Barrel pressing

[vista461]

My trunnion is tig welded to the receiver now.

Next step in my build is barrel pressing, I am going to use a hyd press but have a few questions.

What do you guys use between the ram and the barrel?

How far do you go in before you start check for bolt gap?

Any tips on what to use between the trunnion and the press since it's recessed a tiny bit?
I assume the receiver will deform if there isn't something supporting the trunnion.

The trigger pack doesn't need to be installed to check bolt gap does it?

:thanks:

[Big Steve]

Before you try it make sure you remove the sharp edges on both ends of the trunnion or it will peel metal off your barrel. Use never seize or a high pressure grease. If you go too far sometimes you can tap the barrel back in a little bit with a hammer if it is not too tight. Protect the threads with an old flash hider if you have one. If you dont have one don't try it. Remember that .001 of barrel movement = about .004 of bolt gap. That's why it's hard to stop it where you want it with a hyd. press. The barrel will be pretty much even with the trunnion up inside when you are in the right spot.
Good luck!
Steve

[vista461]

So do you think I would be better off with the press or with the modified gear puller type setup that rustypirate made?

http://img406.imageshack.us/img406/6007/press6dd8.jpg

[rustypirate]

Use press. It is allways a better tool.

That rig I made was because I was living in an apartment and had no space for a press.

[vista461]

Ok sounds good

[drine]

I was going to make or get a buddy to make a "washer" looking piece to go in the front. I say washer because I would get the OD/ID of the trunnion recess leaving a hole in the middle for the barrel. The part that would contact your press base could be left a lot bigger to give you a steady platform. My receiver has little flats around now that will have to come off before a forearm will seat.

+1 on Big Steve's advice to deburr the trunnion. I peeled my first barrel like an apple because I didn't prep.

If you have the ability, time, and space, I'd build a screw press. This would be a lot more precise. Another buddy of mine who helps with a race team actually had one made already only needs a longer ram screw to work for a barrel. I didn't have my camera or I would show it. gw11 over on gunboards has a pic of a good screw press.

[woofert]

I just did a barrel replacement and this is how I did mine (YMMV)

I used a 12 ton hydraulic press and a “jumbo” brass punch from Harbor Freight.

802

803

I modified the press by removing the rod below the bottle jack and welding a ¾” nut in its place. This way I can vary the depth of the press with out having to move the press shelf or pump the jack a lot.

801

The double nut on the end is used with the beveled end of the brass punch to prevent it from slipping during pressing.

804

I made a bracket from a black iron pipe nipple and flange to place against the trunion during pressing so as to not crush the receiver that sticks out past the end of the trunion. The pipe nipple is welded to the flange at the bottom and notched to clear the cocking tube.

800

The brass punch was beveled on the business end to fit the bevel on the barrel at the chamber.

Once the barrel was pressed into the trunion, I reassembled my Cetme and did a BG check.

If the BG was too big I placed the pipe nipple/flange bracket on my bench vise with the jaws open enough to allow clearance for the barrel. I then cocked and locked the action open on my Cetme, placed the trunion against the pipe nipple/flange bracket and let the action close as you would when chambering a round.

Then checked the BG again.

If the BG was too small I locked the action open and tapped the end of the barrel with a soft face hammer, I did use a spare flash hider to ensure no damage the muzzle.

Then checked the BG again.

I worked back and forth as described above until I had a BG of .016” with 8.00 mm rollers, then I drilled and pined the barrel.

I’ve since fired around 125 rounds through it and my BG is right at .014”/.015”.

Hope this helps,

Woofert

[drine]

Your trunnion support is identical to the one I'm making. You've kind of got a hybrid in that you can use the press to get close and threaded screw to finish. Well done.

Can you tell us what method you used to drill the pin slot? I've got all the bases covered from a 5mm tapered reamer to a slightly smaller cobalt drill bit. Were you able to drill it with a drill press or mill? What kind of vise did you use to hold it? I'd like to not take mine to work to finish it since I'd need my bolt carrier, etc. and that would constitute a weapon on the property. A NO NO in our plant.

[woofert]

Can you tell us what method you used to drill the pin slot? I've got all the bases covered from a 5mm tapered reamer to a slightly smaller cobalt drill bit. Were you able to drill it with a drill press or mill? What kind of vise did you use to hold it?


I used a #10 bit in a drill press but didn't clamp it in the vise, just drilled through the barrel pin hole in the trunion and did a little filing to get a good tight fit.

I used a hammer and punch to seat the barrel pin rather than trying to press it

Woofert

[fordruid]

Anybody cool the barrel and heat the trunion to ease the installation? I know we do it for our racecars stuff, often parts go with a light tap, no press needed there (but the press would still be needed for barrel installation, this would just make it easier)

[rpmfly2]

I was going to make or get a buddy to make a "washer" looking piece to go in the front. I say washer because I would get the OD/ID of the trunnion recess leaving a hole in the middle for the barrel. The part that would contact your press base could be left a lot bigger to give you a steady platform. My receiver has little flats around now that will have to come off before a forearm will seat.

+1 on Big Steve's advice to deburr the trunnion. I peeled my first barrel like an apple because I didn't prep.

If you have the ability, time, and space, I'd build a screw press. This would be a lot more precise. Another buddy of mine who helps with a race team actually had one made already only needs a longer ram screw to work for a barrel. I didn't have my camera or I would show it. gw11 over on gunboards has a pic of a good screw press.


you could use an old trunion that you heat and detemper and harden and turn down to fit like I did!

[vista461]

Do I need the trigger assembly on to properly check the bolt gap, or is it sufficient to just use the bolt assembly without the trigger pack installed?

[drine]

The correct way to measure normal bolt gap is to drop the hammer on it. I would/will/did it this way on my barrel swap. It may mean only a .001 or so but still your gap will settle after firing a few hundred rounds.
That's just an opinion. If you have your trigger pack, do it. If it's a kit and your pack isn't ready yet, let another member here chime in.

[vista461]

Fair enough, I'll wait till I have my trigger pack done before I press the barrel

[drhall762]

I am watching you closely Vista461. I have sarted to clean up my parts and get a few things together. The way you're going you should be finished before me and I will follow your lead.

Dave :sniper:

[vista461]

Well I am going to slow down since I am going on vacation for a week. But I hope to make steady progress after that
:thumbup:

[Perro]

cross drill the barrel with a 5mm drill bit
you could even ream it undersize if you want a good press fit.

its really kinda unimportant to use anything but a 5mm bit though cause once it settles, it aint going anywhere.

for those super anal about gap, hkspecialist.net has undersize rollers for the HK21 which work as well

if you gapped it at 16 thousandths with -6 undersized rollers from a HK21, you could slowly work up to minus 4s, then minus 2s, then standard 8mm rollers, then plus 2s, then plus 4s during wear.

i made a mandrel out of 1 inch round 6061 t6 aluminum turned so it fit just inside of the chamber to keep it straight when pressing - the taper on the front of the barrel gets it started straight.

no need to shave metal on the trunnion if you are using a new barrel - none of the manufacturers do this. strip a cetme or g3 parts kit, and youll see that barrel is scored. Clean the inside of the trunnion, and grease is a good idea, but in MY opinion, breaking the edge on the trunnion is not needed cause once that pin is installed, and it settles, that barrel aint moving. It cant hurt anything, but its not needed. If it were needed, the factory would do it.

heating the parts? some will argue this, but that trunnion is heat treated - it is treated to harden it and prevent it from wearing out fast. Heating a heat treated part up anneals it and makes it softer. I know it can be done, but something that completely contains the 55,000 PSI pressure i feel a bit uncomfortable heating up - i know everytime the round fires it gets hot, but id rather wear my gun out shooting it than trying to make it easier to assemble - once again, my opinions only.

one last bit of advice - get an old bolt set that you dont care about
press the barrel close
install the old bolt set and slam it into the barrel face - it will SLOWLY nudge the barrel forward into position where gap is perfect



Mike

[Otis61]

All this syuff looks really cool. The right tools for the job kind of thing. but I didnt know anyone and couldt wait. So I did what fordruid talked about. I let the barrel sit in our deep freeze for a couple days. When I got reddy I put the trunion, still in the old peace of reciever, in the oven at about 250. After a half an hour took it out clamped it in a vise and sacrificed a fashhider and pounded it in with a big hammer. The first part went really good. Towards the end it got harder because the temp eaqualized,but it woked.

[gunnin'thusiast]

My barrel press-in was done by using a grade 8 piece of thread stock through the center of the components. I then drilled a hole in a piece of 3/16" flat stock and viced securely. I placed a tempered nut on the opposite side of the flatstock with two opposing nuts with star washers attached. At the barrel face I placed two forged washers and used a barrel nut. Excellent! The first 1/4" of length, the pops were short then further in, the pops were more lengthy. The last pop put me past my mark and had to back out slightly. My method for aligning the pin was done by placing a drill bit in the trunnion and resting another drill bit on the pin divot. By looking down the line of sight I aligned the two so they were parallel to each other. Placed the entire assembly muzzle down on a block of wood and used a rubber mallet to tap set in place. Then secured the assembly and began cranking. I noticed that the new barrel divot was not drilled deep enough to match the trunnion hole. Used a 3/64" bit or #7 to remove the excess. Now I will cut the back of the drill bit and use it for the pin. Just microns larger than the original pin.

Overall content at the ease of assembly.

[grifter95]

I justpollished the barrel where it slides into the trunnion and smoothed up the inside of the trunnion. I then lubricated everything well and attached an old flash hider. I secured the whole setup trunnion end down and simply beat the barrel in till it got close. I then checked my bolt gap every few hits until it was right. I then drilled and pinned it. I set the bg at .021" and it settled to .016" and has held there with over 500 rounds.

However, if/when I decide to build another I was thinking of using the same setup I use to press AK barrels in. It involves a long piece of screw stock and fittings on each end. You basically tighten the barrel end and it squeezes the barrel into the trunnion. It takes some time but give you really good control for perfect depth! Anyone else used this method for CETMEs of HK builds?

[drine]

When I researched doing mine I thought the best one was a regular hydraulic press fitted with a threaded rod. That gives the best of both worlds. The tell-tale POP one hears when you are getting close signals it's time to measure but it may have gone too far. A screw press you can control closer.
I'm amazed you got it in with a hammer. Your bolt gap doesn't seem to suffer for it so good deal. drine