Just an FYI,
I'm having some blowback from my new Accura MR so I sent an e-mail to bpiguns.com about blowback and this was their response to the issue:
"Blowback is common, the shim kit is designed to move your firing pin bushing forward so that it is flush with the receiver. It is not designed to move the firing pin bushing out closer to the primer. By moving the bushing out from the receiver to make it closer to the primer will cause damage to the receiver. If your bushing is not flush then we have the shim kits available for $4.99 plus $7.95 S/H. These are not necessary for your gun, please be aware that muzzleloaders will have blow back and the shim kit will not correct this problem. If you would like to place an order for one then you can contact our customer service line at 770-449-4687."
Cabelas (Investarms) Hawken .58 Cal, Flintlock
CVA Mountain Rifle .58 Cal, Flintlock
Thompson Center Renegade .54 cal Caplock (Sharon slow twist barrel )
CVA Accura MR .50 cal, Zeiss Conquest 3x9x40