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What Is Free Bore:
Free bore (aka: leade) is just that, it is the area ahead of the bullet ogive (throat) in a rifle barrel to which there is no rifling lands, once the cartridge is fired the bullet travels freely in the barrel until the bullets ogive contacts the lands of the rifling, hence free bore. The leade angle is the angle cut by a chambering reamer on the very end of the rifling lands. This allows the bullet to begin its engraving into the lands on a relatively gentle angle. All centerfire rifles have a free-bore area and handloaders can take advantage of this with prudent reloading skills.
(See Detailed Image Below)
Why Add More Free Bore:
The case for free boring is made this way, if you have a bullet seated deeply in a rifle cartridge case, the bullet is actually decreasing case capacity which in turn lowers the over all velocity of that imparticular bullet and cartridge case loading.
By adding more free bore, the bullet is then able to be seated out further thus increasing the case capacity which in turns allows you to add more powder to the case and thus an increase in velocity, usually quite a substantial increase in velocity at that.
Why Add More Free Bore:
The case for free boring is made this way, if you have a bullet seated deeply in a rifle cartridge case, the bullet is actually decreasing case capacity which in turn lowers the over all velocity of that imparticular bullet and cartridge case loading.
By adding more free bore, the bullet is then able to be seated out further thus increasing the case capacity which in turns allows you to add more powder to the case and thus an increase in velocity, usually quite a substantial increase in velocity at that.
How Much Can It Help:
Usually increases are substantial to the point of standard calibers will be within reach of magnum velocities and magnum cartridges really get to actually earn the name magnum.
Important Points To Consider Before Free Boring:
To gain the full potential of adding more free bore to your rifle there are several issues that you must consider before the process.
1. You must handload your own ammunition.
2. Do you want to limit bullet weights in this rifle for optimum accuracy.
3. Will the magazine box in this rifle have to be altered to handle the longer ammo.
4. Will the increase in velocity that you gain in this process substantiate all the above.
Commercial Version:
All custom Weatherby rifle cartridge chamberings should be free-bored, rifles manufactured by Weatherby for Weatherby cartridges are free-bored, as this is how they achieved higher velocities years ago. Clymer reamers carry a full line of throating reamers.
Bullet Selection:
1. Bullet selection determined by rifling twist rate for proper bullet spin. A good rule of thumb is that the heavier and longer a bullet is, the faster the twist rate needs to be to stabilize the bullet in flight, therefore a lighter shorter bullet needs a slower twist rate to give proper bullet spin for correct flight.
2. Bullet selection determined by bullet construction. Today, bullet manufacturers to stay on top of what the shooting public wants, offer bullets with different construction for different uses. A good example of this is the Hornady bullet line up which offers their V-MAX for varmints, SST for deer and larger game animals and the A-MAX for target work all of which are very accurate with high ballistic coeffecients.
Bullet Precision:
How does anyone really know how precise a bullet is? Well short of x-raying the bullet or using a juenke machine you don't, but you can sort out most bad bullets by weighing them on a very accurate scale.
While bullet manufacturers are very close today of creating perfect precise bullets the occasional bad bullet can be sorted out. Many reloaders still overlook the reloading value of using scales for their accuracy and ease of use for bullet sorting.
When weighing bullets seperate them in increments of 1/10 of a grain. The reason for doing this is that the bullets components when assembled can create slight air pockets or antimony differences depending on the bullets construction which will change the bullets overall weight.
Bullet Seating Depth:
Bullet seating depth has a great impact on rifle accuracy, which directly affects maximum cartridge overall length. The bullet seating depth for each individual rifle free-bore area and bullet varies and should be set accorgingly.
NOTE; Caution: Do not use this procedure for rifles chambered for weatherby cartridges as these rifles have extremely long throats or free-bore cut into the rifles bore.
Step 1. Insert a bullet into the neck of a unprimed resized case. Do not fully seat the bullet but seat it deep enough that it is gripped fully by the cartridge neck.
Step 2. Using a black magic marker or dykem steel layout blue, color the entire bullet.
Step 3. Insert the case and bullet into the chamber of the firearm and gently start to close the action. Stop as soon as you feel resistance.
Step 4. Remove the cartridge from the chamber, now look at the bullet, it should have well defined marks where the bullet contacted the rifling in the barrel.
Step 5. Continue seating the bullet deeper and chambering the cartridge until you only feel a slight amount of resistance when the bolt is closed completely. There should only be marks left on the bullet from the lands of the barrel.
Step 6. Now take another resized casing and with your bullet seating die set, repeat seating another bullet in the cartridge case to verify that this is your maximum cartridge overall length.
(NOTE) Never start working up a load with a bullet set against the lands in the barrel as this will sky rocket your load pressures.
Step 7. Shorten your cartridge maximum length by .06250" or 1/16" this is where you want to start to tune your load for seating depth.
(NOTE) Best overall accuracy, velocity, pressure uniformity and overall bullet performance will usually be obtained with most bullets seated from the barrels lands between .062" - .005".
Checking Accuracy
Once you have loaded a round of ammunition for your rifle there is one final step that you can take that helps eliminate fliers before you go to the rifle range and that is checking bullet run-out.
Bullet Run-Out:
Checking bullet run-out is nothing more than gauging the accuracy of the bullets alignment with the cartridge case. It is this one simple task that can make or break 1 inch groups or tiny 1 hole groups.
RCBS CaseMasterÆ Gauging Tool.
This tool is simplistic in design and easy to use and a must for diagnosing cartridge problems that are not readily seen by the human eye. How the complete cartridge fits in the chamber and throat of the rifle barrel directly affects accuracy. The RCBS CaseMasterÆ Gauging Tool, measures case neck concentricity, case neck thickness, case length and bullet runout.
Just some information for you.
Respectfully
Mike
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