Understanding Crimping with Seating Die

[JeepHammer]

With respect, I beg to differ.

Every Marine Corps M40 Sniper Rifle (A1 through A4) is hand built from blank, semi-finished parts,

Every rifle is proof tested, Function tested, and accurized.
Every rifle has it's own load for that specific serial number.

We hand loaded EVERY ROUND for the M40 Marine Sniper Rifle, for that SPECIFIC rifle,

And EVERY round the primer was staked in place,
And case mouth had a 'Factory' type crimp die crimp the bullet into the case,
(The type that contacts the shell plate to generate the crimp,
Instead of pushing down on the case to make the crimp.)

Not only was every round crimped at both ends,
Every round was checked to make sure it was concentric,
And every bullet and primer got sealed to the case.

We also built the Marine Corps match rifles and ammo the same way.

 

[Road_Clam]

I don't crimp any of my rifle loads as all I shoot is single shot precision generally at milder velocities. I do however put a strong crimp on my .460 s&w mag pistol rounds. The 200 gr FTX bullets are getting launched at about 2100 fps , and the recoil is enough to potentially allow bullet creep from unfired rounds that are in the cylinder. Loading straight wall pistol revolver on my RCBS single stage is a PIA as it is , so I don't need and extra crimp step. I seat and crimp all in one step.

 

[DaleA]

We hand loaded EVERY ROUND for the M40 Marine Sniper Rifle, for that SPECIFIC rifle,

So each M40 Marine Sniper Rifle out in the field gets it's own ammo loaded for that specific rifle? And the ammunition for rifle serial number 123 is loaded different than the ammo for rifle serial number 456?

 

[HiBC]

On loading for the Marine Sniper rifle:

I have no reason to doubt what you say is true,

I wonder if maybe putting the emphasis on precision identical chambering might reduce the variability of ammunition requirements.

Perhaps then carefully crafted ammo within control limits could be expected to perform adequately.

Maybe reject more rifles?As in,the rifle must deliver "X" performance with the Sniper load before it leaves the shop?

Anyway,interesting.Seems like a logistic nightmare .

 

[Bart B.]

Jeep H.,

What's the objectives, conditions and standards for accuracy testing M40's? If it's done the way so many people do, a dozen people doing the tests will get a dozen different charge weights and cartridge OAL's for the same barrel and set of components.

Crimping case mouths into bullets????? Whose idea was that? No center fire rifle I know of producing best accuracy and velocity spread results does so with crimped bullets.

Can hardly wait to see the M40's accuracy standards with the ammo you loaded......

And if every round is "concentric," bullet runout is zero and its long axis is perfectly aligned with the case axis. How do you do and measure that?

HiBC ponders:

I wonder if maybe putting the emphasis on precision identical chambering might reduce the variability of ammunition requirements.

I don't think so. Having observed the same lot of ammo made on two Dillon 1050's shot in 20 to 30 rifles from around the world, all with different chamber, bore and groove specs yet shot about 1/2 MOA at 600 and under 1 MOA at 1000 yards, at worst, reasonably assembled ammo will do that. No military "sniper" rifles of any vintage I know of will do that well accuracy wise with any ammo. No sniper rifle specs I know of are that tight.

Sierra Bullets doesn't work up loads for each test barrel checking bullets for accuracy; they use the same recipie for all component lots. I doubt anyone shoots them as accurate as they do. Their cannelured bullets are tested without being crimped in cases; accuracy suffers with such bullet deforming practices.

A hundred or more chambers can easily be made virtually identical with the same finishing reamer before it needs sharpening when a roughing reamer is first used. So can barrel bore and groove diameters be made to .0001" specs.

One web site states that the M40 will shoot .35 MOA with a barrel life of 10,000 rounds; some as many as 20,000 rounds; no test range nor MOA meaning (average, mean radius, etc.) was mentioned. Sierra Bullets' .308 Win. test barrels open up to that level at 200 yards after 3,000 or so rounds; their test barrels are the best available. Some folks use rubber numbers for ammo that can be stretched to the limit of their imagination.