I have compiled some information, and went as far as to put it into an Excel Spread Sheet/Chart, but I'll be darned if I can get it formatted to be able to post it here. I tried several things, but will need to be able to make it a pdf or something that is compatable, and I am a dummy, so there you have it. Sorry!
I will post some of the results, but will spare you the individual measurements, and just post the high/low/average. I measured 10 random primers from each box, this will give you an average from this size sample, but measureing 10 different primers from the same box could give you different results overall. There is just too much variation to make a 10 piece sample tell the whole story. This could be helpful in finding the right average length primer for your breech plug/rifle. All measurements are in inches to the nearest .0005".
Remington No. 209-4 (.410 bore) Primers. Lot# 419
Average length
.2934
High
.2955
Low
.2920
Extreme Spread
.0035
Remington Kleanbore 209 Muzzleloading Primers. Lot# 38
Average length
.2962
High
.2990
Low
.2945
Extreme Spread
.0045
Winchester triple se7en 209 Muzzleloading Primers. Lot# XEL010
Average length
.2997
High
.3040
Low
.2970
Extreme Spread
.0070
Winchester No. WML209 Muzzleloading Primers (tan box). Lot# WNL038
Average length
.2997
High
.3010
Low
.2980
Extreme Spread
.0030
CCI (Standard) 209 Primers (blue/silver box). Lot#AV655
Average length
.2985
High
.3000
Low
.2960
Extreme Spread
.0040
Winchester W209 Primers (blue box). Lot# YAL151
Average length
.3023
High
.3050
Low
.3000
Extreme Spread
.0050
CCI (Magnum) 209M Primers (red/silver box). Lot# AY427
Average length
.2989
High
.3000
Low
.2960
Extreme Spread
.0040
Federal 209A Primers. Lot# AV492
Average length
.2977
High
.3000
Low
.2950
Extreme Spread
.0050
I will post some of the results, but will spare you the individual measurements, and just post the high/low/average. I measured 10 random primers from each box, this will give you an average from this size sample, but measureing 10 different primers from the same box could give you different results overall. There is just too much variation to make a 10 piece sample tell the whole story. This could be helpful in finding the right average length primer for your breech plug/rifle. All measurements are in inches to the nearest .0005".
Remington No. 209-4 (.410 bore) Primers. Lot# 419
Average length
.2934
High
.2955
Low
.2920
Extreme Spread
.0035
Remington Kleanbore 209 Muzzleloading Primers. Lot# 38
Average length
.2962
High
.2990
Low
.2945
Extreme Spread
.0045
Winchester triple se7en 209 Muzzleloading Primers. Lot# XEL010
Average length
.2997
High
.3040
Low
.2970
Extreme Spread
.0070
Winchester No. WML209 Muzzleloading Primers (tan box). Lot# WNL038
Average length
.2997
High
.3010
Low
.2980
Extreme Spread
.0030
CCI (Standard) 209 Primers (blue/silver box). Lot#AV655
Average length
.2985
High
.3000
Low
.2960
Extreme Spread
.0040
Winchester W209 Primers (blue box). Lot# YAL151
Average length
.3023
High
.3050
Low
.3000
Extreme Spread
.0050
CCI (Magnum) 209M Primers (red/silver box). Lot# AY427
Average length
.2989
High
.3000
Low
.2960
Extreme Spread
.0040
Federal 209A Primers. Lot# AV492
Average length
.2977
High
.3000
Low
.2950
Extreme Spread
.0050