August 18, 2005
Easy Gap Fix On Standing Breech and Firing pin improvements.
When I noticed a loss in accuracy in my 257 Roberts Handi, I found a 0.003" gap in the standing breech I was not pleased. The rifle was never subjected to max pressure loads. But the seat was very poorly machined, this may be accounting for the gap? When a Handi develops a gap in the breech it will also at the same time loose the forearm contact with the action. This contact is as important as a tight breech, because it creates unwanted vibrations if loose.
Of course we all know about the several available fixes. Like gluing in a shim or building up the hinge pin seat with weld. I found the glue in shim is very unsatisfactory. Build up with weld works well but is very involved.
When you look at the hinge pin from the rear you will see two shiny marks one each side with no bearing in the 0.312"wide hole in the underlug. The unsupported center gap became more foods for thought. The hole reduces the bearing surface of 0.361 sq/in by the considerable amount of 26%.
The open end in the underlug is a manufacturing short cut. Instead of a solid steel bock for the hinge pin seat and a stop for the ejector spring a simple split pin is installed for the stop. This pin is not needed to remove the spring also it can be. Installation of the spring and ejector is much easier from the breech end.
The cut-out in the underlug is really a weak spot and reduces the bearing surface of the hinge pin by 26%. The two thin sides are easy peened by the transmitted pressure from the standing breech, which creates the gap in the standing breech.
The fix I came up with kills to birds with one stone, one it eliminates the gap and two, improves the hinge pin-bearing surface by 26%.
Remove the ejector and the spring from the breech end. Make a stick of wood .300x.240 to fit the hole 4" long. Don't remove the spring stop pin. Clean the hole in the hinge pin seat with sand paper or a needle file and dimple the sides with a sharp punch up to the ejector stop pin and dimple the radiused seat. This will make small craters for a mechanical bond of the Steel Putty. Wash and wipe the hole and the hinge seat with acetone.
Note: This hole can also be welded shut and file finished to the curved seat.
With a Q-tip thinly prime the hole with 51CURE or West System 5-1 epoxy. Wax the wood stick and have it in place against the spring pin to prevent epoxy to get into the spring race, fill the hole with Devcon Steel Putty and finish flush with the seat radius. Tap the wood stick to flush the Steel putty in place and avoid overfilling the hole. Let this set up solid.
Once solid apply primer to the hinge seat and apply a thin layer of Devcon Steel Putty and apply thin coat of STP or paste wax for release to the hinge pin. Carefully install the barrel and compress the Devcon Steel Putty. Tap action in place until the latch will lock solid. I would think that this should take care of a gap up to six thousands or more?
The back thrust against the standing breech for cartridge like a 243 or 25-06 is about 7500psi on a 0.173sq/in case head. The effective thrust area is 0.1246 sq/in. The above load is transferred to the hinge pin , which has more than twice the aria at 0.361 sq/in when the hole is filled in. Always use a good grease to lube the hinge pin and seat after the Devcon Epoxy steel is cured. Allow one week to cure, for sure.
For your info back thrust is calculated from the inside diameter of a case at the pressure ring. About a 1/4" up from the base, BT= Inside diameter radius squared times psi.
One problem with a gap is, the loose barrel will add impact to the hinge pin each time the rifle is fired. To demonstrate take a 50lbs hammer and lay it on a 3/8 pin nothing will happen. Take the same hammer and drop it a foot and you will have a dint in the pin. The more gap the more impact. My Handi action developed a 0.003" after about 160 rounds.
Since I have already load data there is no real need to fire another 160 rounds to find out if the putty job is sound. There is one other plus for the Steel putty. If the standing breech and the hinge pin are not perfect parallel, which with all the side play in the action is quite possible, The Steel putty will take care of that too.
Of course a gap in the standing breech will also place the barrel latch in various places on the latch seat. This causes vertical stringing. Let alone the case stretching which causes case head separation in short order. The Devcon Steel Putty may in time compress but can be fixed easy again by another thin layer of Devcon Steel Putty.
Devcon Steel Putty has a 8400psi compressive strength more than enough to keep things tight. I have done my 257 Roberts in a trial fashion as above. The action now locks up tight as a vault with no gap and 20 warm loads with 100 gr bullets have shown no signs of compression. Which is very encouraging because the rifles good accuracy was restored.
You could make you own putty using West System 5:1 epoxy and atomized steel or Tungsten from Brownell. Devcon Putty is also available form Brownell page 253 cat # 57. When mixing your own, mix it stiff so it will just spread with some force. This is important to get a tight fit between the barrel and the standing breech and the hinge piece on the forearm. Both need to be a tight fit.
How long will it stay tight, I don't know, more shooting will tell. From what I have seen it will stay a while. The Steel Putty is nearly solid steel when hard and compression at the above rate would be very minimal. Only the interstices of the metal grains would compress to a tighter formation.
Devcon Steel Putty is available from industrial suppliers. Do not use 1:1 Devcon Epoxy Steel it is too soft for initial compression. That goes for other 1:1 mixes like J-B weld.
putty I have is called Devcon Plastic Steel Putty (A) stock#
It says for industrial use only. The mix by volume is 2.5 Steel Putty and 1 part hardener. 1lbs= 11.9 cub/inches.
By weight 9 parts Steel putty to 1 part hardener. When mixed it is like stiff modeling clay. Soft stuff wont be any good.
Best to find out from Brownell if theirs is the same stuff. Mine is quite old at least 15 years, seems to have indefinite shelve life. I have done a million jobs with it since. One lbs will last forever.
If you are going to use the Devcon putty you should check the standing breech and the barrel face for rough tool marks. Remove them with a light rubbing of a flat mill file. We are looking for the very best tight fit.
Ok here is a quick run down and the order in which to do the job.
1. Remove barrel and then remove the the ejector and spring. Watch out for the little wee spring and plunger.
2. Smoke the barrel face with a candle, hook in the barrel and slowly close the the barel pushing the barrel against the standing breech, any high spots on the barrel face will show up on the smoked face. Remove any high spots with a flat mill file only very little needs to be removed . Try to get a perfect flat fit and keep the file flat against the barrel face. Polish with #1200 grit paper on a flat piece of wood.
3. Sand , clean and dimple the halve round hinge pin seat and the hole and wash with acetone and q-tip several times. All oil must be removed. Note: When dimpling use a very long slender point and place the dimples close together. Do not make the dimples too deep and big, because it raises the metal and will take up the gap or more and prevents the action from closing. This of course will reinforce the Devcon which fills in between the dimples. You can get a very tight fit with the dimples only, but the graters edges wont be strong enough to hold up against the presure.
4. Insert the waxed wood stick. Mix devcon putty and West sytem primer primer. Prime the hole and fill hole with the putty. Tap the inside with the wood stick against the spring pin which is left in place, to keep the putty out of the spring race way. Finish the putty flush with the concave, clean up and wash off any spill over on the concave seat and let it set up hard for one day.
5. Next day clean and wire brush any loose left over putty and primer, redimple the seat if needed. You want a clean down to matal surface.
6. Apply a wax or STP bond breaker to the hinge pin.
7. Make a a small roll of putty and let it sit for an hour, Then mix and apply a thin coat of West system epoxy to the seat. Place the putty roll in the bottom of the concave seat and press it down with your finger to make it stick. Gently hook in the the barre and lower it down tapping it with rubber hammer or a piece of wood until the latch full closes, without the ejector and forearm.
8. Remove the barrel after the putty is set up clean up any squeased out putty. Then put it back together and let it set for a week. Before complete assembly,check the ejector without the spring to make sure the ejector is flush with the barrel face. If it sticks out the action will not close. Remove dirt or little metal under the ejector until it is perfectly flush.
The reason for the two different putty applications is to achieve maximum resistence to force the barrel against the breech face for a tight fit. For a complete accurizing job read my other page. I did bed the barrel into the action and installed 2 shims to the underlug on each side before I did the gap fix. This will prevent rotational torque from disrupting the gap fix. Before doing any of this you should have a good or fairly good dimensinal bore. Because a rifle will not shoot accurately with a poor barrel no matter what you do.
If you have to do a second Devcon Steel Putty application, clean the existing steel putty surface with alcohol (methol hydrate) do not use acetone on Devcon Steel Putty.
End Note: There is no substitude for a solid hardened steel hinge pin seat and a latch that makes 100% contact and stays in that position. The steel forearm hinge piece is a step in the right direction for a tight non wearing fit to the action. A 1/16" larger hinge pin would perhaps prevent the standing breech gap altogether. This is of course a machine shop application. Eventually I will do that. In the mean time we hold things together with Devcon Steel Putty.
Primer Substitude Question 5:1 epoxy.
I don't know of any other epoxy that is as good, the fast setting stuff is too thick and would not get into the small steel pores. Besides you don't want it to mix with the Steel putty, only to bond to it. It also has about the same setting time.
I have the one liter unit and
used it for building a light weight BR stock and it toke a lot of
searching to find it. Check with these guys and see if there is a
small unit. Or try Devcon and tell them what you want they may
have some stuff.
One thing you could try, is to rub a small amount of mixed Devcon Putty vigorously into the steel dimples with a piece of 3/8" of round steel clean and free of oil, don't use wood for this, then apply the Putty that has set for an hour. This may work well since the Devcon Putty is in constant compression. Try to keep solvents away from the applied putty.
Firing pin improvement________________________________________
So what did NEF do to my rifle ? allow the hammer to hit the transfer bar with more force ( less resistance) and remove some material on the hammer to allow the firing pin to extend further out ? Would a replacement hammer extension (better specs or workmanship) solve some of my problems ?
Or did NEF try to get around that by the above mentioned fixes ? Glenn
Bro Glenn I don't know what they did to fix your rifle. It is fixed yes? The hammer spring has only so much power and they do with use relax. It is prudent to remove as much friction from the hammer by polishing the pin on which the hammer rotates and apply a little lube.
Take the hammer extension and turn it to the underside of the hammer and open up the sides of the extension V-slot with a needle file and move the extension forward by 1/4". This places the weight of the extension closer to the center of the hammer rotation and cut off a 1/4" off the hammer tip. This gives the hammer a bit more speed. No need to replace the extension.
Removing metal from the hammer where it hits the frame to get more firing pin protrusion is not a good idea since if overdone would jam the transfer bar. Metal should be taken out of the frame, but only a few thou. The transfer bar has some forward inertia provided by the hammer notch and should not be reduced by much.
The more friction you remove the better the hammer action hence better ignition. That includes the polishing of the firing pin and its seat. Taking a coil off the firing pin return spring removes hammer resistance. I think I removed about 8oz of resistance in this one area.
If you only get 30 thou pin projection, with a needle file work on the hammer seat and take a bit off the face of on the hammer this will give you another 10 -15 thou. I did both my Handi's like that.
Apply some lip stick and you will see that the hammer tip and the spot where the hammer hits are not very well matched, simple to rectify.
I also did polish the firing pin and the firing pin seat. Clipped off one coil off the firing pin return spring. Reversed hammer extension to the bottom opened up the dove tail in the extension and slid the extension 1/4" forward and toke off the top 1/4 " of the hammer.
I also installed a new hammer torsion spring. No more misfires.
The action has to be taken apart to remove the firing pin. The latch release push leaver is held by the same pin that retains the firing pin. The transfer bar and hammer has to be removed.
The pin hole and the firing pin seat hole crosses and leaves burrs at the junction where the return spring gets hung up or bound.
Polish the pin hole and the seat hole and remove the grit and burrs in the bottom also polish the firing pin too. When you’re done and every thing is smooth the firing pin should fall out by gravity
My firing pin and spring created 12oz of resistance and gave me poor ignition. See my web pages with full explanation. This is pretty simple job.
Fred the Reloader and Wildcatter