Cannelure question

[skobrien]

I'm new to reloading and when I seat the bullet for my 270 ammo I see that the cannelure is above the end of the case, but the overall length of the round is correct. Am I loading correctly? Does the cannelure have to be aligned with the top of the case even if it makes the round shorter than the spec?

[condor bravo]

I would say that it is pretty much your own choice on this one. Nothing says that your cartridge has to be the indicated OAL, nor that the bullet must be seated to the cannelure, thereby shortening the round slightly as in your case. If you want to decrease bullet jump before engaging the rifling, go with the OAL (or in some cases even longer if the round will function from the magazine and chamber properly) and apply just a slight taper crimp if necessary into the shank of the bullet to remove any flare. Or, if you might prefer a better appearance with a cannelured bullet (cannelure really not necessary with a .270), apply a light roll crimp into the center of the cannelure. Possibly not much difference in accuracy will be noticed one way or the other. Roll crimping into a cannelured bullet is primarily intended for heavy recoilling rifles to prevent possible bullet set back of unfired rounds in the magazine during firing.

[Marco Califo]

No. It is safe and sometimes desirable to ignore the cannelure, particularly when it is not compatible with your OAL.
You do not need a cannelure for 270. It is mostly used for semi-autos. Buy your next 270 bullets with out the cannelure.

[skizzums]

I load .303/7.7jap bullets for mosin nagant. Of the bullets have a cann, its almost a 1/3 of an inch above the case mouth. I do get a little lucky with these since my expander is only .3005 and my bullets are .311-.312, I get great bullet hold "some call neck tension" without a crimp. If you have have hold issues and not wanting to crimp outside the cannelure, you can chuck you decapper pin in a drill and spin with Emory cloth the bring it down .005 or so, that way your bullets should have plenty of tension w/o a crimp. Don't worry about where the cannelure is, so long as you have sufficient bullet base seated into the case mouth, I usually try to get 1/3" seated at least to know its not going to get shifted off course during chambering. But also don't get overly hung up on OAL, test it out both ways and you y not find a difference seated deep, so long as your engaging the rifling before the bullet fully exits the mouth, you should stay shooting straight, if that makes sense.

[PA-Joe]

How did you determine the correct OAL? Are you using the actual bullet maker's OAL? If you are using a generic or actual measured length then the cannelure may be exposed.

[skobrien]

I use the diagram in the Lyman manual to determine correct OAL. As I said, I'm new to reloading. I thought all rounds of the same caliber had to be the same OAL.

[jmr40]

I thought all rounds of the same caliber had to be the same OAL.

Nope.


Personally I don't give OAL a lot of thought. I load my bullets so they will feed from the magazines in my guns and chamber without the bullets hitting the lands. I couldn't tell you what the OAL is on most of my loads. In other words they are as long as possible and sometimes a little longer than recommended, sometimes a little shorter.

Once I start shooting I may determine some need to be seated a little deeper to get best accuracy, but that is very rare. By starting out as long as possible I know there is only one direction to go and it is a lot easier to seat the bullet a tiny bit deeper after it is loaded than make it longer. The OAL length and how deep they are seated will vary by the individual bullet. Even within the same weight different brands are shaped differently.

[Pond, James Pond]

I use the diagram in the Lyman manual to determine correct OAL.

Being relatively new to reloading I think this is absolutely the way to go if in doubt so wise move there and wiser still to not shy away from seeking clarification.

A couple of things limit/influence my OAL when loading .308: mag length as my rifle has detachable box mags and chamber size, particularly the distance to the lands of the rifling.

The latter never really featured in my calculations before I got a chamber gauge and can often be limited by the former anyway as the box mag is often shorter than the OAL I might ultimately choose, all things being equal.

Like yourself I once bought some 150gn Hornady FMJs that had a cannelure. I asked the same question and the answer was ignore it for OAL and don't a crimp for a bolt gun anyway...

I say load them as per manual and shoot them. When powder charge alterations no longer make any improvements to accuracy, then you can think about playing with the OAL.

Good luck!
(Reloading is fun.)

[mehavey]

Bullets may be of the same caliber (.277) but of different weight (and therefore length);
AND may even be of the same weight -- but different shape (and therefore hit the rifling differently).

EX: Speer's 100gr 270 bullet actually requires a shorter OAL (3.100") that the heavier/longer
130gr GrandSlam (3.240") because lighter bullet has more of a blunt shape)

Lyman gives us a "general" OAL for "general" bullet types, but the manufacturer
(e.g., Speer, Hornady, Nosler, etc) gives you the exact recommended OAL for their specific
bullet. (And if the bullet has a cannelure, that tells you the manufacturer's OAL.)

Now here's the fun part, you don't have to (nor even necessarily want to) crimp bolt
action bullets. Properly-sized/loaded cartridge neck tension is more than enough.

As a "GENERAL" rule when nearing MAX, reduce your load 2% for every 1/10 of an inch shorter
OAL that you seat a bullet from any particular load manual

[T. O'Heir]

You do not need a cannelure for semi-auto's either. You can forget the cannelure altogether and use the mag length like jmr40 says or 3.340"(max OAL with bullet given in my old Lyman manual.).

[Unclenick]

Originally Posted by skobrien

I use the diagram in the Lyman manual to determine correct OAL.

If you look at the individual .270 loads in the Lyman manual, you will note they have different lengths for different bullets. These are listed at the top of each set of load data. The big diagram at the beginning of the .270 load section shows the SAAMI standard maximum length for manufacturers to follow if they want to be sure all the ammunition they make fits all the magazines in different rifles chambered for the round. That number is 3.340" for the .270 Winchester. The SAAMI standard also has a minimum length for smooth feed. That is 3.065". Why loading manuals don't show that, I am not sure. If I authored one, I would include it.

The SAAMI drawing may be viewed here. The cartridge drawing is above, and the chamber drawing is below. These are manufacturing standards, not handloading standards, so your individual gun may allow you to work outside of them, but wait until you know more about what you are doing.

In the meanwhile, I would advise seating your bullets until the case mouth is nearing the top edge of the cannelure; say 2/3 to 3/4 of the way up the cannelure. It doesn't have to be exact, that's just how the bullet manufacturer intended it to be used. It makes a good starting point. Once you have learned how to control how far off the lands of the rifling your bullet ogive is, then you can start experimenting with non-factory seating depths. For now, just be aware that it changes the pressure a load makes, but that, done right, it can improve how precisely the rifle groups.

The illustration below shows why two bullet designs have different overall length in order to have the part of the ogive that contacts the rifling be the same distance from the throat (the thing that affects pressure). It's all about nose contour. As a result, the two require different overall lengths. The two bullets in the illustration are the same distance from contacting the throat (red labels).

[skobrien]

Thanks for all the great information. I guess I'm still in a bit of a quandry though. I seated my 308 and 270 bullets per the diagram and they seem to have shot fine, but wasn't getting the accuracy I would have expected. I guess I'll have to find out by trial and error what the correct seating depth is for the bullets I'm using.

[Marco Califo]

You can place a bullet on a sized case, just start it so it wont fall out, but DO NOT seat it, prime or charge the case.
Single load this inert cartridge, and close the bolt. It may take some effort, because you are pushing the bullet into its correct OAL, if you want the bullet to contact the lands of the rifling.
Eject the round. Measure it, and subtract ~15/1000". This is your COAL for that bullet, in that rifle. You may find better accuracy is @ slightly longer or shorter.
Next question is: Will it fit in the magazine? It should. Or, you may want to seat the bullet deeper, as long as you do not go shorter than published COAL. Deeper than that would raise pressures dangerously.

I found that one of my Savage rifles had a long throat and could chamber (and magazine load) cartridges longer than expected.
While another Savage wont chamber anything 1/1000 longer than spec.

[skobrien]

So I went back to my Lyman manual and I see that where they list Test Components they identify the case Trim-to Length which is different from the SAAMI spec. For example, for the 270 the spec is 2.540" but the tested length is 2.530". Why would anyone deviate from the spec for case length?

[Marco Califo]

Case length is a range, and one/100th of an inch difference can still be in the range. When you trim, you trim to the "trim to" length. That is the shorter number. Maximum case length, beyond which you need to trim, is the longer number. Case length between the two is acceptable.

[skobrien]

Thanks

[Marco Califo]

You do not need a cannelure for semi-auto's either.

I disagree. In some cases, the cannelure, and crimp, are useful. By auto-loader I mean FN-FAL and variants, for one, which are a military design and are "rough" on cartridges and ammo. The rough handling is inherent in the action of recoil, gas operated piston, heavy return spring, cartridge stripped from the receiver and slammed into the feed ramp, locking bolt, and violent ejection. I crimp most rounds I feed through my beast. The exception is 175 gr FMJ or OTM, and only because they have complete contact between the bullet bearing surface and the cartridge neck, giving adequate neck tension to hold the cartridge in spec during cycling. I do not want a bullet to get pushed back into the powder space of the cartridge in a $1,000+ gun. I bought some cannelured bullets, and extruded powders specifically for this rifle. But, I will put anything through my bolt guns.