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Actual Bullet and Barrel Diameters

I've been working on a rifle that has developed disappointing velocity and it has been suggested that the bullets may be on the fat side of things. I got my micrometer out and started measuring and I get .2642 to .2644 with almost all hitting .2643. Since I have never measured bullet diameter before I have nothing to compare it to. Is this fat for a .264 bullet or about average ? Who makes skinny bullets ? Who makes fat bore barrels if my bullets are fat ? Who make skinny bore barrels ? The more I learn the less I'm sure of my knowledge :).
 
It is not uncommon for rifle barrels to vary as much as .0003 inches in bore diameter from breach to muzzle. Competition barrels can be expected to be held to a higher standard, typically within .0001 inches. Combine that with the allowable tolerances in bullet manufacturing and there's no telling what the final relationship between bullet and barrel will be.
If you're looking for the most accurate rifle you'll need to look into lapping the barrel and measuring every bullet used in any reloading session to maintain consistency.
If you're using a caliper you can't expect much in the way of accuracy. Use a micrometer.
 
I'm not looking for competition accuracy in my hunting rifles but I do want half minute accuracy and fast. Never had too much energy down range on big game and the shorter the time of flight the less wind pushes the bullet. I may try competition at some point but I have more wants that I got gots :).
 
cmillard said:
is there a pressure ring on the bullets?
As I userstand it all bullets have a pressure ring from when they are formed but I simply found the fattest point to measure which was right above the boattail.
 
Daveinjax said:
cmillard said:
is there a pressure ring on the bullets?
As I userstand it all bullets have a pressure ring from when they are formed but I simply found the fattest point to measure which was right above the boattail.
Boat tail and VLD bullets have no pressure ring. Flat base bullets have a pressure ring.

My Bib's 25 caliber BT bullets measure .2575. They aren't fat. The "fattest" point will be directly above the start of the boat tail. If your bullets were "skinny" you would have little velocity.
 
Thanks JRS . I just walked back in so I am now going to measure samples of all the 7mm bullets on my bench to see what kind of spread they have. Before I went to lunch I was measuring some 7mm Berger classic hunters and vlds. The classics were running from .2840 to .2844 with most hitting .2842 and the one vld I was starting to measure read .2848. Going to check that some more and then check the Nosler BT's and Hornady SST's. I'm not too sure of my accuracy since it's ball head on one side of the micrometer so I have to play with the bullet position to get it just right. I think I'm pretty close though because I'm able to repeat the measurements.
 
Below is a Hornady 170 grain Flat Point designed for a 30-30 and is .3075 below the cannelure and .2995 above the cannelure. So it depends on who made the bullet and their tolerances in manufacture.

170grain004_zps96343ebf.jpg


170grain003_zpsa4974651.jpg


And normally when kicked in the seat of the pants when fired the bullet is going to conform to the size of the bore.
 
So I measured the 7mm bullets I have on hand. The Nosler 7mm 140gr BT's had the smallest diameter at .2837 to .2839 next was Hornady 7mm 139gr sst's at .2840 to .2841 , then the Bergers at .2841 to .2844 for both the 168gr classics and vld's. Most of the berger measurements were .2842. I measured six bullets each and spun them around and measured three times each. All the bullets measured varied approximately .0001 over the three measurements in the different points around the bullet. Not perfectly controlled but it gives me a good general idea of what the averages are. Now I definitely want an inside micrometer to measure barrels at the muzzle. I don't have a selection of 6.5's to get a feel if the Matrix are really on the fat side of things but I suspect that they are.
 
It's a 6.5 saum and I'm comparing to peers. I don't think there are any manuals listing it and I have a longer throat than most. I built mine on a WSM M70 action not a Remlin but I ddon't want to go into the particular rifle and chambering that has me wanting to know about bullet diameter and barrel bore diameter and their relationship. I want to learn about the relationship of the bullet diameter and bore diameter. Their tolerance ranges and effects.
 
I can't tell from your post(s) or I missed it; have you slugged your barrel so that you know what's the actual bore ? This is very important in shooting cast bullets and I assume it is equally important in shooting jacketed.
 
BEEN THERE DONE THAT MOVED ON SHOOT A LOT OF 6.5 BUT NOT A SAUM NO MORE!!!!!!!!!!!!!!! NO LUCK AT ALL TO FINIKY FOR ME
 
I had one made up 5 years ago before all the hype. Others had before that. I also did a 25 saum 2 or 3 years prior to the 6.5. I still shoot both.
 
To answer your question, the barrel has 2 dimensions, the bore, which is the 'calibre' of said barrel, and the grooves, which is bullet diameter.
So, for a 7mm, the bore is .276", and the grooves are .284". Both have a manufacturing tolerance, as does a bullet, most bullet makers keep their bullets to be +/- .003" nominal groove diameter.
The tolerance for barrels is tighter, bore and groove diameter is held to +/-.0003", and most are air guaged these days.
There is also a third 'reference dimension', which is the number and width of the grooves cut/impacted/broached into the steel, but this is not regulated, any number of grooves and widths can be used though, as most manufacturers choose their own sizes and numbers of grooves.
Hope this helps.

Cheers.
:)
 

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