Flow Through Bolt Problem...

Here's the bolt from the wife's 2250B. The "problem" is fairly obvious:

http://i1100.photobucket.com/albums/...owProbe001.jpg
http://i1100.photobucket.com/albums/...owProbe006.jpg
http://i1100.photobucket.com/albums/...owProbe005.jpg

:huh:

The bolt was always a little bit snug right from day one. Not excessively, and not the whole action of chambering a pellet - just a little "tick" as you lock the bolt into place, and when you first pull the bolt back. Almost like the leade was too small, if that's even possible...At first I thought it was just a bunch of new parts (bolt, handle, breech) needing some time to break in and smooth out. WRONG!!

Took everything apart, probe measured .217", so that shouldn't be the problem.

Turns out that the leade has a small shoulder instead of a smooth transition to the rifling for about the last mm before bolt can be locked into place. Is this normal?

Can I just do a little "crowning" technique, or a tapered reamer to smoothen the shoulder?

On the plus side, I'll get to try my hand at making an extended probe on one of my spare bolts now! :glee:

Todd

That .217 may have been a little bit of the problem. The theoretical bore size would be would be .216-.2168. So the is a bit of interference "possible"

Sure just do a crowning technique with a mandrel cut to a 1deg taper sized to contact that shoulder. Then nick some grooves and apply some paste. (valve compound is a bit harsh for leades)

Oh...yes that shoulder is normal. you may have just been the lucky one in the +- tolerance....you had all +'s

Son of a b!tch.

I am beginning to think the fabricator of these bolts was a bit under the weather when they got made- another bolt has had a problem where it would jam in the breech if the handle was fully tightened. Not the kind of silliness I like to encounter...

Bring the bolt back, I will swap it out.

Nice that the fabricator is trying to get the maximum diameter so he can get the bigger hole inside.... Compare that to the flow through bolt on a QB and it's a LOT bigger, the QB isn't even close to bore size.... I notice that the center hole in the flow through is so deep that it nearly cut through to the O-ring groove, that's why the bolt failed....

I replaced the flow through on a QB (one that I had drilled out for more flow) with an extended probe instead and picked up 30 fps on a 900 fps gun.... Other than the flow through style seating all pellets to the same depth and square I can't see any reason for using one....

Bob

Quote:

---

Originally Posted by rsterne

I replaced the flow through on a QB (one that I had drilled out for more flow) with an extended probe instead and picked up 30 fps on a 900 fps gun.... Other than the flow through style seating all pellets to the same depth and square I can't see any reason for using one....

---

I remember that post (bookmarked it, actually), which is exactly the reason I'm going to try it out. Not so much on this gun as it is staying Co2, hovering around 550 fps, but more for my 2260 HPA. She only plinks/punches paper with me (she wouldn't shoot an animal if it was gnawing her leg off!), so max fps isn't an issue.

Sean:
I think for now I'll leave the leade as is, other than maybe polish/lightly (very lightly) round off the sharp edge so the pellets aren't nicked when chambered.

Eric:
No worries, bud! I'm not looking for free handouts/replacements (wasn't the intent of the post), just some info - which I now have :encouragement:

I'm still in the learning stages - and probably will be for quite some time yet! When I realized it (bolt) was snug, I could/should have just put it in the drill press (don't have a lathe) and give it a wee touch with some 1000 or 2000 grit paper - now that I know I'm looking for .216" (thanks, Sean!). Would have solved everything quite easily!

Thanks guys,

Todd

Quote:

---

Originally Posted by sholo

Sean:
I think for now I'll leave the leade as is, other than maybe polish/lightly (very lightly) round off the sharp edge so the pellets aren't nicked when chambered.

I'm still in the learning stages - and probably will be for quite some time yet! When I realized it (bolt) was snug, I could/should have just put it in the drill press (don't have a lathe) and give it a wee touch with some 1000 or 2000 grit paper - now that I know I'm looking for .216" (thanks, Sean!). Would have solved everything quite easily!

Thanks guys,
Todd

---

The easy way to smooth that transition is to use a .22 bore mop on a standard cleaning rod. Coat the mop thoroughly with a mild abrasive like white toothpaste or JB Bore or those hard wax based abrasives used for buffing wheels can be softened with mineral spirits to a paste...etc. Then give the throat about 100 strokes. That way your efforts are parallel to the axis of the bore and you'll end up with a tiny bit of a leade.

These barrels dont really have a leade to begin with with. It's more of a throat with a hard transition to boreAttachment 458

Could also be that the bore itself is off center.

Have cut the factory "work" off a barrel to find the bore off center by .0075"...this means that using an extended probe bolt could cause the pellets to go in "cockeyed". Would be aggravated by a bolt that actually fit the receiver properly...perhaps why the crosman bolts are so darn sloppy?

Al

Made up a couple of "home brewed" extended probe bolts yesterday with the bolts that came with the steel breech kits from Eric, using Bob's post on the subject as a guideline:


http://i1100.photobucket.com/albums/...edprobe001.jpg
http://i1100.photobucket.com/albums/...edprobe002.jpg

Both probes were made from....and this is where things get a little "redneck"....SS finishing nails!! (insert referances to "KG" here, I'm expecting it!)

The "fat" probe is from the shank of a 2-1/2" SS nail, which has a diameter of 3/32". Necked down one end to 1/16" X 3/8" long (hole in bolt) using the drill press and file, added a few drops of red loctite, then tapped gently into place and left to sit overnight to cure.

The "skinny" probe is from a 1-1/4" SS nail, with a shank diameter of 1/16" (fit perfectly in hole), head diameter of 3/32". More loctite and tapping, and voila!

Both probes were cut 5/8" long, 3/8" of which are inserted into bolt, which gives me a finished bolt length of 1-7/8" - just barely enough room to still load Polymags and still have the skirt completely ahead of TP.


http://i1100.photobucket.com/albums/...edprobe006.jpg
http://i1100.photobucket.com/albums/...edprobe007.jpg


Why use SS nails? Well...short answer is it was all I had laying around that was a possible candidate.

Tried the fat probe this morning, seems to work great! Will compare fps with flow through bolt later on today...

Todd

So long as you're not taping barrels together, it isn't a KG job. :encouragement:

Nice work on the probes. Curious to know how it works out.

Your "fat" probe is effectively like the ones I use.... I drill a 1/16" hole into the bolt for 3/8", insert a piece of 1/16" piano wire with a drop of crazy glue, and then slide on a piece of 3/32" OD brass tubing from a hobby shop and glue it as well..... IIRC, I extend the stock probe 0.150"....

Bob