Hi OPS - I have also done as you mentioned; used the compression plug only to compress the powder and then seated the polywad down on top of the compressed powder. I use a newspaper wad though between the plug and the powder to keep the powder from sticking to the plug during compressing.

I have not made enough tests to confirm what you are saying; that polywads produce better accuracy than the veggi wads. However, the limited shots I did make with the veggiwad reloads I followed these up with polywad reloads and these shot 2 MOA higher than the veggiwad reloads where this was the only difference between the two. If the polywads produce better sealing/higher resistance at powder ignition this would result in higher velocity, I would expect. My testing was limited so this is conjecture at this time.

As an update to an earlier post - I did make a larger diameter compression plug but still got case-swelling compressing the powder with the polywads. Swelling with veggiwads was almost eliminated but not completely stopped. Since I am getting what I think is more case swelling now than some time before I am wondering if the change might be due to my wad punch becoming dull. The polywads have a jagged edge whereas way before I didnt notice this. I also measured the thickness of the veggiwads produced with this punch and I found these to be ~.100" thick when they were punch from .060" thick material (I'll confirm this tonight). Not sure if veggiwads normally get a bit thicker when punched out (hopefully someone can verify this) but I am thinking a dull wad punch might be a big contributer to my case swelling with polywads.

My wads definitely don't go from 0.060" to 0.1" thick after punching them out.  I've found that the Buffalo Arms stuff is slightly thicker than 0.060" though.

Chris.

When walking out to reset chickens I'm always amazed how many poly wads are on the ground between 150 and 200.

Nowadays I only use LDPE wads from Baco as I have been unable to detect any difference in accuracy when using vegi wads and I thought the poly wads may be less abrasive in the barrel.
As the rifle range is only four minutes from  my home, and I'm retired, I usually shoot five days a week testing various loads in both my 45/90 and the 38/56. I shoot fixed ammo in the 45/90 and breech seated bullets in the 38/56, all with poly wads. In either rifle a paper wad is placed between the bullet and the poly wad. The base of the bullet id also carefully wiped of any bullet lube as well.
I shoot mostly at 100 meters into a solid backstop and find dozens of the wads on the ground, I have yet to find one past 35 meters and have found none in the backstop after over five years of shooting. I think the paper wad makes all the difference. As for the vegi wads I think that they probably just decompose after getting wet with the dew or rain.
Mike

Mario - Yes, the trapped air could be the problem. One of the Long Island folks we shoot with at Shippensburg used to load his 38-55 with so much powder that it would bulge the case when he compressed the powder in order to seat the bullet. He simply FL-sized the cartridge after loading to insure they fit in his rifle. Not what I would do, but it worked for him until he rebarreled the rifle as a 40-65 for this season.
Just ask a couple of other 40-65 shooters about their loads. One of them is arguably one of the top 40-65 shooter in the country, having won or placed highly in many matches around the country over the past several years.  He loads loads the BACo 400gr M4 Money bullet over 65gr of Swiss 1 1/2F and the other shooter loads 62gr of Swiss 1 1/2F and the same bullet. As always, whatever works for you in your rifle is the correct load.