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Unburnt powder in the moderator

10 Nov 2014
@ 01:07 pm (GMT)


So, this is one of my friends:
He has a Brno bolt action 455 in .17 HMR. After shooting about twenty rounds through the 18" barrel there is approximately a level teaspoon of unburnt powder left in the moderator. The moderator adds approx 3" to the length so there is about 19" of chamber/barrel length for the powder to burn.

Does anyone have any idea as to why this is happening?

thank you in advance,


10 Nov 2014
@ 01:34 pm (GMT)

chris murphy

Re: Unburnt powder in the moderator
Welcome GB it is simply that the barrel is to short for the amount of powder in the case to fully burn. Make sure he cleans it out regularly or he might end up with a pipe bomb threaded on his barrel
10 Nov 2014
@ 02:28 pm (GMT)


Re: Unburnt powder in the moderator
I did think so Chris and thank you for your reply. My friend was confused as this doesn't happen in his .22 WMR but I don't think he appreciates just how far apart .22 and .177 are in cross sectional area.

11 Nov 2014
@ 03:15 am (GMT)

thomas kitchen

Re: Unburnt powder in the moderator
hi g b
ill try explain how i understand it but might confuse you more
if you got two 1.5L soft drink bottles attached onto one 1metre of 25mm diameter pipe
on the other attach 1metre of 15mm diameter pipe
full both bottles to same level
now if you sat both on a table with pipe pointing upwards and squeezed both bottles til water just bout to spill out of pipe.
the one with 15mm pipe would have more volume of water left in the bottle
one with 25mm pipe would have less because it has to full a larger diameter pipe.
relating it to a rifle, if you want to burn same amount of powder you need same volume of barrel (need longer length for a smaller calibre).
im sure someone else could explain it alot better then i can.
as you said it actually a decent difference between .17 and .22 its similar to a .22 and a .270 indifference



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