot with Pyrodex from the same lot. A Mountain State Spitfire Magnum nipple was installed in all the barrels.

The barrels on average lost 13.5 fps of muzzle velocity per inch of barrel lost. The difference between a 28" barrel and a 20" barrel was around 108 fps, not a significant loss in velocity. This was consistent between all barrel lengths. A very dirty bore will create that much variance in muzzle velocities between shots from the same barrel.

The standard deviations of the strings from the carbine barrels averaged just over 18 fps, well within our standards for an acceptable deviation. Standard deviations between barrels varied only 2 to 3 fps. The close standard deviations lead us to believe that the loading procedures were correct. And that we were getting top performance out of the load in that barrel.

The carbine barrels generated muzzle velocities that are high enough for hunting at 100 yards, with the right bullet. Muzzle velocity is critical when the bullet weighs less than 300 grains and you are hunting past 75 yards. The loss of 104 fps could be critical for a light bullet. It could drop the energy below 800 foot pounds at 100 yards.

Accuracy between the barrels did vary slightly but no more than .5" at 100 yards. We attributed this to the 5-10 mph wind on the day of the shooting. The groups fired from the test barrels were slightly better than those fired from other carbines. And they mirrored those fired from the 28" L.R.H. at 100 yards! The groups from the two test bullets were similar. The 45-70 cast Lyman bullet turned in groups that averaged 1.54" versus 1.9" in the other carbine barrels at 100 yards. The average muzzle velocity from the Green Mountain barrels was 1369 fps. And the 225 grain sabot from Buffalo Bullet turned in an average group of 1.48" versus 2.2" from the other carbine barrels at 100 yards. With an average muzzle velocity of 1485 fps, the Buffalo Bullet isn't a powerhouse at 100 yards. At 75 yards it should easily do the job. Time did not permit us to refire the Buffalo Bullet with a higher charge or a different powder. This could have improved the down range energy. We pushed this bullet at over 1700 fps out of the L.R.H. and it fired a 1.5" group at 100 yards. We are confident that a stronger load could have been used with the shorter barrels and stayed under our 3" standard at 100 yards. The Green Mountain carbine barrels are not picky about the load, unlike some other barrels.

Muzzle velocity and weight are all that was lost by the shorter barrels. The carbine barrels dramatically improved the handling characteristics of the Thompson-Center Hawken and the Lyman Trade rifle. The Green Mountain carbine barrel's big advantage over their competition is the variety of bullets it will shoot accurately. All other things being equal, accuracy is determined by the loading techniques and the components used by the shooter, not barrel length.

Green Mountain Rifle Barrel Company introduced their 21" carbine barrel in July of 1993. A Mountain State Muzzle- loading Super rod and the Spitfire Magnum nipple are furnished. The blued .50 cal. 1" barrels will fit the Thompson-Center's Renegade and Big Boar Rifle. In 15/16's they will fit the White Mountain Carbine as well as the Thompson-Center Hawken, Lyman Trade, Lyman Deerstalker, Investarms Hawken and the Cabela's Hawken.


Chronograph: PACT 1 10 feet from muzzle of rifle
TEMP: 70 - 89 Degrees Fahrenheit
Elevation: 450 feet above sea level
Humidity: 43-73%
Barometric Pressure: 30.1- 30.5
Bench Rest: Lohman Sight Vise
Standards: Group 3" or less at 100 yards
Wind Flags: One every 25 yards out to 100 yards
Powder Measure: Haddoway
Caps: CCI
Lubricant: N/A
Sabots: Modern Muzzle loading used with Lyman cast bullet
Buffalo Bullet used their sabot
Cleaning: After every shot with our cleaning solution.
After every 7 to 10 shots bore scrubbed with a Bore Brush dipped in SHOOTER'S CHOICE or HOPPE'S BENCHREST.
29 W. 4th St.
Williamsport, PA 17701


Green Mountain Rifle Barrel's Carbine Barrel
Ignition; Snail
Length; 28"- 20"
Lands and Groves; 8
Rifling; .005 - .006 Deep , narrow lands and wide Groves
Bore Diameter; .504
Sights; Drilled and Tapped for T/C sights and scope mounts

.177 .430 225 BUFF 80RS 1433 1.9 1.52 680 20
.177 .430 225 BUFF 80RS 1459 1.8 1.36 700 22
.177 .430 225 BUFF 80RS 1485 1.7 1.50 720 24
.177 .430 225 BUFF 80RS 1511 1.6 1.51 741 26
.177 .430 225 BUFF 80RS 1537 1.6 1.50 764 28
.274 .452 #350 LYM FN 80RS 1315 2.1 1.5 1045 20
.274 .452 #350 LYM FN 80RS 1343 2.0 1.6 1081 22
.274 .452 #350 LYM FN 80RS 1369 1.9 1.3 1115 24
.274 .452 #350 LYM FN 80RS 1395 1.8 1.5 1152 26
.274 .452 #350 LYM FN 80RS 1423 1.7 1.8 1193 28

Chart Abbreviations
B.C. = Ballistic Coefficent
DIA = Bullet Diameter
GR = Bullet weight in grains
BULLET = Type of bullet
BUFF = Buffalo Bullet Co.
LYM FN = Lyman flat nose cast bullet
GR = Grains of powder in charge
RS = Grade of Pyrodex
MV = Muzzle velocity
TRJ 50YD = Bullet raise above line of sight
100 YD = Group at 100 yards
KE = Kinetic energy
BRL = Lenght of barrel