Long-throating barrels can provide higher velocities

Shooting Industry, Feb, 1990 by William Schumaker

Many hunters and gun owners place unrealistic emphasis on velocities their rifles are capable of. Shortly after WWII, the large case capacity "Weatherby" cartridges commenced their trek to near immortality. At that time, many shooters didn't realize that chambers such as the .30O Weatherby magnum were long throated about 3/4-inch (called free-boring). This means the rifling was cut away at the throat of the barrel to allow bullets to jump 3/4-inch before engaging the rifling. This, coupled with the high velocity, gives them a double recipe for shorter barrel life and accuracy loss.

Long-throating was done to soften that initial high pressure surge so large powder charges could be burned safely and progressively as the bullet traveled through the barrel. Many custom gunsmiths and wildcat cartridge designers who,for many years, had been expanding and sharp-shouldering cases for greater capacity, had also been longer-throating or partially freeboring as an additional safety factor for years prior to the Weatherbys

Many gunsmiths had their hey-days during the WWII follow-up years when new rifles and actions were scarce and countless Mauser M-98s, 1903 Springfields and 1917 Enfields were everywhere. My own first .300 Weatherby magnum was built on a 1917 military Enfield, chambered and barreled at Weatherby, with their regular 3/4-inch free-boring. Our shop sent out many more guns for customers, many were M-70 Winchesters .270s converted to .270 Weatherby magnums.

In the meantime, gunsmiths were acquiring these magnum reamers and doing conversions. At that time it was a common practice to get chambering reamers without integral throating. A separate spiral-fluted throating reamer for each caliber was standard gunsmiths' equipment. Chambers were throated either in a normal fashion or to handle bullet lengths the customer intended to use.

Minimum Throat Length

in Vogue

The most common .22LR chambering was a minimum chamber with the barrel throat cut to require the bullet to be pushed slightly into the lands upon The theory was: "the train engine is on its tracks, ready to be pushed without slippage." Copper jacketed centerfire rifle bullets were most often seated out to just contact the beveled lands at the end of the throat when the cartridge was chambered. Hunters require ammunition that fits into magazines with ample clearance. Target shooters can single load in their slowfire courses and therefore use extended bullet seating if they wish.

Military Rifle Throating

Ludwig Olson's book, Mauser Bolt Rifles," third edition, pages 104-105 treats the reason for partial long-throating. This was done for positive military functioning, due to the assorted manufacturers of ammunition having bullet shape and seating variations. A throat that was too short could tightly wedge a bullet into the rear part of the barrel upon bolt opening, putting the weapon out of business

Olsoti's information states an excessively long throat could cause sloppy barrel entry, deformation, yawing of the bullet in flight and general inaccuracy. These factors also apply to hunting rifles. Opening a bolt with a bullet stuck in the barrel dribbles powder throughout the action and bolt and puts the hunter out of business too. Usually it means a trip home or to a gunsmith.

Factory Standards

for Reamers

Factory rifle chambers are throated to handle all factory bullet weights, lengths and shapes as best as possible. Chambering reamers manufactured for the gunsmithing trade usually have integral throating and accomplish the same thing unless ordered otherwise. When striving for varmint and target accuracy we like the reamers without integral throating. Then, a separate throating reamer is used to cut a minimal throat.Then as the throat wears, the bullet seating can be extended. This gives a lot of shooting without the accuracy-damaging bullet jump of long throats.

Accuracy Proof Difficult

I've fired thousands of rounds with various rifles, with throats varying from new and ultra-short to worn out with long freebore. While I've had some surprising results with newly-cut long-throated barrels, I've never been able to determine that these out-performed similar short-throated barrels. Accuracy always fell off when the rear portion of the rifling in front of the chamber became worn and eroded.

Our shop has done "set-back" jobs on a number of varmint rifles which were originally fitted with several inches of receiver-diameter barrel in front of the action. This permitted us to remove the old barrel shank plus about 1-1/4-inches extra. We then recut and threaded a new shank and rechambered the barrel forward into the rifling that had not been eroded. In all instances, performance was improved. One such set-back barrel shot better than with its original chamber. This gives me more evidence that long-throating offers little or nothing except for the power-house magnums. The game you shoot can't determine the difference between 2850 fps and 3100 fps. Gunsmiths love more rebarreling work ! Use Correct Powders