The indomitable QB79

[RDB]

Very nicely done Jason. I wish i could hear those super mags slap your first chipper.

[nervoustrigger]

Alright, I got ants in my pants last night so I went ahead and took about 0.3” off the front of the lightweight hammer (and relocated the cocking pin) and shortened the valve stem by about 0.1”.  I left the stem proud by 0.125”, a little over half the throat diameter to ensure it has room for adequate lift.
 
BTW, I don’t know if this is a standard practice for others but I square and polish the end of the valve stem so as to minimize wear to the soft face of the hammer.  I see practically no wear on those I’ve checked after a lot of use so it definitely doesn’t hurt but I don’t know if it’s really necessary.  I’m mentioning it mainly because I see some OEM stems whose ends have been so aggressively beveled that they’re almost sharp.  I definitely wouldn’t want to run one of those with an MDS hammer.
 
Upon reassembly, I was able to back off the hammer spring preload a lot.  That extra 0.4” of travel makes a huge difference.  The cocking effort wasn’t bad before but it’s really nice now.  It also seems to have made a noticeable difference in the trigger pull, albeit very slight.  It’s a drop sear design so pull weight is not as susceptible to the hammer spring tension as a direct sear but there’s still some friction translated from the sear to the blade.  Good stuff.

[mackeral5]

Alright, I got ants in my pants last night so I went ahead and took about 0.3” off the front of the lightweight hammer (and relocated the cocking pin) and shortened the valve stem by about 0.1”.  I left the stem proud by 0.125”, a little over half the throat diameter to ensure it has room for adequate lift.
 
BTW, I don’t know if this is a standard practice for others but I square and polish the end of the valve stem so as to minimize wear to the soft face of the hammer.  I see practically no wear on those I’ve checked after a lot of use so it definitely doesn’t hurt but I don’t know if it’s really necessary.  I’m mentioning it mainly because I see some OEM stems whose ends have been so aggressively beveled that they’re almost sharp.  I definitely wouldn’t want to run one of those with an MDS hammer.
 
Upon reassembly, I was able to back off the hammer spring preload a lot.  That extra 0.4” of travel makes a huge difference.  The cocking effort wasn’t bad before but it’s really nice now.  It also seems to have made a noticeable difference in the trigger pull, albeit very slight.  It’s a drop sear design so pull weight is not as susceptible to the hammer spring tension as a direct sear but there’s still some friction translated from the sear to the blade.  Good stuff.

Very cool.  Ultralight hammers and regulated QB's are a match made in heaven.  I have a 14gram peek hammer in my Cothran valved , 90fpe .30.  Pulling the trigger is just a muted click from the action, with zero twang/vibration.

[nervoustrigger]

Mike, I agree, it makes it so easy to hold the sight picture in the follow through.  Very pleasant shooting experience.  I also like how it benefits slow-mo footage with the scope cam…not so much blurring of the image when the hammer strikes.

[nervoustrigger]

Resurrecting this thread for a quick update at the ~5yr mark.  This rifle developed a slow leak at the poppet and I had been meaning to go in and fix it.  Finally got around to it a few days ago, reassembled it and dialed it in to the knee with the FX 13.4gr pellet, which came in at about 860fps (22fpe).  It seems to really like these pellets, stacking them on the 30 yard target so I decided to move to the 50 yard target and see how it does.

And oh boy was it telling me to take it on a pest control trip.  But before I can do that, I need to know that I can count on it to put the first shot of the day on target.  So the last 4 days I tried a cold shot.  I think it's ready!

[Back_Roads]

Sweet, I need to dig mine out for some Chipper action soon

[Hack21]

Those are awesome results. 

Is there a source for drop blocks any longer? 

[nervoustrigger]

Hey, thanks guys.

I hope someone can answer.  I kinda gave up on finding them ever again. 
 
I ordered a possible alternate from Aliexpress and I think I can make it work but it’s not plug and play.  Looks like I’ll have to shorten the portion that inserts into the air tube, and turn down its diameter slightly.  Way, way easier than building one from scratch at least.
 
https://www.aliexpress.us/item/3256804944341012.html

[Gippeto]

Work hours may be changing in the coming months due to "stuff"...if there is a market, there might be a source. 

Not sure if they're everyone's cup of tea, but started and shelved a batch years ago. Finished one up for a revamp on my QB79 about a year ago.





Al