[Rfleet1066]

It concerns me that the home builders are being advised to use the barrel shroud to check and correct side plate alignment prior to drilling and riveting. The problem is that all barrel shrouds are bent and if used to align side plates, the rifle is built around an error. We use a ground mandrel to measure parallelism. It is fitted in the trunion and the gap between the mandrel and inside the side plates is measured and corrected prior to riveting. Also the barrel shrouds are straightened in a special fixture. Now, if you must use your bent shroud, set the rifle on a flat surface and rotate the shroud to find the high point of eccentricity. Mark that point and finish the end of the shroud (on the threaded end) until it locks up with the marked high point up. This way, any error results in high fire rather than left or right.
We have repaired a number of these misaligned rifles. The telltale signs of misalignment can be found on diagonally opposed buffing of the internals.

Ryland Fleet
Acme Gadget Division

 

[GWR1]

Acme -- isn't that the company that Wile E. Coyote gets all his stuff from? Comeon -- I'm just kidding, but your version sounds like a good, high tech way of our good ol' straight edge way. Thanks for the tip.

 

[7.62x39]

I checked mine and it was straight, fortunately, because with the way that everything locked together, I couldn't have moved it if I wanted to.

I don't understand, if the side plates are flush with the trunnion, how can you change the angle?

 

[Rfleet1066]

Trunion alignment

Your so-called tried and true method is uses a bent indicator. Lay the weapon on its side on a flat surface. Remove the shroud fastening screw. Now measure from the end of the shroud to the flat surface. Now unscrew it 90 degrees and measure again. Try 180 degrees. 499 out of 500 will not maintain parallelism. When you build the rifle using the barrel shroud to determine plate alignment, you make the error permanent when drilling and riveting. And there ain't nothing high tech about a ground gage bar in the trunion. Use the gage bar to ascertain perfect alignment, giving the internals nice parallel plates to run in and true to the trunion. Then straighten the shroud.
You see, before drilling and riveting, a receiver that has been fitted together for this process can be flexed. By moving the barrel shroud left and right, the sideplates can be shifted forward and aft. Then clamping and riveting locks the alignment. A bent shroud is a bent indicator.
I keep hearing about inaccuracies and sticky motion...........no wonder.

Ryland Fleet
Acme Gadget Division
'Expert Since 10 AM'

 

[balming]

My brain hurts now.

 

[Roc Rat]

I use a laser torpedo level with the magnetic mounts,, attached to the rhsp pointed down the jacket,, measuring at trunion and bearing. By turning jacket and repeating the measurement you can tell easily if the jacket is out of line with the receiver.

 

[loboslanding]

I agree with any super accurate method of aligning that professional builders use, but the average home builder can obtain excellent results with a straight edge. I too have seen several misaligned and that was due to not being aligned at the onset (even with a straight edge) or had terribly damaged shrouds. 38 builds with a straight edge and so far I'm not aware of a problem. In addition to the straight edge method it's real apparent if it's not aligned because the backplate doesn't engage uniformly in both side plates and the internals don't function smoothly...so far the straight edge on our builds has produced neither problem (that I'm aware of).

Also, I cannot agree with "all barrel shrouds are bent". I have several and they are plus or minue a few thousandths from end to end. I've been using shrouds from Angola Armory, Sarco and ORF. Maybe the parts sets available now are less quality and builders should defnitely be checking their shrouds if that's the case. One point to make here, if "irregularity" and not "bent" is meant then that I think is correct. The tutorial says to measure at the trunion end and the muzzle end and says nothing about the middle because most barrel shrouds have irregularities including highs and lows in the middle, but has nothing to do with front and rear alignment. The gap should be measured only at the ends and not in the middle.

If anyone has carefully followed the barrel alignment tutorial and had a problem with an out of square receiver we'd like to know so post it here. For many years using the straight edge or laying the weapon on a flat surface has been used satisfactorily by home builders that do not have the tooling to do otherwise. I use a straight edge because all my benches are made of wood and I don't have a "true" bench and a straight edge is nothing more than a "true" bench turned upside down.

I also used a straight edge to check the alignment on my OOW built '28 water cooled by laying the straight edge on the water jacket and measuring down to the receiver at front and rear and it measures dead nuts on so I know the straight edge works for us less than sophisticated builders.

I can't speak for other builders results, but the real proof is on the firing range and on my personal builds I've set the rear windage sight at dead center on the bench and it might require a one or two click adjustment at 100 yds...close enough for this home builder .

The gist of my comment here is that the home builder need not fear about getting their receiver square without the use of special tooling or having your weapon professionally built. Just my .02.

I agree, galling on the internals is a sure sign of misalignment. Here's a pic of my 3 year old bolt with 1000's of rounds fired...parkerizing on the rub areas is still over 95% unmarred.

 

[7.62x39]

The Brasscartridge RSPs have the pintle pad holes drilled to finished size, including the long one that goes all the way through.

As I mentioned earlier, mine came out straight, but I don't see how it could be changed if it hadn't.

I think this hole being in a already known, correct location, pretty much insures that the build will be straight, unless there is a problem with the trunnion.

 

[loboslanding]

The shroud angle is easy to change by sliding the rsp forward or backward. Moving the rsp just a few 1000ths changes the barrel shroud angle tremendously at the booster end. I've played with them and you can move the rsp forward just 1/16" and it will kick the end of the barrel shroud over almost 3/16" out of alignment. That's why I align first and drill and set all the bottom plate rivets before drilling the two big trunny rivets or setting the long pintle pad rivet. You can pound the long front pintle pad rivet in place and the rsp can still deflect enough to misalign the shroud. The whole receiver can be skewed and the existing rivet holes will still line up due to the slop in them. There's enough "play" in the rivet holes to move the rsp fore or aft about 3/32".

Any new builders reading this...align your barrel shroud by whatever means, but align it.

 

[Kali Komrade]

Hey my

Hey my internals have some of the parkerizing rubbed off and thats the way my kit came so does that mean that the government was shipping off mall aligned 1919's. I think J.M. Browning designed enough slop in the design of the gun that the straight edge method is fine... These were built when guns were guns and not the ultra tight tolerance guns of today...

Build'em if ya got'em

 

[7.62x39]

7.62, the pintle pad hole on the BC plate is drilled to 1/2"...the final size of 9/16" has to be drilled by the builder...unless he changed it in the last month or two. If he has please let me know. thx.

Not the pintle bolt, the long pintle pad rivet hole is finished size.

 

[loboslanding]

Sorry, I thot you were referring to all the pintle pad holes...my bad. I corrected my post...thx.