Vickers not running well in 7.62x54r?

[glennp]

Hello!
I'm new to the Vickers MK1 and I have a new to me transferable that I've had the pleasure of taking out twice so far. The conversion consists of a reamed out .303 barrel, a modified extractor, and modified feed block. The modifications were done by known people and appear to be of good quality. The rims clear the feed block and extractor smoothly. I actually have two of each modified for the barrel, feed block, and extractor. The first outing, I took 500 rounds of .303 and 500 rounds of 7.62x54r on PKM belts. The gun ran the .303 nearly flawlessly. Then I changed the barrel, feed block, and the lock for the x54r parts. I left the booster cup off. It didn't run well, it would run 3-15 rounds and then have a fourth position stoppage. The ammunition I'm running is Wolf "military classic". I figured it's a lack of oomf, so I tried lightening the fusee spring. I got it down to about 5-6lbs before I gave up on that approach, knowing that's quite light. The cyclic rate was higher than .303 so it certainly had the "poop" to run, but would still give me a fourth position stoppage frequently. That is, no round in the chamber, but a round would be in the extractor ready to go most times(one charge to get it going). Then I switched out one by one a different barrel, then a different lock, then tried a different feed block. Zero effect!

When I took the gun apart at home, I noticed that my new packing was pretty tight and goopy (graphite yarn). I figured I had it figured out, so I cleaned it up and put it away for the next outing. Fast forward to my next outing, I limped through 750 rounds and getting the same malfunctions. The gun would stop running, but 9/10 times one pull of the crank and a yank on the belt is all it needed to spit out the next dozen or so rounds. Quite perplexing. I even took slow-motion videos of the feed-side of the gun to see if I can see any difference with when it quits, but I cannot. It appears to be fully recoiling and yanking the belt in.

I did notice on the second outing I am getting a couple case-head seperations which are of course a different ball of wax. I of course forgot the shims at home, but I do understand I need to shim under the lock stub to push the lock forward more in relationship to the barrel. However, I don't think that would be causing the more common woe, which is frequent 4th position stoppages.

What does the brain-trust think?

[Countryboy77]

Was somone tailing the belt? All the really old guns are finicky and take a bet to get running.Headspace change between swaps maybe.Not a lot of time on a vickers,but played with my friends.

[themacanerd]

I left the booster cup off.

The gun is recoil operated and a booster is a critical component used to increase recoil to the gun for it to operate properly. Use the gun with a booster. 

I figured it's a lack of oomf, so I tried lightening the fusee spring. I got it down to about 5-6lbs before I gave up on that approach, knowing that's quite light.

If you don't have enough oomp, use the booster. A Vickers gun in 54R should have the fusee spring tension between 7-9 lbs. You want more fusee spring tension if possible as it helps reduce wear and tear on the gun. More spring tension means more power for the lock to extract and feed rounds. 

The gun would stop running, but 9/10 times one pull of the crank and a yank on the belt is all it needed to spit out the next dozen or so rounds. 

Yea, classic case of not having enough recoil for the gun to run. Run the booster and increase the fusee spring tension to 9 lbs then reduce if necessary. 

Also, cloth russian 54r belts work way better than PKM belts. The tabs on the cloth belts help prevent crossfeeds, and the PKM belt is metal which wears on the feedblock. PKM belts can be run more reliably if you have a friend or use a spare hand to lift the belt up + you leave some empty rounds on the last rounds of the belt + you lube the cases (which is not ideal as you don't want lube in your chamber). 

The above knowledge is from me cursing at my Vickers and Maxim gun for four Big Sandy shoots in a row trying to get them to run reliably. Mike Duke and Jim Haack saved my ass and got my guns to run by recommending I install a booster, add more spring tension, and use cloth belts.

Not 100% sure about the case head separations but try the above first and see if they go away. 

[waterdawg2004]

I have used 7.62x54R ammo both with and without booster.  Also used PKM belts and cloth Russian belts.  What worked best for me was the PKM belts with booster and using dry lube on the belts.  I can usually go right thru a 250 round belt, awesome feel.  Sometimes I get a weak cartridge but I can just crank it and finish the belt.

The Rims of 7.62x54R are a lot more narrow in thickness than .303 ammo so you will get head space separation.    For 7.62x54R I added shims until the  crank would not lock up and then took one out.  Worked a lot better.  I tried the book method but could not get the “feel” for it.   Happy trails.