For a low pressure 1oz load I'm migrating to, the closest bushing I have throws .2 grains less than the recipe calls for. Is that difference an issues? The outcome of the recipe is reported to be 5800psi and 1125fps.

Nitro 27
Win209
CB-4100-12
1 oz
16.5gr Clays
5800psi
1125fps

Bill, I'm not qualified to comment on the effects of 2 grains less powder. Others here can jump in. You might want to consider an adjustable charge bar and a digital powder measure. You can set the bar to get the exact powder charge you want and do the same for the shot. A one ounce shot charge weighs 437.5 grains.

Thanks Tom. I'm inquiring about .2gr as opposed to 2.0gr.

I measure 10x the throws along the way to make sure averages are in line.

Yes, sorry Bill. I left off the dot on the number 2

You can carefully file the hole in the bushing larger. Conversley, if it throws slightly more, you can usr tape or fingernail polish to lower it. Use a rat tail file. .2 light is nothing, your normal variation while loading will vary that much. I agree, a universial charge bar is great.

You're worrying about nothing. Shotgun reloading is not the same as pistol or rifle. If you can keep a + or - .2 grains you're doing really good. If you look at reloading manuals you see many loads go up and down 2, 3, or even 4 grains to get different velocities. My old 2006 Hodgdons manual doesn't show the 4100 wad, but all the loads with Clays have a 4 grain spread. At 5800psi you're at the low end. As suggested, take a file to the bushing. Even if you go a bit over you'd be perfectly safe and maybe better off. Try the next size larger bushing. I'd have to bet you'd still be under 7500psi.

As I have mentioned before when clays was hard to get I went to Clay Dot. The recipe I use is 17.5 grs. of clay dot
CB4100b wad
Win. 209
Ren. Nitro hull
7/8 oz. of 7&1/2
Comes out to right around 1175 to 1200fps and 5700lbs. pressure.
Crushes clays and kills phaesants.

Are CB-4100-12 and the "CB4100b" wads above the same item? Would think so, but my bag of 4100's doesn't have the "b" added.

I believe they are the same. Here is CBer contact info information@claybusterwads.com
Customer Service: 800-922-6287 they can answer your questions.

Just have to jump in on the recoil issue. I had a old SKB o/u I was shooting trap with and had a chance to buy a 34 inch unsingle barrel. It fit right on my receiver so I went out and shot 10 shells with the o/u then put the unsingle on and shot the last 15 shells. Shooting them back to back was startling as the unseeingly shot with much less recoil it was noticeable instantly. Weight is a good way to reduce felt recoil but that was not the issue as the 30 in o/u was about the same as the 34 single. The difference was the bore size the newer unsingle was a big bore barrel and that is what reduced the recoil I am convinced if that.The o/u was old and had tight bore vs the bigbore back to back was what made it so noticeable. We know stock fit and weight are big factors in recoil but I waS SUPPRISED on this experience.