Help with fitting a center fire block

Perry Owens · November 25, 2009, 05:21:33 AM

Just started to fit an S&S block to my M1865 Burnside carbine. I found the block dropped in ok but when the action is opened fully it will not close again. A bit of pressure on the back of the block eventually gets it to close. There are some score marks in the groove and on the top of the block so it looks like the block is rubbing on the trigger plate. Comparing the new block with the old it appears that the new one is taller at the front. Is it ok to take metal off the top of the block and the groove or will that affect lockup or feeding?

Herbert · November 25, 2009, 01:50:54 PM

check the slot in the botom of the uper block stem were the leaver screw goes through,wen i fited mine the slot needed opening up slitly,check against original for size,this fixed mine it was doing the same thing wile you are at it stone any sharp edges especily put a vert small raidus on the leading edge of the top of the breachblock this will inprove feeding

Trailrider · November 25, 2009, 05:29:41 PM

Quote from: Perry Owens on November 25, 2009, 05:21:33 AM
Just started to fit an S&S block to my M1865 Burnside carbine. I found the block dropped in ok but when the action is opened fully it will not close again. A bit of pressure on the back of the block eventually gets it to close. There are some score marks in the groove and on the top of the block so it looks like the block is rubbing on the trigger plate. Comparing the new block with the old it appears that the new one is taller at the front. Is it ok to take metal off the top of the block and the groove or will that affect lockup or feeding?

In addition to checking the oval hole through which the screw holding the upper block to the lever/lower block, you need to check the headspace and the length of the block relative to the opening in the receiver. It isn't that hard, but it can be time-consuming, and you need some skill with a metal file...and plenty of patience! (I say this as a former aerospace engineer...who can barely file a flat surface!

Yet, by taking my time, I was able to fit an S&S breechblock to an original M1860 Carbine.)

IF, when you can close the block by simply pushing forward on the rear of the block, then try rounding the top rear surface of the block...just enough to allow easy closing. But that's NOT the whole story.

If the breechblock is hanging up without a cartridge in the chamber, it may really hang with one. The best way is to buy a set of headspace gages. Clymer Manufacturing probably has or can make them, though they might be a bit pricey nowadays. An alternative is to take a bunch (say, 10 or 20) of cartridges and pick the one with the thickest rim. Get some brass shim stock or a set of automotive feeler gages. The breech must close on the thickest cartridge rim, plus .001-.002". Use a permanent black marker or, better, get some machinist's dye. Paint the back and the top rear of the block with the marker or dye and install the block in the rifle.

Start with the chamber empty and try to close the block, and see where the parts are rubbing. Using a 6" Mill bastard file, CAREFULLY, AND SLOWLY FILE AWAY SOME METAL, keeping the file as perpendicular to the sides of the block as possible. Just do a few swipes at a time. REPAINT THE SURFACE OF THE REAR OF THE BLOCK, then install the breechblock and try the action. Keep this up until the block will close properly.

Next, insert the thick-rimmed cartridge and repeat the process until the block will close with the .001-.002" feeler gage inserted between the rear of the cartridge and the front of the block.

So far as the scratch marks in the groove (I presume you mean the one on the top, where the ejector rides), is concerned, use the dye or marker ink to determine where things are rubbing. It may be easier to narrow the ejector, but DO SO SLOWLY AND CAREFULLY!

Hope this helps! Happy Thanksgiving!

DJ · November 25, 2009, 09:47:59 PM

I have found the S&S CF blocks usable, but I suspect they "drop in" much less frequently than S&S suggests. The problem I found on both blocks had to do with the groove in the top of the block not being deep enough--this causes binding on the trigger plate. Try putting your original and your repro blocks side by side and then compare the profile at the *rear* of the block. I have two S&S blocks. I tried each one in five different Spencers (models 1860, 1865, and 1867). Neither block was a "drop in fit" in any Spencer I tried it in.

Glenn · November 26, 2009, 06:45:31 PM

When fitting the block, remove all the springs and insure it will fit freely into the lower BB. I wasted a lot of time on the top of the block and it won't help if the block is not seating all the way down in the lower BB. I've done about 4 of these and have yet to see a real drop in but I am a little picky.

Perry Owens · November 27, 2009, 06:09:30 AM

Thanks for the tips eveyone. I checked that the block moves freely in the lower block and opened out the hole in the stem to the same as the original but still no luck. With the aid of some engineers blue and a flashlight I determined that the front of the block is binding on the front of the magazine tube and the groove is binding on the trigger plate. I am off on a busines trip now so it will be a week before I can get back on to this.

Trailrider · November 27, 2009, 04:39:10 PM

One other tip I forgot to mention, which may go along with problems with the magazine assembly: BE ABSOLUTELY CERTAIN you use a FOLLOWER with a FLAT NOSE. S&S used to sell one with a concave nose, but I would prefer one with a flat nylon tip!

Herbert · November 27, 2009, 05:23:13 PM

the magizine folower should not interfear with action movment unless the screw that stops it moving too fare foward is not engaged with the slot in the magizine,if it is in too far just back it out so it is flush with outside of magizine tube,when the action is open is there a small gap between uper & lower block just before it hits the stop if not you may have to take a small amount of meatal off the curve off the block,also you could try puting sume grafite on the high spots and see if it will smooth things up

Herbert · December 01, 2009, 03:36:13 PM

i eogot to mentuion the fist thing to check is weather the the block is runing squar to the leaver,if not this will cause binding,put block in leaver with screw in if it is not rocking back and forwads freely and squarly thin cutout a bit and square up it does not need much you can at same time take sharp edges of and a bit off the botom if it needs it,i have dun this with 6 S&S blocks since i had the same trouble with the fist one i fited ,all were slitly off square,they all workedafter doing this but i didnot check weater they worked before,after the first one i just repeated the process

Perry Owens · December 07, 2009, 02:16:12 PM

Got it sorted thanks to all your advice. The main problem was the profile of the groove on top of the upper block was wrong and it was binding on the trigger plate.Made up a bunch of dummy rounds of various lengths and seem to have got the optimum length for reliable feeding. Now all I have to do is figure out why the magazine tube won't release without the aid of a drift and hammer applied to the tube base.
Since I live in the UK I now have to have the Spencer added to my firearm certificate before I can load some rounds and head off to the range.