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Discussion Starter #1
I moonlight working for my buddy helping him build guns, and I finally decided to build a semi auto 1919 for myself. I used a KMP side plate and trigger assembly and a nice A4 kit and am having some issues.

The action is very stiff to work, it will slide back 1/8 inch but when it starts to come out of lock, it is very tight and gets in a bind. The lock bolt is not too long or hitting anything. The barrel and extension slide freely back and forth when inserted by themselves. When the lock plate, bolt, and extension is assembled outside the gun, everything moves freely. I have decent clearances around the denial isle. My accelerator doesn't appear to be hitting anything or binding. If you jerk the bolt back real fast and hard it will open but it can not be done smoothly. If you slide the bolt slowly forward, it will stop at lock and not close unless you push it forward. Gun is timed and head spaced correctly. the lock cam screw is backed out 1/2 turn. The lock block slides up and down in the lock freely with the notches forward.

When the top cover is closed and the bolt is in full battery, how much play up and down should the extractor have in it? Should I be able to wiggle it up and down a couple thousandths or 1/8 before it contacts that spring? I see in the trouble shooting section that the spring in the top cover should be arched quite a bit. When my spring is like that, it is even harder to charge the handle and I can see the top cover trying to lift up because of the extractor trying to compress the spring.

The gun is very straight and solid but needs some fine tuning, so, I figured I would ask for some help. To add insult to injury, I built a full auto 1919 for a customer last night, runs flawlessly! Between the binding issues and me grabbing ammo that OAL was too short, but gun runs like garbage 馃榿馃槃
 

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Just some thoughts,in no particular order :
Is the receiver box square ?
Cycle the action a few times and looks for polished/rubbing spots ? Remove the cam block (on bottom plate) and see if that changes anything, also check that piece for burrs. 1/2 turn loose is a bit more than I've ever needed on one.
Cocking handle fits in slot without any rubbing ? Cocking lever in correctly ? All rivets fit flush on the interior ( esp. bottom plate rivets)
Please remove the recoil spring first, then use a bright flashlight looking forward , watch parts move/clear on denial islands.
Loosen headspace a few clicks for grins.
Also, the tang on the rear of the barrel extension has to be milled/beveled to clear the semi trigger.
Please keep us posted.
DanG
 

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Discussion Starter #3
Dan, thanks for those pointers! I did find a couple of rub marks internally, cleaned those up. Cleaned the carbon off of the booster, put a dab of oil on those, and all the rivets are flush internally. All of that helped a lot but still not what I believe it should be. So, I removed the cam block and BAM! it is smooth as butter with very little effort to charge it. I tried the cam block in the barrel extension and it moves freely and without issue when it is on the bench. I took some emry cloth and polished the cam block. Put it all together and it is a little better but still not perfect. What do you suggest I try from here? Should I try another cam block?
 

PhD in Over-Engineering
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Sounds to me like your breech lock and breech lock cam (block) do not like each other. While there may be other issues that are impacting this, I have found that sometimes there are just particular parts that do not get along well. Seems your locking parts are just very snug in that part of the travel. I'd try a different lock, a different block, and even a different bolt if you have one. If changing the combination of parts does not make a difference, then we have to look elsewhere. I've also had a build that had a similar issue. It took a dead blow hammer to break it out of battery, but it functioned fine and "broke in" after a period of time. Still, swap some parts and see if that fixed things.
 

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Dwelling on the cam block a little more. I like to run a large flat file across the bottom, and make sure it's flat and sits true to the bottom plate. Just a tiny ding on the bottom can create a "tilt" when installed, and you did mention setting a half turn loose ? I like to set them tight, see how it functions, then loosen a tiny bit at a time if needed, all the while seeing how easily it cycles along the way.
Swapping parts at this point is a great way to see what the culprit is/was .
 
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