[Fuhrer]

I thought this might be a interesting thread to start.Some SVTs run with lower gas settings than others.Maybe if we list some facts about our rifles we can get a idea as to why that is.I will list the facts of my rifle and lets all add ours and go from there.One important fact to note will be the muzzle test.This can be done with out taking the flash suppressor off the rifle.Just pull a bullet from a 7.62x54r shell.Use the red sealer line on the bullet which is common on surplus ammo that we use as your reference mark.Also note barrel fluteing is important SVT rifles have 3 different types.Early is just the case neck fluted.I will call mid war The neck fluted and slightly down the case shoulder.Late war the neck is fluted and down the shoulder and case sides.Now this is my subject rifle facts

1941 Tula SA marked

Barrel bore = Excellent strong shiny bore lightly frosted grooves

muzzle test= Excellent lots of bullet sticking out

Barrel fluteing= excellent early type (just the case neck is fluted)

Recoil spring condition= New

Gas piston and Cyl= New stainless replacements

Gas setting= 1.7 and runs perfect with no excess recoil noted

Chamber condition= serveral scratches from broken case removal at some point in its history.I have polished the chamber completely with emery cloth

Ammo Russian surplus steel case light ball

Spent case condition= good flute marks noted. Cases do tend to crack at the shoulder and slightly down case side.Case edge were ejector grabs on shows no problems of excess force. Note i have also had a few crack in two original refurbed PU snipers i have.A Rguns and a Sammco.

Ejection distance= right around 5 or 6 ft

If anyone thinks of anything else just add it Thanks !

 

[rocker98]

Just took mine out shooting yesterday. Everything you have listed is the same except for:

1942 Tula refurb. (1941 with a 2 stamped over the 1)

Recoil spring: Looked new when I bought it 5-6 years ago.

Gas piston and cylinder: original refurb

Gas setting: 1.5

Ammo: Bulgarian LB 1952

I also have an occational failure to extract. This is solved with a good chamber/flute cleaning. I am also OCD with pipe cleaners to the gas system ports. That gas system gets clogged, the whole weapon suffers. This is true with AK's, Ar's, SKS's...whatever. Carbon buildup is not your friend when it comes to firearms.

 

[Fuhrer]

Thanks ! any split (cracked shells). Brass or steel case ammo? Average ejection distance? Are you sure it has early type flutes?

 

[rocker98]

No splits or cracks that I remember. I removed the obvious bad cases from the 1200 rounds I bought. All dated 1952-53. The cases are brass. Flute marks only on the neck. Ejection distance? I would say they hit the deck at ~5ft. and then travel from there.

By the way. The failure to extract showed the pressure point to be at the base after extraction. I also had one blown primer yesterday. I have yet to try different ammo. I has taken me about 3-4 years to go through the 1200 rounds. I still have about 200 left. The cases are not the greatest. Most are just fine. The ammo itself is consistant in all my rifles. I need to buy more soon. I'll stay away from the Bulgarian in my semi-auto. It all works just fine in my bolt actions. Pretty dirty stuff too. BUT, my Mosin Nagant chew it up like candy.

 

[saf]

Why do some SVT’s run at lower gas setting than others? I think the present condition of you gas system is the single biggest factor and how close the tolerances are. Start with the gas regulator. Has the hot jet of gas passing through those tiny holes eroded the metal and enlarged those holes. Perhaps lack of proper cleaning when the rifle was in service plays into this. Are the holes still 1.1,1.2,1.3,1.5 and 1.7 mm in dia. Have you ever checked? You need a hand lens, and pin gauges or correct size drill bits to do this check. How do you know if your 1.5 setting is in reality 1.7, or your 1.3 is a 1.5? I have in my possession one such gas regulator in which the 1.5mm is about 1.9mm due to metal erosion (see photo). The 1.1 and 1.2 hole check out, but the 1.3 and 1.7 holes are somewhat enlarged. This could lead to an erronous assumption that the next higher gas setting is needed to function, when in fact you have exceeded that setting and possibly the maximum setting.

I have an SVT that has what I consider a pristine gas system. Wanting to use different parts so as not to damage or wear-out the good parts I made the unfortunate choice of buying the three gas system parts from a well-known parts place, plus an operating rod which is good. The cup is missing metal making it completely unserviceable, the piston is (nearly?) unserviceable, but might work if heated and peened out, and the regulator is as mentioned above.

The piston is another part that seems to get eroded from the hot gases and/or lack of proper cleaning. The body isn’t too much concern but the actual piston portion of that part is. It’s that front part with the largest diameter and that is what uses the pressure to drive the cup. My pristine piston specs at 0.431”dia. and the worn one at 0.428” +/- 0 .001. A worn piston equals less pressure due to bleed off and a need to up the gas setting.

If the cup and/or piston are both out of spec., then the pressure will bleed of quickly and cause a weakened bolt cycle. This could cause failure to extract, failure to eject, and failure to load. Measuring wear on the cup is hard as it is difficult to get interior measurement along the length of the inner diameter. I know my good cup has a 0.4331” +0.010 inner diameter as I can put a 11mm rod into it with little play and it will slide right in. The worn cup is rough and I can't slide the same 11mm drill in.

As for what gas setting are used to operate the SVT is dependent on the amount of wear on the gas system parts. As the parts wear a higher gas setting will be needed to operate until ultimately those parts become unserviceable. Also be aware of the size of your gas ports on the regulator.

Look at the pictures of a good system and a bad system. I realize that there are the two systems I presented, very good vs. very bad, and probably most other are between these extremes.

 

[r1946]

My SVT-40 will 'slam fire' about every other shot letting off two rounds in the process.. I have changed the firing pin spring, the disconnecter, and the disconnecter sear and thoroughly cleaned the gas piston, all to no avail. I have tired different gas settings. Any suggestions would be appreciated.

 

[saf]

I would check the following:
Are you using reloads, commercial primers are softer than mil-spec primers.
Firing pin cavity is clean.
Is the firing pin spring new or is it a surplus spring (used)
How far does the firing pin stick out of the bolt. I think they should stick out a little, mine does just enough to see the circular head of the firing pin. Look to be about 1/32" stick-out.

Doubling is usually the result of the firing pin having enough inertia to over come the spring resistance when the bolt slams into the chamber allowing for a primer hit.

 

[daveccarlson]

1943 SVT-40 Tokarev self-loading rifle, refurbished with AVT-40 naval infantry stock and two-baffle muzzle brake. Metal shows evidence of heavy previous pitting before re-blue. Gas system parts appeared almost as new when I bought it. I have been unable to locate stainless parts to buy.

Bore= good condition, some rounded lands, heavy frost/corrosion/erosion in grooves. Shines when clean.
Recoil spring= like new when I got it.
muzzle=no idea
gas setting= 1.7mm only. Works with 1975 Polish LPS 147gr. ball with copper-washed steel cases and with Yugoslav 182gr. brass cased M30 heavy ball. Throws the cases about twelve-fifteen feet forward and to the right. Lower gas settings and the rifle will not function as a self loader, instead the bolt will jam partially open/unlocked but with the case stuck in the chamber. I have torn off the case head removing the case at least once. The rifle will not reliably work with Czech or ex-Soviet LPS. I'm going to try Hungarian next.

Chamber fluting=1943 type, neck and part of shoulder.

I like it, but mine is capricious. I've still got some tinkering to do, and the front sight needs adjusting, which to date I have not managed with just a hammer and punch.

 

[turbodan]

1940 Izhevsk SVT40
Very good bore, almost perfect. Tight muzzle.
Recoil springs never replaced by me
Gas system all original, set to 1.5
Chamber is clean and smooth
Rifle functions reliably on all varieties of LB surplus, copper washed or lacquered
Fluting down the case necks is clearly visible, casings land approx. 10 feet away
Never torn off a case rim

 

[bananas]

1940 Izhevsk refurb

Bore, gas piston and cylinder: Look almost new

Gas setting: 1.7 as it came

Ammo: New Brown Bear lacquered steel case 203gr

Early flutes. Clearly visible on neck of cases

flings shells ~6-8ft forward to the right. Cases tend to have very small dents on the side from ejection. Functions perfect and I don't mess with the gas setting (don't have the tool anyways) so I stick to heavy ammo. Cases have never gotten stuck with all types of steel cased. Never had a rim torn off. Have not tried brass but don't plan to