Crimping and Accuracy?

[Jeff82]

Does anyone know the extent to which crimping affects accuracy when using cast bullets? I usually need to apply a crimp to my cartridges in order for them to feed well in my Marlin 1894C, it seems like my accuracy improves when I don't crimp (the gun jams though). Can anyone explain why this might effect accuracy?

[Djones]

Could your crimp be deforming the boolit? Have you pulled a bullet with and without a crimp to measure the diameter?

that is my first guess at what could be going on.

Maybe powder. What powder bullet etc?

[Jeff82]

I've measured crimped and non-crimped bullets and they measure the same. I'm using Lee cowboy bullets with a 0.359 diameter, a bhn of about 14 and lubed with NRA Alox. They clock at about 1,450 fps.

[Airman Basic]

Seems to me that cartridge length and different headstamps, affect crimp consistency, which affects accuracy. I trim handgun brass when I scrounge or buy new, to the same length. You only have to do it once. It helps my accuracy.

[Djones]

.359 is too small for my 1894c. I size to 0.361". What does your barrel/throat slug?

[W.R.Buchanan]

On a magazine fed rifle you kind of need to crimp the bullet in place or the recoil can drive the uncrimped boolit back into the case. You don't want this and it has nothing to do with accuracy, it has to do with a pressure spike caused by the boolit being set back into a case.

With a .357 and loads in the 1450fps range this would be a problem. .357 is a 35,000psi+ cartridge and the kind of pressure spike we are talking about could be 10-15,000psi more. Hence the problem.

You'll notice that the crimp groove on your boolits is basically a step tapering out to the OD of the Boolit. When properly crimped this step will not allow the boolit to be set back as the case mouth hits the step.

The crimp also provides a bit of resistance that gives the powder charge a little more time to build pressure. This is especially helpful with powders such as H110 which can be difficult to ignite under cold conditions.

This is what your crimps should look like. This is a .44 Special but the .357 should look exactly the same way as long as your boolits have the same type of crimp groove.

As far as accuracy goes in the case of the .357 the amount of effect a crimp has is minimal and especially so in a rifle. There are a bunch of way more important things to look at. However, the reason I say this is because if you crimp consistently all the time,,, you won't have this problem and can put your attention on other matters.

Randy

[cwheel]

And to add to the above, consistent crimps come from trimmed brass that are all the same OAL.
Chris

[9w1911]

OAL is what makes 1894s work right

[Jeff82]

Thanks for the input. What OAL are you using for 357 loads?

[dragon813gt]

I load mine to almost max at 1.580. Haven't had any issues w/ this length and bullets sized to .359 in my 1894C. I apply a heavy roll crimp as I use H110.

[W.R.Buchanan]

actually a nice .040-.050 chamfer on the chamber mouth is what makes them run nice. They become real "unfinicky" after you do this to the gun.

Randy

[salvadore]

I agree with cwheel, my 32 wspec. is far more accurate when my brass is trimmed. You can feel the difference, the crimp pressure feels the same.

http://i299.photobucket.com/albums/mm297/farcla/DSCN0694_zps129c3008.jpg (http://s299.photobucket.com/user/farcla/media/DSCN0694_zps129c3008.jpg.html)