Home Forums Hunting & Shooting Ask The Gunwriters I need a straight answer........

Don't shoot the messenger.

Test, if you feel the need. Slagging the company is uncalled for unless you have proof to the contrary. I encourage you to try your own test.

I got a hold of Lee Precision and asked them about their claim re: crimping. Specifically, if they tested it, and if it could improve group size. Here is their response.

Hello Stephen,

Yes, crimping has been tested.

Crimping serves two purposes. The first and better known reason is to lock the bullet in position in the case. The second and lessor known reason is to uniform the start pressure of the cartridge. The start pressure is the pressure at which the bullet begins to move in the case. Assuming all the components of the cartridge are equal if the bullet begins to move at the same pressure from each cartridge this will result in a more uniform powder burn and acceleration of the bullet down the barrel. This results in the bullets leaving the barrel with less velocity deviation from one cartridge from the next. The smaller velocity deviation is the smaller the group size will be on the target.

Many bench rest and target shooters control start pressure by loading the cartridge to an overall length that places the bullet very close to or even in contact with the rifling. This type of ammunition is generally finger fed into the firearm. Loading like this is not always possible in all firearms and situations. There are limits to how long the cartridge can be and still fit in the magazine or feed through the action of the firearm. Crimping the cartridge mimics loading close to the rifling and results in greater accuracy in firearms that limits to the overall length of the cartridge the gun will accept.

Testing your own ammunition is easy. Load some ammunition with your pet load recipe. Then crimp 1/2 of the cartridges. The crimped ammunition will almost always out preform the ammunition that has not been crimped. I frequently get comments from the field of small shot groups that have gotten smaller when the shooter crimped their ammunition.

Thanks.

As a Journeyman Tool & Die Maker many of the dies and other work that I made had a tolerance of +/- .00002", that's plus or minus 2 tenths folks. What many don't realize is what a fine tolerance a tenth is, a particle of dust is two tenths thick. Just the very nature of loading ammunition makes achieving tenth tolerances in loaded ammunition no matter what kind of dies or technique. It is a total waste of time and due to cartridge fit in the rifle chamber, throat and leade precision and many other factors striving for that kind of tolerance in loaded ammo will not produce any significant measurable improvement in group size.

I expected this. Machine tolerances are an interesting sidebar, but what about the claim of consistent pressure? Has anyone tested it?

I tested it one a several loads in several rifles. Not many, but of those tested uncrimped shot better. To be fair all bullets had a crimping groove, and all were seated to put the groove at the case mouth. Lee's response sounds good to me, but I haven't been able to get better accuracy with crimping. One test was with the .30-30. Uncrimped shot best, Lee factory crimp second, and Lee roll crimp worst. One test, I don't remember which one, the crimped loads were much worse, but usually the difference was small. All testing was done with 10 shot groups at 100 yards.

Anyone else?

Except for in pistols crimped loads were less accurate for me. Roll crimping can increase run out especially if the case length is not completely uniform. I find the same benefits Lee is claiming by adjusting case neck tension. In a factory chamber I think the run out is less critical unless way out of spec. One test found that even the military O3A3 chambers would straighten out cases with .06 run out to a certain extent.

For a few years now I've straightened all my loaded ammo. I use to seperate ammo that came out .002 or less from ammo that had as much as .007 runout all of which I "straightened" to less than .001. I could not tell any difference often testing loads at 500 yds so I don't separate anymore.



Trystan