Crimping and pressure

[warrenb]

Does crimping increase pressure? I'm thinking yes but don't believe I have read it anywhere directly. I'v crimped all my reloads so far with Lee factory crimps.
I'm thinking of giving it a miss and seeing what happens.

 

[B]

It almost always does, but not neccesarily dangerously. Some slower powders benefit greatly from a crimp. Keep in mind my experience is largely magnum pistol calibres.

 

[oldfart]

I have used the Lee collet dies to crimp on 06 and 375h/h and do not see much difference, over my chrono, in velocity. As far as pressure goes? Lee state you get unifority when crimping with ther collet dies. From my limited experience for hunting loads little if any difference.

 

[mihasic]

Sometimes it does, sometimes it does not. I tried to study this question and assembled series of identical cartridges, the only difference was crimp or no-crimp. I found out that for full-scale loads crimping did nothing - same velocities, same velocity dispersion, same grouping. On the contrary, for reduced loads the difference was very pronounced: in my 30-06 for very light 100-grain hornady bullets over 20.0 grain IMR SR 4759 with crimp I got 1800fps, whereas without it was only 1550. I attribute it to increased pressure that assures better powder burning. One more sign of increased pressure was that with crimp the case neck remained relatively clean outside and without the neck was all covered with soot.

 

[warrenb]

The reason I asked was that my 243 showed slight signs of flattened primers at just a couple of grains above recommended starting loads. This occured with h4350 with 87 grain vmax and h4895 with 55 grain BTs.

I think its likely that my gun likes a little less powder but it got me thinking. I was using Hodgsons web site for my data but I have other data sources which state the starting loads for the combos above which are a few grains less than Hodgsons.

thanks for the info.