Moderate a BSA Lightning GRT XL? Why not?

[OldSpook]

I have this BSA Lightning XL GRT in .25 caliber.

I've written about it before, more than once. It absolutely stones squirrels under 40 yards. It isn't terribly powerful, maybe 16 fpe, not wonderfully flat shooting, but MAN those bowling balls drop all their remaining energy in a squirrel with any hit. Anyway today while I was working out in the shop, I decided to have a look under the shroud on the rifle.


Well I found that the barrel was threaded for a moderator! Never actually thought about it but I knew that. Just remove the tip on the shroud and there you have it, 1/2 UNF threads. Well, I could not leave that challenge unanswered so... I just grabbed one of the .25 moderators I built recently and hung it on the rifle. It's kinda ugly but I can fix that with a CF tube that is the same diameter as the shroud. No worries.



Well it isn't THAT weird looking but a 30mm tube would be just about a perfect match to the shroud. You wouldn't even know it was there at a distance.

ANYWAY! So I set up to test at 5 yards at 12 o'clock and 3 o'clock. My results confirmed what I found on a different test. You can moderate a springer or even a gas ram.



Oh yeah! That is a whole lot of difference. The odd thing is shooter can not hear it. Too much noise from the action for the shooter to ever hear the difference but it's there. Mr. Squirrel won't hear that rifle at 40 yards. I think a moderator made just for that action could improve on these results by a little bit.

 

[Sqwirl57]

Wow that is definitely a huge difference. Thanks for taking the time and posting the results

 

[OldSpook]

I built this little moderator this morning.

It matches the diameter of the barrel perfectly and gives me 8 decibels.
There is a number I like to use I call the range to the noise floor. It converts decibels into something that's easy to think about. If I sample my noise at some distance and I assume a noise floor of 40 decibels which is pretty quiet (about as quiet as a backyard in the country add 10 dB for the city). I can calculate a theoretical distance at which the noise of the moderated rifle drops below the noise floor. Once the signal drops below the noise floor it is extremely difficult to pick it out. People don't generally pay any attention to noises which do not rise more than 10 dB ABOVE the noise floor and one must have VERY ACUTE hearing to pick out anything less than about 3 dB above the noise floor.

For this moderator on this rifle that number is reduced from about 450 yd to about 175 yards.

That's a worthy improvement.

NOTE: The calculation is as follows and is easy to do on a spread sheet.

Let D be the distance to your microphone/sensor (some unit, feet, meters).
Let F be the noise floor (here we assume 40 dB).
Let A be the average noise of the shot measured.
Let R be the range from the shooter until the signal of the shot drops below the noise floor.

D*2^(abs(A-F))/6) = R

R is in whatever units you used when you measured D.

 

[OldSpook]

This morning I pulled the little moderator off and put my Tanto on the BSA. The Tanto has found a new home. .

Average sound level for the rifle (15 feet at 12 o'clock) with the Tanto was 67.7 dB and without it it was 82 dB.

I'll take 14 DB any day. This moderator has never performed so well on any other rifle. Mind you it's always been a fine moderator. But this rifle likes it and it likes this rifle.