16ga.com ~ View topic - Roll Crimps and Overshot cards/Tight Seal

Joined: 04 Mar 2019 Posts: 1837 Location: Central ND

So I did a little work with roll crimps and this load that I 'think' might have a little powder migration.

In one batch I tried using a Precision Reloading 12 ga. Tight Seal. In the other batch I tried a 16 ga. .028" overshot card. These were placed between the powder and the SP-16 wad.

The load:
Federal 16 ga. hull cut down to 2 1/2"
CCI 209 Primer
23.0 Grains 800-X
Remington SP-16 wad
1 1/8 oz.
Roll crimp

Tight Seal loads averaged 1220 FPS with SD of 14 FPS and the ES of 34 FPS. Pretty solid.

The overshot card loads averaged 1218 FPS with SD of 34 FPS and the ES 85 FPS. Pretty bad.

Something tells me that the overshot cards were messing up the chronograph. So I am going to do this again and change a few things so that the cards aren't influencing the readings.

I also shot just regular fold crimped loads (same as above just fold crimped).

Federal 16 ga. hull 2 3/4"
CCI 209 Primer
23.0 Grains 800-X
Remington SP-16 wad
1 1/8 oz.
Fold crimp

Average FPS 1252, SD - 12 FPS, ES - 32 FPS

30 FPS difference in the fold crimp and the roll crimp loads isn't a big deal or a surprise.

The last time I chronographed the fold crimped load (same shotgun/chronograph) was 5 years ago and the average velocity was 1264 FPS. So that matches up pretty well. That was a different lot of powder also. That is with no overshot or tight seal between the powder and the SP-16.

The load through the pressure test rig back in the late 1990's when the load was developed had a velocity of 1277 FPS. So things match up pretty well, no surprises.

Joined: 05 Nov 2010 Posts: 26 Location: Southwest Arkansas

So did you notice any powder migration or did the over powder cards/Tight seal work and prevent that from happening? Still new to reloading shot shells. Federal hulls are supposed to be straight and the SP 16 wad is supposed to be tapered. I guess this is why the over powder cards. Just trying to learn....Thanks....Bobby

Joined: 04 Mar 2019 Posts: 1837 Location: Central ND

The SP16 wad is for Remington hulls, which are not tapered but they are smaller internally than Federals and Cheddites.

There aren't a lot of options for 1 1/8 oz. loads so you pretty much have to use the SP16.

Joined: 05 Nov 2010 Posts: 26 Location: Southwest Arkansas

Joined: 04 Mar 2019 Posts: 1837 Location: Central ND

SP16 wads are a perfect fit in Winchester CF hulls.

FYI- I believe if you put anything on top of powder between wad it increases your pressure significantly. Read that somewhere. I think they even tested thin plastic baggie material.
Just be careful.

Joined: 04 Mar 2019 Posts: 1837 Location: Central ND

Purple16,

Glad you mentioned it and just to clear that up.

A fellow put a square of plastic (no idea how thick the plastic was) on the hull mouth and then inserted the wad pushing and trapping the plastic between the wad and the hull. Depending on how big this 'square' of plastic was, you will create more friction and probably create a better seal. Both friction and a better seal WILL increase chamber pressure.

Tight Seal is nothing more than sheets of tyvek cut into discs. Tyvek is porous and is cut exactly 0.685". The I.D. of a Federal hull is about 0.690" which makes it impossible for Tight Seal to make a better gas seal, but it will stop migration of powder.

Overshot cards placed under a wad will not seal better than the plastic wad. The 16 gauge card wads I have (Butler) are sized at 0.670", again making it impossible to form a better gas seal.

Both methods I have chosen to stop the powder migration were proven years ago NOT to increase pressure. I know that, because I was the guy that did the tests.