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Joined: 07 Sep 2011 Posts: 567 Location: wheeling, wv

Probably been discussed here before, but-- In a low pressure 2 1/2" load listed with a roll crimp, would a regular fold crimp increase the pressure to any significant degree? Got a Mec short kit for Christmas and may load some shells up tomorrow since it appears the weather is going to suck.
Running short of SG-16 wads, but have a bag of Z16, but the load calls for roll crimp.

https://ballisticproducts.wordpress.com/2012/12/14/does-a-shotshell-roll-crimp-raise-or-lower-pressures-versus-a-fold-crimp/

I guess this states the obvious, but it looks like velocity changes correlate pretty well with pressure in these comparisons from BPI. So, the sweeping (but unproven) conclusion is: For the same load with all else equal, the roll crimp reduces pressure, and also it reduces velocity, but in lesser proportion to pressure reduction. It seems to say that if loaded to the same velocities by changing only the amount of powder, leaving all else the same, roll crimps would offer the same exterior ballistics with slightly lower pressures. I think I've crawled out on the limb of speculation far enough for today.

I wish I had Hartin's original info on his crimps, but I recall pressures and velocities with his crimps varied less, and less predictably than this roll crimp data. Was this roll crimped data specially sorted? Woops! more speculation, sorry.

Joined: 28 Mar 2008 Posts: 1460 Location: Eagle, Nebraska

In every load that I have had tested, my roll crimps were less pressure,
velocity unchanged.

Hootch has it right.

Roll crimps will produce slightly less pressure, but the velocities will stay very close.

I have no idea what BPI did with the loads but, their crap is way off base, but that shouldn't be any surprise. You can't roll crimp a 2 3/4" hull and compare it to a fold crimped 2 3/4" with the same components. There has to be some fillers somewhere along the way or you get the same results that they did. You should really cut the hull down to the proper length for roll crimping, then you can do an apples to apples comparison.

Joined: 23 Aug 2009 Posts: 295 Location: Southern Ontario

You give the best answers Mark!

Still using your loads you sent me years ago. Hope this site stays around!

Don.

Member Joined: 06 Oct 2007 Posts: 2346 Location: West MI

for years believed the opposite but after testing a bunch of fold/roll recipes found exactly what Hootch did.