How to fit a bullet to the rifle

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  • Last Post 03 April 2017
John Alexander posted this 02 April 2017

MarkinEllensburg posed this question in another thread.  I believe that a discussion on his question would be interesting.

"Thanks for adding to this conversation. Bullet fit, alloy choice and consistency in loading seems to be what you all are saying is the key to good results.It is probably a different discussion  but how should a bullet fit the throat? I would think that there is a difference between bore riding and non bore riding bullets and both must work some of the time."

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Ken Campbell Iowa posted this 03 April 2017

ha ... after 40 years of casting bullets .... I DON'T KNOW  ...

but my recurring fantasy is the bullet would look like it was molded in the throat and barrel proper ....  ... with the least sharp point that would stabilize the bullet at the distance desired .

next guy .....

ken

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RicinYakima posted this 03 April 2017

I am a military rifle match shooter. Others are happy with bore ride designs, I have had best scores with Lyman 308284 and 311291 in all my rifles. I just seat them long enough to be a press fit into the lead, and go practice.

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45 2.1 posted this 03 April 2017

Copied from my post in the Match Grade Accuracy thread:

MarkinEllensburg wrote:
   It is probably a different discussion  but how should a bullet fit the throat? I would think that there is a difference between bore riding and non bore riding bullets and both must work some of the time.

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Bullets wear the throat........ some, (depending on material, heat and alloy) wear it faster. It erodes into a irregular curvilinear tapered cone. There are specific points where the wear is fairly constant (this was determined from overlaying the results of 100's of impact throat slugs checking wear from different age rifles).... you fit those points. What you want is for the bullet to gradually (if anything that happens this fast can be called gradual) engage (instead of all at once as that limits the pressure/velocity/accuracy that you can achieve) and line up the bullet for a concentric fit in the barrel. Bore riding bullets do not fit this curve well and shoot reasonably at velocities less than 1800 fps in the match grade range. Non bore riding bullets contain many types and shouldn't be quantified unless described fully.

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Computer drawing programs such as AutoCad allow one to layer chamber/leade/throat drawings over the top of each other allowing critical areas to be identified and compared to the one ten thousandth of an inch. When you actually see what is going on, it is easy to design a bullet to fit (even a large majority of barrel throats) or check the fit of others. I have done so myself and have had various current and past mold makers produce them for public consumption. These have a very good reputation for accuracy.

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OU812 posted this 03 April 2017

The best bullet fit will not shoot accurately if powder charge is not correct. Get the powder charge correct and the better fitting bullet will shoot best. Hard alloy bore riding bullets should be round, snug slip fit at muzzle and seated inline with bore. I have experimented with fatter bore riders in my rifle and seen worse to no difference in accuracy...must have been that fatter caused too much pressure rise...needed slower powder. 

I know it is not mentioned nor recommended much, but 748 ball powder works very well in my 223. The muzzle blast also sounds more lazy or softer than the quicker burning stick powders. Some say that 748 is sensitive to outdoor temperature swings...I shall see.

Once you find the perfect powder you will need to keep pressure consistent. Neck sizing only is one way to keep pressures more consistent. 

I bump my bore riders and one thing that I have noticed is that some of the bullets fit die differently before bumping. Some are light slip fit and some must be tapped into die before bumping. After bumping all bullets exit die with near same resistance. Bumping helps keep pressures more consistent because bullets are now more consistent in size.

I know bumping sounds logical, but even this will not work if powder is either too slow or too fast or pressures changed because you have changed something from last accurate test. Such as inconsistent bumping pressure from one batch of bullets to the next or age hardening of alloy. These are just a couple of things that can cause inconsistency when shooting cast.

 

 

 

 

 

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OU812 posted this 03 April 2017

Cheating or Softer alloys such as 20-1 lead tin alloy obturate (spelling?) or form well to throat and barrel when fired, but velocity/pressure must be kept lower. Lower velocities are more wind sensitive ... heavier bullet and faster twist is usually needed.

Lead tin alloy hardness does not change much overtime.

I believe softer alloy bullets can benefit by bumping. Bumping gets bullets nose more inline. Have you ever bumped a 458 caliber, 500 grain 20-1 alloy bullet? I bet it will help shoot more accurately.

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