How Important is Neck Tension?

[stubbicatt]

FGuffey makes a a point. I think, re: bullet tension. At the moment of firing of a cartridge, as pressures build, doesn' t the neck expand away from the bullet before the bullet begins its journey down the bore?

Sure, the pressure necessary to kick the bullet out of the case and into the rifling is less than the pressure required to expand the neck all the way to the chamber wall, however, the pressure necessary to force that slug down the barrel is greater than that required to expand the neck. Right?

So perhaps neck tension serves a different function than holding the bullet in the case against combustion pressure?

[Texascoonhunter]

From my experiences as Quality Inspector on larger caliber munitions, case neck tension is really important. Loose projectiles will not allow consistent pressure build up before release of the bullet from the case. I cannot go into examples for privacy reasons, however test results on ranges show that low bullet pull pressures (gage in lbs of pull) results in lower chamber pressures, slower muzzle velocity (fps) and less down range accuracy. Consistent crimping will help ensure the best bang for your bucks.
Also if loading/firing pistol cartridges in a rifle, the sharp edge of a non-crimp case may hang on the edge of the chamber and cause problems chambering. I crimp everything I load.

[4runnerman]

Texascoonhunter-- From my little knowledge I have in F-Class shooting. Most will leave tension loose as to seat bullet when they chamber the round. And they are very accurate loads.

[Texascoonhunter]

4Runnerman, I did not mean you cannot achieve accurate shooting from non-crimp rounds. I do believe that handling, carrying, loading, unloading of hunting rounds that the rounds need crimping. With non-crimp rounds there exist the possibility of the projectile moving in or out of the case within above circumstances. Maybe at the range where the environment is control, you don't need crimping just for accuracy purposes.
In my previous post I was referencing experiences with Munitions larger than Small arm ammunition but I feel the same will apply to small arms.

[Brian Pfleuger]

Almost no one crimps rifle rounds that aren't for a semi-auto and even then it's not always necessary. I've never crimped a rifle round. I currently load for 8 different rifles in 7 different cartridges (all hunting guns of some kind) and I've not had a bullet move yet.

[Jimro]

The original Mk262 Mod0 77gr OTM ammunition was not crimped. Once in a while you would get a bullet pushed back into the case from a bad feed in an M16/M4. Adding the cannelure to the 77gr SMK and crimping fixed that problem with Mk262 Mod1.

However this is for ammunition designed for Squad Designated Marksmen needing ultimate reliability in war. For my Mk262 clone loads I don't crimp, bullet setback is very rare, and if it happens on the range I just load a different bullet.

Jimro

[Bart B.]

Note that some very accurate ammo has no neck tension at all. These are the arsenal match ammo whose neck inside diameters are a couple thousandths larger than the bullet and that space is filled with a sealer. Bullets are "glued" in and have at least 40 pounds of pulling force needed to remove them

Having measured outside neck diameters on several of them, then pulling the bullets, cleaning out the asphaltum black sealer then measuring the inside and outside diameter (to ensure the neck was the same size), it was easy to see how much clearance there is from the bullet to the neck. And bullets could be dropped in all the way to original OAL cartridge numbers with virtually no seating force needed.

Texascoonhunter, the most extensive test of crimped vs non-crimped very accurate ammo was conduced back around the late 1930's. Frankfort arsenal made two production runs of 30 caliber match ammo both with the most accurate bullets they had in stock. Half had crimped in cannelured 172-gr. match bullets and the othe half not crimped on non-cannelured match bullets. Uncrimped ammo shot 30 to 40 percent smaller groups at 600 yards. From that date on, all the .30-06 M72 match ammo bullets were no longer cannelured nor their case mouths crimped into bullet cannelures.

Several bullet making companies (including Sierra using their match bullets) have proved over the years that crimping otherwise accurate ammo degrades its performance. No decent match grade commercial centerfire rifle ammo has crimped in bullets. Any bullet that's had a cannelure turned or knurled in gets some tiny amount of unbalance; neither process moves/removes exactly the same amount of metal all the way around the bullet. At 150,000 to 250,000 rpms bullets make when the leave the barrel, the centrifugal forces on even slightly unbalanced bullets is catastrophic in the accuracy department.

Lots of benchresters and high power rifle competitors can seat bullets in their primed and charged cases with bare fingers. Release force is a pound or two. They win matches and set records all the way from 100 to 1000 yards with very light bullet release forces.

= = = = = = = = = =

However, if the reloaded or handloaded ammo has some boo-boo's in its components and/or the setup and tools used to make it, crimping bullets in place often improves its accuracy. And this is the situation for what Dick Lee was talking about in his marketing campaigns for his factory crimp dies. They did help bad ammo shoot better. No crimped case mouths on any given centerfire rifle bullet has ever shot it more accurate than properly made handloads or reloads without a crimp when both were properly tested several times wherein the results were the same for each test.