Best way to measure COL?

[mattri]

Have been using a set of calipers to measure COL. Seating bullets the same way, with the same preassure in the same dies sometimes results in different COLs. What is the most accurate way to measure COL?

 

[Cheechako]

mattri

COL will vary because of uneven bullet tips, even with bullets from the same box and lot number. A few thou difference between cartridges doesn't mean much. Even Benchrest cartridges will vary.

Some shooters will use a tool to uniform the meplats while others think uneven meplats mean little in regards to accuracy or ballistics.

Length from base to ojive is a nuther thing altogether. There are tools made to measure this dimension accurately. They vary in price from a couple of dollars to near $100. How nit-picky you want to get depends on how the cartridge will be used. For plinking, casual shooting, hunting, etc, using a seater with a properly fitted seater stem is all that you need.

JMHO

Ray

 

[zullo74]

COAL is the total length of the cartridge. Some bullets will be different specific lengths due to manufacturing tolerances. This total length is important if you are loading from a magazine. It can easily be measured the way you are doing it with calipers.

Now, OTOH, if you are trying to measure the length needed to touch the lands of the barrel, then a bullet comparator is what you need such as this one from Sinclair.... http://www.sinclairintl.com/product/5581/Bullet-Comparators

 

[tenring]

I use the Davidson base and nose piece from Sinclair to measure base to ogive, which is pretty accurate. Use it only in competition guns. For most hunting guns, measuring with your caliper will suffice, especially if you have a box magazine, and cannot exceed its length anyhow.

 

[BoydAllen]

Using calipers to measure from meplat to head is fine for verifying that what you are loading will fit in your magazine. For looking at a bullet's position relative to its point of contact with the rifling, one of the caliper attachments is the way to go. This is the length that I refer to when tuning a load, or setting up a die to replicate a load. Hornady sells attachments that use inserts to measure off of bullets' ogives, as does Sinclair. The Davidson sets are excellent as well.

 

[mattri]

Thanks for the replies and the link. Is there one comparator that is better than another?

 

[fdshuster]

mattri: A matter of choice for each individual. I bought the Sinclair "nut" years ago and it works fine. Then bought the clamp-on gauges that attach to the jaws of my dial calipers, available from Hornady & Sinclair, and I'm sure others also. they all work fine, but I do prefer the clamp-on. For me a little easier to get accurate readings compared to the "nut". The "nut" tended to wiggle around a little.

 

[BoydAllen]

I bought a nut, years ago, and got rid of it. Mine was probably unique. The hole for the caliber that I was loading was not even round. I currently have a tool that used to be sold by Stoney Point, that is currently being marketed by Hornady, and one of the Davidson sets as well. A friend has a Sinclair knock off of the Hornady tool. Any of these will do the job. I like all of them better than the nut. If I had to give one an edge, it would be the Davidson, because it holds the alignment of the loaded round from both ends.

 

[mattri]

http://www.midwayusa.com/viewproduct/?productnumber=231904

So this is what we're talking about correct? Use the correct insert, subtract know length of comparator and that gives an accurate COL?

 

[fdshuster]

mattri: We're talking about two different dimensions here. Cartridge overall length would be from the case head to the tip of the bullet, and is mainly a concern if/when feeding the rounds from a magazine, like an AR-15 that requires a maximum oal of 2.260". This dimension is easily measured with a dial caliper, but it will vary, sometimes by as much as .020", caused by the differences in each bullets oal, and especially so with hollow points with the jagged tip. Polymer tipped bullets are usually more consistant in their oal lengths. "Seated to touch" dimensions are from the case head to a point, somewhere on the ogive surface of the bullet where it contacts the leade (beginning) of the rifling. Different bullets have different ogive shapes, and will contact the leade at different locations on the ogive, and that's why it's important to know the actual point at which the bullet will touch, .020" off, .030" off, etc. This is the dimension that requires the Sinclair "nut" or the Hornady type gauges, as described in the Midway attachment. When this length is taken with the gauges, as they are attached to the jaws of the dial caliper, there is no math to do-- what you see on the dial caliper is what you get. Many consider the "seated to touch" length as the most important of the two since it relates directly to accuracy. Some bullets, seated to touch are outstanding, back them off and accuracy could suffer. Bullet seating depth also relates to pressures during firing: seated to touch = higher pressures. Give them some "jump", and it results in lower pressures. and velocities. The Hornady tool is described in detail, with pictures of the bullet/cartridge in a chamber, on this sites page that details powder measures, and other loading equipment. Also explained in most loading manuals, like the Lyman #49.

 

[Cheechako]

mattri

You never did say what cartridge you were shooting, in what rifle, and for what purpose. It may well be that your particular combination is one that would see little improvement in accuracy using the methods described. The Internet and the various shooting forums may lead you to believe that using a comparator, turning case necks, etc, will result in Benchrest accuracy when, in fact, they may do no such thing and simply result in wasted effort. Your time would be better spent in learning to read wind conditions and developing good bench techniques, and your money better spent for components to allow you to shoot more.

JMHO

Ray

 

[zullo74]

Boy Ray, you are quite the downer. :-\

 

[Cheechako]

Just a realist Joe. I have seen shooters spend tons of money buying Lapua brass, turning necks, uniforming flashholes, neck-sizing and seating with $200 dies, uniforming meplats, measuring bullet jump, striving for single digit SDs, and all of the other things that they read about on the Internet only to find that they still shoot 1/2 inch groups rather than zeroes. A good set of wind flags and good rests would probably have gotten them to the same point, a lot faster and a lot cheaper. :

In my youth I was a pretty good pistol shot. Beginners would come to me and ask where they could get a $200 pistol like mine, so they could shoot good too. I'd tell them to buy a $100 Ruger and a case of ammunition instead. When that ammo was gone they'd be a lot better pistol shot than they would have been with an expensive pistol.

Enough preaching.

JMHO

Ray

 

[mattri]

The above targets were shot at 100 yards.

This one was at 350:

These were all shot with a Mossberg ATR .270 ($240ish at the local walmart) and a Nikon 4.5-14 BDC scope. All loads were made with a Lee Aniversary kit, using the measuring system described above.

Appreciate all the replies so far and agree that chasing groupes with money isn't always the answer.

Have had a few errant lengths along the way and would like to eliminate that vairable. The Hornady set looks like a pretty economical way to go.

Thanks again for the suggestions, Matt.

 

[zullo74]

Good shootin' there Matt!

 

[Cheechako]

Matt

Those are damn good groups. Especially from a 270.

If I had a 270 that shot like that I would not mess with it. I'd weld everything in place, including my powder measure, seating die, and scope.

Ray

 

[mattri]

Thanks, I think the .270 is one of the most under-rated rounds out there. People know its a great deer round but it has a lot more potential than that. It shoots fast and flat, has modest recoil bucks the wind well. Bullet selection isn't as good as the .30s but there are some goods ones out there.